What is required/best for loft felt

[405 TD Estate]

My roof has no felt under the tiles - maybe it never did.

I assume it should have something. What is the best stuff to use, what does it actually do (tiles are supposed to keep water out right?)

[Ian Stirling]

In Scotland, for example, it's almost unheard of for this to be the case, there is a skin of 18mm or so boards covering the roof, covered with felt, on which are battens that carry the tiles.

[Andrew Gabriel]

It provides a second line of defence, e.g. if a tile slips/cracks, or if the wind is such to drive water/snow under tiles. I wouldn't bother refelting just for the sake of it though, only if the roof is in need of replacement for some other reason.

[The Natural Philosopher]

What is does is to stop high winds lifting the tiles actually.

Its there to prevent massive pressure surges under the slates or tiles.

It should have no impact on waterproofing at all.

In high wind areas, board is better.

[Simon Stroud]

When Econoloft did my loft conversion a few years ago they chopped out a few areas of felt so they could slide in big things like the steel and various wood bits. They never bothered to repair the felt (or do a good job of the conversion but that's another long story that I don't want to be reminded of!) and it has been fine ever since.

I read somewhere that it is especially important for stopping the tiles lifting when there is a lot of wind on "the other side" of a house, presumably entering through the soffit vents. In my (loft converted) case I only have a small ventilation gap up each side between the Celotex boards and the felt or tiles, so there isn't really anywhere for big winds to build up and blow off all the tiles.

Regards, Simon.

[405 TD Estate]

Where is the felt suposed to go? Between the battens (corect name for the little horizontal bits?) and the tiles or on the inside of the batens?

[keith_765]

Its laid horizontal on top of the rafter, starting at the eave, then the laths or battens are fixed on top, then the slates or tiles.