What Is a Modified Rubber-Roll Roof?

Modifying the Bitumen

• The polymers impart strength and rubber-like qualities to the bitumen, which -- although waterproof -- is structurally weak. The product is soft enough to deform over small bumps and into small cracks and depressions without splitting. The material was developed with just these qualities in mind, entering service in the European market in the 1960s and the U.S. in the 1970s.

Applications

• Modified rubber-roll roofing is almost universally used to finish flat or mildly sloping roofs. On steep slopes, the weight of the material pulls against the adhesive or fasteners, which can cause puncturing. It is not intended for use in locations prone to extremely heavy rainfall or volumes of snow.

Types

• Both smooth-finished and granulated rubber-roll roofing is available on the market. The granulated product is finished with a course material, most often slag waste from ore processing, that's been treated to give it a color; this can then be matched to the surrounding architecture. Metal-foil finish, intended for use in locations where solar heat is intense, increases the product’s reflective qualities. Several after-market bitumen-based finishing paints also serve this purpose.

Installation

• Rubber-roll roofing is manufactured for several kinds of installation processes. One type is applied over a sheet of base material to which it sticks. Another type is “torched” down, meaning that -- once unrolled -- a torch is passed over the material to melt its underside and stick it to the substrate. Professional installers typically hot-mop tar over the roof then install the rubber-roll roofing before the tar cools; this method is cheap but messy, and not for the faint of heart.

Pros and Cons

• Regardless of the installation process, the rubber rolls are unfurled across the roof -- each one overlapping the previous -- until the entire surface is covered. Once stuck down, the roof is immediately waterproof. This “forgiveness,” allowing the roof to be walked on as soon as the modified rubber-roll roofing is stuck down, makes the material a favorite with professional and do-it-yourself installers alike. The downsides of the product are a short service life, compared to other roofing finishes, and a difficulty in tracking down leaks if they occur.