Difficult as it is to restore old wood windows, trying to make them beautiful is fairly easy compared with trying to make them weather tight.
We're facing that problem with the front facade windows of the house we've been restoring. There was never a question of replacing them; the house is in a historic district and keeping the original windows was essential.
We spent a lot of time and effort stripping, rebuilding, repairing, reglazing and repainting them, so now that it is time to put them back in, we want a simple, reliable, effective way to make them energy efficient.
There are interior storm windows, designed for use on historic properties where the exterior can't be tampered with. If they're installed properly, they're invisible from the outside.
But you can't just throw a storm window across a leaky old window. If the outside window leaks cold air, water will condense on the interior storm. If the interior storm leaks, water will condense on the exterior window. Besides being a nuisance in terms of visibility, the extra moisture won't do your old windows any good.
There's no escape from making the old windows tight.
One immediate problem, however, is that it's hard to make both sashes of a double-hung wood window tight -- the older they are, the harder it may be. There are a number of alternatives; you just have to make some choices.
"One solution is to fix the top sash" -- that is, fasten it so it doesn't move -- "and caulk it in place," says Mike Soper of Soper Enterprises, a Baltimore home-improvement contracting firm. "Try to caulk both sides." (If you elect to do this, remember it has to be extremely neat.)
"If you want the top sash to be operable, use a replacement aluminum compression channel," he said. The channels can be cut to fit into the jambs, and the windows ride up and down in the channels. The sides of the channels grip the window and keep it tight.
However, the maximum width of the channels is 1 3/8 inches. If your sashes are thicker than that (ours are 1 3/4 inches) the channels won't work and you'll have to turn to weatherstripping products.
The strips come in surprising variety: wood, metal, vinyl, rubber or foam, nail-on, adhesive-backed, V-shapes, gaskets. Some are more durable than others and some are much harder to apply. And all of them show -- some only when the window is open, some even while it is closed.
You will probably have to do some research of products available in your area before deciding which ones to apply.
After shopping around, we opted to use one of the more old-fashioned forms, which we've always called "spring bronze." It is basically a piece of metal with a flange for nailing. Once it's in place, you pry out the loose edge, so there's tension between the sash and the jamb, or between top and bottom sash.
We also decided to fix the top sashes in place; only the bottom sashes will slide up and down.
We nailed spring-bronze strips on the top and sides of the top sash, with the loose end toward the outside. Then we put the sash in place -- the spring bronze made it a very tight fit -- and put 3-inch galvanized screws diagonally through the bottom of the sash into the jamb on either side. We predrilled the screw holes to avoid cracking the wood, and we countersank the heads so they don't show. If the next person who rehabs this house wants to make the top sashes operable, he or she can get to the screws easily, cut the caulk and remove the sash. (We'll leave the old sash weights inside the jambs for them.)
This method makes the sash extremely weather tight, but it does make it hard to clean the outside of the glass.
On the bottom of the window, the spring bronze goes on the jamb with the loose end out; stop it an inch or so above the top of the bottom sash so the sash won't catch as it's raised and lowered. (Mr. Soper lines the entire jamb, because he prefers the way that looks; it also provides a solid surface for the sash to ride on.) It also goes on the bottom of the bottom rail of the bottom sash, loose end out, and on the inside of the bottom rail of the top sash, with the loose end down, so it compresses when the bottom sash closes.
Sometimes old windows have a wide gap where the top and bottom sashes meet, and spring bronze may not close it. Mr. Soper's solution for closing such a gap is to install two sash locks, one on each side of the center, to draw the windows together. If the gap is still there, you might use a tubular gasket, made of vinyl or rubber with a nailing flange, on the outside of the top rail of the bottom sash. Closing the window should compress the tube part and seal the opening.
Some old windows have what is called an "integral" weatherstrip. It has two parts, a metal strip with a protrusion, which installs in the jambs, and a groove in the sash in which the protrusion rests. This is an old-fashioned form of weatherstripping that works well as long as it is in good shape.