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This Online Learning Seminar is available through a professional courtesy provided by:

Fiber Composites LLC dba Fiberon181 Random DriveNew London, NC 28127Tel: 800-573-8841Email: [email protected]: www.fiberondecking.com

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Wood-Plastic Composite Cladding for Sustainable Rainscreen Wall Systems

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Wood-Plastic Composite Cladding for Sustainable Rainscreen Wall Systems

Fiber Composites LLC dba Fiberon181 Random DriveNew London, NC 28127

Rain has been cited as the most important thing to control in wall construction. Rainscreen systems have, for over five decades, proven to be highly effective in this regard. Following an analysis of moisture management issues and rainscreen systems, this course then identifies the unique attributes of wood-plastic composites (WPCs) for use in rainscreen applications. It concludes with a detailed description of how WPC cladding should be applied and fastened in rainscreen systems.

To ensure the accuracy of this program material, this course is valid only when listed on AEC Daily’s Online Learning Center. Please click here to verify the status of this course. If the course is not displayed on the above page, it is no longer offered.

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This course is approved by other organizations. Please click here for details.

The American Institute of Architects · Course No. AEC1037 · This program qualifies for 1.0 LU/HSW Hour.

AEC Daily Corporation is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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AEC Daily Corporation has met the standards and requirements of the Registered

Continuing Education Program. Credit earned on completion of this program will be

reported to RCEP at RCEP.net. A certificate of completion will be issued to each

participant. As such, it does not include content that may be deemed or construed to be

an approval or endorsement by the RCEP.






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How to Use This Online Learning Course

• To view this course, use the arrows at the bottom of each slide or the up and down arrow keys on your keyboard.

• To print or exit the course at any time, press the ESC key on your keyboard. This will minimize the full-screen presentation and display the menu bar.

• Within this course is an exam password that you will be required to enter in order to proceed with the online examination. Please be sure to remember or write down this exam password so that you have it available for the test.

• To receive a certificate indicating course completion, refer to the instructions at the end of the course.

• For additional information and post-seminar assistance, click on any of the logos and icons within a page or any of the links at the top of each page.






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Purpose and Learning Objectives

Purpose:

Rain has been cited as the most important thing to control in wall construction. Rainscreen systems have, for over five decades, proven to be highly effective in this regard. Following an analysis of moisture management issues and rainscreen systems, this course then identifies the unique attributes of wood-plastic composites (WPCs) for use in rainscreen applications. It concludes with a detailed description of how WPC cladding should be applied and fastened in rainscreen systems.

Learning Objectives:

At the end of this program, participants will be able to:

• analyze indoor and outdoor environmental conditions to identify potential moisture management issues when designing exterior wall assemblies

• design and specify the appropriate rainscreen wall systems to deal with those issues

• compare various cladding materials for suitability in rainscreen systems

• select the most appropriate WPC cladding to be integrated into a rainscreen system, and

• specify and detail WPC cladding rainscreen systems to ensure their long-term sustainability.






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This CEU is registered with the Interior Design Continuing Education Council (IDCEC) for continuing education credits. This credit will be accepted by the American Society of Interior Designers (ASID), International Interior Designers Association (IIDA) and Interior Designers of Canada (IDC).

The content included is not deemed or construed to be an approval or endorsement by IDCEC of any material or construction or any method or manner of handling, using, distributing or dealing in any material or product.

Questions related to specific materials, methods and services should be directed to the instructor or provider of this CEU.

This program is registered for 1 CEU value. The IDCEC class-code is: CC-106885-1000

• This CEU will be reported on your behalf to IDCEC and you will receive an email notification. Please log in and complete the electronic survey for this CEU.

• Certificates of completion will be automatically issued once you have submitted the online survey for this CEU. • Attendees who do not belong to ASID, IIDA or IDC and do not have a unique IDCEC number will be provided with a

Certificate of Completion after this CEU.






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Table of Contents

Understanding Moisture Management 8

Moisture Management with Rainscreen Walls 23

Exterior Cladding Options for Rainscreen Walls 31

Wood-Plastic Composites in Rainscreen Walls 47

Summary and Resources 67

Click on title to view






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Understanding Moisture Management

Kim Hansen own work CC/BY-SA/3.0 via Wikipedia commons

https://commons.wikimedia.org/wiki/File:Iceberg_with_hole_near_Sandersons_Hope_2007-07-28_2.jpg

https://creativecommons.org/licenses/by-sa/3.0






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Moisture Management

Introduction and scope of course:

Moisture management (MM) is a highly complex topic especially when considered in combination with energy management.

MM is a highly researched and often debated issue, affected by local weather building codes, building materials, interior environmental conditions, and the method of envelope assembly, etc.

While MM applies to the entire building envelope, this course introduces the highlights of MM issues and then focuses on above-grade exterior walls and the role of rainscreen systems for those walls.

Further resources for extended research are listed in the final section of this course.






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The Importance of Moisture Management

“Rain is the single most important factor to control in order to construct a durable (i.e., sustainable) structure.”

-- Dr. J. Lstiburek, highly esteemed building science expert

“The management of moisture migration is by far the most important control function to be addressed by the building

enclosure designer.”

-- T. Kesik, Whole Building Design Guide, 2016

“Except for structural errors, about 90 percent of all building problems are associated with water in some way.”

-- ASTM 241-77






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Impacts of Improper Moisture Management

Moisture damage issues cost the US construction industry $9B annually and also result in considerable lost time and energy due to litigation and repair.

Widespread envelope failures in Vancouver, BC, Wilmington, NC, and Minneapolis, MN have highlighted the potential for major problems affecting all builders across the country.

“The evidence suggests that significant building envelope failures in British

Columbia since the early 1980s ... are a result of numerous factors, including

design features inappropriate for that climate (elimination of cornices in an

attempt to mimic styles found in hot dry climates); a reliance on face-sealed

wall systems*; a fundamental lack of awareness regarding the principles

of enclosure design suitable for our climate; meaningful inspection at

critical stages of construction; and a regulatory system which was unable to

understand that failures were occurring and to redress them.” https://en.wikipedia.org/wiki/Leaky_condo_crisis

* A rainscreen wall system is the opposite of a face-sealed system.Information GNU Free Documentation via Wikipedia

https://en.wikipedia.org/wiki/Indoor_mold

https://en.wikipedia.org/wiki/GNU_Free_Documentation_License

https://en.wikipedia.org/wiki/Leaky_condo_crisis






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Impacts of Improper Moisture Management

Building sustainability and performance can be seriously and adversely affected by improper moisture management, as uncontrolled moisture may reduce the structural soundness of buildings through dry rot in wood, corrosion in steel, freeze-thaw cycles, spalling and efflorescence in masonry, etc.

Moisture also can affect the health of occupants, typically through the potential for breeding harmful organisms.

In essence, uncontrolled moisture will adversely affect the most vital attributes of all buildings.






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Moisture Traits and Behavior

Moisture exists in three states:

1. vapor (mist, clouds, steam, etc.)

2. solid (ice, snow, hail, frost, etc.)

3. liquid (rainwater, condensation, flooding, groundwater, snowmelt, etc.)

A wall assembly may have more than one state of moisture in it at the same time, and this makes it more complex to deal with.

Moisture also moves in multiple directions:

• horizontally (infiltration and exfiltration)

• upwards (through stack effect and pressure differential)

• downwards (by gravity)

Moisture may be moving in multiple directions and in multiple states within a wall assembly (rain coming in and vapor going out) at any given time.

1

2

3






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Building Material Traits Affecting Moisture Behavior

Some building materials may capture water molecules from the surrounding air and collect them on the surfaces of their inner pore structures in what is known as an adsorbed* state.

Hygroscopic (hydrophilic) materials absorb water, and most traditional building materials such as wood, concrete, brick, and plaster are hygroscopic.

Hydrophobic materials repel water; examples include glass, metals, and plastics, including wood plastic composites.

Some materials exhibit hybrid behavior, such as water resistive barriers (housewrap and building felts) that can resist bulk water but freely allow vapor diffusion.

*Adsorption is the adhesion of molecules of gas, liquid, or dissolved solids to a surface. This

process creates a film of the adsorbate (the molecules or atoms being accumulated) on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid.






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Moisture Management Strategies

Most MM strategies begin by carefully considering appropriate control measures for the many sources of liquid moisture (water).

It is important, however, to analyze all directions and states simultaneously and to use strategies and materials that accommodate them all. There can be competing strategies that create new problems (trapped moisture), and these must be avoided.

The four major transport mechanisms are precipitation and splashback at grade, water vapor in the air (including interior air), built in/stored moisture, and liquid and bound groundwater driven by capillary action and gravity.

Other drivers/creators of moisture and moisture movement include wind, gravity, capillary action, pressure differential, stack effect, condensation (dew point), air leakage, and location of building components in the building envelope (vapor barrier, vapor retarder, air and water barriers, interior finish, insulation amount and type, etc.).






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Exterior Moisture Movement Drivers

1. Gravity draws water down through cladding openings and cracks into the construction assembly.

2. Capillary forces act like a sponge, drawing water into small cracks and pores. The smaller the cracks, the greater the capillary forces. A capillary is a narrow, tube-like space or void in a material or assembly that can draw up water by a combination of surface tension and adhesive forces. Materials like wood or concrete can behave this way in wet conditions. The degree of capillarity in building materials can affect their trapped moisture content after a wet event, which reinforces the need to prevent these materials from becoming excessively wet and can limit or eliminate their usage in vulnerable situations.

1

2






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Exterior Moisture Movement Drivers

3. Wind can drive rain through the openings in the cladding.

4. The pressure differential can push or pull water through openings and cracks into the construction assembly.

Note: These movement drivers are the ones that apply directly to the rainscreen portion of the wall (exterior face), but the insulation, interior surfaces, and vapor barrier affect moisture migration from inside to outside.

3

4






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Impact of Energy Management on Moisture Management

The increasing emphasis on energy efficiency in building enclosures (30% increase in mandated amounts of insulation in the last decade) often results in wall and roof cavities that are highly insulated with air and vapor permeable insulation materials and/or barriers. This can create strong temperature gradients across the wall cavities, and experimental research has shown that any moisture in the cavity will migrate toward the cold side of the assembly, driven largely by vapor pressure differences.

The impact of envelope airtightness on moisture movement is an issue of placement and detailing of vapor barriers and retarders and of allowing any moisture entering the envelope to escape while ensuring the dew point is outside the vapor control layer.

For further detailed information:

http://www.wbdg.org/resources/moisture-management-strategies Dew points occurring within the wall system create condensation and trapped moisture.

http://www.wbdg.org/resources/moisture-management-strategies






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Moisture Management in Building Envelopes

For a moisture problem to occur in the building envelope, there must be five conditions present:

1. a moisture source must be available; root causes for presence of moisture are external moisture, internal moisture, and trapped construction moisture (uncured concrete, rain-soaked framing or sheathing)

2. there must be a route or means for this moisture to travel

3. there must be some driving force to cause moisture movement

4. the material(s) involved must be susceptible to moisture damage, and

5. the moisture content must exceed the material’s safe moisture content for a sufficient length of time.

Construction materials can become wet and must be allowed to dry before being enclosed in order to avoid trapped moisture.






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The key to effective MM is to limit moisture penetration ASAP and then to provide an easy escape route for any moisture that gets in.

Eight of the top ten reasons for moisture issues are related to problems with the building envelope:

1. water leaks around windows; poor flashing

2. water leaks at roof/wall intersections

3. poorly installed building wraps

4. inability of walls to drain and dry

5. wrong product selection

6. misplaced vapor barriers

7. ineffective air barrier system

8. poorly installed insulation

9. poorly designed/installed HVAC

10. plumbing leaks






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The underlying premise for good MM is that the envelope workmanship and materials will be imperfect, construction moisture is unavoidable, and the most practical strategy involves redundancy of critical control measures.

MM must also be reinforced through proper construction, quality assurance, and commissioning of the building enclosure.

MM must take into consideration the climate and precipitation exposure (many experts advise rainscreen installations for all houses in areas with an average annual rainfall of 60″ or more and suggest it is still a good idea in areas of less rainfall); choice of materials and their physical attributes and arrangement, especially those on control layers; and bulk water, capillary water, and vapor migration mechanisms.

Improper detailing (lack of gap between siding and roof) caused this siding to rot from capillary action of water entering the pores of the engineered wood siding.






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The Four Ds of Exterior Wall Design

The first step in any wall design is the selection of an appropriate method for the climate (see impacts of improper MM).

Following that, there are four basic areas of consideration:

1. Deflection: The more water you can deflect from the exterior surfaces, the more you reduce the moisture load on the assembly, and the less you have to drain from the assembly.

2. Drainage: The faster assemblies can drain water, the less water will be absorbed by building components.

3. Drying: The greater the assembly’s drying potential, the less chance there is for fungal growth and decay.

4. Durability: The less the components are impacted by water, the longer they are likely to last.

Appropriate overhangs are critical in deflecting

rain from the exterior surface. National Research Council of Canada

http://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n34






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Moisture Management with Rainscreen Walls






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Moisture Management with Rainscreen Walls

Rainscreen walls offer two lines of defense from moisture penetration into the building envelope:

1. a first line of defense that minimizes rainwater passage into the wall by minimizing the number and size of holes and managing the driving forces acting on the wall, and

2. a second line of defense that intercepts all water that gets past the first line of defense and effectively dissipates it back to the exterior.

A rainscreen wall is an exterior wall* system where the visible wall cladding acts as the primary moisture barrier and stands off from a second hidden moisture resistant surface (air/moisture barrier) applied to the sheathing.

This arrangement creates a capillary break and allows drainage, evaporation, and drying of any moisture that penetrates the cladding as well as any moisture trapped in the wall.

* Rainscreen principles can be applied to below-grade walls and slabs on grade, but as noted earlier, this course focuses on rainscreens in above-grade walls.

1. Primary moisture barrier stops most of the water.2. Air gap (vented in this case) disperses any that

gets past it.3. Secondary moisture barrier stops the small

amount of moisture remaining while allowing the skin to breathe.






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Rainscreen Wall Components: Outer Cladding

A rainscreen is a system of four basic components. Each component functions to complement that of the other components.

1. The outer cladding or primary water/rain/moisture barrier takes the greatest velocity and volume of moisture. Depending on the material and details, some moisture (water) may pass through it in much lower volumes and greatly reduced velocity. This water then drains vertically within the gap behind the cladding down to the vents at the bottom and out onto the ground.

If the cladding layer is formed with absorptive or hygroscopic materials (stone, brick, or wood), it may become saturated over time. This moisture must be allowed to escape to the gap or the exterior face.

Ideally, the outer cladding layer will be nonabsorptive or hydrophobic, aesthetically pleasing, impact resistant from hail and ice, and resistant to abuse, UV degradation, etc.






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Rainscreen Wall Components: Air Gap

The second component is:

2. An air gap behind the exterior cladding. This gap (sometimes referred to as a channel or cavity) may be vented at both the top and bottom or just the bottom*. Its primary function is to provide the route for any moisture (water) that passes through the outer cladding or is trapped within the interior wall assembly (vapor) to escape. The other functions of the air gap include the drying of exterior cladding and wall sheathing and assembly materials, the prevention of wicking, breaking the capillary bond of the exterior materials to the wall, and allowing collected moisture to escape through evaporation, diffusion, and gravity.

The gap can be as small as 3/8″ and can be formed with bumpy house wrap, furring, foam pads, etc.

* The adjacent image shows vents at top and bottom, and at flashings.






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Rainscreen Wall Components: The Weather Resistive Barrier

The third component in a rainscreen system is:

3. The Weather/Water Resistant Barrier (WRB). This layer is also often referred to as the drainage plane. In order for a drainage plane to be effective, it must be continuous and integrated with flashings.

The most common material used for this layer is house wrap, which resists the penetration by water from the exterior into the sheathing but which also allows the passage of vapor/trapped moisture from the interior to the gap. House wrap also functions as an air barrier preventing external air from passing through the envelope to the interior.

Building felts, various troweled materials, and foam insulations are also used for this layer. The capacity of this second line of defense compensates for any inadequacies in the first line of defense. In an ideal system, this layer never gets wet, but in the worst case it should only have a small amount of moisture under low pressure to deal with.

By Samdogs, Putting on Housewrap CC BY-ND 2.0 via Flickr; brand name of product has been erased

https://www.flickr.com/photos/samdogs/537519898

https://creativecommons.org/licenses/by-nd/2.0/






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Rainscreen Wall Components

The fourth and final rainscreen wall components are:

4. Flashings which are thin pieces of impervious material installed to prevent the passage of water into a structure from joints in the WRB system.

Flashing is intended to prevent water penetration at windows, doors, vents, pipes, chimneys, etc. in order to make buildings more durable and to reduce/prevent moisture management problems.

Flashings must be carefully sealed into the WRB in order to function properly. (Note how the WRB overlaps the flashing upstand.)

Metal flashing materials include aluminum, copper (very expensive), stainless steel, and galvanized metal.






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Rainscreen Types and Terms

In some cases, a rainscreen wall is called a pressure-

equalized rainscreen or PERSIST (pressure equalized rainscreen insulated structure technique) where the ventilation openings are large enough for the air pressure to nearly equalize on both sides of the rainscreen.

They are also called basic, vented (openings at bottom only), ventilated (openings at top and bottom), unventilated, cavity walls, drained walls, drainscreen, conventional, and pressure-moderated rainscreen systems or assemblies.

The terms may be used inconsistently and can become confusing, but all of them refer to the key rainscreen principle of a primary and secondary line of defense.

Pressure Equalized Rainscreen WallNote the various directions of moisture movement






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Rainscreen Performance and History

Vetruvius initially described the virtue of ventilated cavities in his The Ten Books on

Architecture 2000 years ago, but the modern term and interpretation was not introduced until 1960 in Norway and then in Canada via the National Research Committee in 1963.

It has since been described as the perfect wall (J. Lstiburek, building science expert, 2010)

A perfect wall has four control layers, listed in descending order of importance:

1. rain control layer

2. air control layer

3. vapor control layer

4. thermal control layer

The rainscreen concept and its details have been refined and proven over the five decades since their introduction, and they address three of the four Ds (drainage, drying, and durability).

Deflection is addressed with the building configuration (overhangs).






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Exterior Cladding Options for Rainscreen Walls






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There are many options for rainscreen cladding, but the individual performance of each material in this role varies with its specific attributes. This course reviews several of the most common materials and their relevant attributes and issues.

Brick (Masonry) Veneer

Because masonry is absorptive, codes have required a gap behind brick veneers for some time. Those gaps also need weep holes at the bottom to allow any trapped moisture to escape. It is important that the gap or channel be kept free of mortar droppings in order that these weep holes are not blocked.

Weep hole with plastic grid insert

By Erik Wannee (Own work) CC 1.0 via Wikimedia commons

Brick vent with plastic insert

https://commons.wikimedia.org/wiki/File:Open_stootvoeg.jpg

https://creativecommons.org/publicdomain/zero/1.0/deed.en






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Synthetic stone and natural stone are both porous (like brick masonry) and are known as reservoir claddings (i.e., they hold and store water readily).

They therefore also require gaps behind them for drainage and weep holes at the bottom of the gaps to discharge the water.

For synthetic stone, two layers of #30 felt with a three-dimensional drainage mat or dimple mat between them creates the drainage cavity. Wire lath over the felt paper allows the mortar to adhere to the wall.

Natural stone set on a ledge can have a gap similar to that for brick.

For details see, “Improving Drainage and Drying Features in Certain Conditions: Rain Screen Designs for Absorptive Claddings” and “Stone and Synthetic Stone.”

http://www.greenbuildingadvisor.com/green-basics/stone-and-synthetic-stone#ixzz4n8LzKXyp

http://www.cosella-dorken.com/bvf-ca-es/pdf/articles/RainScreenDesigns.pdf






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Vinyl Siding

Because it already has an airspace behind it, vinyl siding does not require a rainscreen installation unless it is installed on top of rigid foam that is more than 2″ thick, in which case it should be installed over vertical furring strips.

Engineered Wood Siding

In the lower image, this siding has rotted because it has been installed in contact with the roofing.

Proper detailing would have left a gap between the two materials.

Engineered wood also requires a gap behind it to function like a rainscreen, and installation requires careful detailing to avoid the sort of rot shown here.

By Capt. Elizabeth Brown public domain via Wikimedia commons; brand name has been covered

https://commons.wikimedia.org/wiki/File:U.S._Army_1st_Sgt._Benton_Gill_measures_the_length_of_the_house_before_he_installs_the_siding_in_Edinburgh,_Ind.,_Aug_110812-A-DX536-003.jpg

https://en.wikipedia.org/wiki/Public_domain






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Stucco

There are various types of stucco. From a distance they look identical, but they are very different. Conventional stucco (upper image) is a cladding made of inorganic cement (Portland cement and/or lime), bonded sand, or earth as used for thousands of years. It is also known as a reservoir cladding and it requires venting.

EIFS (exterior insulated and finish system) (lower image) uses an acrylic co-polymeric (organic) bonded aggregate and cement reinforced with a glass mesh. The material is bonded to insulation boards, which are adhered to the WRB on the substrate.

EIFS can be applied in a drained or nondrained system. The former is a rainscreen approach and is the most common today because it is among the most robust and advanced moisture control assemblies available. It is often the required approach in building codes.

The most common method of forming the gap is to use vertical beads of adhesive on top of the WRB.






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Cement Board Siding

This type of siding also absorbs and stores moisture (note the dry spot under the overhang and the wetting pattern around the window and above the roof).

It requires the same level of detailing (gaps and separations, etc.) as other rainscreen materials.






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Wood-Plastic Composite (WPC) Claddings

WPCs are composite materials made of wood fiber/wood flour and recycled high-density polyethylene plastic (HPDE). In addition to wood fiber and plastic, WPCs may also contain other ligno-cellulosic and/or inorganic filler materials; colorants; coupling agents; stabilizers; blowing, forming, and foaming agents; and lubricants.

They may contain as much as 94% recycled material (plastics and lumber mill scraps) and they are available without toxic chemicals or finishes. In addition they release no carcinogens when cut.

Some products are capped on all four sides with polymeric plastic to offer long-term resistance to staining and fading.

Since their introduction to North America in the 1990s, they have demonstrated that they never need painting, staining, or refinishing.






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Durability Attributes

Look for:

• a high ratio of plastic to cellulose; high ratios of cellulose are cheaper but less durable

• nature and completeness of cappings: plastic surfaces that provide wood fiber weather, fading, and staining protection (look for capping on four sides)

• resistance to cracking, splintering, mold, decay, and insect infestation

• dimensional stability

• UV resistance, and

• water absorption characteristics; products capped on all sides absorb negligible amounts of water and the core remains dry.






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Aesthetic Attributes

Look for:

Texture options A wide range of colors Color streaking options






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Green/Sustainable Attributes

Look for:

• source and percentage of recycled material in product and recyclability of product itself

• green manufacturing processes (percentage of material recycled in plant, nature of plant energy system, efficient usage of renewables and clean energy sources, proximity of plants to markets and method of transport, etc.)

• history of company (length of time in business, track record of products), and

• strength, length, and comprehensiveness of product warranty as well as exclusions and cautions in warranty.






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Installation, Maintenance, and Life Cycle Cost Attributes

Look for:

• ease and flexibility of installation

• easy to cut

• no special tools or trade-specific labor required

• no protective equipment required

• boards prefinished on top and bottom

• ability to fit onto curves

• maintenance requirements, if any, and

• long- and short-term costs.






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Codes, Standards, and Best Practices Attributes

Building codes are essentially one step above illegal practices, and green/sustainable buildings must far exceed these minimum standards. Recent codes have gotten stricter and may require WRB, flashings, and moisture management. Simultaneously, increasing industry demands and code requirements for energy efficiency affect wall construction including the amount and type of insulation which, in turn, affects moisture movement. In some climates (BC and Oregon) rainscreens are mandated.

The National Green Building StandardTM ICC 700-2012 states in Flashings 602-1-9:

“(5) A rainscreen wall as follows is used for exterior wall assemblies:

a) A system design with minimum 1/4″ airspace to the exterior of the WRB vented to the exterior at top and

bottom of wall

OR

b) A cladding material or a water resistant barrier with enhanced drainage, meeting 75% drainage efficiency

determined in accordance with ASTM E2273”

.






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The International Residential Code (IRC) Section 1403.2.2 states:

“Envelope walls shall be designed and constructed to prevent the accumulation of water by providing a WRB behind

the exterior cladding and a means for draining the water that enters the assembly behind the cladding to the exterior

unless the wall passes a water resistance test according to ASTM E331.”

Please remember the exam password COMPOSITE. You will be required to enter it in order to proceed with the online examination.






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The pass/fail criteria for IRC Section 1403.2.2 (previous slide) states:

“The exterior wall envelope design shall be considered to resist

wind-driven rain where the results of testing indicate that water did

not penetrate control joints in the exterior wall envelope, joints at the

perimeter of openings penetration or intersections of terminations

with dissimilar materials.”

WPC claddings can exceed code and test requirements for exterior walls because of their enhanced durability and water resistance attributes; a WPC rainscreen is considered a best practice even when not required. Builders are increasingly applying rainscreen principles voluntarily because of their reliability.

WPC claddings also help to qualify buildings for better ratings from LEED®, BREAMM, WELL Building Standard®, and Green Globes®, etc. and to meet/exceed various standards such as ASTM, the Building Enclosure Moisture Management Institute (BEMMI), and the National Green Building Standard. ASTM E331 water penetration test simulates 8″ rain/hr

with 50 mph wind.






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Install with concealed deck fasteners or composite material screws.Longer board lengths replace splices and labor.






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Wood-Plastic Composites in Rainscreen Walls






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Wood-Plastic Composites in Rainscreen Wall Systems

Primary WPC attributes specific to rainscreen suitability:

• It is hydrophobic and absorbs almost no water.

• It is aesthetically pleasing with a wide range of appearances.

• It provides the warmth of wood with a more favorable cost of ownership.

• It provides ability to mix and match colors for dramatic effect.

• It is not affected by freeze-thaw cycles.

• It resists fading and staining.

• It never needs painting, staining, or refinishing.

• It has minimal, manageable maintenance requirements.

• It significantly reduces moisture load on building assemblies.

• It won’t crack, splinter, peel, decay, or suffer insect infestation.

• It can be used in a vented system to aid drying.

• It is simple, safe, quick, and straightforward to install and does not require specialized labor or tools.






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Wood-Plastic Composites in Rainscreen Wall Systems

Further benefits include:

• high percentage of post-consumer recycled material that diverts wood and plastic from landfills

• no toxic chemicals or preservatives used or released

• no chemicals after manufacture

• boards are prefinished, saving labor, time, and expense

• no carcinogens are released during cutting

• material is available nationwide with short lead times

• easily bent to enable curved and radial wall installation

• longer board lengths speed installation and reduce splices

• no protective gear is needed, and

• it is backed by long-term residential and commercial warranties

• 25-year performance limited residential warranty

• 10-year performance and finish limited commercial warranty.






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WPC Installation for Rainscreens

Installation on furring is

straightforward.

DO NOT use “toed” screw fasteners: drive perpendicularWhere boards butt, add more furring

*use 1x3 doubled as shown or

use 1x4 PT SYP* or engineered equal

*PT SYP means pressure treated Southern yellow pine *






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Gaps are created between planks and above grade and fasteners are carefully spaced.






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End, butt, bottom and side gaps are also specified. Proper gapping and spacing is essential. While wood is affected by moisture gain and loss, WPC cladding is affected by temperature gain and loss.

Space 1/4″ from hard surfaces like walls andposts.






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Detailed, illustrated, sequential instructions and specifications from the manufacturer make installation even simpler.

Sample specification excerpt for horizontal applications:

1. Determine and begin at lowest point of cladding

installation.

2. Butt joints to occur only over vertical furring and centered

on furring. As WPC board courses are added, stagger

butt joints in a consistent “stair step” manner.

3. Board lengths to span a minimum of three furring

members.

4. Gapping: Provide minimum 3/16-inch spacing between

board edges. Spacing at end of boards is temperature

dependent; refer to manufacturer’s published technical

data for spacing dimensions.






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Siding may be installed vertically using both horizontal and vertical furring. Sample specification excerpt for vertical WPC installation:

1. Prior to installation, verify required horizontal and vertical furring

strips are in place to receive vertically-orientated board installation.

2. For walls exceeding available board lengths, separate boards with

a noncorrosive metal z-flashing. Allow ¼-inch clearance between

top of lower cladding boards to underside of z-flashing. Maintain

½-inch clearance between z-flashing and start of upper cladding

boards.

3. Start cladding board installation by first securing the top of the

board and then working downward.

4. Using 3/16-inch spacers to maintain gapping, secure the next

WPC board course starting from the top and working downward.

5. Where a balanced symmetrical WPC board layout design requires

less-than-fullwidth end boards, maintain a minimum 3-inch width

for ripped boards. Increase board-to-board gapping to

accommodate; not to exceed 5/16 inch.






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WPC Fasteners for Rainscreens






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Fastener specification involves several considerations:

Visibility Hidden or visible

Aesthetic Blend in or stand out

Environment Stainless steel is always recommended; salt spray may require SS316

Installation Speed of installPredrill or not to predrillImportance of vertical fastener alignmentStandard install: • Through cladding, wood furring, sheathing into framing

Nonstandard install: Variances in sheathing • Wood vs. gypsum vs. insulation• Variances in structural materials (steel studs, metal gauge)






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Fastener Types:

Composite screws are designed specifically for the materials through which they are moving (WPC or PVC boards) and into which they anchor (typically this is wood).

Composite screws have :

1) a head configuration designed to prevent mushrooming

2) a thread configuration that enlarges the hole to prevent splintering, and

3) a point thread design for low torque and smoother drive (no predrilling and faster penetration).






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Conventional (i.e., noncomposite) screws need to be predrilled and their heads countersunk.

Predrilling is needed to eliminate mushrooming.

Predrilling is through the cladding only.






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Concealed deck fasteners are approved face fasteners that provide a near invisible installation.

These screws:

• use special drill bits

• feature a very small head that is driven below the surface, and

• include color-matched plugs to minimize the appearance of the screw head (lower image).






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Best Practices

� adhere to all spacing requirements

� test aesthetic of fastener

� change driver tips often

� align screw lines perfectly

� use erasable chalk snapping lines

� drive screws perpendicularly

� fasten into center of furring

� never try to “toe” a screw

� use SS fasteners or screws designed specifically for project or aesthetic

Poor Practices

× ignore spacing requirements

× do not test fastener aesthetic

× use worn driver tips

× create erratic screw lines

× use permanent chalk

× drive screws at an angle

× fasten into edge of furring

× try to “toe” a screw

× use inferior quality screws or screws not designed for project or aesthetic







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WPC Rainscreen Installations

Horizontal installation on a contemporary residence






< >


A horizontal commercial application harmonized with other materials






< >


A vertical, single material, single (variegated) color, commercial installation






< >


As the entire envelope cladding






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On a tall wall in two board lengths with intermediate flashing






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On small walls, doors, and fences horizontally, vertically, and diagonally on a curve






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Summary and Resources






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Summary

There is considerable evidence that moisture, and in particular, rain, can be very destructive to building envelopes and interiors, and that managing this moisture is critical to building durability and occupant health. There is a parallel body of evidence demonstrating that rainscreen walls are most effective in managing moisture, especially rain, and in ensuring the durability and integrity of building envelopes.

While there are a number of ways to create or describe a rainscreen wall, they all offer two lines of defense to moisture penetration. Of those two lines, the outer cladding, or first line of defense, deals with the vast majority of rain and the highest water and air pressures. The attributes of the materials chosen for this outer cladding and their ability to resist these and other forces over long periods of time are critical to the performance of a rainscreen wall.

WPC cladding has many attributes that make it most suitable to a rainscreen exterior wall cladding application. In addition to absorbing negligible amounts of water, it is resistant to impact, freeze-thaw cycles, UV degradation, fading and staining, cracking, splintering, peeling, decay, and insect infestation.

When installed according to manufacturer’s instructions, WPC rainscreen cladding provides a maintenance- and problem-free, aesthetically pleasing façade, which in turn behaves as a superior and reliable first line of defense over long periods of time.






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Resources

Brown, W.C. et al. “Designing Exterior Walls According to the Rainscreen Principle.” National Research Council Canada. Government of Canada, December 1999, http://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n34. Accessed July 2017.

Erikson, Brian. “EIFS vs. Stucco: What’s the Difference?” Pie Consulting and Engineering, 8 June 2012, http://www.pieglobal.com/articles/eifs-vs-stucco-whats-the-difference. Accessed July 2017.

Fink, Justin. “Keep Siding Dry with a Vented Rain Screen.” Issue 213. Fine Homebuilding. The Taunton Press, Inc., n.d., http://www.finehomebuilding.com/2010/07/15/keep-siding-dry-with-a-vented-rain-screen. Accessed June 2017.

Holladay, Martin. “All About Rainscreens.” Green Building Advisor. The Taunton Press, Inc., 20 December 2016, http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens. Accessed June 2017.

Kavanaugh, Catherine. “New Uses for Composite Building Materials.” Plastics News. Crain Communications, Inc., 1 February 2017, http://www.plasticsnews.com/article/20170131/NEWS/170139966/new-uses-for-composite-building-materials. Accessed June 2017.

Kesik, Ted. “Moisture Management Concepts.” Whole Building Design Guide. National Institute of Building Sciences, 5 August 2016, http://www.wbdg.org/resources/moisture-management-concepts. Accessed June 2017.

http://www.wbdg.org/resources/moisture-management-concepts

http://www.plasticsnews.com/article/20170131/NEWS/170139966/new-uses-for-composite-building-materials

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-rainscreens

http://www.finehomebuilding.com/2010/07/15/keep-siding-dry-with-a-vented-rain-screen

http://www.pieglobal.com/articles/eifs-vs-stucco-whats-the-difference

http://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n34






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Resources

Kesik, Ted. “Moisture Management Strategies.” Whole Building Design Guide. National Institute of Building Sciences, 16 August 2016, http://www.wbdg.org/resources/moisture-management-strategies. Accessed June 2017.

Lstiburek, Joseph. “Drainage Plane/Water Resistive Barrier.” Info-301. Building Science Corporation, 20 May 2009,

https://buildingscience.com/documents/information-sheets/drainage-plane-water-resistive-barrier. Accessed June 2017.

Lstiburek, Joseph. “EIFS - Problems and Solutions.” BSD-146. Building Science Corporation, 11 July 2007,

https://buildingscience.com/documents/digests/bsd-146-eifs-problems-and-solutions. Accessed July 2017.

Lstiburek, Joseph. “Insulations, Sheathings and Vapor Retarders.” RR-0412. Building Science Corporation, 1 November 2004, https://buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders/view. Accessed June 2017.

Lstiburek, Joseph. “Mind the Gap, Eh?” BSI-038. Building Science Corporation, 15 November 2013, https://buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh. Accessed June 2017.

Lstiburek, Joseph. “The Perfect Wall.” BSI-001. Building Science Corporation, 15 July 2010, https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall. Accessed June 2017.

https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall

https://buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh

https://buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders/view

https://buildingscience.com/documents/digests/bsd-146-eifs-problems-and-solutions

https://buildingscience.com/documents/information-sheets/drainage-plane-water-resistive-barrier

http://www.wbdg.org/resources/moisture-management-strategies






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Resources

NAHB and Mark F. Williams. “Improving Drainage and Drying Features in Certain Conditions: Rain Screen Designs for Absorptive Claddings.” National Association of Home Builders, December 2008, http://www.cosella-dorken.com/bvf-ca-es/pdf/articles/RainScreenDesigns.pdf. Accessed July 2017.

Rousseau, M.Z, et al. “Pressure Equalization in Rainscreen Wall Systems.” National Research Council Canada. Government of Canada, July 1998, https://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n17. Accessed June 2017.

“What You Need to Know About Rainscreen Codes.” Primex Blog. Primex, 15 September 2014, http://www.primexfits.com/hvacventing/need-know-rainscreen-codes/. Accessed June 2017.

Wikipedia contributors. “Leaky Condo Crisis” Wikipedia, The Free Encyclopedia, 22 March 2017, https://en.wikipedia.org/wiki/Leaky_condo_crisis. Accessed June 2017.

Wikipedia contributors. “Rainscreen.” Wikipedia, The Free Encyclopedia, 14 June 2017, https://en.wikipedia.org/wiki/Rainscreen. Accessed June 2017.

https://en.wikipedia.org/wiki/Rainscreen

https://en.wikipedia.org/wiki/Leaky_condo_crisis

http://www.primexfits.com/hvacventing/need-know-rainscreen-codes/

https://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n17

http://www.cosella-dorken.com/bvf-ca-es/pdf/articles/RainScreenDesigns.pdf






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Conclusion

©2017 Fiber Composites. The material contained in this course was researched, assembled, and produced by Fiber Composites and remains its property. Questions or concerns about the content of this course should be directed to the program instructor. This multimedia product is the copyright of AEC Daily.

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