Why Is My Wood Deck Rotting Near the House?

The junction where your deck meets the house is a moisture trap. Rain runs off the deck surface and down the wall, collecting at the ledger board. Snowmelt in winter adds more water. If the gap between the deck and siding is narrow, water has nowhere to drain.

The wood stays damp for hours or days. Over time, that constant wetness breaks down the wood fibers. Fungi that cause rot thrive in damp, shaded spots. The area near the house often gets little sun, so it dries slowly. This is why the rot appears first near the wall, not at the outer edge of the deck.

The ledger board is usually attached directly to the house framing. If the siding is not properly flashed, water can run down the wall and into the joint. Even a small gap lets water in. The deck boards themselves may be too close together, trapping debris and moisture between them.

Gutters and downspouts can also play a part. If a downspout empties near the deck, it dumps extra water onto the wood. In winter, ice dams on the roof can force water under the siding and down the wall. All of this keeps the area near the house wetter than the rest of the deck.

If the rot is extensive, or if you notice the deck pulling away from the house, do not delay. Structural rot can weaken the connection and make the deck unsafe. A professional can assess how far the damage goes and what needs to be replaced. They can also check for hidden moisture in the wall behind the ledger.

Water damage pros use moisture meters and other tools to map out the affected area. They can help dry out the wood and the wall cavity to stop further decay. In some cases, the wall sheathing or framing behind the deck may also be damaged. Catching it early can save you from a bigger repair later.

• Rot extends more than a few inches into the wood
• The deck sags or feels unstable
• You see water stains on the interior wall behind the deck
• The ledger board is soft or crumbling
• Mold is growing on the siding or inside the house