Ponding water sometimes occurs on membrane roof systems as a
result of snow, rainfall or runoff from equipment. Although you may
be held responsible for ponding on new or re-covered roof systems,
many elements that determine how well a roof assembly will drain
are outside your responsibility or control. Coordination with the
building owner, roof system designer or general contractor often is
necessary to address potential drainage deficiencies. Ponding water
for short durations is unavoidable and considered acceptable by
NRCA and membrane roof system
manufacturers, but ponding water in excess of 48 hours can be
detrimental to the roof assembly.
Many building codes have a slope requirement for membrane roof
systems. International Building Code,® 2012 Edition (IBC
2012) Section 1507—Requirements for Roof Coverings states all
membrane roof covering systems except coal-tar built-up roofs have
a design slope minimum of one-fourth unit vertical in 12 units
horizontal (2 percent slope) for drainage. Previous IBC editions
have...
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