How to Repair Rotted Wood Siding

Siding represents the first line of defense for your home's structure against the elements. When wood begins to soften, crumble, or retain moisture, you aren't just looking at an eyesore; you are looking at an entry point for pests and water damage that can eventually compromise the wall studs behind it. Ignoring rot is a guarantee that a simple patch today becomes a full-wall replacement tomorrow. Doing this job well means ensuring you have removed every trace of the rot before introducing new material. You want a tight fit, proper flashing, and a seal that breathes just enough to prevent the cycle from repeating. Once you master the cut-and-patch, you can stop the decay in its tracks and keep your exterior solid for years to come.

  1. Map the Rot Boundaries. Identify the extent of the rot by probing the wood with a screwdriver; it will sink easily into soft, decayed areas. Use a pencil to mark a clean rectangle at least two inches beyond the softest points to ensure you are anchoring into solid wood.
  2. Extract the Decay. Set your circular saw depth to match the thickness of the siding boards so you do not cut into the house wrap or sheathing. Carefully plunge-cut along your lines and use a pry bar to gently remove the rotted pieces.
  3. Kill Lingering Fungal Spores. Inspect the house wrap or sheathing beneath the hole. If it is damp, let it air dry completely, then apply a wood preservative or fungicide to the surrounding healthy wood to kill lingering spores.
  4. Size the Replacement Board. Measure your opening precisely and cut a replacement piece of siding to fit. Leave a tiny 1/16-inch gap on the sides to allow for natural wood expansion and contraction.
  5. Secure the Patch Flush. Apply a bead of high-quality exterior sealant to the edges of the existing siding. Secure the patch using stainless steel or hot-dipped galvanized siding nails to prevent rust streaking.
  6. Seal and Paint to Match. Fill the nail holes and the perimeter seams with a paintable exterior caulk. Once dry, sand lightly and apply at least two coats of exterior paint that matches the surrounding finish.