The asphaltic layer I2 is further protected by upper and lower brous layers or sheets I4, I6, preferably comprising saturated asbestos felt, which are adhesively affixed to the metal foundation member l0 by the asphaltic or bituminous layer I2 in such manner as to cover the surfaces of the asphaltic coated metal sheet I0 and to leave portions of the fibrous sheets I4, I 6 projecting beyond 'the op