How to Repair a Rotten Wooden Windowsill

Wet rot can lower the structural integrity of wooden windows. If such damage is not repaired early, it can result in the loss of the entire window. This article discusses how you can repair a rotten section of a wooden windowsill.

How to Identify Wet Rot

Timber affected by wet rot usually softens due to the high moisture content within it. The wood also cracks in the affected area. Fungal growth is also evident in areas affected by wet rot. This fungal growth may or may not be accompanied by a musty smell. The damp wood may become discoloured.

Wet Rot Repair Steps

Identify the source of the moisture. The windowsill may have rotted due to moisture seeping through a damaged tile on the roof. The water may be from a blocked gutter that is discharging water onto the wall close to the window. Fix the root cause of the water that has affected the windowsill before you proceed with the rest of the repair process. For example, replace a broken tile on the roof so that water ingress is halted.

Remove the rotten portion of the sill. Use a router to cut out the timber affected by wet rot. That segment will be the template that you use to determine the size of the replacement timber. Mark the position of the drip groove (the hole in the timber that allows water to drain away from the wood) on the portion of the wall where the cut out piece of timber previously rested.

Cut the replacement patch. Cut a patch that is slightly longer than the rotten timber section that you removed. Place this replacement wood against the bottom of the window so that you can mark off where the drip groove should be. Use a router to drill the drip groove into this patch.

Install the patch. Place the replacement timber in the gap left by the rotten section that you removed. Countersink the screws that you use to anchor this patch. This will enable you to plane the patch without the screws getting in the way.

Finish the patch. Stain or paint the patch so that it is uniform with the rest of the windowsill. Let the stain or paint dry as per the instructions on the package of the product that you used.

You can use this repair method to replace any rotten section of wooden windows in your house. Hire a timber window-repair company, such as Stop the Rot, in case most of the window has been affected by wet rot.