Solid vinyl windows, guide: this article explains the properties of solid vinyl windows, vinyl window choices, and how to install and maintain vinyl windows. In this article series we discuss the selection and installation of solid vinyl windows and doors, following best construction and design practices for building lighting and ventilation, with attention to the impact on building heating and cooling costs, indoor air quality, and comfort of occupants. We review the proper installation details for windows and doors, and we compare the durability of different window and door materials and types.
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While improvements in extrusions have made vinyl windows less bulky looking, they still do not have the crisp lines of a wood window, particularly on the interior, and vinyl window sash are unmistakably white plastic.
Still, vinyl windows have shed their stigma as a low-end product and are finding their way into more and more new homes across the spectrum from spec to upper-end custom.
The thin-walled plastic ranges in thickness from about .065 to .085 inch. All other things being equal, the thicker the plastic, the stronger the window component. However, extrusions can gain strength from having a well-engineered profile, as well (many European windows use much heavier .125-inch plastic, but U.S. manufacturers feel this would make them less competitive).
The extrusions are then cut and joined to create frames and sash. Nowadays, most corners are heat-welded, producing the strongest joints, although some corners are still mechanically fastened. Some manufacturers add steel or aluminum reinforcing, particularly to larger windows, to stiffen them and help them meet structural load requirements. Typical places for reinforcing are sills, which have a tendency to sag in hot weather, lock rails, and mullions between mulled units.
All vinyl windows have an integral nailing flange, simplifying watertight installations (see Window Flashing & Sealing Guide).
All standard window types, including tilt-turn, are available in solid vinyl today. All glazing types, except for true divided lites, are also available.
For the look of divided lites, the options are either snap-in grilles or between-the-glass grills.
Typical exterior trims include brickmold or nominal 4-inch flat casings with either an integral or snap-on J-channel to receive the ends of wood, vinyl, or fiber cement siding.
Window trims designed for stucco are widely available in the western states and Florida. Colors are generally limited to white and beige, since dark colors absorb heat and raise vinyl temperatures to near 165°F, where it begins to soften and sag.
On the interior, most vinyl windows will accept either wood extension jambs or drywall returns.
A solid vinyl replacement window may not be so easy to spot during a building survey, as our photo (above left) illustrates. The replacement window is coverd by an aluminum storm and screen window, aluminum covered trim, etc.
As with any building products, not all vinyl windows are created equal. Many early models were poorly made and subject to excessive thermal movement, often opening at corners, fading prematurely, and losing structural integrity from UV exposure, particularly in hot climates.
Warping was a complaint for some PVC vinyl windows, as we discuss at VINYL / PVC WINDOW WARPING.
Most window manufacturers today have overcome these problems with better vinyl formulations, improved extrusion design, and heat welding at corners. Many also use metal reinforcing at strategic points, such as meeting rails, sills of large units, and between mulled units.
Since the chemistry, extrusion design, metal reinforcing, and other determinants of quality are hidden from view, however, the best approach is to stick with an established manufacturer and to look for a certification label from the American Architectural Manufacturers Association (AAMA).
AAMA established a separate standard for vinyl windows in 1997, which includes tests for strength, dimensional stability, strength of corner welds, heat and impact resistance, and weathering. The main features to look for include:
In general, vinyl windows install the same as other flange-type windows, although the installer must take into account vinyl’s high rate of thermal expansion.
A 6-foot-wide window can expand as much as 5/16 inch from 0°F to 100°F. To prevent problems, It is best to leave a 1/8 - to 1/4 -inch gap between the window and siding or wood trim (more in cold weather, less in hot). Good detailing of this joint is especially important with stucco, which can crack if set too tightly against the window or leak if the caulk joint fails.
Thermal expansion can also cause window sash to bind in hot weather if the rough opening is too small to accommodate the movement. And in very cold weather, some vinyl windows can bow inward due to temperature differences on either side of the window.
Sturdy extrusion profiles with metal reinforcing can help prevent this. A related concern is sagging of the sill during hot weather— vinyl starts to soften and distort at about 165°F, a temperature easily reached on the surface of a dark building in direct sun. To prevent sagging, some manufacturers reinforce the sill, and all recommend specific shim spacing under the sill.
Some vinyl window installations require continuous support along the length of the sill, which is easiest to achieve by using a double 2x sill with leveling shims in between.
Nailing recommendations for vinyl windows also vary among manufacturers. Some recommend driving nails tight; some suggest leaving the nail heads proud. Some recommend against nailing the head flange or corners; others require it. To avoid warranty problems, it is always best to closely follow the manufacturer’s instructions regarding the rough opening, shimming, nailing, and other installation details. Other general recommendations that apply to all windows include:
Also see WINDOW TYPES - Photo Guide.
American Architectural Manufacturers Association (AAMA) www.aamanet.org
Efficient Windows Collaborative www.efficientwindows.org
National Fenestration Rating Council (NFRC) www.nfrc.org Sustainable by Design www.susdesign.com
Shareware calculators for sun angles, solar heat gain, and shading
Window and Door Manufacturers Association (WDMA) www.wdma.com
-- Adapted and paraphrased, edited, and supplemented, with permission from Best Practices Guide to Residential Construction.
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