Solar Permits Requiring lateral load calcs

Within the last year, a number of building departments in Orange County have started including the following requirements for Solar Permits.

Provide structural lateral calculations by a licensed professional engineer or architect per 2007 CBC. Showing that affected existing lateral resisting elements are no more than 10% overstressed according to 2007 CBC. Exception:Lateral analysis is not required if total area of solar voltaic equipment / PV arrays is less than 200 sq.ft. for two-story or 300 sq.ft. for single story.

The first time I came across this requirement was in Newport Beach where we negotiated our way around it.  Recently, I noticed the requirement in Mission Viejo and most recently in the City of Orange.   Out of curiosity, I was wondering how many solar installations would be affected in Orange County and San Diego county if the lateral load calcs requirement became epidemic.

An analysis of the California Solar Initiative data for the past six months in Orange County and San Diego County reveals the following:  The number of total residential installations was 2010.  Using a module size of 40 inches x 64 inches or 17.78 sq.ft. per module, I calculated the following for the past six months worth of data:

Median number of modules was 22
Average number of modules was 24
Median area was 391 sq.ft.
Average area was 435 sq.ft
Number installations less than 200 sq.ft.  313
Number installations greater than 200 sq.ft.  1697
Percent of installations greater than 200 sq.ft.  81%

The percentage of installations greater than 200 sq.ft. in San Diego County and Orange County were both the same at 81%.  I would expect these numbers to be similar across the State of California as well.  What this means, should this requirement spread across all building departments, is that at least 80% of all solar permits would require lateral load calculations.   

Brooks Engineering (Bill Brooks), prepared a “Expedited Permit Process for PV Systems” for New Mexico State University Solar America Board for Codes and Standards.  Within this document, there is the following when reviewing structures for solar permitting.

Explanation: The 5 lbs/ft code 
limit is based on two things: 1) the roof is typical of standard code or compliant roof structures so that the structure either has the proper spans and spacing proper use of engineered trusses (first item under “Step 1: Structural Review”); and, 2)there is a single layer of roofing so that the normal weight allowance for additional roof layers is unused and available for the weight of the PV system. For applications on lightweight masonry roofing materials and other lightweight roofing products (e.g. metal, shake, etc…), these materials do not accept multiple layers and therefore the 5 lbs/ft limit is based on two things: 1) the roof is typical of standard compliant roof structures so that the structure either has the proper spans and spacing allowance is used to identify the maximum allowable additional weight for roofs that are exchanging the allowable live load for a dead load that prevents live load such as people walking on the roof.

Most Solar Photovoltaic systems weigh less than 3 lbs. per square foot totally installed.  Many cities, in fact, don’t require any Engineering calculations if a homeowner does a re-roof and the roofing material is less than 6 lb./sq.ft.  In some cases, building departments don’t require Engineering Calcs if the roofing material is less than 9 lbs./sq.ft.

I am now wondering who came up with the 200 sq.ft. limitation that would require lateral load calcs on 80% of solar installations.  Was this a number based on an Engineering analysis or did some permit clerk pick the number out of the air.  Right now, I don’t have an answer, but my conclusion is that this could have a profound affect on the cost of solar installations in California.

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