Rotten Rafters, Battens Or Roof Timbers

What's happening?

Roof timbers rot when they stay wet. Rafters, battens, wall plates and the ends of joists where they sit in damp masonry are the usual victims. Wet rot is the more common: timber that is dark, soft, cracked along and across the grain, damp to the touch, and confined to the wet area. Dry rot is less common but spreads. It can carry water in its own strands into timber that is dry, and shows grey or white strands, a fleshy fruiting body and a mushroom smell. Either way the sign that matters is soft timber that a screwdriver sinks into. The cause is a leaking tile, flashing or gutter, condensation in a poorly ventilated loft, or a damp wall at the timber's bearing. Replacing wood without ending the water means it rots again.

What usually causes it?

• A leak at a slipped tile, flashing, valley, chimney or gutter wetting the timbers
• Condensation in a loft with blocked eaves ventilation
• Rafter ends and wall plates sitting on damp masonry or behind a leaking gutter
• A long-term leak from a water tank or pipe in the roof space
• Timber that was damp when installed or boxed in without drying
• A previous repair that covered a leak instead of stopping it

Is it dangerous?

Yes. Rot weakens the timber that holds the roof up, and dry rot can run through the structure. Rot also means the roof has been letting water in for some time. Do not walk on suspect timbers, and do not spray treatment on them without first fixing the water.

Can I fix it myself?

From the loft hatch, photograph timber that is soft, dark, or covered with white strands, and note any damp smell and the area. Do not poke or stand on suspect timbers, and do not paint or spray over rot. Fix the water source with a roofer. If you have to go into the loft, step only on joists or boards, never on the ceiling between them.

When should you call a roofer?

Call a roofer to find and stop the water and to replace rotten rafters and battens. If you see strands, a fruiting body or a mushroom smell, call a specialist in timber decay for dry rot. If rafters or a wall plate are affected over a span, ask a structural engineer to say what can be kept.

What will the roofer actually do?

• Inspect the roof covering and the timbers to find where water is entering
• Probe the timbers to establish how much is sound
• Stop the water: repair the tiles, flashing, valley or gutter, and improve ventilation
• Cut out and replace rotten timbers or splice new sections to sound ones
• Treat remaining timber where a specialist advises, and for dry rot follow a specialist's plan
• Re-cover and check the roof is watertight and ventilated

Who fixes this

• Roof inspection
• Roof leak repair

Questions people ask

Sources & References

1. Property Care Association: wet rot
2. Property Care Association: dry rot
3. Property Care Association: structural repairs
4. NFRC: choosing a roofing contractor