Wood-built “stick” wallscome in two sizes: 2x4 with plywood on the out-side and drywall on the inside to create a wallthickness of 45⁄8 inches, and 2x6 that providesa total wall thickness of 65⁄8 inches. This makesit easy for window manufacturers to producestandard jamb depths. And since windows inwood-frame construction are always set in wood,installation is relatively easy. Many window man-ufacturers make installation even easier by at-taching a plastic “fin” in the window jamb at theright depth. The fins come with predrilled holesfor screws or nails, so workers can quickly po-sition the windows flush with the wall surfacesand fasten them.

Concrete walls, on the other hand, are chal-lenging for manufacturers because there aremany different building systems, each withunique requirements.

THE CHALLENGE

Only a few companies specialize in makingwindows for concrete walls—usually basementwindows for foundation walls. Over time they’vedeveloped units that install easily. Manufacturersof traditional wood-frame windows, however, arebeginning to notice concrete homes; some arewatching the interest level in concrete housing todetermine future product development.

All of the major manufacturers are, however,making windows that meet the special needs ofhurricane states where building codes mandatewindow glass with high impact resistance andattachments between window jambs and build-ing frames that will withstand code-specifiedwind loads. Florida, with the most stringent windcodes also leads the nation in concrete homeconstruction—causing window manufacturers to

Rew

ard Wall S

ystems

Vin

yl T

echn

olog

ies

Above: Fortunately forconcrete homes, the buy-ing public favors thickexterior walls. Windowopenings can help toachieve this look. Thewood trim shown hereprovides a nice way to fin-ish a window well for thisICF home. Left: Using thePVC plastic window bucksystem by VinylTechnologies, workerscan quickly assemble thebuck to any size window.The reusable cornerbraces keep them squareand support the buck dur-ing concrete placement.

There are differences between installing windows in wood and in concrete walls

By Joe Nasvik

WindowsFORCONCRETE

HOMES

develop products that meet the code require-ments for both wood and concrete homes.

WHAT’S DIFFERENT ABOUT CONCRETE?The greatest difference between wood-frame

and concrete construction is the variety of con-crete home-building systems. They fall into fourgeneral categories: cast-in-place removable forms,insulating concrete forms (ICF), precast con-crete, and concrete block (CMU). The primaryconstruction issues for window manufacturersare wall thickness, the attachment system, andmoisture movement between jambs and walls.

Until concrete home-building systems stan-dardize wall thicknesses, window manufactur-ers will find it difficult to produce a standard“off-the-shelf” window for concrete walls. Re-movable form homes have typical wall thick-nesses of 4 or 6 inches plus the thickness of theinsulation. ICF manufacturers, according to PieterVanderWerf, Building Works, Brookline, Mass.,produce wall systems with as many as 50 dif-ferent thicknesses. CMU walls are typically 6or 8 inches thick plus insulation and inside andoutside finishes. Precast walls can be any thick-ness the customer wants. Window manufactur-ers will probably meet this challenge by sellingstandard windows with custom jamb extensionsincluded with each unit.

The second most important difference be-tween wood-frame and concrete is that there aredifferent methods for attaching windows to con-

crete walls—influenced in part by the locationof insulation on or in a wall. ICF systems have2 inches of expanded foam on both sides of awall. Removable form concrete wall systemsplace foam insulation on either side of the wallor in the center (referred to as a “sandwichpanel”). Precast wall systems are increasinglyusing the sandwich panel approach.

WINDOW BUCKS

Rough openings (inside the window buck)are different for windows designed for concretewalls versus wood-frame walls. Anthony Head,the Regulatory Product Planner for Marvin Win-dows, Warroad, Minn., says that the shim spacefor wood construction should be 1⁄2 inch, butonly 1⁄4 inch for concrete walls. It’s also im-portant that pine jambs not come in contact withconcrete because rotting can result.

The selection of a windowbuck system determines howwindows will be attached towalls. A buck is the form usedto block out openings for doorsand windows in concrete walls.It is either removed after con-crete placement or left in placeto become the attachment pointfor windows. Some form man-ufacturers sell removable metalbucks that block out for stan-dard window dimensions. Pres-sure-treated, rot-resistant woodis the most often used formingmaterial for bucks that are leftin place and anchored to theconcrete for attaching windows.

PVC plastic window bucksare also increasingly popular.Vinyl Technologies, Logan,Utah, makes a product called“VBuck,” which is fast be-coming the standard for ICFconstruction. It is shipped in16-foot lengths that workers

onsite cut to the proper size and insert the cor-ner pieces to the ends. Removable galvanizedsteel corner braces keep them square and sup-port the buck during concrete placement. Thebuck also surrounds the ends of the ICF formsto provide them with support. A fin in the cen-ter projects into the concrete for anchorage. Af-terwards, windows are anchored to the PVC withscrews. Justin Anderson, Vinyl Technologies’president, adds that it’s important to drill holesin the bottom buck to allow air to escape dur-ing concrete placement.

THE RECESSED LOOK

Thick walls are in vogue. Recessed windowscan help create this look. Dave Pfanmiller, Se-curity Built Homes, Raleigh, N.C., says its re-movable form concrete wall system is 6 inchesthick, including 2 inches of insulation. He in-

4"

The Recessed LookWindow

Window jamb

Caulk sealant

PVC windowattachment fin

Concrete

Molding

Air void andshim space

Finished surface

Foam insulation

Peel-and-stick seal

Outside

Wood sillBuck

Fig. 1. Here’s a method for installingwindows for either “removable form”or ICF wall construction. Windows arerecessed to show the thickness of thewall on the inside.

4"

6"

Stucco Bucks

Window

Window jamb

Window attachment

Caulk sealant

Stucco finishcoat

Foam insulation

Concrete

Attachmentto concrete

Wood buckformed into

concrete

Air void andshim space

Outside

Peel-and-stick seal

PVC windowattachment fin

Fig. 2. The detail for recessing windows to reveal thethickness of a wall on the outside of a home is shownabove. This works for both “removable form” and ICFconstruction.

Duk

ane

Pre

cast

The method ofattachment alsodepends onexterior wallfinishes. Thefinished surfacefor this homewill be brickveneer, so thefin on the window wasattached to theoutside of theconcrete wall.

stalls windows designed for 2x4 stud walls (jambwidths of 45⁄8 inches). To make this work, hiscompany constructs window bucks from 2x6pressure-treated lumber, nailing 1⁄2-inch plywoodgusset cross braces to the outside to make a 6-inch width and also to brace the frame. Next herips the buck to 45⁄8 inches wide to match thewidth of the window jamb then re-attaches this“ripper strip” to the buck prior to concrete place-ment. Afterwards he removes the strip to pro-vide the recess. (See Figure 1.) His companyusually installs a wood sill and drywall on theother three sides, careful to follow the windowmanufacturer’s air space requirements betweenthe buck and the jamb.

VanderWerf says that it’s also possible to cre-ate what he refers to as “stucco bucks.” (See Fig-ure 2.) This involves recessing the outside of thewindow jamb a couple of inches from the out-side wall surface, exposing the edge of the in-sulation. Polymer cement finishes are then placedover the insulation edge to give the impressionof a thick wall on the outside.

With CMU walls, window jambs made fromwood or metal designed for particular windowproducts are often set into window openings dur-ing the construction of the wall. Windows areeasily attached to the jambs afterwards.

Dukane Precast, Naperville, Ill., uses a par-ticularly interesting method for window installa-tion. It manufactures precast “double wall” pan-els for home construction which have 23⁄8-inchconcrete wythes (panels) on each side and a 31⁄4-

inch-thick void in the center, filled witha soybean derivative foam insulation.Brian Boch, Dukane’s director of mar-keting, says that by increasing the insidewythe opening, windows can be installedfrom inside the building. Workers use thefin strip that comes mounted on the win-dows and secure it to the outside wythewith screws rated for use in concrete. (SeeFigure 3.) The walls are 8, 10, or 12 inchesthick, so the window is recessed on theinside. The recessed area is trimmed withwood or drywall, and the window mold-ing covers the wythe opening.

PROVIDING WATERPROOFING

DETAILS

Planning for waterproof connectionsbetween walls and windows is very im-portant, and is best done before wall con-struction begins. Unfortunately, it oftenhappens after the walls are constructed,causing remedial solutions.

Framing carpenters typically installwindows. But Julio Chiarella, manager

of the Architectural Services Commercial Groupfor Pella Windows, Pella, Iowa, thinks that work-ers specifically trained for window installationshould do the work. His company is encour-aging its distributors to install the windowssince they are the most familiar and experi-enced with the issues and details that affectweatherproofing.

Chiarella recommends a three-step approachto moisture control. The first level of defense isto design the opening for a 3⁄8-inch-wide spacebetween the window and the finished outsidewall surface. This gap is filled with sealant. Thesecond level of protection is the application ofa “peel-and-stick” waterproofing tape betweenthe window buck and the jamb. The tape musthave good temperature and weather resistance,and be compatible with sealants. Chiarella’s thirdstep is placing a caulk sealant between the in-side wall and window jamb. “Winds cause pos-itive pressures that can push water and air through

walls. During the winter months many furnacescause negative air pressures inside homes, whichsucks moisture and air inside from leaks aroundwindows and other places. An inside sealanthelps to prevent that.”

WHAT MANUFACTURERS ARE DOING

European concrete building systems are moreadvanced than those in the United States, wherewood construction has dominated. But U.S.concrete housing is growing now, and so is thedevelopment of systems for window and doorinstallation, HVAC, electrical, and other homesystems for concrete buildings.

As noted previously, some of this develop-ment is due to concrete home construction inhurricane areas. Wind code requirements in manystates now mimic the Florida requirements, solarge window companies like Pella, Marvin, andAnderson are designing windows to meet thesecode requirements and to provide more effec-tive installations.

Head says that Marvin Windows has solvedthe problem of variable width walls by offeringjamb extension kits with their standard-sizedwindows in 1⁄8-inch width increments to workwith any wall thickness. This is becoming stan-dard for their window orders.

Pella Windows established a service to helpcustomers plan for window installations. Chiarellasays Pella consults on 300 to 400 projects eachweek to help work out installation details.

These big window manufacturers now com-pete with the manufacturers of basement win-dows who have considerable experience witheasy attachment systems for concrete walls. Ben-efiting from this, some of the basement windowmanufacturers are moving above grade, provid-ing quality vinyl windows for concrete homes.

Progress on the development of window sys-tems for concrete homes has paralleled the slow-growing popularity of concrete homes. Now thatconcrete home construction is poised to take off,the major window manufacturers have taken aninterest and new, simpler systems, and some stan-dardization, should soon emerge. •

With the “dou-ble wall” pre-cast system,windows caneasily bemounted frominside the home.The fin for thewindow isattached to theback side of theoutside wythe.

Installing Windows in

Precast–Double Wall Panel

Window

Window jamb

Caulk sealant

Concrete

Molding

Foam insulation

Painted or polymerstucco surface

Outside

Cast-in-placewood buck

Fig. 3. Using double-wall precast panelsthere’s the opportunity to install windows fromthe inside. This is how windows are fastened.

Joe Nasvik

Publication #R04K025, Copyright © 2004 Hanley Wood, LLC. All rights reserved