Roofing felt.

[BigEars123]

I am installing a pitched roof on a building project.

I intend using breathable felt but am getting conflicting messages regarding it's purpose.

I have been told once the felt is laid the roof should be completely water-tight so it has to have no gaps and lapped over the ridge and hips etc.

I have also been told that the felt is nothing to do with weathering as the tiles will do the job.

A little confusing so advice would be appreciated.

 

[noseall]

The roofing felt/membrane is a watertight layer but not a weathering layer. It will not tolerate wind rain and sun for prolonged periods of exposure but will perform admirably below your tiles and will keep out the weather whilst the roof is under construction.

Your roof tiles are your primary weathering surface, the felt is a bonus.

Modern breathable felts help cut down on the need for additional venting and perform in similar fashion to sarking felt insofar as they keep the weather out whilst the roof is being built.

A roof can live without felt but can not survive without tiles.

THE ROOF TILES ARE YOUR WEATHERING LAYER.

 

[^woody^]

Another thing to bear in mind is that traditional clay rosemary tiles wont leak and do not need felt underlay (but building control will want one fitted), but concrete interlocking tiles can let some water in, and over time when the roof has moved a bit and the interlocking runners snap, then some rain will drip in

But once felted, you can leave the roof for months if need be, and get on with other things