★★★★★ 4.9 from 145+ reviews | Google · Thumbtack · Angi · Yelp | 20-yr glass warranty · 3-yr wood warranty
Open 7 days · 8am–8pm | Fully insured
Call or text(224) 209-0862
★★★★★ 4.9· 145+ reviews· 20-yr glass warranty
Rotted & damaged sills · 40+ nearby towns

Rotted Window Sill Repair. Stop the Water at the Sill.

The sill takes more water than any other part of a window, so it rots first. We rebuild or replace it — and fix what let the water in — with a 3-year warranty on the wood.

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  • All window types & brands
  • Fully insured
  • Price match
Can it be fixed?Usually — repaired or rebuilt in place
Typical price$200 – $700per window · confirmed before work starts
How long1–2 visits — paint needs to cure
Peace of mind3-year wood repair warranty
The Problem

The Window Sill Is Where Water Attacks First

The sill is the sloped ledge at the base of your window, built to shed water away from the house. Because it catches every drop of rain, snow, and condensation that runs down the glass, it's the part of the window that stays wet the longest — and the first to fail.

When the sill's protective finish breaks down — cracked paint, failed caulk, worn flashing — moisture soaks into the wood and stays there. Over time it turns the sill soft, stained, and crumbly.

A damaged sill isn't just a cosmetic problem: it's a breach in the window's water defenses, and water that gets past the sill doesn't stop there. It moves into the frame, the wall framing below the window, the insulation, and eventually the interior finishes.

That's what makes sill repair one of the most cost-effective things you can do for a window. Caught early, it's a small, contained repair. Left alone, a failing sill turns into structural and drywall damage that costs many times more to fix.

Repair or replace the sill?

It depends on how deep the damage goes, and we tell you honestly. Partial damage — soft spots or surface decay over sound wood — is rebuilt in place with structural epoxy shaped to the original profile.

A sill that's rotted through or structurally gone gets replaced with a new sill matched to the original and pitched correctly to shed water.

Both keep the rest of the window and cost a fraction of full replacement. If the damage is decay-driven, it connects closely to our rotted wood repair work.

Whether you need window sill repair or a full window sill replacement depends on how far the rot goes. A soft front edge — the sill nose — can often be rebuilt in place.

A rotten window sill that's soft all the way back is replaced with new wood, with the slope and drip edge restored so water runs off. We repair both exterior sills and interior sills (the stool inside the room) damaged by condensation.

Not sure this is your problem? Use our window triage guide — pick the symptom and see the likely cause and cost. Related reading: Seasonal window maintenance calendar

Soft or spongy sill

A sill that gives when pressed, or that a screwdriver sinks into, has decay beneath the surface.

Peeling paint & stains

Flaking, bubbling paint and dark discoloration on the sill signal moisture and decay working in.

Water pooling or leaking

Water that sits on the sill after rain, or shows up on the wall or floor below, means it's no longer shedding water.

Cracks or pulling away

Visible cracks, gaps, or a sill separating from the frame let water in behind it and need attention.

Rotted, peeling window sill at the corner of the frame
Recognize this? It's a common, repairable problem.
Why sill slope matters
Sheds waterHolds water1234
  1. Correct slope — the sill tilts away from the house, so water runs off.
  2. Drip edge — a groove under the front edge makes water drop off instead of creeping back underneath.
  3. Lost slope — after years of settling, water pools on the sill instead of draining.
  4. Rot starts here — where water sits against the wood and the joint with the frame.

When we rebuild a sill, we restore the slope — so the new wood lasts.

The Fix

Window Sill Repair and Replacement

Assess the Damage

We probe the sill to find how far the decay goes and check whether it's spread into the frame or wall below.

Remove & Rebuild or Replace

Partial damage is cut back and rebuilt with epoxy; a sill that's too far gone is removed and replaced with a matched new one.

Restore the Slope & Seal

We re-establish the correct pitch, drip edge, flashing, and caulk so water sheds away instead of pooling or seeping behind.

Prime, Paint & Match

The repaired or new sill is sealed, primed, and painted to match — leaving it protected and blended with the window.

BeforeRotted window sill removed down to the framing before rebuilding
AfterRebuilt and painted window sill after repair
Inside Too

Rotted Interior Sills (Window Stools)

The flat ledge inside the window — the stool, or interior sill — can rot too.

It happens when winter condensation runs down the glass for weeks and soaks into the stool, or when a leak at the exterior sill travels inward. Signs are dark stains near the glass, soft spots, and paint that keeps blistering. We cut out the rotted section or replace the stool, match the profile, and seal and finish it.

Stopping the cause matters as much as the repair: that usually means fixing the exterior sill, a failed glass seal, or indoor humidity — see why windows fog up in winter.

Repair vs. Replace

Window Sill Repair Cost

Replacing the window$800 – $2,500+
Repairing itFrom $200

Typical prices

Per window · typical local prices
Sill repair or rebuild$200 – $700
Rotted sash bottom rail (often found with sill rot)$400 – $700
Alignment after the repair (if needed)$50 – $500
Why the final price can differ: these are typical ranges, not quotes. What moves the price: the size and type of glass (tempered, low-E, triple-pane, decorative), how far rot has spread once the wood is opened up, second-story or ladder access, parts availability on discontinued brands, and how many windows are done in the same visit — multi-window jobs cost less per window. Minimum service visit: $150. We confirm and agree the price with you before starting. Compare all repair prices →

A rotted sill is one of the clearest cases where prompt repair pays off. Replacing or rebuilding the sill targets just the damaged base of the window — a fraction of the cost of a whole new window, and a tiny fraction of what it costs to fix water damage once it has spread into the wall.

There's rarely a reason to replace an entire window because the sill has gone. The sill can be rebuilt or replaced on its own while the frame, sash, and glass stay in place, and matching it to the original profile keeps the window looking as it should — important on older and character homes across McHenry County.

We give you an estimate after a free assessment, and we'll always tell you honestly whether a rebuild or a full sill replacement is the right call for your window.

Why McHenry County sills fail

Snow piles against sills for weeks at a time, then melts and refreezes in every crack in the paint. On south- and west-facing windows, summer sun bakes the paint until it splits. That combination is why sills on older homes in Crystal Lake, Woodstock and Harvard so often rot through while the rest of the window is still sound.

DIY or Pro?

Window Sill Care You Can Do Yourself

Safe to do yourself

  • Keep snow and ice cleared off exterior sills through the winter.
  • Repaint the sill when paint starts to crack or peel — before water gets into the wood.
  • Check that the sill slopes away from the house; standing water means the slope is lost.
  • Probe the sill with a screwdriver and text us a photo of any soft spots.

Call a pro

  • Covering a rotted sill with aluminum or vinyl wrap — it hides the rot while it spreads.
  • Filling deep rot with filler or caulk — moisture gets trapped underneath.
  • Water stains on the wall or floor below the window — the damage may already reach the framing.
  • Removing a sill that runs under the frame — it supports the window.
Warranty

3-Year Warranty on Rebuilt Sills

3 yearson wood we rebuild or replace — if it rots, we replace it
20 yearsmanufacturer warranty on insulated glass units
Redoif we install hardware incorrectly, we come back and fix it

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.

Free Second Opinion
FAQ

Window Sill Repair Questions

The sill is the horizontal ledge at the base of the window, and it's built with a slight slope specifically to shed water away from the house. That means it takes the full brunt of rain, snow, and melting ice, and it's where water naturally collects and sits the longest. Add condensation running down the glass and pooling at the bottom, and the sill stays damp more than any other part of the window. Over time that constant moisture breaks down the wood, which is why the sill is almost always the first component to rot — and why catching it early keeps the repair small.
It depends on how far the damage has gone, and we'll tell you honestly which applies. If the rot is partial — soft spots or surface decay with sound wood underneath — we can often rebuild the sill in place: removing the decayed material, treating the surrounding wood, and rebuilding the profile with structural epoxy. If the sill is rotted all the way through or structurally gone, we replace it with a new sill matched to the original profile and pitched correctly to shed water. Either way, the repair targets the sill while keeping the rest of the window, at a fraction of full replacement cost.
A failing sill is a water-entry point, and water doesn't stop at the sill. Left unaddressed, moisture works past the sill into the frame, the wall framing below the window, the insulation, and eventually the interior finishes — turning a small, inexpensive sill repair into structural and drywall damage that costs far more to fix. A deteriorated sill also lets in drafts and pests. Because the sill is the window's first line of defense against water, repairing it promptly is one of the most cost-effective things you can do to protect the wall around your window.
Press the sill firmly with a screwdriver or your thumb: sound wood is hard, while a sill that needs repair feels soft, spongy, or flakes away. Other signs include peeling or bubbling paint on the sill, dark stains or discoloration, visible cracks or gaps, a sill that's pulling away from the frame, and water pooling on or near it after rain. Interior signs matter too — staining on the wall or floor beneath the window, or a musty smell, can mean water is already getting past the sill. If you notice any of these, it's worth having it looked at before the damage spreads.
Yes. The exterior sill (sometimes called the sill or, on some windows, the exterior stool) is the sloped ledge that sheds water and takes the weather — it's the one that most often rots. The interior sill or stool is the flat ledge inside the home. We repair or replace both, and we address the connection between them, because water getting past the exterior sill is what damages the interior side. During assessment we identify exactly which parts are affected so the repair stops the water and restores the whole assembly.
Yes — repairing the sill without addressing why it failed just sets up the next round of rot. As part of the work we look at what let water sit on or get behind the sill in the first place: failed caulk or sealant, worn or missing drip edge and flashing, blocked weep holes, or a sill that has lost its proper slope. We correct those so the new or rebuilt sill actually stays dry. A sill repair done right restores the water management the window was designed with, which is what makes the repair last.
Yes. We repair and rebuild window sills throughout 40+ towns within about 40 miles — Lake in the Hills, Crystal Lake, Woodstock, Cary, Algonquin, Huntley and more. Call or text (224) 209-0862, or send photos for a free quote.
Sill repair or rebuilding typically runs $200–$700 per window, depending on how deep the rot goes and whether the sill can be rebuilt or needs a new section. If the bottom of the sash has rotted too, that adds $400–$700. A new window typically costs $800–$2,500+ installed. Our minimum service visit is $150.
If the rot is limited to the front edge or a small area, repairing it is faster and cheaper. If the sill is soft through most of its depth or has lost its slope, replacing it with new wood lasts longer. We'll show you what we find before deciding.
Window sill repair or replacement typically runs $200–$700 per window, depending on the sill's length, how deep the rot goes and whether the bottom of the sash needs repair too. Our minimum service visit is $150.
A partial sill repair is usually done in one visit. A full sill replacement, or a repair with extensive rot, may need a return visit to prime and paint after the wood and filler have cured.
More Repairs

More Wood Repairs

Rotted Wood RepairRot in sashes, frames and trim.Learn more →Leaks & DraftsStop the water before it reaches the sill.Learn more →Frame RepairThe sill sits in the frame — often repaired together.Learn more →Window RestorationFull rebuild of worn wood windows.Learn more →

Sill Repair in these towns and more

Lake in the HillsCrystal LakeAlgonquinCaryHuntleyCarpentersvilleWoodstockMcHenryMarengoJohnsburgIsland LakeLakewoodAll service areas →

Based in Lake in the Hills, serving homes within about 40 miles.

Stop the Water at the Sill.

Call, text, or send a photo. You'll know what's wrong and roughly what it costs — before anyone comes out.

(224) 209-0862Free Quote

★★★★★ 4.9 from 145+ reviews · 20-year glass warranty · Price match