FLAT ROOF OPTIONS FOR MID-CENTURY HOMES
Houses identified as Mid-century Modern often have flat or low-pitched roofs, which may lead to water pooling and drainage problems. This list of roofing-material options considers their pros and cons.
BUILT-UP ROOFING Long the most common system, and least expensive, it uses multiple layers of asphaltimpregnated roofing felt and mopped tar (bitumen) topped with gravel for fire-retarding and UV protection. It protects the roof against wind, snow, and pooled water, but is out of favor as a petroleum product that gives off noxious fumes during application and beyond. It can be difficult to find a leak with this system. The black tar is not best for a hot climate.
MODIFIED BITUMEN (MBR) roofing is related to tar and gravel, but uses a sheeting material made of several layers of polymer-modified bitumen. It’s roll roofing applied with heat or liquid mastic, with a surface finish of small rock granules. The mineral surfacing is factory-applied and a reinforced layer provides better flexibility at low temperatures. Durable and easy to repair.
RUBBER or EPDM (thermoset) roofs are made of recycled synthetic rubber. The membrane (black for UV protection or white for reflectivity) is chemical-, weather- and UVresistant. It must be installed by a trained contractor, it’s somewhat costly, and, while very durable, the roofing can be damaged by branches or foot traffic.
PVC MEMBRANES (thermoplastic) are applied in rolls, and the seams heat-welded. They are pliable and durable with good puncture resistance— but PVC cannot be used with asphalt (tar), which destroys the membrane. A separator goes over existing asphalt.
SPRAY POLYURETHANE FOAM (SPF) roof systems boast easy installation. A liquid is sprayed over the cleaned, existing roof and expands into a surface-conforming foam. SPF delivers thermal, air, and moisture barriers, resulting in a very high R-value per inch. With no seams, leaks are unlikely. A qualified, experienced contractor is a must, and the system is relatively expensive.