Reflective Roof Coating
Technology Snapshot & Benefits:
According to ENERGY STAR®,
Americans spend about $40 billion annually to air condition buildings - one-sixth
of all electricity generated in this country. In areas that are sunny and warm
for most of the year, or have a very hot summer, the costs to individuals are
particularly devastating. Reflective roof coating is protective coating that can
be applied to roofs to keep a home cool without having to use as much air
conditioning. Reflective roof coating is also called albedo coating, since the
materials used have high albedo, or ability to reflect the sunlight. Reflective
roof coatings have other benefits as well: they can increase efficiency in some
air conditioning and ventilation units on the roof and because UV radiation
expedites roof ageing, they also slow roof decay. These special coatings work by
reflecting the sun's light and releasing absorbed heat.
Reflective roof coating is most effective for flat roofs because flat roofs
usually absorb more energy than slanted roofs. The effectiveness also varies
with the thickness and color of the coating, with lighter colors and thicker
coatings being significantly more effective. In fact, bright white reflective
coatings can have a solar reflectance of 85 percent and cut a roof's cooling
load up to 70 percent.
Reflective roof coatings can be made from various materials. Paint-on coatings
include acrylic paints, polyurethane, and elastomeric. These types of coatings
do not require professional installation. Single-ply reflective sheets made from
plastic, PVC, or rubber are effective, as are reflective roof tiles made from
concrete, clay, or metal. In terms of total cost (raw price, installation fees,
and maintenance fees), white titanium dioxide paint and aluminum sheets are the
best choice. However, elastomeric and acrylic coatings reflect a higher fraction
of solar energy. Longevity of the material used should also be considered.
No matter which materials are used, most homeowners who employ reflective roof
coating experience cooler indoor temperatures and lower cooling costs.
Estimated Cost Savings:
Reflective roof coating can cut cooling costs from 10 to 70 percent depending on
the coating used, climate, and the degree of sunlight to which the roof is
exposed. Hot areas that are sunny for a majority of the year benefit the most
from reflective roof coatings. The decrease in monthly energy bills far
outweighs the costs of installation. Coatings that are painted on typically cost
$15 to $25 per gallon and can be applied by the homeowner. Professional
installation of single-ply roof sheets or tiles typically costs the same as
installing any other type of shingle or tile; so, if installed at the initial
building of a home or rebuilding of a roof, there will be little to no extra
cost for the homeowner. Cost for single-ply PVC membranes averages $3 per square
foot.
Issues:
Reflective roof coatings are a simple way to cut costs and help the environment.
Virtually all roofs can be made to absorb less heat and reflect more sunlight
using some type of reflective roof product. However, if the roof membrane is
decaying, the coating will not be as effective and it is recommended that the
membrane be replaced before the coating is applied. It is best to consult a
professional or product manufacturer about the ideal type of coating for a
specific roof.
Regional Issues:
Reflective roof coatings are not recommended for areas that are cool or cold for
much of the year and/or experience high cloud coverage. They most benefit people
in areas that are warm and sunny for most of the year. In warm and/or sunny
cities, this coating can help fight the "urban heat island" effect, or increased
temperatures due to greater reflectance and absorbance of sunlight by a
conglomeration of dark, metal buildings. Decreased indoor temperatures in areas
that can become extremely hot can increase comfort and reduce the likelihood of
heat-related illness or death.
Installation:
Paint-on coatings are applied using a roller, a brush, or airless spray
equipment, and require minimal skill to apply. The roof should be properly
cleaned before applying the coating. It is important to consult with the coating
manufacturer for tips and advice on how to apply a specific coating to a
specific roof. Single-ply reflective shingles and roof tiles must be installed
by a professional roofer.
Videos On This Topic:
Install of a Supertherm White Roof (10:02) - Sierra Club Green Homes -
The Obama
administration is looking to paint roofs white to increase energy reflection and
minimize absorption and transfer of heat through the roof. In this video from
Sierra Club Green Homes, watch a typical installation of a white, reflective
roof coating and learn more about how this can help save on energy bills
For more information on this topic:
Reflective Roof Coating Institute
ENERGY STAR®
Reflective Roof Products
U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy:
Cool Roof Calculator