Should I Remove Rotted Boards Before Installing New Siding?

Lydia Schapiro
Written by Lydia Schapiro
Updated October 18, 2021
White house with a new siding
David Chapman via Getty Images

Learn how to stay one step ahead of Mother Nature when it comes to your siding

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When installing new siding, you’ll inevitably need to replace the old 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. 

What is Siding?

Siding is any type of material that acts as a cover around a home exterior. Some of the most popular types of siding include vinyl, fiber cement, stucco, wood, and brick. The purpose of siding is to shield your home from the outdoor elements, such as rain, snow, and wind. Siding also increases the value of your home’s exterior, whi

Why Does Wood Rot?

Wood rots because it decomposes naturally–for nature, this is a positive. At the end of the rotting process, what was once wood becomes soil. However, the consequences for your home are another story.

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 siding 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. According to HomeAdvisor, 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

In order to repair a wooden board affected by rot, you’ll need to first remove the damaged areas. To do this, use a screwdriver to gently scrape away the rotted wood. This step is critical to saving the rest of the board. 

To repair the rotten board, you'll need to purchase wood hardener and wood filler for about $35. Apply wood hardener to the rotted areas, and then create a mixture of wood hardener and filler. Use a putty knife to fill the affected areas with your mixture. Afterward, you’ll have 10 to 15 minutes to work until the hardener hardens. Use a putty knife or chisel to shape and flatten the wood filler and hardener. 

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