Abstract: Sheet of roofcovering material, consisting of a porous base layer provided with apertures distributed over its surface, over which base layer a bituminous covering layer has been applied under insertion of a perforated plastic film so that the covering layer is adhered to the base layer through the perforations of the film, such, that by the exceeding of a certain shear stress between the base layer and the covering layer, the bituminous bond of the base layer with the covering layer on the spots of the perforations is torn loose coupled with a shifting of the base layer and the covering layer with respect to each other.