Should I Repair or Replace Rotted Wood Under Siding?

When installing new siding, you’ll inevitably need to decide whether to repair or replace the rotted boards under your siding. Unfortunately, this is not always a one-and-done job–often, uncovering old siding reveals rotted wooden boards.

In order to stay on top of your home’s protection, it’s important to know how to recognize rotted areas and what to do when you find rotted wooden boards beneath your siding.

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Should I Repair or Replace Rotted Wood?

Whether you repair or replace rotted wood depends on the extent of the damage. If most of the piece of wood is rotted to the point where it can split, then the entire board should be replaced. But, if only one or a few relatively small areas are affected, then you can spot-repair the board.

Why You Should Replace Rotted Boards Before Installing New Siding

If you or your local siding repair pro uncovers severely damaged wood while removing siding, it’s important to remove it before installing new siding. If the wood is cracked, you run the risk of water damage and problems, such as the wood collapsing, rotting drywall, soggy insulation, and insect infestations. The average cost to repair siding is around $778.

Signs You Might Need to Replace the Wood Underneath Siding

When wood has rotted, it can’t properly carry out its functions (i.e. defending your home)–wood is prone to moisture damage, which can get through your siding and then cause issues such as damage to your insulation or fungi and mold growth.

Once the siding is removed, look for the following warning signs for rotted wood:

• Abnormally darker areas 

• Discoloration spots–these may be black, white, yellow, brown, or grey

• Wood that feels soft or weak 

• A damp, moldy, or musty odor 

• Missing nails

• Visible impacts from weather conditions, such as falling trees and debris accumulation

Different Types of Wood Rot

There are different types of wood rot, which each affect the wood differently:

• Brown rot: Also known as “dry rot,” brown rot destroys the cellulose within the wood. As a result, the wood turns brown, shrinks, and breaks down. This type of rot tends to spread quickly. 

• White rot: White rot causes wood to turn white or yellow and is often the cause of spongy, weak wood. White rot breaks down lignin, which is another key structural part of the wood. 

• Soft rot: Soft rot, like brown rot, breaks down the wood’s cellulose. It is more commonly found in logs and trees than in houses but can arise under extremely hot or cold temperatures. 

If you see any of these signs, first try to recognize if this could be a repair job–if there doesn’t seem to be extensive damage, you can likely fix the wooden boards yourself. If you’re not sure or are concerned that there is significant damage, call in a local carpenter who can diagnose the problem and help you fix the issue. 

How to Repair a Wooden Board

Repairing a rotted wooden board involves a few steps to ensure the wood is restored and fully functional. Here’s a step-by-step guide to help you tackle the task:

1. Remove the Damaged Wood: Use a screwdriver, chisel, or claw hammer to scrape away the rotted portions of the wood. Take care not to damage the healthy areas surrounding the rot. If the rot is deep, continue to remove wood until you reach solid, unaffected wood.

2. Clean the Area: After removing the rotted wood, clean the surface thoroughly to remove any dust, dirt, or debris. This step will help the wood hardener and filler adhere better and create a stronger repair.

3. Apply Wood Restorer: Apply wood restorer (available online or at your local hardware store) to the remaining rotted area using a brush. Allow this to dry per the manufacturer’s instructions.

4. Fill the Area With Wood Filler: Use a putty knife to apply wood filler to the area. For deeper repairs, apply the filler in light layers and allow it to fully cure in between each layer.

5. Sand the Area Smooth: Once the filler has hardened, sand the area smooth to blend the repair with the surrounding wood. 

6. Prime and Paint: Prime and paint the repaired section to match the original wood color and protect it from further moisture exposure.

Why Does Wood Rot?

Wood rot occurs when wood is exposed to excessive moisture over a period of time, which provides the perfect environment for certain fungi to thrive. These fungi break down the wood fibers, causing the wood to lose its strength and structural integrity. A few common causes of wood rot include leaks, poor drainage, high humidity, and prolonged contact with water. 

When wood rot is left untreated, it can weaken the structure of your home, causing further damage to underlying materials such as insulation and drywall; this is why it’s crucial to remove rotted wooden boards before installing new siding. If rotted wood is not replaced, the new siding may not adhere properly and moisture could seep through, potentially leading to issues like mold growth, pests, and structural instability.