Rotted Window Sill & Trim Repair

Why is it always the sill
that goes first?

Because it's supposed to. Of every stick of wood on your house, the exterior window sill has the worst job description: sit at a shallow angle, catch everything that runs off the glass, hold snow through February, bake in July, and do it for decades protected by nothing but a paint film. The sill is the window's bumper — the sacrificial part engineered to take the hit so the frame and sash above it don't. So when a sill in Millburn or Chatham finally goes soft after forty years of service, it hasn't failed. It's finished its shift. The correct response is wood window sill repair or a clean sill replacement — not the whole-window replacement quote that treats a worn-out board as a $23,000 emergency.

Know your bottom edge: sill, stool, apron

Exterior window sill repair starts with knowing which piece is actually rotten, because homeowners and contractors alike blur three different boards into the word "sill." Outside, the true sill slopes away from the house, usually with a drip kerf cut under its nose so water falls off instead of curling back to the siding. Inside, the flat shelf is the stool; the trim panel below it is the apron. The window stool and apron are interior finish — when they show water stains or soft spots, they're not the problem, they're the messenger. Water is getting past the exterior sill or its joints and migrating inward. We diagnose the whole path: replace or rebuild the exterior sill, repair the stool and apron, and reseal the joints where casing meets sill so the assembly drains as one system again.

Reading the symptoms on the paint

Sills announce their decay in a fixed order, and you can read it like a timeline. First comes paint that dulls, hairline-cracks, and peels along the sill's top face — the film is being pushed off from below by moisture in the wood. Next, dark gray-to-black staining spreads from the joints and end grain: fungus is established and eating. Then the surface checks into a grid of small cracks, the classic dry-rot pattern, and finally the wood goes spongy enough that a fingernail leaves a dent. Most calls we take from Summit and Maplewood come in somewhere around stage three — often prompted by a painter who refused to repaint a sill he knew would shed the new coat within a year. Wherever your sill sits on that timeline, an early photo costs nothing: text it over and you'll have an answer today.

How we rebuild a sill — and when we swap it outright

A rotted sill offers two honest repair routes, and we use both, sometimes on the same window. When decay is shallow and localized — a wet corner, a stretch of degraded nose — we excavate to sound wood, saturate the area with penetrating epoxy consolidant, and rebuild the slope and drip edge in structural filler, tooled to the original profile. When the sill is gone through its thickness, partial patching wastes your money: we cut the old sill out, mill a new one from rot-resistant stock to the traced profile — horns, slope, kerf and all — back-prime every face, and splice it under the existing frame with sealed, flashed joints. The same dutchman splicing handles rotted casing and brickmould in matching sections. Either way the window above never moves, the repair carries our 5-year workmanship warranty, and we are fully insured on every job.

The replacement math, one more time

A sill is one board. A full window replacement project runs $23,000 and up. Between those two numbers is roughly 80% of your money — which is why our first move is always to prove whether the board can be saved, and our written estimates show the repair figure and the replacement figure side by side. Homeowners across Essex and Union counties have kept their original windows, their original glass, and their original trim lines for the cost of honest carpentry. Google has us at 5.0 largely because of it.

Sills, stools, aprons & trim repaired across Millburn, Summit, Chatham, Maplewood & greater Essex County · Mon–Fri 8:00 AM – 6:00 PM · (973) 564-0958