Rotted Window Sash Repair. Rebuilt or Replaced — the Window Stays.
Soft bottom rails, corners coming apart, rot hiding under cladding — we rebuild rotted sashes, or make a new sash to fit your existing frame.
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How Window Sashes Rot
The sash is the movable frame that holds the glass. On wood and clad windows, its bottom rail and lower corners take the most water — and that's where rot starts, usually long before anyone notices.
Rain and condensation run down the glass and collect on the bottom rail. When paint, glazing or cladding seals fail, water soaks into the end grain at the corner joints.
The wood softens, the joint loosens, and the sash starts to sag, stick or let in drafts. On clad windows (wood under an aluminum or vinyl skin) the rot hides under the cladding until the sash feels spongy or the corner separates.
Most rotted sashes can be saved. Localized rot is cut out and a matched piece of wood is spliced in and shaped to the original profile; loose corner joints are reglued and reinforced.
When rot has spread through most of the bottom rail and both stiles, a new sash made to fit the existing frame is usually the better choice — the frame, trim and interior finishes stay untouched, and the new sash is sized to your opening.
Homeowners search for this as rotted window sash repair, rotten sash replacement, window sash rot, a rotted bottom rail, or a sash coming apart at the corners.
Not sure this is your problem? Use our window triage guide — pick the symptom and see the likely cause and cost. Related reading: Window sash repair (all problems) · Rotted window repair (every part)
Soft or spongy bottom rail
A screwdriver sinks in along the bottom of the sash.
Corner joint opening up
A gap where the bottom rail meets the side stile.
Peeling paint along the glass
Water has been getting under the paint and glazing.
Sash sagging or sticking
Rotted joints let the sash drop out of square.
Bulging or loose cladding
On clad windows, rot hiding under the aluminum or vinyl skin.
Rotted Sash Repair — or a New Sash
Probe & decide
We check how far the rot goes and tell you whether rebuilding or a new sash lasts longer.
Cut out the rot
Soft wood removed back to solid wood; sound wood treated with consolidant.
Rebuild or replace
Matched wood spliced in and shaped — or a new sash made to fit your frame.
Seal, paint & rehang
Primed, glazed, painted and rehung so it opens, closes and locks tight.
- Find the rot — soft, dark wood — usually at a sill, a corner or the bottom of a sash.
- Cut back to sound wood — every bit of soft wood is removed, so the rot can't keep spreading under the repair.
- Splice in new wood — matched wood is fitted, shaped to the original profile, then primed and painted to blend.
The rest of the window — and its original wood — stays in place.
Rotted Sash Repair Cost
Typical prices
Per window · typical local prices| Rotted sash section rebuilt (rail or corner) | $200 – $700 |
| Sash repair & restoration | $400 – $700 |
| New sash made to fit | Quoted per sash |
Repairing or replacing only the sash costs a fraction of a new window: rebuilding a rotted section typically runs $200–$700, and full sash restoration $400–$700, while a new installed window typically costs $800–$2,500+. We'll tell you honestly which option holds up better for your sash.
What we see in McHenry County sashes
Clad casements and double-hungs from the 1980s–2000s around Lake in the Hills, Algonquin and Crystal Lake often have rot hidden under the cladding at the bottom corners. Older painted wood sashes in Woodstock and Cary usually rot where the glazing putty failed along the bottom rail.
What You Can Check Yourself
Safe to do yourself
- Press a screwdriver gently into the bottom rail and corners to find soft spots.
- Keep condensation wiped off the glass in winter so it doesn't soak the rail.
- Photograph the corners of the sash, inside and out — it helps us quote.
Call a pro
- Covering rot with wood filler — it traps moisture and the rot keeps spreading.
- Removing a sash with springs or weights attached.
- Pulling back cladding to look underneath — it rarely goes back watertight.
Warranty on Sash Wood Repairs
Parts we don't make (cranks, balances, locks) carry only their supplier's warranty. Leaks from roofs, flashing or siding aren't window defects. Full warranty terms → · Read our reviews
Got a quote to replace these windows?
Send it to us before you sign. We'll tell you — free — whether a repair would solve it for less.
Rotted Sash Questions
Rotted Sash Repair in these towns and more
Based in Lake in the Hills, serving homes within about 40 miles.
Save the Sash. Keep the Window.
Call, text, or send a photo. You'll know what's wrong and roughly what it costs — before anyone comes out.
★★★★★ 4.9 from 145+ reviews · 20-year glass warranty · Price match