why do you have to felt a roof before tiling/slating it?

Answer 1

Roofing felt is put down for several reasons, the first of which is most codes require it. The felt does several things:

1. Acts as a temporary roof until the permanent materials are placed.
2. Acts as a shield to the wood decking.
3. Some roofing felt has lines to allow for easier alignment of the roof tiles/slate.
4. Acts as backup should a leak occur in a tile/slate.

Roofing felt generally comes in two "weights" , 15lb and 30lb, the real difference being the thickness and durability of the material. Traditionally it was impregnated with tar, but now synthetics are used. There's also newer "felts" that are fiberglass weaves that perform the same thing.

Additionally, many building codes require specialized material along the eaves, valleys and ridges. This is a rubberized material that sticks to the wood decking and self-seals around any nail holes. Should ice form on these areas, the melting ice may leak under the tile/slate and the membrane will keep the water from entering the house.

Hope this helps. Go here for more info: http://www.doityourself.com/stry/roofingfeltsapply

Good Luck!

Answer 2

This felt prevents wind driven rain and snow from getting behind the slates / tiles and entering the roof space. It acts like a secondary waterproofing layer and can also help prevent water ingress if a slate gets blown off during a wind storm etc.

Answer 3

Contrary to popular belief, on asphalt shingled roofs, felt paper is not used to seal against rain or even act as a moisture barrier. It is surprising how common that reason is given as a requirement for its installation and cost.

The reason felt paper is used is to level the surface and prevent your shingles from taking the rough shapes of the plywood below, and bond to the plywood itself and hamper expansion and contraction. It furthermore keeps the shingles flatter as they age and give and compress against the surface and is required by nearly ALL shingle maker companies in order to honor their warranty.

On a shingle or slate roof, in most areas, synthetic roll material purchased in wide widths is used to act as an insulation barrier and protect the subroof structure below. If you are installing new slate or tile this is what you should be using today.

Answer 4

It's also used to stop condensation from moist air in the building rotting the battens when it contacts the cold slates/tiles and condenses.This can also cause nail rot due to the battens not getting a chance to dry out.Also a back up in case of failed slates/tiles and wind entering the roof and lifting it or making it colder.Probably a few others too.Well worth fitting,as are vents.

Answer 5

Felting is just a new trendy term for tar papering. You always put down tar paper & staple it down, over lapping as you go. This forms a water proof barrier over top of the boards or plywood before you put on the roofing asphalt shingles or slate tiles, or what ever you choose to use.