Window Sill Repair

Why sills fail first

Of every part of an exterior window, the sill works the hardest. It's nearly horizontal, so water sits on it after every storm. Pollen, leaves, and grit pile on it through fall. Snow and ice cycle through it in winter. The underside rarely sees sun, so it stays wet longer than the top. Most window rot we see in Nashville starts at the sill.

What sill repair involves

1. Probe and map the damage

We test the top, the front edge, the underside, and the corners where the sill meets the casing. Soft, spongy, or hollow-sounding wood gets marked. Surface paint often hides several inches of decayed wood below.

2. Cut back to sound wood

For contained rot, we cut out the damaged section and rebuild with epoxy consolidants and a matched profile. For more extensive damage, we remove the whole sill. Patching active rot under fresh paint just hides it for a season.

3. Check the slope and flashing

A sill should slope away from the house so water runs off. A flat or back-sloped sill ponds water and rots again. Where we find a bad slope or missing sill-pan flashing, we correct it during the repair.

4. Prime, caulk, paint

The patched or replaced area is primed on all sides, the appropriate joints are re-sealed, and the finish is matched to the rest of the trim so the repair disappears.

Signs your sill needs attention

• Paint is peeling or bubbling specifically on the sill
• The top of the sill feels soft when pressed with a screwdriver
• Dark vertical stains running below the front edge
• The sill looks bowed, cupped, or wavy
• Visible gaps where the sill meets the side casings
• You can see the underside is darker or stained

When repair beats replacement

If the damage is limited to a few inches in one corner or along a front edge, repair is the faster and more affordable choice. Once rot extends across more than a third of the sill or shows up on both ends, full replacement is usually the better call — and that's what our window sill replacement service handles.

Materials we use

For repair patches, we use marine-grade epoxy consolidants and matched wood or PVC fillers. Where we rebuild sill profiles, we work in cedar, cellular PVC, or composite depending on the home's style and how exposed the wall is.