Sheet based membranes come in the form of rolls. these are unrolled and laid on the firm surface. one of the most common sheet based membranes is the bituminous waterproofing membrane. this membrane is stuck to the roof surface by melting a tar based adhesive on the membrane using blowtorches.
these membranes can be measured and cut to the surface area requirements of the roof.
Adjacent membranes should overlap using the same tar based adhesive. the overlapping width can around 100 mm . This will prevent vulnerable joints and water from seeping in through the gaps between the membrane.