26 September 2006
roofing, labor costs are generally lower. Properly constructed PVC membrane systems
may last 15 years or more.
Mechanically Fastened PVC Systems. Mechanical-fastened PVC
systems allow some billowing of the roof membrane; however, this is greatly limited by
Fully Adhered PVC Systems. Fully adhered PVC systems do not allow
billowing of the roof membrane and are the preferred method of installation.
Ballasted PVC Systems. Ballasted PVC systems can make use of larger
sheets to reduce the amount of field seaming. The ballast is relatively heavy at 4.5 to
5.5 kg (10 to 12 lbs) per 0.1 m2 (1 ft.2). The downside of ballasted systems is the need
for stone ballast, the increased cost of the building structure, and the difficulty of finding
the source of leaks. Factory Mutual accepts ballasted systems for Class 1-60 wind
resistance rating; however, higher wind resistance ratings cannot be achieved using a
Spray Polyurethane Foam (SPUF) Membranes.
SPUF systems provide good serviceability where non-planar surfaces prevent the use
of other roofing systems. SPUF roof systems should be considered when leaking
corrugated metal roof systems require repair and for curvilinear shapes that do not
permit the use of other approved roof systems. In use over existing metal roofs careful
review of impact on fire classification is required.
The principle components of the SPUF system are the polyurethane foam and the
Foam. Trained and certified applicators are required because the foam is
difficult to apply in uniform thickness, and is highly sensitive to moisture, UV radiation,
and wind velocities in excess of 19 km/hr (12 miles/hr). Even brief exposure to UV
radiation in sunlight significantly degrades the foam. Degradation is progressive and
will eventually result in system failure.
Coating. Coatings are required for all SPUF roof systems. The coating
protects the foam from UV degradation and must be applied to the foam as soon as
possible after the foam has cured, but not more than 72 hours after foam installation.
The base coating should be a distinctly different color to provide an indication of the
need for re-coating the roof system. The cost of replacing coatings is a significant
component of the life cycle cost of SPUF roof systems.
LOW SLOPE ROOF SPECIFICATIONS.
The UFGS are more appropriate for the long-term needs of the military than the low
slope specifications provided in the NRCA Manual. UFGS shall remain the basis for all