Window Sill Replacement

When it's time to replace, not patch

A patch holds when the damage is small and the rest of the sill is sound. Once you've got rot spreading along the full length, decay reaching back to where the sill meets the casing, or active leaks below the window, replacement saves you time and money over a string of repairs.

How a sill replacement gets done

1. Remove the failed sill

The existing sill comes out carefully, without damaging the surrounding casing. If the casing has rot at the joint with the sill, that gets addressed at the same time so the replacement isn't compromised on day one.

2. Inspect the substrate

What's behind the sill matters as much as the sill itself. The sheathing, the WRB, and the framing all get checked for moisture damage. If any of those need attention, they're handled before the new sill goes in.

3. Correct the slope and flashing

A sill should pitch outward so water can't sit on it. The correct slope gets re-established, and sill-pan flashing installed or corrected where required, so the new sill doesn't end up failing the same way.

4. Install the new sill

All six sides of the new sill get primed before installation, fastened correctly for the material, and the right joints sealed. Wrong joints sealed will trap water inside the wall, so intentional weeps stay open right where they belong.

5. Finish to match

The replacement is caulked, primed, and painted to match the rest of your trim. From the curb, it should be invisible.

Material choices

Cellular PVC

The default for replacement sills on most Nashville homes. PVC will not rot, doesn't feed insects, and stays dimensionally stable. It costs more up front and pays off over decades of weather.

Fiber-cement or composite

Strong performance in humid climates, closer-to-wood appearance, and fewer movement concerns than PVC. Cut ends and fastener holes must be sealed during install.

Cedar or matched wood

For historic homes where authenticity drives the choice, cedar is a defensible option. Profiles get milled to match originals so replacements blend with the home's character.

What's included

• Removal and disposal of the failed sill
• Substrate inspection and repair as needed
• Sill-pan flashing correction
• New sill installation in your chosen material
• Priming, caulking, and finish paint to match
• Cleanup and haul-away

If you're not sure whether your sill needs a targeted repair or a full replacement, that's exactly the kind of thing worth a free professional look.