Ethylene propylene diene monomer (or EPDM) rubber is a form of synthetic rubber that is often applied as a single-ply membrane to flat roofs. As it is simple to apply, it is a much cheaper option for flat roofs, and when correctly installed, has an expected lifespan of 30 to 50 years.
A built-up felt roof is a method of weatherproofing flat roofs by using several layers of felt which are bonded to the layer underneath. Often, the layers are covered with a layer of chippings or a mineral cap to protect the felt from sunlight. Felt sheets are made up of a mat of fibres coated on both sides with a bituminous coating and covered with a light sand to prevent the layers from sticking together. Felt roofs typically have a lifespan of 15 to 30 years and come in a range of different colours, including green, red, white, grey and brown.
Another option for flat roofs is lead. Lead is common in use on historic buildings, such as churches. It is ideal for areas that experience high levels of precipitation and cold temperatures, as it is very durable. The larger the surface of the roof is, the thicker the lead sheet needs to be, in order to prevent heat shrinkage. If installed correctly, lead roofs can last 50 to 100 years without a need for replacement.