Is It Worth It to Wrap Window Sills?

Water and Windows

• Water and windows do not get along on their own. While walls are excellent at keeping water out, windows are a hole in an otherwise solid wall that leave room for water to leak through. If enough water gets under your window sills and onto the rough opening, the wood will start to rot. Not only will this affect the overall structural integrity of the window frame, it will also attract termites and carpenter ants.

Rough Opening Preparation

• The first step to properly wrapping the window sills is wrapping the rough opening. The rough opening is the bare wooden space into which the window fits. Measure the rough opening and cut long enough strips to overlap each surface by 1 inch on each side. Start with the two side sills by placing the adhesive side of the wrapping on the wood. It should overlap the front and back of the rough opening. Then wrap the bottom, overlapping the side pieces for an extra seal.

Flashing Tape

• After you’ve wrapped the sills, the next step is to apply a layer of flashing. Flashing is a self-adhesive material that is completely waterproof and more structurally sound. The added advantage of flashing is that the adhesive seals around nails, so even where nails are used, you don’t need to worry about leaks.

Moisture Seal

• The last piece of wrap to go on the window sills sits between the window frame and the window box. This barrier, known as a moisture seal, prevents leaking between the two layers of the window by allowing you to tuck the barrier tightly into place.