Window fabrication. The actual assembly of vinyl windows, using vinyl profiles, glass, and hardware, is performed by a window fabricator (see Figure 2, below). Some larger manufacturers produce their own profiles and run their own fabrication plants; others purchase extrusions on the open market and subcontract fabrication to small, local companies.

Figure 2. Vinyl window assembly is often performed by subcontractors, called fabricators. To avoid warranty complications, ask the manufacturer how claims related to fabrication will be handled.

Buying Vinyl Windows

Given the variety in product quality, what should you look for when you buy a vinyl window? Vinyl window manufacturers, especially small local fabricators, tend to come and go, so there is an advantage to choosing an established manufacturer ( and ). You may want to ask, however, whether the "manufacturer" actually fabricates the window, or subcontracts the fabrication to another company. The more fabricators there are for a single brand of window, the more complicated it can be to make claims against the warranty, even when that warranty is backed by a major manufacturer. When shopping for a vinyl window, consider the following features:

• Heavy, thick-walled extrusions. If the window is a double-hung, examine the edge of the extrusions at the side jambs, where the sash slide up and down. If possible, examine a wide window rather than just a narrow sample window in a showroom. With a wider window, it will be easier to test the frame at the window head for flex.
• Metal-reinforced profiles. Since you can’t see this feature by looking at the window, check the spec sheet or ask the manufacturer.
• Welded corners. Mechanically-fastened corners are more likely to separate as the window expands and contracts.
• Streamlined design. Avoid windows with small plastic parts that might easily get snapped off.
• Substantial, solid-feeling sash locks and balance hardware. As with wood windows, good hardware will operate longer without problems.

Allow for Expansion

When installing vinyl windows, keep in mind that vinyl has a higher thermal coefficient of expansion than wood or aluminum (see, Figure 3). "A vinyl window is always moving," says Karl Kardel, a window consultant in Piedmont, Calif. "An 8-foot-wide window can expand 7/16 inch." That’s why it’s essential to leave a 1/4-inch gap between the window frame and the siding. In hot weather, a vinyl window can expand with enough force to crack stucco.

Figure 3. Vinyl windows expand and contract much more than other types of windows. To ensure proper performance, vinyl windows must be carefully installed to allow for movement. The coefficient of thermal expansion is a material constant. A higher number indicates a greater rate of expansion as the temperature rises. The values given in this chart are for temperature differences in Fahrenheit degrees.

That’s also why most vinyl windows are white: When exposed to the sun, white windows generally don’t get as hot as dark-colored windows, so the vinyl is less likely to soften or expand excessively. Window manufacturers have, however, developed a limited number of dark colors, which are carefully formulated to minimize problems from overheating. Thermal bowing. In cold weather, gaps can open up between a vinyl window frame and the sash. This occurs when the sash shrinks, while the frame is held fast by the nailing fins. Cold temperatures can also cause "thermal bowing." "When the outside of a vinyl window is trying to contract, and the inside is trying to expand, it bows," says Charles Deer, owner of Alaska Window, a manufacturer in Fairbanks. "Thermal bowing starts when you have a 40-degree temperature differential between the two sides of the window." In cold climates where thermal bowing is a problem, it’s best to choose a vinyl window with metal-reinforced profiles. Experts disagree, however, on the best way to accommodate the thermal expansion of vinyl, beginning with the size of the rough opening. On one hand are those like Rich Walker, eastern regional director of AAMA, who feels a small rough opening prevents expansion problems. "The window is confined by the rough opening," says Walker. "It’s better to have a tight rough opening than a sloppy rough opening." Jeff Ward, marketing manager for Jeld-Wen Windows, disagrees. "If the opening is too tight and the window expands, it can bind. You need enough room for expansion." Allen Hinkle, head of sales at Kasson and Keller Windows, also likes a generous rough opening. "Sometimes, when a window expands, it bows. If there is bowing, it’s because the rough opening is too small."