Guide to Window Materials & Construction Methods

Wood and Clad-Wood Windows

Earliest wood framed windows were left open, such as this example (below) from Xotolar, Mexico. Later in areas of more hostile climate windows were glazed with animal skins, then parchment, and finally, beginning with Roman windows built as early as 100 AD, glass.

But for centuries, even after the early and opaque Roman glass was used for glazing, most windows were framed with wood set into building walls and either left open or could be closed by wood shutters.

Below we show an antique wood window in a stone wall in Rugat, Spain, photographed by D. Friedman.

Behind the original wood framed window guarded by two vertical wood bars you can see that modern owners added a smaller wood-framed glass-enclosed window.

Our next window photo below illustrates a wood-built casement window set into an ornate stone wall in Barcelona, Spain. This wood framed window is more than 100 years old. These antique windows were photographed by D. Friedman.

Wood is the traditional material of choice for residential windows. It can be milled into highly detailed designs, such as true divided lites, and easily fashioned into just about any custom configuration.

In addition to its aesthetic appeal, wood has excellent insulation value, and if well maintained can last indefinitely.

On the downside, wood must be stained or painted and well-maintained or, over time, it will be vulnerable to peeling paint and decay. Windows with wood exposed directly to the weather, such as open casements, are particularly vulnerable.

Although wood is dimensionally stable with temperature changes, it does swell and shrink with changes in relative humidity, causing tight-fitting windows to stick in humid summer weather.

When selecting a wood window, look for materials that are factory-treated with a water-repellant preservative, which will help prevent decay and also improve paint retention and dimensional stability.

The vast majority of wood windows made today have a vinyl- or aluminumclad exterior. A clad exterior is the most practical choice, providing a maintenance-free exterior with the look of a wood window on the interior. The only downside is a limited color choice.

Construction Details for Wood Windows

Some very high-end wood windows are manufactured from rot-resistant species, such as mahogany, but most use clear pine for the sash and visible portions of the frame.

The hidden portions of most wood windows use some combination of solid wood, finger jointed lumber, and various types of engineered lumber, including laminated-strand lumber (similar to oriented strand board, or OSB).

Watch out: Leaks into wood window or door components can cause severe rot even on newer products, as our photo (left) illustrates.

And where finger-jointed wood is used for window or other wood parts exposed to the weather, if the wood is not kept painted and sealed, we find that finger joints may swell, separate, and invite rot or insect damage - DF.

Composite windows are beginning to be used as well, such as Fibrex, a proprietary wood-vinyl composite used in the subsills of some of Andersen’s replacement windows and patio doors.

In general, wood windows are sufficiently strong and rigid for most residential applications. However, it is always best to use windows approved by one of the three agencies that certify windows and doors (see Window Certification).

In coastal areas or other areas prone to high winds or hurricanes, look for products with a suitable pressure rating from the American Architectural Manufacturers Association (AAMA) or the Window and Door Manufacturer’s Association (WDMA).

In 2020, AAMA merged with the Insulating Glass Manufacturers Alliance (IGMA) to form the Fenestration and Glazing Industry Alliance (FGIA)

Vinyl Cladding on Wood Windows

While vinyl cladding is only offered by a few manufacturers, one of them is Andersen Windows, by far the largest supplier of residential windows in the United States. Andersen’s clad windows’ strong record of durability, reliability, and moderate cost has helped make vinyl-clad windows one the most popular options today.

Good quality vinyl-clad windows have a heavy-gauge covering, and heat-welded corners to provide a durable seal against water entry. Vinyl cladding is also more energy efficient than aluminum and is preferred by some in coastal environments subject to salt spray.

Watch out: on some older versions of vinyl clad windows that leave wood exposed (typically at the ends of sills projecting outdoors) or where vinyl cladding over wood has been damaged, broken, or cracked, we often find rot as well.

On the downside, vinyl comes in only a few colors, typically white and beige, and cannot be painted.

Some manufacturers, such as Andersen, now offer a limited number of dark tones as well, using newer technologies that resist the fading and heat problems characteristic of dark colored vinyl.

Vinyl is also vulnerable to cracking in cold weather if struck by an errant baseball or hammer.

While all manufacturers cover the exterior frame and exterior face of the sash, some also protect the top of the sash, which is important in casement windows.

Andersen wraps the entire sash inside and out, providing excellent protection (see Figure 3-3 at left).

But for those seeking the look of wood on the interior of the sash, consider windows with exterior-only cladding, such as those from Weathershield and MW Manufacturing.

See vinyl window details at VINYL WINDOWS GUIDE.

Aluminum Cladding on Wood Windows

A number of manufacturers offer aluminum cladding, using either relatively thin roll formed aluminum or heavier-gauge extruded aluminum.

The advantage of extruded aluminum is that it adds strength and rigidity to the window and resists denting better than thinner stock.

Also, aluminum can be formed to crisper profiles than vinyl, creating a less bulky appearance. Other advantages of aluminum include a wider choice of colors and the ability to be painted if desired.

One downside to aluminum cladding is a slight reduction in energy-efficiency compared to vinyl-clad windows.

On average, a vinyl-clad unit has an R-value about 10% higher than for a comparable aluminum-clad window.

For complete details about aluminum or aluminum-cladwindows see

ALUMINUM WINDOWS GUIDE

Properties of Fiberglass Clad Windows

A few manufacturers, including Marvin and Milgard, offer wood windows clad on the exterior with a tough fiberglass composite manufactured in a process called pultrusion (se

e FIBERGLASS WINDOWS).

Pultruded fiberglass is an ideal cladding material due to its durability, energy efficiency, and very low rate of thermal expansion. Unaffected by heat, cold, and moisture, manufacturers claim that pultruded fiberglass will never crack, peel, or warp. Fiberglass-clad windows come prepainted with a factory finish and can be repainted on site if desired.

Where to buy window and door products

As noted in Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) Chapter 3, BEST PRACTICES GUIDE: WINDOWS & DOORS:

• Andersen Windows and Doors www.andersenwindows.com Vinyl-clad windows and patio doors, including storm resistant models
• Atrium Companies Inc. www.atriumcompanies.com Vinyl and aluminum windows and patio doors
• Certainteed Corp. www.certainteed.com Vinyl windows and patio doors
• Crestline Windows and Doors www.crestlinewindows.com Wood, vinyl, and aluminum-clad windows and patio doors
• Eagle Windows and Doors www.eaglewindow.com Extruded-aluminum-clad windows and sliders with LVL frames and steel entry doors
• Fibertec Windows and Door Manufacturing www.fibertec.com Pultruded fiberglass windows and doors
• Hurd Windows and Doors www.hurd.com Wood, vinyl, and aluminum clad windows and patio doors
• Jeld-Wen Windows and Doors www.jeld-wen.com Wood, vinyl, aluminum-clad, and aluminum windows and patio doors
• Kolbe Windows and Doors www.kolbe-kolbe.com Wood, vinyl, and aluminum-clad windows and patio doors
• Marvin Window and Doors www.marvin.com Wood and extruded-aluminum-clad windows and patio doors, including true divided lites and storm-resistant models
• Milgard Windows and Doors www.milgard.com Wood, aluminum, vinyl, and fiberglass-clad windows and patio doors
• MW Windows www.mwwindows.com Wood, vinyl, and vinyl-clad windows and patio doors
• Peachtree Doors and Windows www.peach99.com Vinyl-clad and aluminum-clad windows with optional hardwood interior; aluminum-clad, steel, and fiberglass patio doors with optional hardwood interior
• Pella Windows and Doors www.pella.com Wood and aluminum-clad windows and patio doors with optional between-the-glass shades and blinds, including storm-resistant models
• Thermotech Windows Ltd. www.thermotechwindows.com Complete line of fiberglass pultruded windows
• Weather Shield Windows and Doors www.weathershield.com Wood, vinyl, vinyl-clad, and aluminum-clad windows and patio doors, including historic replacement windows and storm-resistant models
• WindsorWindows and Doors www.windsorwindows.com Wood and vinyl windows and patio doors, including a line of wood windows with a cellular-PVC exterior
•  Fenestration and Glazing Industry Alliance (FGIA)
• Window and Door Manufacturer’s Association (WDMA).

Skylight Suppiers

• Andersen Windows and Doors www.andersenwindows.com Skylights and roof windows with exterior sash clad with glass-fiber-reinforced material
• Milgard Windows and Doors www.milgard.com Skylights with aluminum frames (thermal break optional) with vinyl subframes on operable models; optional motorized controls with rain sensor
• Pella Windows and Doors www.pella.com Wood interior, aluminum exterior, optional motorized controls, and manual or motorized fabric-pleated shades
• Roto Frank of America www.roofwindows.com Wood interior, aluminum exterior, optional motorized controls, and manual or motorized fabric-pleated shades; Sweet16 model fits 16 in. o.c. framing
• Velux America Inc. www.velux.com Skylights and roof windows with wood interior and aluminum-clad exterior. Options include insect screens, blinds, motorized controls and shades with rain sensor, electrochromatic glass, and flashing kits for metal and tile roofs and mulled units
• Skylight Light Tube Manufacturers & Sources
• SolaTube www.solatube.com Light tubes from 10 to 21 in. in diameter; options include electrical lighting, daylight dimmer, and integral bath fan
• Sun-Tek Skylights www.sun-tek.com Light tubes from 10 to 21 in. in diameter; options include electrical lighting and multitube Spyder skylight
• Velux America Inc. www.velux.com Sun Tunnel light tubes from 14 to 22 in. in diameter with flexible or rigid tubes