As part of my roof upgrade I've been putting felt on the roof. I used two layers of felt, the underfelt does not have the stone chippings on it that protect the felt from the effects of the sun. I've still got to finish off some of the edges, particularly around the window where mastic will be needed as well as clout nails. I've put some planks on there for the time being to stop the wind blowing the felt off.
There seems to be some disagreement with regards the facia boards, are they just cosmetic or do they help signficantly with holding the felt in place?
Here's a handy video from B&Q on how to do it.