Don't let a rotten sill cost you a whole window.

Window sills rot. It's not a matter of if, but when. The sill sits at the bottom of every window — exposed to rain, snow, ice, and seasonal temperature swings. When paint peels and water gets into bare wood, fungal decay starts. Left untreated, rot spreads from the sill into the sash, then the frame.

The good news: we can repair almost any rotten sill — even severely damaged ones — for a fraction of replacement cost.

Signs your window sill is rotting

• Wood feels soft or spongy when pressed

• Visible cracks, splits, or peeling paint

• Discoloration — gray, dark brown, or greenish patches

• Loose or crumbling sections

• Water stains on the wall below the window

• You can push a screwdriver into the wood with little resistance

How we repair rotten window sills

Our approach depends on the extent of the damage:

Method 1: Epoxy consolidation (light to moderate rot)

For early-stage rot, we remove the soft wood, saturate the area with liquid epoxy consolidant, then rebuild the missing shape with epoxy filler. Once cured, the epoxy is harder than the surrounding wood and will outlast the original sill. The repair is then primed, painted, and matched to the existing finish.

Method 2: Wood splicing (advanced rot)

For severely rotted sills, we cut out the damaged section entirely and splice in new solid wood — typically Spanish cedar or treated pine — matched to the original profile. Joints are reinforced with epoxy and stainless fasteners. The result is structurally stronger than the original sill.

Method 3: Full sill replacement

When the entire sill is beyond repair, we fabricate a new sill on-site, custom-cut to match your existing profile. Original architectural details are preserved.

Why repair instead of replacing the whole window?

A typical full window replacement costs $800–$2,500 per window. A rotten sill repair costs $200–$600 — and the new sill will last decades. There's no need to replace the entire window when only the sill is damaged.

Schedule your free estimate

If you suspect sill rot in your Boston-area home, call (617) 982-1211. The longer rot is left untreated, the more expensive the repair becomes.