THIS FACILITY WANTED TO CONTINUE USING COOL ROOFING STRATEGIES FOR
THE ENERGY SAVINGS, but its previous white roofs reflected too much sunlight into
the windows of neighboring buildings. We laid out 10- by 10-foot mats of sample
products during periods of intense sunlight and observed them from an adjacent
building to see which ones were most reflective. The owner ultimately opted for a
tan roof as a compromise – the reflectance and SRI values weren’t as high as a white
membrane would have been, but it still met industry cool roof standards.
How to Compare Materials
Armed with roof rating information, you
can now start evaluating products to see
which ones best fit your specific application. Thermoplastic membranes like TPO
and PVC are often lumped in together
because both are plastic and heat-weldable,
and both are likely to have cool roof rated
products available in white, gray and tan.
White EPDM now features new formulations that promise better performance
than past iterations, making it a valid option
for a cool roofing system.
Fluid-applied and retrofit coatings are
a catchall category for coatings in white or
other light colors that can be applied to a
variety of roof systems. Many are intended
for existing roofs that don’t yet meet cool
roof requirements and can help add a layer
of protection to the roof underneath. For
example, you could apply a coating to an
older built-up or modified roof to both
capitalize on the benefits of cool roofing
and lengthen the life expectancy of the roof
Modified bituminous systems can
achieve cool roof ratings in a number of
ways. Some vendors offer factory-coated
systems where a light-colored coating is
added to the top ply during manufacturing.
Factory-ply systems involve a separate ply of
white material that is bonded to the sheet in
the factory. Other products feature reflective
granule surfacing bonded to the top ply.
Ballast and aggregate surfacing generally has a reflectivity of around 0.30, but
this can vary depending on the surfacing.
Make sure to take a look at emittance ratings – studies by Chicago roofing contractors have shown that it may take longer for
the layers of surfacing to release accumulated heat, which is a bigger issue in cooling
climate states. If the roof is still emitting
heat hours after the sun goes down, the air
conditioning has to continue working into
the night to maintain moderate temperatures inside the building. Aggregate surfacing qualifies as cool surfacing in some parts
of the country, but not others.
Cool roofing technologies for steep slope
roofs have come a long way. The most common cool roof materials for these buildings
are architectural metal systems where
the metal is coated with reflective finishes
or light colors. A quick review of current
product shows a wide SRI range of 24-81
and reflectance values of 0.26 to 0.67, with
white or light-colored materials achieving
higher reflectance and SRI values.
BELIEVE IT OR NOT, THERE’S A ROOF UNDER THIS GRIME. This coal-fired power
plant is a great example of a situation where you cannot possibly keep a cool roof
clean. Industrial environments should prioritize durability over color and even