laying a bead of caulk on casing
Photo: Keller & Keller Photography
1. Double-check the storm window's fit (see "Ensuring a Proper Fit" on page 3 of this article) by centering it in the opening and making sure all the screw holes in the fins land on solid wood. Lay a fat bead of butyl or elastomeric caulk on the casing where the storm's fins will be attached. (Do not use silicone, which makes future repairs or replacement more difficult.) Do not caulk the sill.
It's a familiar story. Your old windows leak copious amounts of air, which makes for chilly drafts in the winter and higher cooling costs in the summer. Leaky windows may even be hurting your house by allowing windblown rain to seep into the structure.

Time for new windows? Not necessarily. High-quality storm windows may be all you need to banish leaks, at a fraction of the cost of replacement windows. "A good storm stops air infiltration about as well as most replacement windows, and the upfront costs are much lower," says This Old House general contractor Tom Silva. "It's like putting money in your pocket."

The typical aluminum "triple-track" — so called because it holds two glass sashes and one screen that slide up and down on separate tracks — won't win any beauty contests, but it can also play an important preservation role by protecting valued old-house windows from the elements.

On the following pages, Tom demonstrates how to measure for and install an aluminum exterior storm over a double-hung window. (Outward-swinging casement or awning windows require interior storms.) Tom has the window up in less than 10 minutes, but while installation is simple, he says, there are still ways to mess it up. "The most common mistake people make is to caulk the storm's bottom edge, along the windowsill," he says. That can trap water that leaks in or condenses on the inside of the glass. "You want to give water a chance to escape before it causes any damage."

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