01 May 1999
this is achieved by allowing a flow of outdoor air between the insulation and the roofing system.
This air cools the roof in summer, dries out any moisture that condenses in the roof, and greatly
reduces the formation of icicles and ice dams along eaves. For regions prone to severe hail,
ballasted EPDM roofs are very good and PMRs are excellent. Tiles, shingles, bare BUR, and
metal systems are easily damaged by hail. In regions of semitropical climate (high temperatures
and humidity), asphalt shingles should be treated to be fungus resistant and wood
shakes/shingles should be pressure treated for rot resistance.
i. Installation in Cold or Wet Weather. Most membrane systems are difficult to install in
subfreezing weather. If frequent precipitation during construction is a problem, factory fabricated
single-ply systems with field welded seams may have advantages over systems where field
application of adhesives or hot bitumen is needed. Torch applied modified bitumens are one of
the few systems that can be applied, albeit slowly, in wet windy conditions.
j. Warranties. The NRCA Commercial Low-Slope Roofing Materials Guide contains a
comprehensive side-by-side comparison of commercial roof warranties. The roofing industry
offers two general types of warranties: Materials Only and Materials & Workmanship. Carefully
read exclusions and limits. Note: The longest warranties are not necessarily the best, nor does
the length of the warranty directly relate to roof durability. In many cases, manufacturers may
restrict their warranties.
k. Maintenance Considerations. Sloped roofs require less routine maintenance and may be
preferred when the facilities management is incapable of providing routine inspections and minor
repairs. Modified bituminous and BUR systems may be superior in abuse resistance to thin
single-ply systems. Various protection boards/walkways can be used around equipment where
traffic is anticipated. Protected membrane roof systems (PMR's) are abuse resistant but more
difficult to inspect and repair.
Roof Access, Fumes and Property Protection When Reroofing.
Fumes. In reroofing situations fumes from kettles and solvents may be
objectionable. Hot coal tar pitch is especially objectionable; hot asphalt is also noticeable but less
noxious. Cold applied systems with taped or welded seams and metal roof systems generate few
odors. It may be necessary to coordinate air-conditioning shutdown to avoid taking fumes into the
Ease of Construction Access. If the area around the construction site is
congested it may make heating and hoisting of roofing materials difficult.
Specifying Construction Procedures. Site access, material storage area, layout
area, building and landscape protection should be identified on drawings.
Safety and Disturbance to Occupants. The presence of occupants, vehicles, and
pedestrians may be of concern. Reroofing is noisy. Dust and overspray may affect those nearby.
Roofing requires skilled installers. Qualified contractors and
inspectors are more likely to be available if the system is customarily used in the region. It should
be determined whether there are several manufacturer-approved installers capable of bidding the
n. Owner Preferences. Verify that the contemplated system is acceptable to the owner,
occupants, and maintenance personnel.
2-8. CONSIDERATIONS WHEN SPECIFYING LOW-SLOPE (HYDROSTATIC) MEMBRANE
ROOFING. With the exception of SSSMR, membrane roofing requires a suitable roof deck. Most