Roof Tips. - Norbord

Roof Tips.

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Minimizing Buckling For Asphalt Shingles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Raised Heel Trusses Improve Energy Efficiency While Reducing Costs . . . . . . . . 4

Causes Of Telegraphing Through Roof Shingles: It’s Not Always The Obvious! . . . 5

Best Ways To Save Money On Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

The Ten Most Important Fasteners For Installing Roof Sheathing . . . . . . . . . . . . 9

Effects Of Roofing Shingle Color On Energy Efficiency . . . . . . . . . . . . . . . . . . . 10

Roof Sheathing Got Caught In The Rain? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Energy Efficient Walls: Build With Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Plenum Truss: Get Your Ducting Into A Conditioned Space . . . . . . . . . . . . . . . . 13

Which Way Should You Install OSB On A Roof? . . . . . . . . . . . . . . . . . . . . . . . . 14

The Pros And Cons Of Unventilated Attics . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Soffit Dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Seal Eyebrow Roof To Improve Energy Efficiency . . . . . . . . . . . . . . . . . . . . . . . 17

Can Solarbord Be Retrofitted? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Wood Roof Trusses: Advanced Technology In Building Design . . . . . . . . . . . . . 18

Can A Floor Be A Roof? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

9-Foot Trims Increased Popularity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

How Much Weight Load Is Solarbord Able To Support? . . . . . . . . . . . . . . . . . . 21

Raised Heel Trusses: Environmentally Friendly Money Savers . . . . . . . . . . . . . 21

Dry Time For Solarboard After Being In The Rain . . . . . . . . . . . . . . . . . . . . . . . 22

Can You Use Pinnacle Subflooring On A Roof? . . . . . . . . . . . . . . . . . . . . . . . . 23

Can You Install Roof Sheathing Over Real Wood? . . . . . . . . . . . . . . . . . . . . . . 23

Replacing Cedar Roof Shakes With Asphalt Shingles . . . . . . . . . . . . . . . . . . . . 24

Spray Foam Vs. Radiant Barrier Sheathing: Pros And Cons . . . . . . . . . . . . . . . 25

Wet Spray Cellulose Insulation Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Orientation Of OSB Roof Boards When Installing . . . . . . . . . . . . . . . . . . . . . . . 28

Radiant Barriers: Myths Busted And Facts Explained . . . . . . . . . . . . . . . . . . . . 29

The Importance Of Attic Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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Correct Panel Spacing

Minimizing Buckling For Asphalt Shingles

As much as 95% of US roofing starts with wood panel sheathing. This is because it’s easy to work with and provides a sturdy substrate for roofing materials. However, if the wood sheathing panels are not installed correctly, bucking may occur and this will telegraph through to the shingles causing a ‘wavy’ look. This can result in very expensive call backs for the construction company, so ensure that you follow these guidelines and the manufacturer’s instructions as well as your design professional’s outlines in order to avoid problems.

Vent Your Attics

Keep moisture out of your attics and allow for the free passage of air so that moisture that does get in can escape. Combine eve or soffit vents with ridge ventilation so that air can come in at the eve or soffit and be exhausted along the ridge vents.

Do not vent bathroom fans, dryers, dishwashers and other appliances into the attic where moisture-laden air can cause many issues including buckling of the roof sheathing. Always vent appliances outside.

Attic ventilation may not be required if a vapor guard is installed or where a building inspector deems it unnecessary.

Install A Vapor Barrier

Vapor barriers are effective in cooler climes which, when installed on the warm side of the ceiling, prevent moisture from entering the attic. Always check your local building codes or with your building official to determine the local requirements.

Proper On-Site Storage

Roof sheathing panels swell when exposed to moisture and this may contribute to buckling. Allowing your sheathing panels to acclimate on-site before installation will help to mitigate this problem. Follow the APA guidelines for correct on-site panel storage.


One of the best ways to ensure sheathing panels don’t buckle is to adhere to the 1/8” spacing that manufacturers require or recommend. The way in which roof sheathing panels are manufactured leaves them with a relatively low moisture content. As they adjust to accommodate the ambient moisture of their new environment, they need space to move. When installers adhere to the correct panel spacing, there is room enough for panels to acclimate and buckling is avoided. The 1/8” space acts as a mini expansion joint.

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Stand Over Trusses Chords Or Rafters

During installation, standing between supports can cause the panels to bend and the fasteners will hold the bent shape in place. Although this makes no difference to the structural integrity, it can telegraph through to the shingles making the roof look uneven.

Installing Roofing Underlayment

Install the underlayment as soon as possible over dry sheathing panels. This will prevent the exposure of the roof sheathing panels to excess moisture. Installing underlayment over wet panels will trap moisture between the two layers. If your panels do get wet, allow them to dry before continuing with the installation. Ensure that there are no wrinkles or creases in the underlayment which may affect shingle appearance.

Shingles

Heavier weight shingles tend to show underlying imperfections less. This is also true of darker colored shingles. Always follow the manufacturer’s instructions when installing shingles.

Raised Heel Trusses Improve Energy Efficiency While Reducing Costs

Stringent new building codes require improved efficiency of building envelopes through better insulation. While more expensive insulation methods, like spray foam, may have greater R-values, it is possible to meet the required high R-values using less expensive fiberglass or cellulose insulation with a raised heel truss.

Traditional Problems With Conventional Rafters Or Trusses

While batt or blown insulation does provide an excellent R-value, construction professionals have been limited by the depth of the wall top plates on traditional rafters or trusses. Here the small space between the

wall and roof requires the use of baffles, for ventilation, and the insulation to be compressed. That compression reduces the insulation efficacy along the affected walls of the home. To compensate for that, higher R-values are required throughout the rest of the attic floor.

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Raised Heel Trusses

The raised heel truss offers the perfect solution to these insulation problems. Equipped with a heel where the bottom chord intersects with the perimeter wall plate, the raised heel truss enables the top chord to be raised by a foot or more. With all this extra room, there is additional space for cheaper attic insulation options such as fiberglass batts, blown cellulose or blown fiberglass and the full depth of insulation to be extended right to the outside of the top plate where it is needed most. This helps to prevent the formation of ice dams during the cold winter months. In some climate zone, because of the greater efficiency of full depth insulation to the outside edge of the top plates, the IECC allows lower R-values to be used over the entire attic area. There are further savings because the baffles are no longer required and when longer length sheathing is used, hurricane clips may not be required.

Lateral Support Options

According to the APA: “When properly installed, these vertical truss elements are in alignment with the exterior surface of the wall framing elements. However, the increased distance between the roof sheathing and the top plates of the wall complicates the required lateral support for these trusses.”

Traditional trusses usually require a 2×4 or 2×6 blocking between trusses for lateral support at the eve. However, with a raised heel truss, the alignment of the truss heel with the outside of the wall framing means that wood structural wall panel sheathing can provide effective resistance to lateral loads without any additional blocking. See full details in the APA Systems Report 103 here.

Additional Benefits Of Raised Heel Trusses

Not only do raised heel trusses allow for more insulation and provide support against wind uplift and lateral loads, they also provide a greater aesthetic appeal. Raised heel trusses are engineered so their sizes are consistent which makes for a more uniform pitch. The engineered trusses are ready to install which saves you time with framing and the increased attic space gives you more room for HVAC systems.

Causes Of Telegraphing Through Roof Shingles: It’s Not Always The Obvious!

Recently we had a call from a builder complaining that their roof sheathing was buckling, causing a telegraphing effect through their roofing shingles. Concerned about the structural efficacy of the roof, they asked us to take a look. The builder and dealer thought it was a number of problems with the roofing panels themselves but, on closer inspection, we discovered that installation issues were the real culprit.

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The Home

This 3,200-Foot Home Has:

• A 2×6 conventionally-framed roof at a 10:12 pitch with rafters spaced 24” on-center.

• Roof sheathing panels are 7/16 category OSB with a 24/16 span rating, Exposure 1.

• Spacer-type edge-support clips were placed between panels along the 8-foot panel edge.

The Problem

Notice in the photo on the right how the roof sheathing panel 4-foot edges telegraph though the shingles. There was no evidence of moisture trapped under the shingles and the presence of adequate ventilation points to installation issues.

Fasteners

The framer used 2” nails to install the roof sheathing with 5” to 8” o.c. spacing. While there is no provision for use of 2” nails in the International Residential Code, the ICC-ES Evaluation Report ESR-1539 from the International Staple, Nail and Tool Association does allow for a 0.099” diameter, 2-1/4” long deformed-shank nail, with a recommended nail spacing of 3” o.c. along panel edges, and 6” o.c. at intermediate supports. Proper fasteners and spacing is necessary to keep sheathing flat and provide the holding power in a high wind event.

Not only were undersized nails used which weren’t properly spaced but, in many instances, the first nails were more than the recommended 3/8” from panel edges. Several nails had missed the roof framing altogether, which resulted in lifting panels. You have to hit something for the fastener to hold the panel in place.

Always refer to your manufacturer’s instructions for fastener patters and spacing. Use the right fasteners for the job and ensure that all fasteners hit their mark. Inspect the framing before installing the shingles to prevent expensive callbacks.

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Incorrect Panel Spacing

Buckling and ridging of the roofing panels was caused by incorrect panel spacing. Both the manufacturer of the sheathing panels and the APA recommend a 1/8” space between panels to allow for swelling as panels adjust to the moisture conditions onsite. The 1/8” spacing acts as a mini expansion joint.

From the APA Technical Note D481: “Buckling of wood structural panel sheathing such as plywood or oriented strand board (OSB) occasionally results when increased moisture conditions cause the wood to expand. Such buckling may occur between supports or between nails along supports. Although structural properties are

unaffected, the waviness affects the building’s appearance and may lead to complaints.

Wood will expand when it gets wet. Even increases in the moisture conditions around the panel can cause expansion. If at all possible, allow the panels to acclimatize to the conditions where they are being installed. Always use the proper fastener size and type and never forget to provide the 1/8” spacing on the edges. Panels are cut to a size that allows for that 1/8” spacing.

The tendency of expansion to cause buckling in structural panels is related to mechanical properties, physical properties and natural characteristics of wood. It is also a function of not spacing panel ends and edges to allow for expansion. A thin panel has a greater tendency to buckle upon expansion than a thicker panel. Include the natural growth variability of wood, moisture absorption rate of the wood, and always refer to the manufacturer’s instructions and leave a 1/8” gap between panels.

When the builder came to us with complaints of telegraphing through his roof shingles they assumed it was edge swell and the fault lay with the roof sheathing. Most often, swollen edges and buckling panels are caused by common installation mistakes.

The Problem

When we inspected the roof sheathing panels in the attic, we noticed gaps between the roof sheathing and the framing. In some places, the gaps were big enough to slip a metal feeder between the OSB panel and the framing.

One panel was raised and the homeowner believed that it was decayed as the deflection was severe when stepped on. When we removed the panel in question it was discovered that a ceiling joist was sticking up above the surface of the rafter and the panel had been installed right over the joist causing a bump in the roof, and the sheathing panel had been attached around this protrusion.

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We solved the problem by trimming the corner and attaching a new panel.

In addition to the other issues, many of the panel edges were not aligned with the roof framing. The framer tried to overcome the fact he had not spaced the panels properly by simply nailing a supplemental board to the framing, but many of these supplemental boards were not even with the top of the rafter and that meant the panels were not flush. This caused telegraphing through the roof shingles.

According to the APA Technical Note D481: “Close attention should be paid to proper nail size and spacing and, of course, to assure that fasteners do not miss the supports. Fasteners should be 3/8 inch from panel ends and edges.”

Any mistakes present in the framing will telegraph through the shingles. Before installing the shingles, inspect the framing to ensure that panels are level and aligned. This will prevent expensive call-backs like this one.

Best Ways To Save Money On Framing

Framing is the single biggest contributor to the construction budget, accounting for (on average) around 18%. With rising costs and labor shortages, framing is becoming increasingly expensive. It behooves the small to medium construction firm to find ways in which to make the framing as efficient and cost effective as possible. You can mitigate some of the framing costs with careful planning, an efficiently run jobsite and the right tools.

Careful Planning

Compile an exhaustive list of all the corners, tees and openings that your new job requires, then set up a small factory operation on your jobsite to create all the necessary components. Create an area that is safe and organized and do the requisite prep work that will make your framing faster.

The devil is in the details, so find ways to cut time everywhere. Small things like color coding the nail containers so that framers aren’t wasting time searching for the right fastener really make a difference. All those minutes you shave off each process add up to time and money saved.

Create a storage area for tools so that they are easy to find. Organize your materials and keep the jobsite clean and neat. Take a few minutes at the end of the day to properly store tools and stack materials out of the way of the next day’s work.

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Have estimating systems for labor-hour goals, the sequence of tasks to complete and an ordering schedule for materials so that you always have everything you need to reduce delays on the jobsite. Go back and adjust material and time estimates to accurately reflect what has been used and the time required to accomplish the goals. That way the next house will go even faster and at lower costs.

Efficient Jobsites

Plan every detail of the job before you start and assign tasks and timeframes clearly so that everyone knows what’s expected of them and when it’s due so that your jobsite runs like an assembly line. There should be no time wasted looking at blueprints or waiting for instructions; everyone should know exactly what they are doing each day.

This means taking a little time out at the end of each day to discuss the work over the coming week and to ensure that all necessary equipment is in place and that the jobsite is set up to accommodate those tasks.

Keep a planning binder onsite or on a handheld device which includes the schedule, specs, purchase orders and trade quotes so that problems can be solved and questions answered without wasting time.

Tools And Materials

Investigate equipment options and keep abreast of advances in the industry. While equipment carries an upfront cost, it may save you money by reducing the amount of time you spend framing. Every hour you save is an hour in wages that you don’t have to pay.

Handheld devices and construction apps can really expedite your processes. Ensure that you keep up to date with the latest developments in these fields.

The Ten Most Important Fasteners For Installing Roof Sheathing

The Norbord experts, in collaboration with APA representatives, offer a solution for roofing panels which are lifting slightly.

All fasteners are critical. The ten “most important” fasteners in a roof panel are the ones in each corner and the six in the intermediate panel edge connections. The critical placement of these fasteners are key; spaced 3/8” of an inch from the edge and corners.

If an installer can get the ten most important fasteners applied correctly it will make the remaining (twenty seven) fasteners do a better job. Conventional framing at 16” o.c. would of course have more fasteners.

This was the simplistic description that Roland Hernandez (APA rep) used when explaining how to eliminate the horizontal joint (8’ panel edge) telegraphing on a roof. This issue was accentuated by the

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misplacement of fasteners on the intermediate trusses. The framing crews were starting their nails 2 to 3 inches and as much as 6’ to 8’ from the edge of the panels (on the intermediate trusses).

This installation error caused the panel edge to lift slightly which created a slight shadow on the roof when the sun was at a certain angle. Typically this phenomenon is mistaken as an edge swell issue and is seldom identified or diagnosed as an installation problem.

Effects Of Roofing Shingle Color On Energy Efficiency

The color of the shingles you choose for your build can have a significant impact on the building’s energy efficiency. The color shingles your clients choose can have significant effect on the temperature of the upper levels of the building. Attic temperatures can vary as much as 20 to 40 degrees F which in turn can reduce energy consumption by 20%.

A study by the United States Department of Agriculture found that wood roofing panels under black shingles were ten to fifteen degrees warmer than the same panels under white shingles on a sunny day: “… for

most recorded locations, the black-shingled roofs were generally 10°F to 15°F warmer than identical white-shingled roofs on sunny days. However, during the evening, the black-shingled roofs also tended to lose heat faster than did the white-shingled roofs. In obtaining equilibrium with ambient outdoor temperature, both black-shingled and white-shingled roofs generally experienced similar nighttime temperature profiles. …. shingle color or, more appropriately, radiant absorptivity of the shingle was a predominant factor in dictating peak roof sheathing temperatures…”

In warmer climates, lighter colors will reduce heat absorption from the sun while cooler climates will want black shingles that help to melt winter snow. You can compromise the shingle color to better suit home design by selecting shingles with flex of white or grey in warmer climates. Consider blends like grays to get the most out of your shingles all year round.

Roofing is a long-term commitment that must balance aesthetic appeal with energy efficiency. Be sure to compensate for shingle color when considering energy efficiency and the efficacy of your building envelope.

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Roof Sheathing Got Caught In The Rain?

Question

My contractor is using Norbord’s Trubord to sheath the roof of our renovation. It has been left uncovered for the last three days and it has rained consistently for those three days. Does this exposure undermine the integrity of the product? I was told by another contractor that it should have been covered.

Joan M, Port Orange Florida

Answer

Thank you for the e-mail Joan and your question. Our OSB is rated “Exposure 1” and that means that it will withstand normal delays in construction. Normal delays and the rain you indicated will not affect the structural properties of the panels. Certainly it would have been better to have covered the roof with a tarp or roofing felt before it rained. OSB, like all other wood, will expand when exposed to moisture and I assume the contractor spaced the panels the required 1/8” along the 4’ edges and installed H clips along the 8’.

The OSB (and in fact any wood panels) must be allowed to dry completely (depending on how wet the panels are this could be a few days) before any roofing material is applied to avoid trapping moisture under the roof material that could cause edge-swell and buckling. If your contractor has access to a moisture meter he can take multiple readings in various areas and compare the average of those readings to some taken from a piece of OSB that is known to be dry (i.e. in a store). Also, with that amount of rain, plywood and OSB may have some swelling at the edges and a thorough inspection of the panels should be done after the panels have completely dried. Address any edges that are of concern to make the roof level and flat before installing the finished roof material but this should not be done until the panels have had time to dry.

Fixing Telegraphing Issues On Horizontal 8’ Panel EdgesThe Norbord team offers some solutions for a telegraphing issue that one of their clients is having with their roof that appears on the horizontal 8’ panel edges (sometimes running the length of the roof).

This issue seemed to be installation related. The proper panel installations calls for fasteners to be placed 3/8” of an inch from panel edges and this also holds true for the intermediate trusses. Their installers are positioning fasteners between 2’ to 4’ from the panel edges (on the intermediate framing members). This mis-application

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is allowing the 8’ edge to lift slightly creating a horizontal telegraph line on the roof. The telegraphing is accentuated by the angle of the sun that cast shadows on the roof. On a flat roof with an 1/8”variation of the roof deck it will cast a very visible shadow. We also found a number of other issue. They are using #3 lumber for their trusses, plenty of wane, knots and twist. This lower grade lumber also opens the door for more uneven surfaces that ultimately effect the flatness of the roof area. There were also a number of shiners (fasteners that missed framing).

Energy Efficient Walls: Build With WoodIn this first installment of our five-part series on building energy efficient walls, we look at building with wood. When a ‘whole house’ design approach is adopted, construction professionals can effectively improve energy efficiency with little or no increase in construction cost as higher costs may be offset by using a smaller HVAC system or less material. Efficient wall systems enable the construction professional to secure the building envelope and prevent energy loss.

Improved Framing Efficiency

2×6 wood framing can boost energy efficiency and is a growing trend thanks to the durability and flexibility it offers designers. 2×6 framing spaced at 24 inches on center can improve energy efficiency as the two-inch increment from the standard 2×4 framing means a deeper wall cavity which in turn allows for an R-19, R-20 and R-21 insulation. The 2×6 at 24”oc. means fewer studs are required and this poses fewer opportunities for thermal bridging. Increased costs can be offset with a reduction in the amount of framing lumber required.

Wood Sheathing Panels Improve Strength

Wood sheathing has the benefits of durability, strength and flexibility. According to the APA: “Of the many sheathing materials on the market, plywood and OSB structural panels offer the best balance of energy efficiency structural performance and affordability.” In addition to strength, durability and efficiency, their impact-resistance keeps residents safe from debris during high wind events.

Wood wall sheathing panels are able to resist lateral and uplift forces as well as inward and outward wind pressures during high wind events. Structural wood sheathing, especially longer length OSB, can mean less need for metal connectors or bracing systems which reduces construction time and cost.

Taller Wall Sheathing Panels

The energy-efficiency of wood wall sheathing panels can be further augmented with the use of taller panels. The use of taller wall OSB panels means fewer lateral seams which can reduce air leakage by up to 60%. Taller panels also eliminate the need for blocking at horizontal joints which leaves the entire wall cavity open for insulation.

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Plenum Truss: Get Your Ducting Into A Conditioned SpacePlacing notoriously leaky HVAC ductwork into an unconditioned space will not make for an energy efficient heating or cooling system. Luckily, there are a few different options which locate the ductwork within the thermal enclosure of the home. Options include moving the ceiling plane to the underside of the roof with an unvented attic or placing the ductwork in a conditioned basement. A third option is the installation of plenum trusses which allow for a compact ducting system to be placed in a conditioned bulkhead.

In a recent study by the Building America Program partner IBACOS, one story slab-on-grade homes were

fitted with plenum trusses and compact HVAC systems were installed in reverse bulkheads to see if they could meet 2012 International Convention Energy Code (ICEC). Plenum trusses create a reverse bulkhead in the center of the attic space where ducting can be housed in an insulated area; “The plenum truss bulkhead adds only the amount of “inside conditioned space” required to house the ductwork by modifying the roof framing to create a boxed-in area in the otherwise unconditioned attic.”

Note the central rectangular bulkhead space and raised heels on the truss

First they moved the air handler into the home in a mechanical closet. While this did take up some space, it provided a convenient, accessible location in a conditioned space. It also reduced the amount of ducting required as ducts don’t need to go around the house perimeter.

Installing and sealing an air barrier over the top and sides of the reverse bulkhead means the pressure and thermal boundaries now include the bulkhead interior. The bulkhead is also insulated and all penetrations are properly sealed.

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The cost of plenum trusses is higher than other truss options but some of this cost may be offset with the use of a smaller HVAC system since the ducting is in a conditioned space. There is also a reduction in the amount of ducting required and a saving in energy consumption.

The integrity of the bulkhead must be maintained at all times during the lifetime of the system. This means ensuring that the bulkhead is effectively insulated and sealed and that other trades take care when moving through or working in the attic space not to damage the bulkhead in any way.

Another advantage to this method is the option to have raised heels on the trusses. This would allow more depth of attic insulation right to the outside edge of the top plate and using longer length sheathing like TallWall would remove joints at the top plate, the hinge point and likely the metal hurricane clips.

Which Way Should You Install OSB On A Roof?

Question

Which way should my OSB roof board’s be installed?

Answer

OSB roof panels should always be installed with the grade stamp facing into the attic and the screened surface (with the nail guide lines) facing up. When the grade stamp is covered by roofing, the building

inspector will not be able to confirm that the correct OSB roofing panel was used. The screened surface also provides a little more traction for construction workers during installation. The same goes for wall sheathing and flooring panels; always install with the grade stamp up so that inspectors can do their jobs easily.

Having said that, it is very important that the sheathing be installed with the strength axis perpendicular to the trusses/rafters. The strength axis is usually the long direction of the panel but the grade stamp will indicate it. Be very careful on hip roofs along the hip to make sure the strength axis does not mistakenly get parallel to the supports as that may result in the panel exceeding the maximum span allowed for that thickness. Sagging may result if panels are installed incorrectly.

The Pros And Cons Of Unventilated AtticsUnventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. The energy savings touted by unvented attics can be as high as 20%. However, if moisture is able to enter the unvented attic space, it may lead to roofing panel issues.

Wood roofing panels endorsed by the APA usually contain an in-service water content of between 4 and 16%. At

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these low levels, the moisture has a negligible effect on the strength and structural integrity of the wood panels. However, when roof panels are exposed to extensive periods of moisture that reach levels 20 to 25% higher than the industry standard, their structure will be compromised and it may lead to buckling, mold and mildew. It is imperative, therefore, to expedite building during periods where panels are exposed to the elements or to allow panels to properly dry and acclimate before utilizing them.

While both vented and unventilated attics are permitted in both the IBC (IBC 1203.3.2) and IRC (R806.4 (a)), should the wood panels get wet, they may not be able to dry out and buckling or loss of structural integrity may result. Protecting roofing panels from moisture damage requires proper planning and storage during the construction phase, proper design and installation and proper maintenance on behalf of the end user.

The Pros

Unventilated attics are common where roof assemblies are complex and it’s difficult to create a sealed ceiling plane. Poorly insulated ducting can cause heat loss in colder months and the loss of conditioned air in the summer in vented attics. The loss of energy efficiency means some designers choose to move the ductwork into the conditioned areas of the home and leave the attics unvented.

In warmer climates, unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces.

Unvented attics are also said to perform better in areas where high wind events and storms are common. Joseph Lstiburek from Building Science Corporation: “In high wind regions – particularly in coastal areas, wind driven rain is a problem with vented roof assemblies. Additionally, during high wind events, vented soffit collapse leads to building pressurization and window blowout and roof loss due to increased uplift. Unvented roofs – principally due to the robustness of their soffit construction – outperform vented roofs during hurricanes – they are safer.”

Unvented attics are also said to be safer in the event of a fire.

The Cons

Roofing panels can get wet when design or construction flaws allow moisture in, when ice dams damage shingles or when strong winds and storms damage the roofing.

Wet roofing panels have even less of a chance of drying in an unventilated attic when insulation has been applied directly to the underside of the roofing panels. This problem is substantially exacerbated when there is an impermeable layer on top of the roof sheathing (or example, some adhesive underlayments for shingles).

While the National Roofing Contractors Association considers unventilated attics a ‘viable alternative’, they do warn that some shingle manufacturer’s warranties may be rendered void by unventilated attics: “Steep-slope roof system performance problems caused by condensation and heat history unmitigated by ventilation are cited by some asphalt shingle manufacturers as grounds for their limiting or entirely disclaiming liability under product warranties for asphalt shingles installed over unvented attics. Homeowners considering asphalt shingle installation over unvented attics should consult asphalt shingle

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manufacturers to verify warranty coverage.”

Spray foam insulation is more expensive than batt insulation and needs to be expertly installed to prevent missed areas or pockets that can reduce the efficacy of the building envelope.

Poor workmanship during attic and roof installation will result in expensive callbacks and repairs as insulation will have to be replaced.

A study recently done in South Carolina showed that open cell foam can accumulate moisture that could potentially cause structural issues for roof sheathing. The researchers speculated that exterior moisture (dew or rain) between the roof shingles is forced into the roof sheathing by inward solar vapor drive. Another study’s computer model indicated that open-cell foam insulation is riskier than closed-cell foam in all US climate zones.

An alternate to spray foam insulation in an unvented attic is plenum trusses which allow you create a reverse bulkhead above the ceiling plane that is insulated. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. The trusses do cost more, but this added expense can be mitigated by a reduction of the size of the HVAC system thanks to the ducts being inside a conditioned space.

Over the lifetime of every roof, there is bound to be a little moisture that creeps in; improper installation of roofing materials and flashing may allow some moisture to enter, or poor maintenance, deterioration of roofing materials or storms all contribute to increasing the moisture content of roof sheathing panels. In an unvented attic, this moisture must have a way to get dried up or roof panel issues may result.

Soffit DamsInsulation settles over time and older homes may not have enough insulation to make them comfortable or to keep heating and cooling costs within reason. A common practice in older homes or even homes built over the last couple of decades is to add a new layer of blown insulation. One problem that is not always obvious is that, if one isn’t careful, blown insulation can unknowingly block the soffit vents.

New homes will either have raised heel trusses where the wall structural sheathing can block the insulation or

they may have baffles installed in each bay to keep the insulation from blocking the soffit vents. Either of these methods allow air to move freely from the soffit to the exits near the peak of the roof.

Here is a solution for older homes with low pitched roofs that make getting close enough to the eves to install baffles a real challenge. In those low clearance areas start by pulling back the existing insulation (a rake works well) to make a working area. You should see light through the soffit vents but if you don’t, investigate further to find the blockage. Next cut a 34” piece of 6-inch R-19 fiberglass batt insulation and lay it between the ceiling joists. Next cut a 20-inch piece of 3 ½-inch thick R-13 fiberglass batt insulation

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and lay it over the first piece so that the two edges that are facing you are flush and there is a step on the side nearest the soffit. Next cut another piece of 3 ½-inch R-13 about 8-inch in length and place that as another step on top of the last piece.

Push your “step” insulation back towards the soffit, making sure you leave a 2-inch gap between the insulation and the roof sheathing. Continue to create these “steps” for each bay along the eves. Now you can add your blown insulation without the risk of inadvertently clogging the soffit vents and you have maximized your insulation. Of course if your ceiling joists are deeper or the roof pitch is greater you can adjust the batt depth and length to maximize the R-value you are trying to achieve.

Seal Eyebrow Roof To Improve Energy EfficiencyWhen roof protrusions such as eyebrow roofs and porch roofs are installed prior to sheathing or around partial Sheathing they inadvertently allow cold air to leak into the building’s interior in heating months and cold air to escape during the cooling months. When the areas around these roofs are not sealed and insulated, air leakage and moisture reduce the effectiveness of the building envelope.

It’s best to properly seal and insulate while you are installing these roofs rather than trying to plug leaks

after the fact especially if a call back is required. You can do so with the following tips:

• If you have a complicated assembly like a rim joist, its best to seal all of the joints for a more energy efficient building envelope.

• You can frame the roof as a stand-alone structure rather than framing the eyebrow roof with small rafter-tail pieces which creates irregular holes which are difficult to insulate and seal.

• Sheathe the wall prior to attaching the eyebrow roof.

Can Solarbord Be Retrofitted?

Question

I was at my local Lowe’s Home Improvement center this weekend and came across your 4’x8’ Solarbord product. I realize that it is designed for use at the time a roof is being sheathed and roofed. However, is there any way it can be retrofitted between the rafters of an existing roof?

Jim, Temple Texas

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Answer

Thank you for the e-mail James. The only way I can think of to make panels work for an existing roof would be to cut and fasten them to the underside of the rafters. Do not try to install them to the underside of your existing roof sheathing for fear of fasteners penetrating the sheathing and the finished roofing. I suspect you would likely have to cut the panels in any case just to get them into the attic space. How much cutting you need to do of course depends on how the roof was constructed.

There are radiant barrier products (we do not manufacture them) that come in rolls that are likely available at your Lowe’s store. These can be installed to the underside of the rafters. These may be more expensive than buying the panels, but would likely be easier to work with in the attic space and they work to block the radiant heat the same way Solarbord does.

Regardless of which way you might decide to go, be sure that you do NOT block off the attic ventilation, either at the soffit or ridge and that air can freely move from the eves to the ridge vents without being blocked. This is very important because you want and need to allow that air movement.

Wood Roof Trusses: Advanced Technology In Building Design

Engineered wood roof trusses provide a wealth of benefits for designers, engineers and construction professionals. The uniformity of their design make it easier to build pitch-perfect roofs. Designs can be more complex and trusses provide broader freedom with roofing styles for a greater aesthetic appeal. While they may cost a little more, they save on construction time and require less expertise to install.

The Advantages Of Using Engineered Wood Truss Products

Nationally recognized standards for truss designs ensure that trusses are of a very high quality and uniform standard.

Trusses are able to have longer spans than those of traditional methods which gives the design professional more space to work with inside the building and larger spans require fewer internal load-bearing walls.

Uniform design and manufacturing ensures a stronger roof and proven durability, unparalleled performance and a more uniform pitch that adds to the structural integrity of the building.

Raised-heel trusses create larger attic spaces which can be utilized for greater volumes of cheaper insulation. This helps to reduce the cost of insulation and provides a more effective building envelope and a greener home.

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Traditional framing methods take much longer to build and trusses use wood efficiently which makes them more economically and environmentally viable.

Complex roofing designs are easier to accomplish when using engineered wood trusses and this gives the designer more versatility.

Wood is a very sustainable building material and much research has gone into making trusses last longer and use as little wood as possible in their manufacture.

Ready to install on delivery; engineered roof trusses reduce construction time significantly.

Engineered wood trusses do not significantly contribute to onsite waste and can usually be installed without the use of heavy machinery.

Advanced Technologies In Roof Trusses

Much research has been put into truss designs and each individual truss is optimized for its specific roof configuration. A design professional will create a truss based on North American building codes specific to the home’s location.

The Canadian Wood Council describes the process of truss design: “Structural analogues and methodology have been developed and standardized by the National Associations representing the manufacturers of the metal plate connectors.

Lumber design values are determined in accordance with the wood design standards. Truss connector plates are proprietary and each plate has different structural properties.

Design values for truss plates are developed through tests and analyses in accordance with referenced standards.

Approval of the design values is overseen by National certification organizations.

Truss design is facilitated by the use of computer software that designs all truss members and connections and produces a design drawing with all the essential truss information.”

Truss Manufacture

The computer truss designs are translated into fabrication instructions. Each piece of lumber is inspected for suitability and strength. The lumber is cut and arranged according to templates before the metal plates at each joint are pressed into the lumber using a hydraulic press. These joints are checked before the trusses are ready for shipping to the job site.

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Can A Floor Be A Roof?

Question

Hi, I am working on a project here in CT where the contractor wants to use TRUFLOR for roof decking on a low-sloped roof application. Is this recommended over the TRUBORD? What are the pros and cons of using the two for this application?

Bill Copeland, North Branford, CT

Answer

Thank you for your interest in our OSB products. Certainly you can use our TruFlor for a roofing application. Our 23/32TG sub-flooring will give the roof more rigidity at equal truss spacing. It comes with a TG edge which could eliminate the need for roof clips, your local inspector will have to be the judge on that. TruFlor, because it is thicker than our Trubord, will be proportionately more expensive and heavier than Trubord. Other than that, given proper installation, you will have a very solid roof using our TruFlor for your project.

9-Foot Trims Increased Popularity

9-foot trims are becoming an increasingly popular choice and prices have reflected that preference.

The trend toward more 9-foot ceilings in both single-family and multifamily housing starts is really gaining traction. A survey by Random Lengths showed 2011 production of 9-foot and longer trims had increased to 31% of total output. Another survey by Wood Markets Report conducted in 2012 showed 9-foot and longer output had grown to 36%.

9-foot ceilings continue to take a bigger market share in new housing and it’s easy to see why; it just makes

sense to use longer panels. Taller wall panels reduce air leakage significantly; in fact, TallWall sheathing reduces air leakage by 60%. Taller wall panels are also faster to frame with less cutting, errors, and waste. Using taller wall panels is a common sense approach – with a

9 foot panel (or Windstorm’s 109 1/8” or 10’ TallWall or Windstorm’s 121 1/8”) using 4×9 and 4×10 panels allow you to cut out the window and door openings instead of cutting pieces and potentially leaving gaps. This also means stronger walls and less air leakage.

Taller wall panels like Windstorm and TallWall can provide a continuous load path and eliminate blocking and they can eliminate gable end hinge points because the panels extend beyond the top plates into the truss members.

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How Much Weight Load Is Solarbord Able To Support?

Question

We have SolarBord decking under Tru Slate. It weighs around 550 lbs. per square foot. We are replacing it with Spanish tile that weighs close to 1000 lbs. per square foot. Our rafters are on 24″ centers. Is the SolarBord capable of carrying that load?

Terry Allen, Oklahoma City, OK

Answer

Thank you Terry for your question. Table 30 of the APA Engineered Wood Construction Guide provides recommended load span information. The data in the table is based on 10 pound per square foot (psf) dead load. If actual dead load is greater than 10 psf the allowable live load is reduced proportionally. At 1,000 lb per square it equates to 10 lbs. per square foot dead load. Use the table and the thickness of the roof sheathing to determine what the allowable live loads are and if you are unsure, contact a professional designer to get their opinion because other variable may come into play. If you are going to change products – be sure to check that the structure below will support what you are doing.

Raised Heel Trusses: Environmentally Friendly Money Savers

Pre-fabricated trusses already save builders and framers time and money and offer other advantages such as a more uniform pitch. Their larger spans result in fewer internal load-bearing walls which reduces installation time and costs. Now discerning construction professionals are turning to raised-heel trusses thanks to the increased attic space they produce. This space is then utilized for larger amounts of cheaper insulation which reduces the cost of insulation and provides a more effective building envelope and a greener home. Raised-heel trusses offer many environmental and cost-saving benefits.

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Saving Money On Insulation

Traditional truss designs do not provide enough space for full-depth insulation. This means that the insulation has to be compressed which reduces its R-value. The raised-heel truss is fitted with a heel where the bottom chord intersects with the perimeter wall plate which enables the top chord to be raised by a foot or more. The extra height provides additional space for cheaper attic insulation varieties such as fiberglass batts, blown cellulose or blown fiberglass and the full depth of insulation to be extended right to the outside of the top plate. When full depth insulation extends to the outside edge of the top plate newer energy codes allow a lower R-Value across the entire attic area. This is allowed because the extra depth is at the outside wall—right where it’s needed the most.

The increased height of the raised-heel truss and the underlying insulation mean that heat is less likely to leak out at the eaves where insulation is thinnest. This prevents the formation of ice dams which can damage roofs during cold winter months.

Modern Techniques Increase Curb Appeal

Raised-heel trusses are engineered and manufactured to exacting standards making for a more robust roofing structure and an even pitch. The raised-heel truss allows roof lines to match up for an even, aesthetically pleasing result.

Saving Money And Time

Pre-fabricated trusses enable the installation of the roof framing in under a day. Getting a roof over the house prevents the structural components from unnecessary exposure to inclement weather and is instrumental in preventing buckling and moisture-related issues in roofing, flooring and wall systems.

When attics are adequately ventilated and properly sealed, raised-heel truss installations reduce the temperature and pressure differences between the attic and the building beneath it. This, in turn, reduces the heat transfer from the attic into the living space which means the HVAC system has to work less. This saves money on utility bills and means the HVAC system will last longer. A raised-heel truss roofing system also makes the attic space a more viable option for HVAC ducting as it provides more space for equipment.

Dry Time For Solarboard After Being In The Rain

Question

What is the required dry time after the solar board gets wet from rain (moisture) when it is installed on the rafters and ready for shingles to be installed. We do not want to trap moisture. Please advise the length of dry time. I have been forwarded from the website: “Solar board on roofs”. Thanks,

John Baker, Oklahoma

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Answer

Thank you for your e-mail John. If you get SolarBoard roofing panels wet, then wait for them to attain 15 to 18% moisture content. As a rule of thumb, in approximately 3 days of no rain the board should be ready for roof covering material. If it is going to be a rainy period you may want to felt it in to help retard some moisture and make sure the board is good and dry before shingles are applied.

Can You Use Pinnacle Subflooring On A Roof?

Question

Is your Pinnacle Subflooring suitable for roof applications?

Eric Noel, Carbonear, Newfoundland

Answer

Thank you for the email Eric. I assume you are referring to a pitch roof with typical rafter/truss spacing. It will make a very strong roof for sure and if you proceed I recommend you install the panels with the groove facing the eve as that would reduce the chances of moisture getting trapped in the groove. You would, of course, still need to space the square edges 1/8”, cover the roof as quickly as you can, and you may need to use longer nails to accommodate the thicker panels. If this is a flat roof with wider spacing of the supports please refer to your designer, code official, or architect to ensure the dead loads are within the roof system capabilities.

Can You Install Roof Sheathing Over Real Wood?

Question

Can a roofer put Norbord 7/16 on my roof when I have real wood on it too?

Dona Bruce, Powell, TN

Answer

Thank you for the e-mail and question Dona. I suggest you check with your local building department to make sure there are no building code regulations regarding this. Ideally the boards would be removed but that certainly would add to the cost. Many roofers have

installed OSB over roof boards if the boards are in good condition. If the boards are cupped or in bad condition you may want to consider replacing the ones with issues or sanding down any places where the edge of the boards are not even.

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Any variations that exist currently in the roof (i.e. rafters that are out of alignment) will still be there even when overlaid with OSB. The flatter and smoother the surface, before installing the new OSB, the better the finished job will be. You must have a good solid nailing base for the panels and your new roofing material. As with any roof please make sure you have proper attic ventilation and the roofer spaces all the edges of the OSB 1/8” to allow for expansion due to changes in moisture conditions.

Replacing Cedar Roof Shakes With Asphalt ShinglesIf it’s time to replace your roof, cedar roof shingles are an attractive but more expensive option than asphalt shingles. In fact, cedar roof shakes can be six or seven times the price of asphalt roofing. Asphalt shingles are ubiquitous for a reason; they are inexpensive and easy to maintain, although they do require replacement every 10-20 years. Their tar-like hydrocarbon and crushed stone, sand and gravel composition is naturally water-repellent and they come in a variety of colors and styles to suit your home. Asphalt shingles are relatively easy to install and perform well in harsh climates. If you are considering a shift from cedar shingles to asphalt, there are a number of factors to consider.

Asphalt Shingle Installation Considerations

Cedar roofs will keep the attic up to 15-20 degrees cooler than asphalt shingles. This means that if you are converting to an asphalt roof, your summer cooling costs will increase. One option here is to install radiant barrier sheathing. Radiant barrier sheathing is able to reflect up to 97% of radiation and can keep your attic temperatures up to 30 degrees cooler and you may find that your cooling costs are less than they were with cedar shingles.

Cedar roofs are installed with boards running perpendicular (spacing of those boards depends on the length of the cedar shingle) and the shingles are applied directly to these boards with no plywood or OSB roof sheathing.

When cedar shingles are removed and radiant barrier sheathing is installed over these boards, the efficiency is reduced by the percentage of the foil which comes in contact with the boards. You can overcome this by removing all the boards and installing the sheathing or by removing some of the boards and gaining some benefit from the radiant barrier sheathing. The efficacy of the radiant barrier will depend on the spacing of the boards. Removing some or all of the boards will add to the cost of your roofing. While the roof is open it is a good opportunity to investigate whether installing hurricane clips is possible as those may prove vital in saving your roof if you ever experience a high wind event.

95% of residential roofs in the U.S. are sheathed with structural wood panels. To prevent buckling of the asphalt shingles, the roof sheathing must be correctly installed (see APA guidelines here.) Attics must be effectively ventilated utilizing a combination of eave and ridge vents. In colder climates, an effective vapor retarder must be installed.

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Space wood sheathing panels 1/8” apart to allow the panels some room to move when adjusting to humidity levels and to prevent buckling.

Install a proper roofing underlayment and edging to ensure that the roof is completely waterproof. Install the underlayment over dry panels as soon as possible to protect the panels from exposure to the elements.

Install drip flashing flush along the eave and (in colder climates) prevent ice dams by applying an ice barrier such as self-adhesive waterproof underlayment, which sticks to the roof sheathing and seals around nails driven through it. If you live in a zone which experiences inclement weather, your building codes may require applying it 3 to 6 ft. up from the eave (minimum of 2 ft. past the exterior wall). Consult your design professional and building inspector for local code requirements. Ice dams can also be prevented with effective attic ventilation.

Felt or fiberglass underlayment is then installed with an overlap of 2 inches. Always lay upper pieces over those beneath to prevent water or ice from getting in under the layers. Underlayment protects the roof from rain and increase the fire resistance. Refer to manufacturer’s instructions for shingle installation.

Spray Foam Vs. Radiant Barrier Sheathing: Pros And Cons

When installing attic insulation, a case can be made for both radiant barrier sheathing with typical types of insulation as well as spray foam insulation. A number of factors should be taken into consideration when choosing between these two, especially the climate zone that you’re building in. Radiant barrier sheathing is inexpensive and reflects thermal radiation to keep attic spaces cool. Spray foam offers insulation and provides some sound proofing from outside noise.

Radiant Barrier Sheathing

Attic spaces are predominantly heated through radiation. The foil surfaces of radiant barriers reflect the heat and prevent it from radiating into the attic space. That means the home will be more comfortable and the efficiency of attic insulation and the AC system will be improved.

OSB radiant barrier sheathing can reflect up to 97% of radiation and can significantly reduce attic temperatures. Dave Lewis from Norbord: “The use of radiant barrier sheathing can reduce the attic temperature by about 30°F. Estimates put a payback for the radiant barrier of 1 to 2 years in energy savings from then on it acts as a passive energy saving system that never wears out.”

This means that your attic stays cooler in hot summer months and radiates less heat into your home which translates into savings on your summer cooling costs of up to 17%. Cooler attics and more comfortable living spaces improve your cooling system efficiency and prolongs its life by reducing

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cycle times. Radiant barrier sheathing may only cost an additional few hundred dollars per house over regular sheathing and it requires no special tools or trades to install. Radiant barriers increase shingle temperature by only a few degrees and do not affect shingle warranties.

Elizabeth D Kaufman, Architect: “I have long been skeptical of radiant barrier products. I was completely surprised when I found that the shell building I inspected yesterday was 80- 90 degrees inside. It was 106 outside!!!! The only possible explanation was the Norbord Solarbord decking. The building had no ceilings, no wall insulation, and no gypsum board. The windows and door were not caulked. The windows were low quality, dual pane, not Low-E and faced south and west. I really expected it to be beyond sweltering when I arrived at 1:30pm. I had to insist that the door be kept closed to keep the ‘cool’ air inside.”

Radiant barrier sheathing should only be used in cooling climate zones 1, 2, & 3. Radiant barrier sheathing can only be retrofitted to existing homes when the roof is being replaced. It is installed with the foil facing the attic and must have air space (minimum of ¾”) in front of the foil to work and of course code required ventilation.

Spray Foam Insulation

Spray foam is a great way to keep heat in your home in the winter and increased R-values will also make your attic space cooler in the hotter months. In small homes where space is at a premium or in areas that are difficult to insulate, spray foam may be a good option.

Spray foam insulation does provide greater R-value per inch as well as a way to seal your home. Spray foam insulation also helps to reduce the temperature difference between the home and the attic space. If you are placing ductwork in this space, this will help your heating and cooling systems to function more efficiently. However, since you are conditioning an additional floor, you will have to weigh energy savings with the cost of heating and cooling that extra space.

Spray foam is expensive and may cost you thousands of dollars over conventional types of insulation. It also requires trained and skilled installers because, like any insulation, there can be gaps and holes if installation is not done properly. In most cases it is the installer that tells you the R-value in your home and not an independent agency.

Spray foam installed to the underside of your roof leaves no way to cool that side of the roof system. This may cause your shingles to overheat which may reduce their longevity and require you to replace them sooner. Check your shingle manufacturer’s warranties as some void or limit warranties or require special roof details when foam is used on the underside of the sheathing.

Spray foam insulation doesn’t protect attic spaces from radiant heat, but does protect them from convection and conduction. In the summer, radiant heat is the biggest contributor to heated attic spaces, so spray foam insulation may not be as effective in keeping attics cool.

Combining these two insulating methods in order to optimize your insulation won’t work. Placing materials up against the foil negates the benefit of the radiant barrier and heat will simply be conducted through the materials and into the attic space. When it comes to hot attic spaces, radiant heat is the main culprit and radiant heat barriers are an effective and economical option. Both radiant barriers and spray foam offer benefits so all options including a cost/value analysis should be considered. Also consider a third option;

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raised heel trusses as they create space for more insulation. Using more blown cellulose or fiberglass batts can exponentially improve your R-value and give you more bang for your insulation buck.

Wet Spray Cellulose Insulation GuidelinesWhile wet spray cellulose insulation has been utilized in some parts of the US for decades, other builders are just beginning to use this highly effective insulation method. Wet spray cellulose insulation is used in lieu of spray foam or fiberglass batts in attics and walls and is a mixture of insulation, water and adhesive. Wet spray cellulose insulation offers a number of advantages including reduced air infiltration, effective sound reduction, increased fire resistance and savings of 20-50% on utility bills. There are a couple of vital steps to remember when installing wet spray cellulose insulation to ensure an effective building envelope.

Things To Consider During Installation

Ensure that all the sealing has been done first. Insulation is moot when gaps in the building envelope allow conditioned air out. A blower door test can be performed to evaluate the effectiveness of the building envelope.

Determine what settled thickness or R-value you want from your insulation. Wet spray cellulose insulation will lose about 13% volume through settling when the hose is held at a 45° angle. While the hose is usually held at a 45° angle during installation, smaller areas may restrict movement. When the cellulose is sprayed at a different angle, less settling may occur. Settling will impact the performance of the building envelope.

Do not blow insulation up against chimneys. Leave at least a two-inch gap between the wet spray cellulose insulation and your chimney. See the technical document from National Fiber for specifications on chimneys, vents and recessed lights here.

When installing wet spray insulation into walls, bulges between studs will occur. These can be eliminated by rolling with an aluminum roller designed for this purpose.

A 1,600 sq. ft. home with 2×6 studs will add over one hundred gallons of water to the house. Ensure that the insulation is completely dry before hanging the drywall. Drying times will vary according to the ambient climate and moisture content of the cellulose.

Space heaters are often used to expedite drying times. Moisture content can be measured with a moisture meter to ascertain suitability (usually less than 20-25% moisture; check your manufacturer and design professional’s specifications). Factoring added drying times into the building schedule will prevent delays.

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Drying times may increase when insulation is installed during inclement or cold weather. To mitigate installation failures, the insulation must be kept above freezing and the indoor moisture content must be controlled.

Hanging drywall too early before the insulation has had time to dry can lead to trapped moisture. That moisture may lead to buckling of the wall sheathing and other significant issues.

The wood framing will expand as it absorbs moisture from the wet spray cellulose insulation. If it is not afforded sufficient time to dry out, the subsequent drying over time may result in buckled wall sheathing, nail and screw pops and gaps in the wall assembly that could compromise the integrity of the building envelope.

Not allowing sufficient time for the insulation to dry out will result in corroded copper pipes, fasteners and other metal building components. Mold may also start to form in areas where insulation is not sufficiently dried.

Moist wet spray cellulose insulation will also result in swelling and uneven drywall. Always check with your local building department and your supplier to determine if a vapour barrier should or should not be installed.

Infrared thermographic inspections can be utilized to determine the efficacy of the wet spray cellulose installation.

Find more installation documents and specifications from CIMA here.

Orientation Of OSB Roof Boards When Installing

Question

Can your OSB roof boards be installed either side up?

Adrian, Fort Lauderdale, FL

Answer

Thanks for your question Adrian. The OSB roof panels should be installed with the grade stamp facing into the attic and the screened surface (with the nail guide lines) facing up. Structurally it doesn’t make a difference but

if the grade stamp faces up it will be covered by the roofing material and the building inspector will not be able to confirm the right OSB panel has been used for that application. Also the screened surface provides better traction for anyone working on the roof during installation.

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Radiant Barriers: Myths Busted And Facts ExplainedRadiant barriers are utilized to reduce summer heat gain in attics. Attics heat up when the sun’s radiant energy heats the shingles and the heat is transferred to the interior attic space through the roofing materials via conduction. The temperature of the attic space increases and that heat is transferred to the building below; increasing summer energy consumption and cooling costs. A radiant barrier can lower that heat transfer, keep the attic space cooler and lower cooling costs by up to 17% in warmer climates.

Radiant Barrier Myths

Radiant barriers have become somewhat shrouded in urban myth. They were not, for example, invented by NASA, but rather by the far less exciting German businessmen Schmidt and Dykerhoff in 1925. NASA has employed radiant barriers since the Apollo program for use on equipment, astronaut suits and spacecraft to protect against thermal radiation and for insulation in the fluctuating temperatures of space. It’s also a fact that the color and reflectance of a substance doesn’t add to its efficiency as a radiant barrier. While radiant barriers do contribute significantly to the reduction of cooling (and in some cases heating) costs, they are not the panacea to energy efficiency some make them out to be; they need to be utilized as part of a cohesive building envelope.

Radiant Barrier Sheathing

Radiation from the sun is the primary source of heat affecting your attic temperature. Radiation (infra-red) is augmented by convection and conduction. Convection is when heat is transferred through the air inside the attic and heats the insulation and conduction occurs when heat moves through the insulation to the building below. While heat is radiated and conducted in all directions it always moves from hot areas to cold areas. The hotter the attic, the more the heat moves down to the cooler building below.

The most effective radiant barrier sheathing is a structural roof sheathing panel which consists of an OSB panel with heat-reflecting foil laminated to one side. Other kinds of radiant barriers combine reflective materials (usually aluminum foil) with materials like plastic films, cardboard and kraft paper. A radiant barrier must have an emissivity of 0.1 or less to be effective.

Benefits Of Radiant Barrier Sheathing

• When utilizing OSB radiant barrier sheathing, you can reflect up to 97% of solar radiation which translates into an attic heat reduction of up to 30°F.

• A cooler attic space means less heat moving to the cooler space below the attic.

• The hotter it gets the better radiant barriers work.

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• The reduced attic temperature increases the efficiency of attic ductwork which prolongs the life of your heating and cooling systems because there are fewer cycle times.

• In warmer climates your may be able to reduce A/C requirements by up to ½ ton.

• Radiant barrier roof sheathing helps to improve comfort in the building interior during the warm summer months and reduces energy costs. Because heat always moves from hot areas to cold areas, radiant barrier sheathing also prevents heat transfer from the warm interior during the cooler winter months.

• Radiant barriers may help you qualify for Energy Star: “Seal and Insulate with Energy Star”.

Installation Notes

Radiant barriers require expert installation to work effectively. They should be installed with the foil side facing into the attic, adjacent to an open air space. You must ensure the attic ventilation is not blocked. If dust accumulates on the foil surface it will render the radiant barrier less efficient.

When installing radiant barrier roof sheathing, ensure that the manufacturer’s instructions are followed carefully. When installing any structural roof sheathing you are required to ensure the sheathing is spaced a minimum of 1/8” at all joints, to allow for expansion and contraction due to changes in moisture conditions. Check your local building codes, your design professional’s specification’s and the APA’s Construction Guide E30V.

Attics must be properly ventilated to meet code and to ensure that hot air can escape from the attic and to remove moisture that builds up too.

Once installed, don’t let other materials like insulation come into contact with the foil. Leave at least a ¾” space or use baffles to create a sufficient air space.

Building or retrofitting your attic with a radiant barrier will improve the value and saleability of the home. The savings on energy usage and size and duration of HVAC systems can translate into savings for the home owner and provide an excellent return on investment.

The Importance Of Attic VentilationWhile it may seem counterintuitive to insulate an attic for warmth and then install vents that allow outside air in, ventilating your attic is key to reducing moisture, avoiding mold and preventing the formation of ice dams.

Vented Attics Help Mitigate Moisture

In the winter, air flowing through the attic will help to keep the area above your insulation cool. This prevents ice dams which can form when heat from the interior migrates through the insulation, melting snow that has

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collected on the roof. The resulting water can freeze, build up and expand under the shingles where it can cause leaks. Moisture from the house can also condense on attic insulation.

Wet insulation is less effective and can lose up to 1/3 of its R-value. Having a dry attic can result in lower heating costs over the winter months and lower cooling costs in the hot, summer months.

Condensing moisture on roof sheathing can result in edge swell (ridging) in the roof sheathing panels or lead to the growth of mold and mildew; a problem which can be avoided with proper ventilation.

Prevent Damage To Shingles

In the summer, well-ventilated attics help to remove hot air and moisture from the home. Attics are ventilated actively with an attic fan or passively utilizing a combination of vents on the soffits and gable and natural air flow. Ineffective ventilation can void the roof shingle manufacturer’s warranty. This intense heat can also transfer to the building interior which will increase summer cooling costs.

Adequate ventilation of the attic works by allowing air to be drawn in through soffit vents and exhausted through ridge vents. The peak is the hottest area in an attic and the best place to exhaust that hot air. Building codes require ventilation of the attic at a ratio between 1:150 and 1:600 with the most common being 1:300. Consult your local building codes for specifications or follow your design professional’s specifications.

Attics in more complex roof designs (like those in hip roofs, cathedral designs, multiple dormers, trey ceilings and around skylights) should all be ventilated and may even require attic fans to encourage air flow. If attic fans are used, a thermostat along with a humidistat can monitor temperature and moisture levels so that the attic fans get turned on only when required. For even better energy consumption, opt for solar-powered attic fans.

Cool-Roof Or A Double-Sheathed Roof Designs

Locating ductwork or other mechanical systems in attic spaces is another trend common in the south and where slab-on-grade construction means ducts must be in the attic. As ductwork is generally only insulated to a rating of R-6 and is often leaky, energy losses will be higher. Always ensure the ducts are sealed well, insulated as much as possible, and run in straight lines with a minimum of bends wherever possible. Having a radiant barrier roof sheathing is an efficient way to keep attic temperatures cooler in hot climates. Having a large pressure and temperature difference between the attic and the conditioned rooms below will only add to energy loss through the ductwork.

If not applied properly insulation on the underside of panels can lead to ridging (swelling of the edges of the wood panels) and may void sheathing and shingle warranties. When moisture cannot escape and is trapped, swelling of the roof sheathing can result in buckling, mold, mildew and ultimately in a reduction of structural integrity.

From the APA TT-111: “The use of insulation materials that inhibit the drying of wood structural panel wood sheathing, such as some direct applied insulation on the underside of the sheathing, could lead to structural panel performance issues such as buckling and other moisture-induced problems. When such insulation materials are used in combination with an impenetrable layer on top of the roof sheathing, such

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as some adhered shingle underlayment materials, the risk of moisture problems due to reduced drying potential of the system will increase substantially. This could lead to potential long-term accumulation of moisture in the roof system resulting in costly and potentially hazardous structural deterioration as well as possible health risks.”

Ken Joliffe from Norbord suggests that one solution is to install a: “vented area underneath the shingled deck when under-sheathing foam insulation is utilized—basically a cool-roof or a double-sheathed roof with an air space allowing air to flow from soffit vents to ridge vents under the shingled sheathing.”

The quality of a finished roof system is a combination of quality materials, design, and attention to installation details. Ventilation is a critical factor in ensuring that moisture and hot summer air issues are addressed correctly. This will help to preserve the structural integrity of your roof system, reduce energy costs in the warm summer months, improve the effectiveness of your insulation in the winter months and prevent the formation of ice dams.

Roof Tips. - Norbord

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