Why Is My Window Sill Rotting After Every Storm?

Storm water finds the weakest spot around your window. Check the top flashing, the side jambs, and the caulk line where the sill meets the siding. If any of those seals have gaps or cracks, wind-driven rain pushes water behind the sill. Once water is trapped there, it seeps into the wood grain and stays wet for days.

The sill itself should slope downward and away from the glass. If it is level or slopes back toward the house, water pools on top and soaks in. Over time, even a small puddle can saturate the end grain of the sill. That constant moisture is what feeds the rot.

Rot returns when the source of moisture is not fixed. If you only scrape off the soft wood and paint over it, the water gets in again at the next storm. The wood stays wet inside, and the decay spreads further. You need to stop the water entry point first.

The climate in your area includes cold, snowy winters and coastal nor'easters. That means a lot of wind-driven rain and meltwater hitting your windows. A sill that survives one storm may still fail after repeated soakings. The fix has to address both the seal and the slope so water drains away.

If the rot is deep, extends into the wall, or covers a large area, you may need a professional assessment. A water damage inspection can map where moisture is hiding and confirm the extent of the decay. That helps you decide whether a simple sill repair is enough or if the window needs replacing.

For storm-related damage, emergency water extraction and structural drying may be necessary if water has soaked into the wall cavity. If you live in Quincy, keep the contact information for local water damage pros handy. Acting quickly after a storm can limit how far the rot spreads.