"Christian McArdle" wrote in message
. ..
But the way, what are the stones for that you sometimes see ?

UV protection?

Christian.

The chippings are required on cheaper BS747 type bitumen felt roofs in order
to achieve AA rating for spread of flame. Under Building Regulation B4, any
roof within 6m of a boundary needs to be AA rating. The more expensive
"High Performance" mineral-surfaced felts comply with AA rating without
needing chippings.

Peter