[RE-wrenches] Roof Loading request for help

[William Miller]

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 we’re 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:Allan at positiveenergysolar.com>Allan at 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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Please note new e-mail address and domain:

William Miller
Miller Solar
Voice :805-438-5600     Fax: 805-438-4607
email: william at millersolar.com
http://millersolar.com
License No. C-10-773985
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