26 September 2006
Metal Foil Surface MB Systems. Metal foils surfaced MB roof systems
may be used to achieve for solar reflectivity or to improve fire resistance. Field
experience indicates that metal foils can delaminate from the MB sheet, resulting in
degradation of appearance and longevity.
Smooth Surface MB Systems. Many APP roofing systems are smooth
surfaced. These membranes must be field coated for heat reflection and UV protection.
These systems typically require maintenance recoating at five- to eight-year intervals.
Ethylene Propylene Diene Monomer (EPDM) Membranes.
EPDM roof membranes provide exceptional serviceability in roof systems where
exposure to extremely cold temperatures is normal.
EPDM sheets are resistant to the effects of UV radiation and are very durable. Field
seams of EPDM sheets have been problematic; however, seaming technology and
adhesives have improved reliability with the use of tape-applied adhesive. Tape applied
seams should be used when possible. Due to the adverse effect of moisture on seam
adhesives, most manufacturers prohibit the use of EPDM membranes over deck
materials with high moisture content such as lightweight insulating decks or poured
Mechanically Fastened EPDM Systems. Mechanical fastening of EPDM
roof systems allows some billowing of the membrane. This can be reduced by the use
of fabric reinforcement sheets. The amount of billowing is dependent on the spacing of
the mechanical fasteners and the pressure differential between the interior of the
building and the exterior surface of the roof. Excessive billowing has been known to
cause failure at the fasteners and at the seams.
Fully Adhered EPDM Systems. Fully adhered EPDM systems do not
allow billowing of the membrane and are the preferred method of EPDM installation.
Ballasted EPDM Systems. Ballasted EPDM roof systems use larger
sheets with factory made seams which are proven to be superior to field seams. The
downside of ballasted roof systems is the need for stone ballast or concrete pavers, and
the increased difficulty in detecting sources of leaks. The ballast is relatively heavy at
4.5 to 5.5 kg (10 to 12 lbs.) per 0.1 m2 (1 ft.2) that also increases the cost of the
structural system. Factory Mutual accepts ballasted systems for Class 1-60 wind
resistance rating; however, higher wind resistance ratings cannot be achieved with
Weldable Thermoplastic (PVC) Membranes.
Thermoplastics are materials that are soften when heated and regain their physical
properties upon cooling. PVC membranes are appealing as roofing systems because
when the seams are properly heat welded they can exhibit seam strengths comparable
to the membrane sheet. PVC membranes are usually white or other light colors to
reduce solar heat gains. While the material costs are higher than bituminous-based