Leaky window sash is a simple fix

If there is no visible damage, you should be able to quickly block the leak using weather stripping.

By Observer Staff
| 7:00 a.m. December 31, 2014

Winter Park - Maitland Observer
Neighborhood

Q: One of the windows in our bedroom is leaking air underneath the bottom sash. On cold days I can feel air flowing between the sash and the windowsill, and condensation often forms along the bottom of the windowpane. In the summer, this is the window that we put our air-conditioning unit in. I checked underneath the sash to see if there is any damage, but did not see any. How can I stop the leak? – Drafty in Durham, N.H.

A: The window frame may not be damaged, but some slight warping may have occurred over time as the window braced the air-conditioning unit. If there is no visible damage, you should be able to quickly block the leak using weather stripping.

As far as the condensation: If the condensation is on the outside or inside of the window — and not forming between double panes — it probably is a normal occurrence during winter. (If it forms between double panes, it may be time to replace that pane or bottom sash.) However, its location can help you pinpoint where a gap exists between the sash and the sill.

In this case, the condensation is forming along the bottom of the window. On really cold days it may even drip down and puddle along the sill. It signals that warm and cold air are meeting much more frequently along that sash than other parts of the window.

As I mentioned, weather stripping should resolve this problem quickly. Your main concern is what type of weather stripping to use. This Old House has a nice, quick guide to the different types of weather stripping here: http://bit.ly/1uWvFON.

Because you need a fix in a hurry, consider either felt stripping or foam tape. You probably will need to replace the felt stripping each year, but it's fairly inexpensive, and easy to install with finishing nails or a staple gun. Foam tape comes in several widths and can be rapidly installed by peeling off the backing and sticking into place along the bottom of the sash.

A pricier, but longer-lasting option is a vinyl-tube type of weather stripping. It's durable and can be purchased in different widths, and typically has the option of either a peel-and-stick backing or screw-in fasteners.

Before installing weather stripping, clean the contact surfaces of the window thoroughly with soap and water and make sure they are completely dry. Measure the width of the bottom sash and cut the stripping with an extra inch on each side. When you install the stripping, use a utility knife to trim away excess at each edge.

HOME TIP: If the windows in your home or a room fog up regularly in winter, try increasing air circulation to reduce humidity: open curtains and crack windows for a few minutes daily, or run a dehumidifier.