Combining and Mulling Windows · Starting at the top of the replacement windows, slide the “H”...

WEB BASEDAPPLICATION SPECIFIC INSTALLATION INSTRUCTIONS

Combiningand MullingWindows

Although all possible measures have been taken to insure the accuracy of the material presented, WIXSYS, and the author are not liable and do not assume any liability in case

of misinterpretation of directions, misapplication, improper installation, or typographical error.

Combining Two or More Windows

The Illustrated Guide to Installing Vinyl Windows Contents © 2004-14 Do not reproduce without permission

A mulled unit is the combining of 2 or 3 (or more)units into one opening. Replacement windows can be mulled side by side (a picture window flanked bydouble hung on each side or two double hungs), or“stacked” on top of each other (a transom over a double hung or a picture window over an awningwindow). The most common mulled units are side by side.

Basically, windows can be placed together in multiple units into any opening.In fact, the sameinstallation procedures (blindstop installation orother techniques) will still apply. Mulled units, inessence, become a single unit that will install andmount similarly to single units. The mull systemseffectively seal the joint.

There are two common ways to join windows togeth-er. One uses an "H" mull which is provided by themanufacturer. This vinyl shape is made to slip overthe frame of two windows as shown in the drawing.

The other mull system is most commonly used invinyl products that contain a "groove" in the outsideand inside surfaces of the frame - on top, bottom,and both sides. A "U" shaped, snap-in mull is usedto join the windows. The "U" mull is stronger struc-turally than the "H" mull, but both systems workwell.

How to Join with "H" MullsIf you desire to mull two or more units, order windows to include an “H” mullion for each joint and a continuous head expander, and sill angle long enough to fit the entire width of mulled unit.

After the opening is prepared for the replacementwindows, remove all sashes of the windows to bemulled. Note: Leave strap (if provided) on all win-dows until fully installed.

Measure the opening height approximately whereunits are to be mulled. Cut “H” mullion 1/4” lessthan opening height. Then measure opening width at top and cut continuous head expander 1/8” lessthan the measured width. Also measure openingwidth at bottom and cut continuous sill angle 1/8”less than that width.

Starting at the top of the replacement windows, slidethe “H” mullion onto windows side by side. Liquidsoap on inside of mullion can make this easier.Install the continuous head expander over top of the windows and “H” mullion.

Install a full-length sill angle if necessary and setwindows into openings. Shimming the sides andaligning the windows carefully, try to keep the units tight to the “H” mullion for maximum support.Once mounted, check plumb and square. Then re-install and align all the sashes. Complete theinstallation with caulk, capping and trim as necessary. Now you can remove any provided straps.

To mull vertically (stacked units), remove any operating sash. Using the “H” mullion, cut it 1/8”less than opening width. Place the head expander ifprovided) on the top window, and mount the sillangle (if necessary) “below” the lower window.

Carefully install mulled unit into opening. Re-installand align any removed sash. As before, remove anyprovided straps, and complete the installation withcaulk, capping, and trim as necessary.

How to Join with "U" Mulls

It is possible to join and stack multiple windows to accommodate various architectural, design, and structural situations. When stacking windows,or where you want the windows joined prior to installation, snap-in "U" Mulls work better than "H" mulls because they are structurally joined toboth sides of the windows.

Common to welded (fusion corner joints) vinyl win-dows and especially in awning and casement types,the frame - inside and outside on all perimeters -contains a groove that will accept a specially extruded "U" shaped mull that snaps in to "lock" the units together. If the windows you are installinghave this groove, then it is preferable to use the "U"mull. It is important to note, however, that the weightof vinyl replacement windows with 3/4" insulatedglass can be excessive and the mulls may not bestrong enough to hold the weight if a multiple unit isto be lifted into an opening already mulled. The ruleof two people per window also applies to multipleunits. Therefore, be sure you have enough help whenlifting mulled units into place.

When stacking windows or mulling more than twounits together, in most instances, it is easier andmore efficient to mull the units prior to installation. However, when the combination unit will be unwieldyor extremely heavy, partial mulling can be donebefore installation, and the remaining units attachedafter they are placed in the opening.

The available, U-shaped, “snap” mulls are applied onthe inside and the outside of the multiple windowunits. Place the two windows together and press thelegs of the mull down into the slots in the windowframe. As shown in the diagram, the tabs on themull legs snap into the slots holding the two windowsfirmly together. It is important that the mulls beaccurately pre-trimmed to the proper length prior touse because they are difficult to remove. Since themulls protrude from the face of the window frame,they should be trimmed to allow for any moulding ortrim to be applied after installation. This will providea neater, more easily weather-sealed job.

Head Expander

"H" MullionSill Angle

Snap-inMullSnap-in Mull

Lower Window

Upper Window


“H” Mulls and Snap Mullsare Mechanical Mulls,designed to join two or morewindows where the windowsdo not need to be structuralor support any weight.

Stacking two windows, oneon top of the other, wherethose windows can beanchored to the surround-ing rough framing is accept-able for most residentialapplications where windowpressures are not near hur-ricane or even tropical force.

When windows (and doors)are joined in an area nearthe ocean or where highwinds can be expected, a structural mull is required to meet mostbuilding codes.

A Structural Mull is usually a piece of steel with legs at top andbottom that allow the mull to be securely fastened to the headerand sill - or even to the jambs where a horizontal mull is required.

Then the window units are anchored to the mull with high perfor-mance fasteners so that the finished assembly is a structural unit,secured to the surrounding framing and forming a weather andwind resistant fenestration unit.

Where codes demand it, the structural mull is used in testing of thewindow and door units themselves in order ot get a rating whichthen is used to determine compliance with the required perfor-mance for the climate and region.

When it is necessary to install window and door assemblies thisway, there are usually engineering drawings showing the propermull size and anchoring details of both the mull(s) and the windowor door units.

Structural Mulls


1. Begin by removing the sashes andany foam insulation, jamb adjustersby backing out the screw for theadjuster.

2. Cut a piece of plywood, exteriorgrade preferably, to fasten to one win-dow jamb. Take care to align to thetop and bottom. Secure with three#8x1/2” Philips Head Pan Screws.Repeat this step on the other window.

3. Apply a bead of caulk sealantalong the interior edges of the “H”Mullion legs.

4. Place the ”H” Mullion on to thejamb of the first windows and alignthe Mull with the top and bottom ofthe window.

5. Nest the second window into the“H” Mullion and squeeze the windowstogether making the frames seatedcompletely into the Mull. Use a puttyknife to help slip the Mull over thetwo windows.

6. Stand the assembly upright andcheck the alignment. If necessary usea rubber mallet to align.

7. Starting with the upper installationholes, screw the windows into the “H”Mullion using #8 x 1-5/8” Phips PanHead Screws.

8. Repeat by anchoring through thelower installation hole. Do this withboth windows, angling both screws soas not to interfere with each other.

9. Using Silicone Sealant, seal theopen cavities completely on both endsof the “H” Mullion so there are novoids where water can penetrate.

10. Place two metal straps along thetop of the Mulled Unit and use#8x1/2” Philips Pan Head Screws tosecure the straps. Repeat on bottomof the Mulled Unit.

11. Re-install the upper and lowersash of each window. If a HeadExpander and Sill Angle are needed,they can span both windows.

Fastening the Mechanical “H” Mull


AWDI recommends anASTM C920, Class 50sealant such as OSI®QUAD® MAX that isdesigned for exterior/inte-rior use for sealing around windows, siding anddoors. Sealants like OSI®QUAD® MAX bond best to a wide variety of materi-als and their versatility inperformance providesvaluable features and ben-efits for all installers.

AWDI understands that the application of a sealant isas crucial as the choice of sealant. When a bead ofsealant is applied to a joint there are three factors toconsider:• Adhesion• Flexibility• DurabilityWithin these three performance aspects there arecountless combinations of applications, substratesand conditions a sealant is exposed to.

Bedding Joints: For bedding joints, it is especiallyimportant that the sealant is of theright consistency and made up of100% solids so it will not shrinkafter cure, unlike solvent and latexbased sealants that shrink and cre-ate gaps after curing.

Fillet Joints: A fillet joint is formed whentwo surfaces come together toform a right angle. Thesealant used to join these twosurfaces is triangular inshape. The sealant mustadhere to the variety of sub-strates you’re faced with.Without strong adhesionthere is a high chance thatthe sealant will pull awayfrom the substrate allowingfor air and water infiltration.

Control Joints:A control joint is formed when two similar or dissimi-lar materials meet or when substrates do not form aright angle. This joint will require both a backer rodand sealant for proper application. This joint can beas wide as 5/8 inch and be prone to extreme movement, a highly flexiblesealant is necessary for a reliable seal with thisapplication. In order to successfully install a win-dow or door and effect alasting weathertight seal,

Picking the Proper Sealant

Desired Properties

Contractors Guide to Installing Vinyl Windows ©2015-2016 All Rights Reserved

ADHESIVE JOINT

BOND BREAKER

TAPE

ANGLED JOINT

BACKER ROD

No Shrinkage

Locks out air and water infiltration to protectintegrity of the seal

Proven Wet Surface Application

Ability to use the same sealant in warm and cold temperature situations to produceconsistent results. 0F – 140F cold and warmweather application

Strong Adhesion / All Surfaces Will stick toeven the most difficult to bond buildingmaterials

5X stretch, 50% joint movement Long termdurability assurance even with expansionand contraction of building materials

24 hour fast cure, paintable 1 HR. Fast cureto protect the building structure from outsideforces and quick paintability saves time

Achieves bubbling resistance faster to ensureoptimal aesthetics

4,600 + Color Matches ensures perfect colormatch to all primary building materials

Dirt & Dust Resistance ensures optimal visual appeal long after an installation

UV Resistance

Long term durability to compliment the durability of the building structure

••

••

•

•

•

•

•

•

••

While the term “Spray Foam” is often widely used inconstruction, there are two different types and eachhas its advantages and disadvantage.

Spray foam has been shunned by window installersand manufacturers over the years because foams, inthe past, have either continued to expand after trimhas been applied deforming the more pliable vinylwindow frames, or because they have been over usedto fill the gaps left when old windows are removedand the underlying rough opening has been exposed.

Make sure the foam you use has been tested toindustry standards and is labeled conforming tostandards as a low expansion, low pressure foam.

Most standards applying to window installation donot delineate between open cell foam and closed cell foam, the more popular “minimal expansion”foams are most frequently used and they are mostlyclosed cell. More confusing yet, is when foams arerecommended, the compressed foam tape alternativesare called out to be open cell.

When it comes to Spray Foams, it helps to under-stand the differences.Open-cell spray foam (ocSPF)has a cell structure where the cells are filled with air.The open-cell structure renders soft, flexible foam,with a density of about 0.5-0.8 pounds per cubic foot(pcf).

The R-value per inch of open-cell foam typicallyranges from R3.6 to R4.5 per inch. Unlike fiberglassand cellulose, the fine cell structure of ocSPF makesit air-impermeable at certain thicknesses. The air-impermeability of ocSPF qualifies it as an air-barriermaterial, dramatically reducing air leakage throughthe building envelope, significantly lowering thebuilding’s heating and cooling costs. However, ocSPF, like fiberglass and cellulose insulations, is moisture-permeable, and may require the installa-tion of a vapor retarder in colder climates.

Closed-cell spray foam (ccSPF) has a closed cellstructure which yields rigid hard foam, with a

density of 1.8-2.3 pound per cubic foot (pcf), and can provide structural enhancement in certainframed buildings. The smaller cells trap insulatinggas from the curing, which has a lower thermal conductivity than still air, and increases the R-valueto anywhere from R5.8 to R6.9 per inch.

Like ocSPF, ccSPF is also air impermeable at certainthicknesses and can qualify as an air-barrier materi-al. The bigger benefit is that the closed-cell structureof ccSPF also makes it water-resistant, and is theonly spray foam that can be used where contact withwater is likely.

At a thickness of 1.5 inches, no additional vaporretarder is required for most applications.

Spray Foam Insulation


Industry tested and labeled as a LowPressure/Low Expansion; i.e., will not warp or deform windows & doors

Quick Setting Formulation: can be cut ortrimmed in less than 1 hour

Cold Temperature Application: can beapplied in temperatures as low as 14F

Insulation Value of R5: makes it an efficientmethod for stopping air and moisture infil-tration

Remains Flexible Once Cured: will not crackor dry out

•

•

•

•

•

Desired Properties

Using Spray FoamFor the best installation, it is necessary for the gaparound the window or door to be sealed to block outair, water and vapor penetration. ccSPF can do thatwell if selected and used properly. Improper use cancreate water traps, impede drainage and exert exces-sive pressure to the window frame during expansion.

Remember: Vapor barriers need to applied on thewarm side of the opening. Double vapor barriers (one on the warm side and another on the cool side)encourage condensation between and will trap theresulting condensation. Also, window installationcavities (the space between the window frame and the rough opening, or left-in-place old window frame)need to “breathe” to the outside, and allow drainageof collected water to the outside.

Used wisely, ccSPF can be the best solution. AWDIrecommends ccSPF’s like OSI® QUAD® Foam whichis a polyurethane closed cell, low pressure/lowexpansion sealant to fill the gaps as protectionagainst moisture and air. OSI's closed cell foam alsoachieves a thermal performance of R5 per inch.

ApplicationOSI® QUAD Foam is applied using a Foam ApplicatorGun. This foam and gun combination allows for moreprecise application than the straw grade foam alter-native. This gun offers a rear valve used to controlthe size of bead applied into the openings. The valvealso allows the life of the foam to be extended by clos-ing the opening of the barrel for future use.

For even smaller openings, a detachable screw on topis included with the gun to be able to fill gaps assmall as ¼” wide.


Important tips:• Similar to the sealant gun, it is critical that you balance the movement of the foam gun or straw barrel and how you dispense the foam so that thefoam makes contact with both the rough or existingwindow frame and replacement window frame.

• If the dispensed foam does not make contact withboth the rough frame and the window frame, therewon’t be an adequate bond to seal out water and air.

• Industry Standards suggest application of 1 inchbeads, separated by an equal space. Be careful not to create two vapor barriers - one at the exterior andone at the interior. Make sure there is the ability forthe opening to breathe to the cold side for drying anddrainage. Use backer rod about one inch in the sill asa stop to make a workable back dam

• When applying foam around the perimeter of the window or door, you must maintain a minimumdepth of 1 inch. This depth is required to provide the correct thermal performance, to help improveenergy savings, and to protect against condensationproblems.

• When applying foam as a back dam to the gapbetween the window frame and the rough sill, do not allow the foam to extend to the exterior edge ofthe opening. Maintain a minimum of a 1 inch gapbetween the foam and the exterior edge of the roughsill. If foam fills this gap at the sill, any water fromleakage will not be able to drain to the drainage planeor exterior cladding surface. Place backer rod thelength of the sill, 1” from edge and use it as a backdam guide.

Backer Rod

1”Set Back

FoamBead

FoamBead

Combining and Mulling Windows · Starting at the top of the replacement windows, slide the “H”...

Documents

Transcript of Combining and Mulling Windows · Starting at the top of the replacement windows, slide the “H”...