Key Criteria for
YOU MAY NOT SEE IT OR HEAR IT – and probably
don’t want to – but there is a lot of activity happening
on your roof, which represents one of the larger invest-
ments that owners have in their buildings.
The fact is that a roof is subjected to a barrage of impacts from
chemicals, wind, foot traffic, sunlight, temperature and moisture.
And although it seems that a roofing system is stolid and silent,
it is responding continuously to these impacts. The complex
chemistry and materials behind a roof membrane are major factors in their long-term performance and return on investment.
When evaluating roofing systems, commercial building owners will profit from a quick overview of a few material and installation principles.
SYSTEM TYPES, INSTALLATION AND BEHAVIOR
It’s useful to recognize the major types of roofing systems, not
only for the behavior of their materials but also to identify their
manufacturing and installation components.
BY JERRY BEALL
Bituminous roofing is a category of built-up roofing (BUR)
consisting of asphalt distilled from crude oil or tar distilled from
coal. Both materials are installed in the field, often by heating
them to high temperatures and applying with a mop or mechanical
spreader. Cold-applied versions of asphalt do not require heating,
and so they avoid the potential danger of high temperatures (450
degrees F. plus). Modified bitumen materials consist of asphalt
or coal tar materials that have been modified with polymeric materials and manufactured as roll sheet. The sheets may be installed
in multiple layers with heat, flame torches or cold materials.
Single-ply roofs consist of a flexible membrane that is factory fabricated, thus diminishing installation errors that can affect
field fabrication of built-up roofs. As roll materials, single plies are
seamed in the field. Thermoplastic single plies are seamed by
a heat weld in the field while the material in thermoset single
plies is “set” and must be seamed with adhesives or tapes by the
contractor. EPDM membranes consist of a thermoset material
(ethylene propylene diene monomer).
Thermoplastic single plies consist of various materials with
quite different properties, including TPO (thermoplastic polyole-fin), PVC (polyvinyl chloride), and KEE (ketone ethylene ester).
Manufacturing of KEE materials begins with a flexible material,
while PVC is an inflexible material that requires the addition of
other chemicals to make it flexible. The molecules in these added
chemicals tend to break down when subject to heat, ultraviolet
light, and some chemicals, all of which shorten their service life
compared to KEE.
For long life, roofing materials must resist a number of degrading factors, and each roofing material tends to respond in its own
way. (See “Material Factors for High Performance” at right.)
NAVIGATING THE EVALUATION AND PURCHASE PROCESS
Given the range of materials and factors, building owners need
to narrow down their options – but without oversimplifying them –
in order to get the best possible return on investment. There are no
magic bullets in the process.
Keep in mind that you should investigate existing roofs on
buildings in your climate zone. Performance as measured by lab
tests can be valuable, but they are limited; you must evaluate real-world weathering. Another key principle is the expertise of the
contractor. As we have seen from the survey of roofing systems,
BALANCE THE FACTORS THAT DRIVE YOUR
RETURN ON INVESTMENT
Four years after installation, an EPDM roof on this Rubbermaid
facility in Greenville, TX, failed during a storm. It was replaced with
a 36mil KEE single-ply roof from Fiber Tite that is still going strong
after 30 years. The Greenville area has strong winds and hail.