solar energy away from the structure.
Cool metal roof panels have increased
solar refl ectance and thermal emittance
properties when compared to traditional
roof panels. Cool metal fi nishes are standard
for a majority of metal panel manufacturers
and available to the end user at no addi-
tional cost.
In an overlay retrofi t, the insulation through the air gap and outside the building. Architects also have the option to
under the existing roof remains in place, This simple concept achieves energy savings specify BIPV solar panels on top of a new
resulting in energy savings. If the existing with minimal additional costs to the new overlay retrofi t roof system. Thin-fi lm
insulation is 6-inch fi berglass (R-19), you roof system. PV is laminated directly to the fl at sur-
can achieve an R-Value of R-30 at a minimal Building owners and architects should face of the new metal roof panels for a
cost by installing a layer of 3 1/2-inch layer of consider specifying a new cool metal roof single-source installation by the roofi ng
fi berglass insulation between the existing as part of the overlay system because it will contractor. When considering renewable-
and new roof systems. For extreme energy boost energy savings, as well. Cool metal energy sources, architects and building
effi ciency, the architect or building owner roofi ng is a new paint system that creates owners must evaluate the return on invest-
can request spray foam or polyisocyanurate energy savings by refl ecting and transferring ment of the system. The electricity savings,
rigid insulation under the new roof system. along with federal and state tax incentives
The addition of 3 1/2- inches of closed-cell and grants, can create payback on thin-fi lm
spray polyurethane foam insulation in solar in as little as four years.
combination with existing 6-inch fi berglass
/ definitions /
Patented overlay retrofi t systems, which
insulation can result in an R-Value of up have numerous benefi ts at little to no
to R-40. additional cost to the building owner, are
The gap between the existing and new
(
intended to be installed as an engineered
) SOLAR REFLECTANCE
metal roof systems allows for the design system. Always consult with a registered
of above-sheathing ventilation, or ASV,
is the fraction of solar energy that
engineer with experience in retrofi tting
systems. Recent research by the U.S. Depart-
is refl ected by the roof.
when replacing an existing metal roof.
ment of Energy’s Oak Ridge National Labora-
( ) THERMAL EMITTANCE
tory has proven that the combination of ASV
is the ability of the roof surface to
and refl ective cool metal roofi ng can reduce
release absorbed heat.
the heat transmission between the attic of
the building and outside environment by
Traditionally only white colors had high
up to 45 percent. (Visit
www.ornl.gov for
more information.) The process of venting
refl ectance and emittance, but new cool
the eave and ridge of the roof system causes
coating technology allows a wide range
natural convection to force the hot air
of roofi ng colors to be energy effi cient.
54 FALL 2009 // RETROFIT MAGAZINE
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