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:
Mary Pickering says
September 12, 2016 at 2:32 pmHi I was hoping you could give me some advice. I am a first time buyer and I have received my home buyers report. It has noted the below issues regarding the roof, and I was wondering if you could give me a guide on how much you think the work would cost and how urgent you believe it is. Any advice would be greatly appreciated.
Many thanks
The chimney stack is of masonry construction above the roofline with lead at the stack/roof abutment to prevent damp penetration occurring internally. The chimney stack is in a serviceable condition for its age and type. We noted dampness in the chimney breast in the roof space where the chimney stack passes into the property and repairs are required. However, even with the detailing and pointing in good condition, the lack of a damp proof course (DPC) within the stack will allow periodic water penetration.
The roof is pitched and covered with concrete tiles laid over a lining. The roof covering appears to be in a serviceable condition for its age and type. Some defects were noted including repointing the ridge tiles. Repairs should be carried out to ensure that the roof remains weather tight and does not leak. Cement mortar fillets close the junctions between roof surfaces and adjacent walls. These appear in generally satisfactory condition however they are prone to frequent failure and should ideally be replaced with more durable metal flashings.
Chris Wilkinson says
September 7, 2016 at 8:54 pmI have had a problem with decaying felt along the bottom edge of the tiles letting rain water into the cavity. The solution my roofer came up with was to put a felt support tray along and under the bottom of the tiles. I would have thought that the tray should go under the felt but he has put it over the top. When challenged on this the answer was that it’s only to catch water dripping off the bottom tile edge and direct it into the guttering. This doesn’t seem right to me. Some water will always come down the felt from above when it’s driven in by wind or melting snow and so the trays should be positioned under the felt. If they are over the top of the felt then they’ll do nothing to catch water coming down the felt from above.
Anyone have an experience of what’s the right place for these trays?
Shadow says
September 24, 2014 at 9:04 amHello
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Our product list:
ASTM D-226 15# 30# roofing felt,
ASTM D-4869 15# 30#roofing felt, .
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Shadow
Keith Mead says
January 16, 2014 at 3:09 pmGreat article – very timely as I have the problem you mention regards felt around the eaves. Nice to see some “advice” with likely costs for having work done.