Wood Rot on Window Sills and Sashes: What to Look For

Wood windows can last a long time, but they have one weak spot: water. When water gets into the wood and stays there, rot follows. It usually starts small on the sill or the bottom of the sash, where water collects, and it is easy to miss under a coat of paint. Caught early, rotted wood can often be cut out and replaced. Left alone, it spreads.

Where rot starts

Rot needs water that sits. The usual spots on a window are:

• The outside sill, especially if it is flat or slopes toward the house instead of away from it
• The bottom rail of the sash, where water runs down the glass
• The bottom corners of the sash and frame, where joints open up over time
• The trim boards around the outside of the window
• Anywhere caulk or paint has failed and left bare wood

In Michigan, freezing and thawing make it worse. Water that gets into a crack freezes, opens the crack wider, and lets in more water the next time.

Signs of rot

• Paint that blisters, peels or cracks in the same spot year after year
• Dark staining, or wood that looks gray and dried out
• Wood that feels soft or spongy when you press it
• Cracks, splits or wood that crumbles at the edges
• A sash that sticks, sags or feels loose in the frame
• A musty smell or mold around the window inside

The screwdriver test

Take a flat screwdriver and gently press the tip into the wood at the suspect spots: the sill, the bottom of the sash and the corners. Sound wood resists. Rotted wood lets the tip sink in or feels soft, and it may come up in stringy pieces. Try a few spots so you get a sense of how far it goes.

Repair or replace?

Rot does not always mean a new window. If the damage is limited to part of the sill or sash, the rotted wood can often be cut out and replaced with new wood, then sealed and painted. Our wood rot replacement service does exactly that, and our wood window reconstruction and reconditioning work covers windows that need more than a patch. You can see sash repairs like this in our gallery.

Replacement starts to make sense when:

• The rot runs through much of the sash or frame
• The window is out of square or the joints are falling apart
• The rot has spread into the framing around the window
• Several windows are failing at the same time

In some cases, a new sash in the old frame is the middle ground. Our post on whether to repair or replace goes through the decision.

Fix the water, not just the wood

New wood will rot too if water keeps getting to it. Part of any rot repair is finding out why the water got there:

• Cracked or missing caulk around the frame
• A sill that does not shed water away from the house
• Peeling paint that left bare wood exposed
• Damaged trim boards that hold water against the window

That is why our caulking and trim board work is often done alongside a rot repair.

Keeping rot from coming back

After a repair, a little upkeep goes a long way. Keep paint in good shape on the sills and the bottom of the sash, since paint is what keeps water out of the wood. Check the caulk around each window every fall. Keep gutters clear so water does not pour down over the windows, and trim shrubs back so the wood can dry after rain.

What affects the cost

Every rot job is different, so we price it after we see it. The cost depends on how much wood is damaged, whether the sash, sill, frame or trim is involved, how many windows need work, and whether the window needs paint and caulk afterward. A free quote is the way to find out.

Get your windows checked

If the screwdriver sinks in, do not wait for spring. Call (248) 250-8000 or request a free quote, and we will come out within 24 to 48 hours. We repair wood rot on windows for homeowners across Metro Detroit (Macomb, Oakland and Wayne Counties), and our workmanship comes with a 5-year warranty.