The Facts About PVC Roofing Part I

EDITOR’S NOTE: A
roofing system covering millions of square feet across the globe with a
50-year track record is hard to keep a secret. Yet PVC and PVC KEE HP
roofing membranes may be the one type of roof installation even seasoned
contractors are relatively still in the dark about. While it’s earned
the confidence of the design community and prominence among architects,
consultants and other building professionals, roofers aren’t as familiar
with PVC as TPO and EPDM in the low-slope world.

With our partners at Mule-Hide Products, RC presents the first in a two-part series of articles to close that information gap.

Check
out this brief history of PVC use in roofing, the environmental
considerations related to PVC roofing, and the performance advantages it
offers. Part II will cover the types of PVC roof membranes and the
warranty options offered in an upcoming edition of Roofing Contractor.

Five Decades of Performance

PVC
roofs debuted in Europe in the 1960s and first appeared in the United
States in the 1970s. ASTM D4434 – the ASTM International PVC roofing
standard and the first ASTM International standard for single-ply
roofing membranes – was published in 1985 and has been updated various
times since.

Some of the first-generation PVC membranes did not
contain scrim reinforcement, which often resulted in poor performance.
Plasticizers make PVC roofing membranes extremely flexible and easy to
work with. However, over the membrane’s lifespan, the plasticizers
migrate out, making it more brittle. When enough plasticizers migrated
from the non-reinforced membranes, they would often shatter and crack.

Non-reinforced
PVC roof membranes were deemed unviable for use in the United States,
and scrim reinforcement was required under ASTM D4434. Reinforced
membranes, on the other hand, have the weather-ability to deliver
long-term performance, allowing them to build a 50-year track record of
successful use.

Today, three types of scrim-reinforced PVC
roofing membranes exist in the ASTM D4434 standard. Each has its own set
of physical performance requirements that must be met. These will be
outlined in Part II of this article series.

PVC roofs boast many advantages over other roofing types, including their overall durability against chemical and fire damage combined with being energy efficient.

PVC and the Environment

The
fact that architects, consultants and other design professionals
specify PVC roofs so frequently should be a strong indication to roofing
contractors that they are an environmentally responsible, sustainable
choice.

PVC is the only thermoplastic roofing membrane that is not
100% derived from fossil fuels; it is 57% salt water and 43% natural
gas — a formula that helps achieve two important goals: decreasing the
use of fossil fuels and significantly reducing the risk of supply chain
disruptions.

The United States has both components in abundance,
giving manufacturers ready access to the materials they need without
having to rely on foreign suppliers.

PVC roofing membranes are
recyclable. Scrap and old material can be used as feedstock for
producing new membranes and in manufacturing products ranging from
window frames to luxury vinyl flooring, rooftop walkway pads and
concrete expansion joints. However, contractors should keep the
following in mind:

To be recycled, the membrane cannot have adhesive on it.
As
with TPO, EPDM membranes, and polyisocyanurate insulation boards, PVC
membranes cannot be thrown into a recycling dumpster. The contractor
must hire a company to pick them up and haul them to an appropriate
recycling facility.
When a
project involves tearing off existing roofing materials, the designer
may specify that the old membrane and other system components must be
recycled. Contractors should watch for this stipulation so they can
build the recycling-related costs into their bids. (Note: this holds
true when tearing off various roofing materials, not just PVC
membranes.)

Cool roofs are so named for their ability to reflect the sun’s heat from a building and for absorbing less solar energy.

Performance Advantages

PVC
membranes offer several performance advantages in installed roof
systems, including chemical resistance, fire resistance, energy
efficiency, heat-welded seams and crew-friendly flexibility.

Chemical Resistance

PVC
roof membranes are highly resistant to greases, animal fats, jet fuels,
acids (particularly sulfuric acid) and other chemicals. This makes them
the ideal choice for restaurants, food processing plants, airports,
manufacturing facilities and other buildings where the roof will be
exposed to these chemicals.

However, PVC is not chemical-proof.
Where higher levels of chemical exposure are expected, such as around
rooftop vents, the membrane should be protected with a grease trap or a
second, “sacrificial” layer of membrane.

Fire Resistance

PVC
is exceptionally fire-resistant and self-extinguishes once the flame’s
source has been removed. It outperforms EPDM and TPO in this arena by
far and will achieve steeper-slope UL fire ratings than is possible with
these other single-ply options. It is ideally suited to buildings with
an elevated risk of rooftop fires — such as those with solar panels or
other electrical components on the roof and restaurants where there is
the potential for a rooftop grease or oil fire. It is also a good choice
when the building’s occupants, such as senior care facilities and
hospitals, will have greater difficulty evacuating in the event of a
fire.

“Cool Roof” Options

Like white TPO and
white-on-black EPDM roofs, white PVC roofs can significantly enhance
the energy efficiency of buildings in warmer climates. They reflect much
of the sun’s energy away from the roof and then emit much of the energy
absorbed back into the atmosphere. This lowers temperatures on the
rooftop and inside the building, keeping occupants comfortable while
reducing air-conditioning costs and helping maximize the performance of
HVAC equipment.

Heat-Weldable Seams

As with
TPO roofing systems, PVC sheets are welded together to create
exceptionally strong, waterproof seams. If done right, the seams will be
stronger than the membranes themselves.

Test welds verify the
quality of field seams completed with automatic welders. Hand-welded
details are inherently more open to human error. Here, bleed-out — when
the darker bottom ply of the membrane spills out of the lighter top ply
slightly — is a helpful visual indicator of a strong weld.

Flexibility

PVC roofing membranes are more flexible than TPO membranes, making them easier for crews to handle on the roof.

Conclusion

Over
five decades, PVC roofing systems have become a favorite choice of
design professionals. Armed with a greater understanding of PVC
roofing’s history, sustainability and performance characteristics,
roofing contractors can be equally confident in recommending it to their
customers. Options abound to meet various requirements. Check out Part
II of this series, which will outline those choices and the warranties
available on PVC roofing systems.