Wood Rot in Frames, Sills, and Thresholds
Windows are collection spots for moisture and water that can cause wood rot and structural damage. It’s important to keep water out and to seal against water infiltration and moisture buildup to prevent damaging rot.

Wherever heat, moisture, and wood are found, rot will eventually find a home. The wood sill, threshold, and framework that surround windows and doors are particularly susceptible to rot. Rot in doors and windows can compromise the home’s envelope, affect energy efficiency, impact structural integrity, and weaken a home’s security. Fortunately, locating and treating wood rot is a fairly straightforward process that starts with assessing wood health.

Inspecting Areas for Rot
Rot thrives in moist environments. Where water is permitted to linger, pool, or leak, rot can grow and spread. With windows and doors, rot typically attacks the sill and threshold, but the rest of the frame can be affected, too. Persistent rainfall, inadequate flashing, and aging untreated wood can leave these parts of a window or door particularly vulnerable to rot. Although a visual inspection can alert a homeowner to the presence of rot, the surface does not always tell the whole story.

Fungi affect wood and cause rot by sending tiny threads into the wood to feed on and break down the wood fibers. Decomposition takes place within the wood, invisible at first to the human eye. Where yellow, white, or brown discoloration appears on the surface of the wood, a thorough inspection into the integrity of the frame, sills, and jambs around doors and windows should involve probing suspected areas with a screwdriver or pick. Homeowners should look for soft, spongy areas—wood that crumbles apart, breaks off in cubes, or falls away with little effort is likely rotted.

Rot Treatment – Repairs and Replacement
Treatment for rotted wood depends on the scope of the rot. Where rot has been discovered early and existing wood can remain intact, putties, sealers, and epoxies are an option. Once the rot-affected wood is removed (by scraping, boring, or cutting) and the healthy wood is dried, a penetrating epoxy sealer can be applied to the remaining wood. An epoxy filler can then be used to fill in the missing wood and sanded, shaped, and painted to look like the original wood. Most local building-supply stores carry these wood-restoration products. Homeowners should follow the manufacturers’ instructions when using products to repair rotted wood.

In cases where little or no wood can be salvaged, a replacement job will be in order. For the inexperienced homeowner, it is best to consult a contractor who specializes in wood-rot repair. As a DIY endeavor, care should be taken to identify and extract all affected wood—a job best done with a hand or reciprocating saw and chisel. Extracting rotted window and door sills, thresholds, jambs, and other framework might expose additional rot in the subfloor, surrounding walls, and adjacent structures. Replacement pieces, such as a door threshold or window sill, should match the dimensions of the original piece. Aluminum, vinyl, and composite-wood replacement sills won’t rot and can be painted to match the existing components. Replacing an entire rotted frame allows the homeowner to properly install flashing, caulking, and sealant around the new frame.

Repairing or replacing rotted wood is an exercise in futility if the cause of the rot is not addressed. Preventing moisture buildup and infiltration around sills and jambs requires proper flashing and sealing. Check with the manufacturer of your doors or windows for their recommended moisture-barrier solutions.

Moisture will infiltrate cracks in wood, so keeping wood sealed and painted can go along way to extending the life of the wood. Regular inspections can help a homeowner catch a rot problem early, before entire replacement is necessary. Likewise, water will infiltrate joints and cracks, so proper caulking is necessary to preserve a uniform seal and keep water out.

Credit: Renovate with Tommy Mac