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What fails on a house, why it fails, and what it should cost

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Windows · Check the framing

Rotted wood sill under an older window

Water has been sitting there for a long time. The sill is the visible part. Check the framing below before pricing a window.

Quick answerA window sill is the lowest, flattest part of the window, so it’s where water collects. When paint fails or caulk opens up, water soaks in and stays. By the time the sill is soft, water has usually reached the framing beneath it: the rough sill, studs and sheathing. Probe below the sill before you price anything. A new window set on rotted framing won’t last.

A rotted sill is a symptom of years of water. Sometimes it’s a small patch. Sometimes it’s the corner of a wall. You can’t tell which from the sill alone.

A white wooden window frame with peeling paint on a light green wall
Peeling paint lets water into bare wood. Probe the sill and the wall below before pricing a window. Photo by Max Dery on Unsplash.

1Why sills rot

  • Flat surfaces hold water. A sill that has lost its slope, or never had much, lets rain sit.
  • Failed paint and caulk. Bare wood and open joints soak up water.
  • No sill flashing. Older windows were often installed without a pan or flashing under the sill.
  • Condensation. Water running off the inside of the glass every winter rots the interior side.

2How to check what you’re dealing with

  1. Probe the sillPress a screwdriver or awl into the sill. Note how far the soft wood extends.
  2. Probe below itCheck the trim, siding and sheathing just under the sill on the outside.
  3. Look insideCheck the wall below the window for stains, bubbling paint or soft drywall.
  4. Find the sourceLook for open caulk joints, peeling paint, a missing drip edge, or a gutter overflowing above.

3Fixing it

Do it yourself

  • Small, shallow soft spots: dig out the rot, use a wood consolidant and epoxy filler, then prime and paint
  • Recaulk and repaint to keep water out
  • Fix the water source above the window

Hire a pro

  • The rot goes through the sill or below it
  • The framing or sheathing under the window is soft
  • The window needs to come out to replace the sill
  • New sill flashing needs to be installed
Lead paint on older windows

Older wood windows often have lead paint, and scraping or sanding sills creates lead dust. In a pre-1978 home, paid work that disturbs paint should be done by a lead-safe certified firm.

4What drives the cost

How far the rot extends, whether the window has to come out, whether framing and sheathing need replacing, and lead-safe requirements on an older home. Ask for rot repair priced by the unit so the bill reflects what’s found when the wall is opened.

Windows cost

Soft below the sill too?

Talk to a window contractor who will open the wall and price the framing before quoting a window.

877-360-4657

5Questions

Can a rotted sill be repaired instead of replaced?

Small, shallow rot can be consolidated and filled. Rot that goes through or below the sill needs replacement.

Do I need a new window?

Not necessarily. Sills can often be replaced in an existing window. Decide after the framing is checked.

How do I keep it from happening again?

Keep the paint and caulk sound, make sure the sill slopes outward, and control indoor condensation.

Written by Jaylan Jones. I Like To Exterior Services earns a referral fee when a call connects to a contractor. See our business-model disclosure.

877-360-4657