Replacement Windows

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Most stock windows come in even increments of four inches in width and odd increments of two or 4 inches in height. You can get a stock window that is 2' 2" or 2' 6" wide, and 3' 5" or 4' 1" high but not one that's an even 2' wide and 4' high.

Older homes will probably require custom-made custom-sized windows. Happily, window makers are so computer automated these days that they will build odd sizes with four to ten weeks' lead time and will charge no more than the price of the next-larger stock size. Don't be afraid to demand precisely what you need.

Glazing and Jamb Widths

You have a choice in glass. Plain glass offers little resistance to the passage of heat into or out of a building. Such resistance is measured in R value. A wall with 5 1/2 inches of fiberglass insulation has an R value of 19...leaving a single-pane window with its R value of 0.88 looking like a direct hole to the frigid winter air. A second pane of glass, with a 1/2 inch air space between the layers, increases the glass R value to about 2. Such insulated glass is the standard in today's windows.

More recent innovations have achieved window R values approaching 4 or more. Low-E coated glass with argon gas between the sealed layers adds a third R point. The invisible low-E metallic film reflects long-wave heat energy back into the house in winter and reflects it back out in summer. Argon gas has greater insulative value than air (though it shouldn't be used in high-altitude situations). Triple insulation glass contributes the fourth point to the R value by adding a third layer of glass, but currently is very costly.

Is low-E with argon worth the 10% added cost? From the standpoint of condensation alone—where warm inside air condenses on the surface of the glass on cold nights-the answer is yes. The windows I bought were insulated glass only, and moisture damage is already evident where a bead of ice has formed along the lower edge of the sash. Low-E would have helped by increasing the inside glass temperature and decreasing the likelihood of condensation. Glass manufacturers are giving better deals on low-E too, so it can be expected to continue to drop in price.

You must also specify your window's jamb width. Stock jambs are 4 9/16' wide—to fit neatly into a conventional modern frame wall comprised of a 2 x 4 stud (that is actually 1 1/2" thick and 3 9/16" wide) with a inch of sheathing on both sides. Don't expect a stock jamb to fit your old house wall with roughly planed board sheathing, plaster lath, and varying-sized framing members. You can order windows with custom-width jambs and should if you question your carpentry skills. I find it more economical to order standard jambs and decrease if needed by hand-planing off the excess. If more depth is needed I nail on wood-strip jamb extensions.

Once-popular all-aluminum replacement windows are hard to insulate and are being phased out. You can buy windows in all-vinyl ...in wood left plain or primed or finish-painted ...or in wood that is clad in aluminum or vinyl (wood is still the best insulating of window materials). The choice factors are cost (cladding costs 10 to 15% more and comes in whites and beiges to match most paint schemes) and how much you hate getting on a ladder and painting your house trim every five years.

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