Wood Siding Repair: How to Fix Rotting & Damaged Boards
Rotting wood siding is caused by prolonged moisture exposure, poor drainage, or lack of maintenance, and can spread quickly if left unaddressed. Replacing a few damaged boards costs $50–$200 in materials, while ignoring rot can lead to structural damage costing thousands. This repair involves identifying soft spots, removing compromised boards, and installing new pressure-treated or cedar siding to match your existing exterior.
Step-by-Step Fix
- 1
Inspect and Mark Damage
Press a screwdriver into suspect areas along the siding to identify soft or spongy wood. Mark all affected sections with chalk or tape, paying special attention to areas below gutters, around windows, and near ground level where moisture collects. Take photos to document the extent before starting removal.
- 2
Remove Damaged Boards
Use a pry bar to carefully lift nails and detach rotted boards from the house frame. Work slowly to avoid damaging surrounding siding. Dispose of rotted wood properly—do not compost or reuse it, as it may harbor fungal spores that spread decay.
- 3
Treat the Underlying Surface
Scrape away any remaining soft wood or fungal growth from the exposed wall with a putty knife or wire brush. Apply a wood preservative or fungicide to the bare sheathing and let it dry completely according to product instructions, usually 24 hours. This prevents new rot from starting behind replacement boards.
- 4
Cut and Fit Replacement Boards
Measure the gap precisely and cut new pressure-treated lumber or cedar to match the length and width of removed pieces. Sand the edges smooth and apply a wood stain or exterior primer to all surfaces, including ends, to protect against moisture. Install the boards with galvanized or stainless-steel nails to prevent rust staining.
- 5
Seal Gaps and Paint
Fill any gaps between old and new siding with exterior-grade caulk to prevent water infiltration. Paint or stain the new boards and blend them with the existing siding color using a matching exterior finish. Allow all finishes to cure fully before exposing the repair to rain or sprinklers.
- 6
Improve Drainage Prevention
Install or repair gutters and downspouts to direct water away from the siding, extending downspouts at least 6 feet from the foundation. Trim back vegetation to allow air circulation, and ensure grading slopes away from the house so water doesn't pool against the base.
⚠️ Safety Notes
- Wear a respirator when handling or sawing rotted wood, as mold spores and fungal particles are inhalation hazards.
- Do not apply wood preservative or fungicide on windy days, and keep children and pets away until surfaces dry completely.
- If rot extends deep into wall sheathing or framing, or affects more than 30 percent of one wall, consult a structural engineer to assess foundation or frame integrity before proceeding.
When to Call a Pro
Call a professional if rot has penetrated the house wrap, structural framing, or sheathing, or if you discover widespread decay affecting multiple wall sections or the foundation trim. Water damage on this scale may indicate hidden mold or structural compromise that requires professional assessment and remediation.
Frequently Asked Questions
- How do I know if wood siding is rotting?
- Press a screwdriver into the board; rotted wood feels spongy and the tool sinks in easily. Look for soft spots, discoloration, peeling paint, or fungal growth, especially near gutters and ground level where moisture accumulates.
- Can I paint over rotting wood siding?
- No. Paint traps moisture and accelerates rot. You must remove rotted boards and treat the underlying surface with fungicide before installing new siding and painting.
- What type of wood should I use to replace rotting siding?
- Use pressure-treated lumber or naturally rot-resistant cedar or redwood, both rated for exterior use. Pressure-treated wood costs $2–$5 per linear foot and lasts 15–20 years; cedar is more expensive but lasts longer and looks better.
- How much does wood siding repair cost?
- Replacing a few boards costs $50–$200 in materials plus labor. Professional repair averages $500–$2,000 per wall section depending on damage extent and siding type.
- How do I prevent wood siding rot in the future?
- Keep gutters clean, direct water away from the house, trim vegetation for airflow, and repaint or re-stain siding every 5–7 years. Inspect after heavy rain and repair any damage immediately to stop rot early.
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