Roofing felt was introduced in the 1930s. It served two main functions. It acted as a protective barrier to the house before the main roof covering was constructed. It also functioned as a secondary barrier to wind driven rain and snow which penetrated under the roof covering as well as potential pests like insects and birds. Roof felt is impermeable to water and if adequate ventilation is not available then condensation can build up on the underside of the felt. This condensation can then drop onto the attic floor, causing damp to appear on ceilings.
In the 1980s breatheable membranes were introduced as a replacement for roofing felt. This reduces the condensation problem as water vapour can evaporate through the membrane.
The introduction of thicker layers of insulation in houses has increased the condensation problem associated with roofing felt, as improved insulation means the roof space is at a lower temperature and water is more likely to condense.
Repairing Roofing Felt
Many roofs function quite well without any roofing felt, so small tears and damage to roofing felt are not in themselves reasons to spend money on repairing it. Where wind driven rain is working under the roof and causing leaks then the felt will need to be replaced.
To replace a small section of roofing felt involves stripping the tiles from the roof and replacing felt between two joists. This will cost around £460-£510 made up of:
- £150-£200; Access tower
- £260: Labour (1 day x 2 people, 1 x £160 + £1 x £100)
- £50: Materials ( breathable membrane plus mortar for ridge tiles removed)
Repairing Felt Around The Eaves
A common problem is when roofing felt, on a roof with an enclosed soffit, disintegrates around the eaves of a roof. Wind driven water that would normally flow down the felt and into the gutter instead drips onto the soffit and then back onto the ceiling of the room below through gaps in the felt. This normally shows up as damp patches around the perimeter of the exterior walls of upstairs rooms. To overcome this a section of felt around the eaves of the roof can be replaced. To replace the eaves level of felt with breathable membrane on two sides of the average house would be around £770-£870 made up of:
- £150-£200; Access tower
- £520: Labour (2 days x 2 people, 1 x £160 + £1 x £100)
- £100: Materials ( breathable membrane plus replacing any damaged tiles at eaves level).
This would involve stripping the lower layers of tiles from the roof, and adding a 500mm strip of eaves protection felt before reinstating the tiles
If the damage is more extensive and the roof is leaking it is normally a sign of other problems with the roof and the entire roof may need to be refurbished.
For more information and costs on a complete re-roof see: