Paint keeps peeling off one sill on our triple-decker. Is it rot?

It may be. Peeling or bubbling paint on a sill usually means moisture is trapped under it. Press the wood with a screwdriver: if it's soft or gives, rot has started. The National Park Service notes a decayed core can hide under a sound-looking surface, so a sharp probe that sinks in deep is the warning sign.

Do new replacement windows come with new sills?

Usually not. Cost guides note that most replacement windows don't include a sill, so the old one stays. That's why a rotted sill should be fixed before the new window goes in. The Department of Energy's guide says cracked or rotting sills have to be replaced before any other window work is done.

Water drips in at the top of the window every hard rain. What's wrong?

Water at the window head often points to failed or missing head flashing, according to the Department of Energy's guide, but it can also come from the roof, siding or a gutter above. Ask for the leak to be traced before any trim is torn out. A flashing repair runs about $270 to $570 in national data.

Can aluminum capping fix rotted trim?

No. Capping covers trim; it doesn't repair it. Bent aluminum over soft wood hides the rot and can trap moisture against it, so the bad wood should be cut out and replaced first. Capping is a finish over sound trim that saves repainting, and the factory paint on some coil stock starts to chalk in about five years.

Our rental is pre-1978. Does that change a sill repair?

Yes. Cutting out a rotted sill disturbs layers of old paint, and lead-safe renovation rules for pre-1978 homes can reach even a small sill job. Ask whether the crew is certified and how they'll contain the dust before the work starts.

Window Sill & Frame Repair in Lowell, MA

Typical cost: most sill replacements run $250 to $800 per sill for a 3- to 8-foot sill in national cost data; a partial sill repair is about $150 to $350.
Frames: replacing the frame of a standard window runs about $200 to $600; oversized or custom openings $600 to $1,200.
Leaks: a flashing repair is about $270 to $570.
Time: a standard sill takes 1 to 2 hours to replace; a bay or bow sill can take 4 to 5.
Labor share: 70% to 90% of the bill on frame and sill work, so access and condition set the price more than materials do.

Lowell Window Replacement arranges a site visit from an independent replacement contractor, free of charge, to look at soft sills, rotted jambs and brickmold, and leaks around the window. Most of this work is carpentry around a window that stays in place.

Window Sill and Frame Repair Types: Rot, Leaks and Capping

Close view of a rotted exterior wood window sill with peeling white paint and soft gray wood crumbling at the front edge

Rotted Wood Window Sills

Rain and condensation run down the glass and sash and collect at the sill. The National Park Service names the sill and the joints between the sill and the jambs as typical places where decay begins. It suggests checking that the sill slopes down and away from the house, and cutting a dripline along its underside so water runs off. National cost guides price new sills by length:

3-foot sill: about $250 to $300.
4-foot sill: about $300 to $400.
6-foot sill: about $500 to $600.
8-foot sill: about $600 to $800.

Surface weathering can be built back with epoxy consolidant and filler, the method used in historic window restoration. A sill that's soft through, cracked or rotting has to be replaced.

Wood window on a clapboard house, the bottom of the side casing and brickmold rotted and split by the sill

Frame, Jamb and Brickmold Rot

A window frame is the head at the top, the sill at the bottom and the jambs at the sides, with the casing outside. The Department of Energy's guide ranks the frame and casing next after the sill. It separates them from decorative trim, which can rot without letting water into the wall. National cost data puts a frame repair at $150 to $600 and a frame replacement at $200 to $600 for a standard window. In Massachusetts, the Windows, Doors and Siding (WS) construction supervisor license covers repairing and replacing damaged window or door framing less than 4 feet wide, so ask which license the contractor holds.

Water stain and bubbled paint on the interior wall below the top corner of a wood window, a towel on the sill

Leaks at the Head and Missing Flashing

The Department of Energy's guide lists the warning signs of a window leak:

Inside: water stains, peeling paint or wallpaper, and stained trim or flooring below the window.
At the window head: water there often means failed or missing head flashing.
Hidden: leaks between the window and the rough opening often stay inside the wall.

Not every leak is the window's fault. The same guide warns that siding, roof and other problems can send water to the same spot, so the source has to be diagnosed first. A flashing repair runs about $270 to $570 in national cost data. If the wall is getting new insulation at the same time, fix the leak first, since a wet cavity full of insulation dries out more slowly.

White aluminum capping bent around exterior window casing and sill on a gray-sided multi-family house

Aluminum Trim Capping Over Old Wood

Capping is aluminum or vinyl coil bent on a brake and fitted over the exterior wood trim. Factory-painted aluminum is the common choice. It cuts out repainting. The downside is that metal and vinyl don't breathe: capping over wet or rotted wood traps the moisture and hides the rot. Good capping keeps the drip edge at the front of the sill so water falls clear of the wall, and leaves water a way out if a seam leaks. The finish isn't forever; the factory paint on some aluminum coil starts to chalk or fade in about five years.

Installer seen from behind pressing a new white double-hung window into an old painted wood frame, with a level on the sill and shims and a caulk gun on a drop cloth

Why Lowell homeowners call Lowell Window Replacement

One independent window contractor gets your request
Ask for the HIC number: MA contracts must show it
Written contract on any job over $1,000
The call and the referral are free

Sill and Frame Repair Cost: Repair, Rebuild or Replace the Window

Labor is most of the bill here: 80% to 90% on a sill replacement and 70% to 90% on frame work. So the window's height, access and the condition of the wood matter more than the material. Sill stock costs only $5 to $40 per linear foot for vinyl, aluminum, fiberglass or wood, and $20 to $80 for stone. Weigh the three levels of work against each other:

Repair a sill
about $150 to $350, when the damage is on the surface and the structure is sound.
Replace the sill or frame
$250 to $800 per sill, or $200 to $600 per standard frame.
Replace the whole window
$700 to $2,000 or more for a full-frame replacement when the frame can't be saved. A full-frame job removes the frame, sash, trim and sill.

Fix the sill and frame before a sash kit or an insert window goes into the opening. Both reuse the old frame, and the Department of Energy's guide treats the sill's condition as critical to every option short of full window replacement.

What to Ask Before Sill and Frame Work in Lowell

On Lowell's prewar houses, plenty of sills have taken more than 85 winters.

Probe test
Ask the contractor to probe the sill and lower jambs on every window being quoted, not only the visibly bad one.
Lead-safe work
Pre-1978 homes need lead-safe work when painted wood is cut out.
Written scope
Ask for a written scope that names the parts being replaced (sill, jamb, casing, brickmold) and whether capping goes back on afterward.
Rot past the window
Damage around a window can spread to the siding, so ask what happens if the rot goes past the window.