Roof felt or not?

[tulipcocoa]

We are in the process of trying to get quotes to repair the clay tiled roof of our Georgian house. One of the contractors tendering has said that we should strip the whole roof and put felt down before retiling. Another contractor thinks that areas of the roof need repairing and that the rest can be left as is and has not recommended the use of felt.

Any thoughts on whether we should felt or not? The roof which is above unoccupied attic rooms appears to be in an original state (with no felt, just tiles and pins with hardboard as a "ceiling" to the attic rooms).

Thanks

 

[Gervase]

Felting is pretty much standard these days. It does stop rain from being blown into the roof void in high winds, but it is important to specify a breathable felt like DuPont's Tyvek - your roof needs a reasonably free flow of air to avoid mould, rot and general decay in the timberwork, and period houses don't lend themselves to many of the modern venting systems.
Certainly if you ever intend to use the attic rooms, a liner under the tiles will protect whatever finish you choose for the ceilings.
As to whether it's best to strip the roof and relay or merely fill in patches, much depends on the sort of tiles and the general state of the roof. Some tiles, like pantiles, are very easy to remove and stitch back into an existing roof, but pegged tiles may be more difficult.
Whatever roofer you're tempted to go for, have a quiet word with your local conservation officer first and see what s/he says. They're not supposed to make recommendations, but they can steer you in the right direction.

 

[Penners]

Gervase is an expert in such things, so well worth listening to.

Here are a couple of amateur thoughts.

Firstly, is the good area of unfelted roof letting in water? If so, then of course you need to strip and felt (with a breathable membrane as Gervase says). If it's not, then - depending on the next comment - you could consider leaving it unfelted.

Secondly, how much of the roof is going to have to be repaired? If it's just a smallish area, then you might want to apply the principle above (particularly if funds are tight). However, if a significant amount of the roof is gonig to have to be retiled anyway, then you might as well strip the lot, felt and re-tile.

Ultimately, like most things, it comes down to a balance between cost and doing what's best for the building.

 

[NT]

Felt is only used when reroofing, not usually for repairs.

If you only need to repair a couple of patches, why are you considering a complete reroof? Builders will get as much money from you as they can, obviously. Reroofs can make sense with slate roofs when nails are rotting through at a fair pace.


NT

 

[Lime]

It depends on the size/area of roof that needs to be repaired and also WHY it needs to be repaired.
My experience of such tiles is that felt underneath them not only stops water and snow seeping beneath them but also minimises the chances of the tiles being blown/sucked off in a gale.

If the area of repair is quite large I would have it all felted.
Of course, it is possible to just have the area repaired felted just by itself depending on where the area is on the roof. The felt would have to extend down to the guttering to be any use.

In my perverse way, all things being equal I'd offer the refelting job to the contractor who suggested it did not need to be done. It is possible that they may show more care rather than the "rip-it-all-off" contractor.
However I would also try to see some roof work of the contractor you choose before you make any agreement and don't be afraid of knocking on the door of the house roof that you are viewing. most householders will be quite honest in their opinions of builders/contractors once they have finished the job. Think of some questions to ask them beforehand.

 

[tulipcocoa]

Many thanks to everyone who replied. We need to clarify the extent to which we need to re-roof. The wooden beams and battens generally appear sound and there is little leakage through the tiles so, subject to further advice, I think we will go for a repair rather than a total re-roof. Where we need to re-roof (one of the small roofs is pretty bad) we may look at including the breathable felt. We'll liaise with the conservation officer for further advice (hopefully).

Thanks again!

 

[plumbers mate]

My roof was stripped, felted and the old slates replaced 2 winters ago and the upstairs of the house is cleaner, there are fewer draughts on the landing and the thick layer of muck that fell on the insulation already in place has added another layer of insulation.... erm well, it's about an inch thick so should be doing something up there. (Luckily anything stored in the roof was covered before work started.)

 

[Nemesis]

In general, with a historic roof it's better (as with so many things) to try to conserve what's there as long as possible.

In ye olden days roofs were often torched with lime under the tiles - same idea as breathable membrane really.

Some wider reading:

http://www.collywestonstoneslaterstrust.org.uk/specificationguide2.htm

http://www.ehsni.gov.uk/roofs.pdf

http://www.buildingconservation.com/articles/pdf_roofsbreathe/roofsbreathe.pdf