1. How do you select the appropriate low slope roof system?
The Department of Defense owns one of the largest
portfolios of buildings in the world. They have developed
what they call the Unified Facilities Criteria. Roofing
falls under their publication: UFC 3-110-3. The full
document may be found at the following link:
http://www.wbdg.org/ccb/DOD/UFC/ufc_3_110_03.pdf
Here are some interesting quotations from this document:
“Thermoplastic Polyolefin (TPO) shall only be allowed
on roofs with an anticipated life of 10 years or less. See
additional guidance below for TPO.”
“BUR systems have broad applicability for dependable
low-slope roof systems with low service life cost.
Consider this roof system unless it can be shown that it
fails to meet important design criteria. Positive attributes
of BUR membranes include:
“The allowable types of top surfacing for BUR
membranes are granulated modified bitumen cap sheet
and aggregate.”
“MB roofing systems have low maintenance cost, and
must be considered when long service life is required. The
polymers used to modify the asphalt bitumen improve the
performance characteristics of the asphalt. The addition
of polymers increases low temperature flexibility and
high temperature stability. MB membranes are reinforced
with fiberglass, polyester, or a combination of both. MB
membranes must have at least two-ply or as specified by
the UFGS.”
“EPDM roof membranes provide predictable
serviceability in roof systems in all climates. The
minimum sheet thickness shall be 90 mil. All lap seams
shall be fabricated with 6-in. (150 mm) seam tape and
stripped-in with self-adhering, semi-cured EPDM cover
strips.” “Mechanically fastened EPDM are not
permitted.” “Fully adhered EPDM systems do not allow
billowing of the membrane and are the preferred method
of EPDM installation.”
“Thermoplastics are materials that soften when heated
and regain their physical properties upon cooling.
Weldable thermoplastic membranes are appealing as
roofing systems because when the seams are properly
heat welded they can exhibit seam strengths comparable
to the membrane sheet. Weldable thermoplastic
membranes are available in white or other light colors to
reduce solar heat gains. While the material costs are
higher than bituminous-based roofing, labor costs are
generally lower. Properly constructed weldable
thermoplastic membrane systems may last 15 years or
more. Of all weldable thermoplastics, PVC systems have
the longest time in service.”
“Mechanically fastened weldable thermoplastic systems
allow some billowing of the roof membrane; however,
this is greatly limited by reinforcement fabrics. Cool roofs
in ASHRAE Climate Zones 4-8 shall be fully adhered and
not mechanically fastened.”
“Fully adhered weldable thermoplastic systems do not
allow billowing of the roof membrane and are the
preferred method of installation.”
“TPO membranes are a relatively new roof membrane in
the commercial roofing market and have seen several
reformulations in the past decade. They are typically
white in color and, as a thermoplastic, the seams are heat
welded. Since they are new, long-term performance is
unknown at this time. TPO should be specified with
caution and only with 72 mil (1.8 mm) minimum
thickness.”
“Mechanically fastened systems are popular but are
restricted to the ‘rhino bond’ system and are not permitted
in ASHRAE zones 4-8. Fully adhered systems are
recommended. A cover board shall be utilized in all
systems.”
“As noted above, TPO shall only be allowed on roofs with
an anticipated life of 10 years or less.”
The more you know about roofing, the better we look. Go with the #1 name in roofing, XtraFlex by
Polyglass. Polyglass is the #1 manufacturer producing over 450 million square feet of modified bitumen in
the United States during 2014.