Do soffits need vents?

A cold pitched roof needs a ventilation path, and on most UK houses that path is at the eaves — through vented soffit board, a continuous strip, or individual vents. BS 5250 covers moisture management in buildings and the eaves airway is central to it for this construction. A sealed soffit on a cold roof traps moisture in the loft.

Why is my soffit rotten when the gutter is fine?

Usually loft condensation. Moist air from the house reaches the cold underside of the soffit and condenses there, wetting it from inside. The giveaway is insulation packed into the eaves blocking the airway, plus mould on the nearby rafters.

Can I just clip uPVC over the existing soffit?

Only over sound, dry timber. Over decayed board it hides active rot and often blocks what ventilation there was. Ask whether the existing timber has been exposed and checked, and whether the new board is vented.

There are birds nesting in the soffit gap — can it still be fixed?

Not while the nest is in use. Wild birds, their nests in use and their eggs are protected under the Wildlife and Countryside Act 1981, so work has to wait until the nest is no longer active. A contractor should raise this rather than proceed, and can plan the repair with proofing for afterwards.

Caution

Updated 30 August 2026

Rotten Or Sagging Soffit

The horizontal board under the eaves overhang is soft, stained, bowing down, or has a hole in it.

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What's happening?

The soffit is the board on the underside of the eaves overhang, running from the wall out to the fascia. It closes the gap into the roof void and — critically — it is where most UK pitched roofs get their ventilation, either through a continuous vent strip, circular vents, or a purpose-made vented board. That ventilation is what lets moist air out of the loft; BS 5250 covers how moisture in buildings should be managed and the eaves airway is a key part of it for a cold roof. So a rotten soffit is two problems at once: decayed timber that needs replacing, and usually a clue that the roof void has been holding moisture. A soffit that has gone soft across a whole elevation has normally been wet from inside as well as out.

What usually causes it?

Overflowing or leaking gutter above wetting the board from the outside
Loft condensation on the underside of the soffit where eaves ventilation is blocked — insulation stuffed into the eaves, or vents painted over, blocked with debris or never fitted, so the roof void cannot breathe
Underlay dressed short at the eaves so water reaches the soffit and rafter feet rather than the gutter
Wet rot decay in softwood held persistently above about twenty per cent moisture content
Rafter feet and wall plate decay behind the board removing the fixing points, so the soffit bows
Birds, squirrels or wasps enlarging a small gap into a hole
uPVC soffit clipped over rotten timber, keeping the decay damp and hidden

Is it dangerous?

Moderate, with a hidden dimension. Pieces of a decayed soffit fall, usually onto a path or patio directly beneath the eaves. The bigger concern is what the decay tells you: soffit rot commonly runs back into the rafter feet and the wall plate, and the wall plate is the timber the roof structure bears on. Blocked eaves ventilation is also its own problem — a loft that cannot breathe accumulates moisture, which condenses on the underlay and rots the roof timbers from inside. Holes in the soffit let birds and wasps into the roof void, and nesting birds bring legal restrictions on when work can be done.

Can I fix it myself?

Look up from directly below and along the eaves from an angle. Note staining, sagging between fixings, gaps at the wall or fascia joint, holes, and whether vents are present and clear — painted-over or debris-blocked vents are extremely common and easy to spot. In the loft, check whether insulation has been pushed hard into the eaves, blocking the airway; pulling it back to leave a clear gap is a legitimate and useful homeowner job. Look for mould on rafters near the eaves, which points at condensation. Do not fill or paint over a soft soffit, do not board over a hole with a nest behind it, and do not work overhead from a ladder.

When should you call a fascia, soffit and guttering installer?

Call within weeks for staining or localised softness, and sooner if the board is sagging, holed, or if there is any sign of birds or wasps using the gap. Ask specifically about ventilation as part of the quote — a new soffit fitted with no working eaves airway leaves the underlying cause running. If you can see mould on loft timbers near the eaves, mention it, because that changes the job from a board replacement to a ventilation fix as well.

What will the fascia, soffit and guttering installer actually do?

Remove the soffit and inspect rafter feet, wall plate and the underlay at the eaves rather than assessing from below
Identify decay and its source, separating external wetting from loft condensation
Cut out and replace decayed timber, splicing rafter ends or wall plate sections where decay has reached them
Fit new soffit — sealed and primed timber or a full-replacement uPVC board on sound substrate
Provide or restore continuous eaves ventilation to the roof void, sized appropriately for the roof, and fit eaves ventilation trays in the loft so insulation cannot block the airway again
Fit an eaves carrier tray so the underlay discharges into the gutter rather than onto the timber, and close gaps against birds and rodents with mesh that maintains the airflow

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Rotten Fascia BoardCaution Birds Or Wasps Getting In Behind The SoffitCaution Torn Or Sagging Roofing Felt In The LoftCaution

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