What to look for in replacement windows

June 13th, 2007

Some of our 20-year-old double-pane windows have developed condensation between the panes of glass. We are looking to replace these windows. One window from a European manufacturer has a lifetime warranty; so does another window that is made locally. Both are triple-pane products. The other window we’re considering is double-paned, has a 20-year warranty and is made in New Jersey. We want to prevent condensation, and price is not a major consideration. Each window model has an Energy Star rating. We don’t know if we need triple-pane or double-pane windows.

Barbara and Ted Klenosky, Island Park

First, the condensation between the panes means a seal has been broken. You can’t fix the seal, but you can replace the glazing, or the double-pane glass. Check with a glass company in your area.

It’s not uncommon for the glazing or the seal to experience some type of failure, whether on a double- or a triple-pane window. If your goal is to eliminate the condensation between the panes, consider the product with the lifetime warranty. In case of failure, depending on the coverage, either the entire window or the glass likely would be replaced. But I would wonder about prorating.

As for which window is best: I edited names of the manufacturers from your original e-mail for a couple of reasons. Virtually everything you want to know about a window’s performance can be found at nfrc.org, the site of the National Fenestration Ratings Council, which administers the only uniform, independent rating and labeling system for the energy performance of windows, doors, skylights and attachment products. Each window mentioned in your e-mail is highly rated.

In a subsequent e-mail, you said the major reason you are considering new windows is your rising winter heating bill. In terms of energy conservation, windows are probably the least- effective improvement a homeowner can make. Whether double or triple pane, window glass is a poor insulator, so outdoor air and rays from the sun still will make quite an impact on the indoor temperature. If you really want to reduce your heating bill, consider upgrading the insulation in your 50-year-old home. An insulation contractor can add fiberglass batts to the attic and apply blown-in cellulose to eliminate air leaks in walls.

As for choosing between triple- and double-pane windows, the difference in energy savings will be negligible. In some rooms, like one on the north side of the house that always gets the cold shoulder from Mother Nature, a triple-pane window might be desirable. But for most of your home, highly rated double-pane windows are fine.

Really, buying windows can be a personal preference. Some people might want big windows for a room with a southern exposure. Others might prefer smaller windows, to prevent the same type of room from being overtaken by the harsh rays of the sun. Here’s my advice:

When comparing windows, make sure the NFRC ratings for each are either identical or as close as possible.

Windows are rated in five major categories – U-factor, which measures how a window prevents heat loss; solar heat-gain coefficient, which measures how well a product blocks heat from sunlight; visible transmittance, which measures how much light comes through a window; air leakage, or how much air passes through a square foot of window area; and condensation resistance, or the ability of a product to resist condensation forming on the interior surface.

Installation is crucial to proper window performance. I would prefer buying windows from a company that has its own installation workforce.

More rating information is at nfrc.org.

I have a 30-year-old 12-by-14-foot elevated deck behind my home. It is constructed of lumber treated with CCA (a chemical preservative that protects the wood), but is not in the best condition. I would like to have the wood decking replaced by a composite material, perhaps Trex or Home Depot’s Veranda. I cannot afford to have the work done by a professional. I figure I can do the work myself, by installing the new composite decking directly over the existing wood decking. Is this a practical solution? And if not, what are the pitfalls?

Kenneth Harris, Northport

The issue is the condition of the structural lumber. If the lumber is strong and can be reinforced, you have a chance at renovating your deck. Composite lumber can’t be used in structural applications, so even if you build a new deck from composite material the structure would have to be made from conventional lumber.

Let’s say your original structure is sound. Would you want to place the new composite planks over the old decking planks? I doubt it. It would look awful. And installing new decking over old will add a tremendous amount of weight to the structure. If your original structural framing is sound, you must remove the old decking material before installing the composite.

In addition to making sure the structural lumber is sound, you should check that it is properly designed to hold the new decking. For example, in residential applications, many composites should be installed on joists spaced 16 inches on center when the deck is running perpendicular to the support joists. In a diagonal pattern, decking can be installed on joists spaced 12 inches on center.

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