LEFT // Sub-frame installation at edge
zone RIGHT // Sub-frame overlay retrofi t
method BELOW // Additional insulation
dead-load capacity of the existing structure.
(Visit manufacturer Web sites for informa-
tion performed by independent engineering
and testing facilities.) The increased dead-
load capacity supports the weight of the new
roof system and allows for the installation
of additional rooftop equipment, such as
fi re sprinkler systems or PV.
In addition, hurricane-prone coastal
areas require stringent engineering design.
Higher wind-uplift areas located in the
critical edge and corner zones can require
clips to be located as close as 1 foot to 6
inches on center. A majority of existing met-
al buildings have purlins spaced at 5 foot
on center. Previously, the only way to meet
these tough clip-spacing requirements was
to install new framing from the inside of the
building. This is very costly and interrupts
building operations. However, contractors
now have the ability to install a defl ection
ing Code now treat wind loads the same as
limiter in combination with the sub-frame
Eliminate demolition costs by not
requiring removal of the existing roof gravity and snow loads with no reductions
overlay system. The defl ection limiter is in-
allowed. Previously, the code allowed a 1/3
stalled vertically over the existing metal-roof
No interruption to building operations
during construction stress reduction for wind. Thus, millions of
ribs and is fastened to the existing framing.
square feet of metal buildings that were
This provides a direct structural attachment
Improve safety by working over a
solid structure built in the past 30 years would not meet the
of subframe members between existing
new building code. Simply removing the ex-
purlins. Standing-seam clips or fasteners
Provide fast and effi cient construct-
ion techniques isting roof and replacing it with a new roof is
now can be installed at various intervals
not suffi cient because it requires the existing
to meet the design requirements of
Increase strength of the existing
roof structure structure to be reinforced or additional fram-
virtually any new metal roof system.
ing installed. This is very costly and requires Allow for additional insulation and
other energy-effi ciency improvements access from the inside of the building. Energy-effi ciency
Certain sub-frame-overlay retrofi t Support the installation of photovoltaics Improvements
systems can increase the strength of the ex- The overlay retrofi t method includes
Let’s look at some of these benefi ts in isting roof structure. Attaching a sub-frame space for additional insulation or
more detail. to the existing framing creates a “composite above-sheathing ventilation, installation
purlin” that essentially increases the depth of of refl ective cool metal roofi ng, and the
Structural Upgrades the existing roof purlin. Numerous engineer-
option to install crystalline panels or
Recent revisions to the International Build- ing tests confi rm this increases the uplift and
thin-fi lm building-integrated PV .
RETROFIT MAGAZINE // FALL 2009 53
Retrofit_sept09.indd 53 9/22/09 8:36 PM
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