In years past, having a flat roof on a home was a disaster waiting to happen. The chances of keeping a flat roof from leaking, especially in places where significant winter snow is common, was nil.

That all changed with the advent of residential membrane roofs.

A membrane is a large sheet of EPDM rubber (short for ethylene propylene diene monomer), formulated to be resistant to the sun's ultraviolet rays. A membrane roof is relatively simple to install and is impervious to water in ways that more typical residential applications, such as roll or selvage edge roofing, are not. This has lead to the resurgence of the flat roof as a viable design characteristic for residential construction.

The typical membrane used for residential applications is 45 mils thick, most commonly black, but also available in white.

A flat roof is actually not flat. There has to be some pitch,no matter how slight, or the water cannot drain. This pitch can be so slight as to be non-existent for all practical purposes. Pitch can either be built in when the roof is framed, which would be common in new residential construction, or can be added with a shaped insulating underlayment, as is done in commercial applications.

The first step in the installation of a membrane in a residential application involves applying some sort of cushioning base to the roof deck. This could be an insulation board or a fiberboard sheathing material. There should be a minimum slope of 1/2" in 12" to prevent water ponding. The underlayment board is fastened down with plastic or metal washer nails which are then covered with adhesive rubber patches to prevent damage to the rubber membrane.

The roof surface is swept clear and then a specially formulated contact cement is applied to both surfaces and allowed to dry to the touch. The next step may well be the trickiest of the application process. The membrane must be carefully applied to the surface. As with all contact cements, once the two surfaces have touched they are nearly impossible to reposition. A roller is then used to press the membrane to make sure that uniform contact is achieved.

If more than one piece of membrane is required, a special glue is applied that seals the two membrane pieces together at the lap, fusing them into a single sheet. There are also special products for handling the places where the sheets meet the roof edge. The easiest of these to use are self adhesive.

Installation of residential membrane roofing is straightforward enough that it can be accomplished by moderately skilled homeowners. The advent of the rubber roof membrane has been a boon for designers, and a life saver for the owners of older homes with problem flat roofs.