Roof Rot (Fascia, Soffit and Deck)

Roof rot is decay of the wooden parts of a roof by wood-destroying fungi. It needs wood that stays wet, typically above about 20 percent moisture content for extended periods, so it is almost always a symptom of a water problem rather than a problem in itself. The most commonly affected parts are the fascia (the board along the eave that gutters attach to), soffits, rafter tails, the roof deck or sheathing, and timber around chimneys, skylights and valleys.

Common causes

• Missing or poorly fitted drip edge, letting water wick behind gutters into the fascia.
• Overflowing or clogged gutters, or gutters pitched the wrong way, that spill water onto the fascia.
• Ice dams that push water under the roofing at the eaves.
• Flashing failures at walls, chimneys and penetrations.
• Damaged or worn roofing letting rain reach the deck.
• Attic condensation soaking the underside of sheathing.
• Unprimed cut ends and paint failure on exposed trim.

Signs

Peeling paint, soft or spongy wood, dark staining, gaps where gutters have pulled away, and, on the roof, soft spots underfoot. In the attic, dark, damp or crumbling sheathing and rusted nails point to deck rot. A screwdriver or awl that sinks easily into the wood confirms decay.

Repair

Rotten fascia and soffit sections are cut out and replaced, often with primed or naturally durable timber, or clad with metal or PVC trim. Deck rot is repaired by replacing affected sheathing, usually during reroofing, and sistering or replacing decayed rafter ends. Repairs only last if the moisture source is fixed: a correctly installed drip edge, cleaned and correctly pitched gutters, sound flashings and a controlled attic environment. Some regions also see insect damage alongside rot; termites and carpenter ants favour damp wood.