Sunlight hitting water ponds
is particularly damaging to
Foot traffic on the roof is
much like the wear and tear
of traffic on floors. If contractors and maintenance people
are always walking to the
same location, the roof needs
an extra layer of protection
on their route.
Roof blow-offs typically
start at the flashings on the
building edges and overhangs.
Metal termination bars provide reinforcement for wind
resistance along L-shaped
edges without parapets. The
bars need to be appropriately
placed and flashed.
thickness and a regular
maintenance program also
contribute to service life.
These are small investments
for the payback to building
owners of additional years of
For more information
about managing service life,
see the box on the RoofPoint rating system.
6) Renewable Energy
Options for renewable energy include photovoltaic
(PV) systems to generate electricity and solar thermal to
heat water. A less common rooftop method is small wind
turbines to generate electricity.
Elevated, rack-mounted PV modules allow for easy
roof and PV maintenance compared to systems where the
modules rest directly on the roof. Certain PV modules can be
adhered directly to the roof membrane or metal roof panels.
The thin profile of building-integrated photovoltaics
(BIPV) is another alternative. BIPV is a single product that
can do two jobs – keep out water like a membrane while
generating electricity. Dormitories and laundromats can be
effective applications of solar hot water.
Rooftop wind turbines can provide electricity on
overcast days and at night, when solar power is ineffective. Boston’s Logan Airport is one of the most commonly
referenced wind energy rooftops in the country. It uses a
number of smaller turbines mounted on the roof parapet. B
James R. Kirby, AIA, is a licensed architect in Illinois. He
has a Master’s Degree in Architecture from the University of
Illinois and a Graduate Certificate in Sustainable Building
Design and Construction from Boston Architectural College.
Kirby has expertise in roof system design and construction,
weatherproofing and energy efficiency of the building envelope,
and rooftop PV systems. He also is an accredited Green Roofing Professional. He can be reached at jameskirby47@
concrete, housewraps, and some
spruce-pine-fir lumber and
oriented strand board. However,
all seams, joints, transitions, and
penetrations must be effectively
sealed. In many cases, well-ad-hered tape on seams and around
penetrations can be enough.
A primary place for air leakage is where the roof meets the
top of a wall. Installing batt or board insulation at roof/
wall gaps reduces air leaks but may not eliminate them.
A spray foam or other solid materials may be required at
such intersections. Although some options are possible
for new construction only, the industry is developing
good methods to install air barriers in existing buildings.
From a thermal efficiency perspective, air barriers are
like the new kid on the block. But we need to recognize that vapor barriers are not the same thing as vapor
retarders. For example, a sheet of plywood blocks air but
allows vapor to pass.
5) Service Life
Durable materials clearly have an impact on service
life but so does the installation and maintenance of the
Installing wet materials or damaged insulation will affect performance, so ensure that materials are protected
prior to installation and throughout the service life.
Ponding water can damage materials, but a good roof
drainage design gets water off your roof very quickly.
on the roof (right)
is a significant
factor in service
life and lifecycle
edge seams are