Allan:
I bid a job for a fellow that designed roof trusses for a living. Here is
what he said: Each roof is designed for live loads and dead loads. Live
loads, as I understand it, are workers and materials to be installed. The
dead loads are for wind and snow. If you put solar modules on a roof
surface, you can no longer stock materials or walk on that
area. Therefore, you can claim the extra capacity reserved for live loads
to use for your dead load increase -- the PV modules.
Santa Barbara County has a sensible approach: If your roof is a modern
truss roof, you are not required to provide engineering. If your roof is a
site-framed roof, you are required to provide some kind of engineering.
Allan, if you find you lose this battle and are required to provide
engineering, see if you can work this around so that you receive a generic
engineering report that might apply to any modern truss based roof
system. This means you only pay for this once (unless you do older homes
frequently).
When we had our first commercial job reviewed by a structural engineer, I
learned an interesting point: It is easy to attach upper land lower rack
supports to the same trusses since they are usually in line with factory
built racks we use. This concentrates loads. If possible, stagger the
attachments across adjacent trusses.
I hope this helps.
William Miller
At 05:26 PM 7/7/2009, you wrote:
Wrenches,
We are currently facing a city permitting bureaucracy that has recently
discovered solar that is, suddenly each department in the permitting and
plan review departments is coming up with standards for PV systems. Some
of the standards, of course, make no sense.
PV systems typically add about three pounds per square foot to the loading
on a roof. We are facing a city requirement for structural engineering
work for standard roof attachment if the mounting approach is to make
penetrations into the roof structure. This is a typical requirement that
will only add considerable cost to each PV system, and were looking to
have our ammunition to fight this well stocked in advance. Specifically,
are building authorities in other jurisdictions requiring structural
engineering work for this type of roof attachment?
Thanks
Allan
Allan Sindelar
<mailto:al...@positiveenergysolar.com>al...@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
<http://www.positiveenergysolar.com>www.positiveenergysolar.com
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