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Solar Panel Discussion Summary from May 29, 2019

On May 29, 2019, the Mill Valley School District hosted a public meeting at Edna Maguire Elementary School regarding solar panels and why the roof's structure cannot hold the load of the panels based on the construction of the school. Mill Valley School District Director of Maintenance and Operations, John Binchi, and Wallace Gordon, the architect of the school, led the discussion.

Below is information from Mr. Gordon.

 

BACKGROUND:   
 
The Edna Maguire school was initially designed to accommodate solar panels with a weight allocation of approximately 3 lbs per square foot placed upon the roof. This was designed under the governance of the 2010 California Building Code. All California Public Schools are State property and therefore come under the jurisdiction of the Division of the State Architect (DSA) and not local building departments. Hence, any modifications would be subject to DSA reviews and approvals. The approximate design loads for structures include the two (2) basic load components of 1) live loads which are transient and include people, toolboxes, leaves, re-roofing equipment, debris, snow (not applicable at Edna) and other items that are not fixed as part of the building structure, and 2) dead loads which are composed of the elements that are fixed and make up the building structure and other fixed components such as lights, ceilings, roofing, etc. The original building design assumed accommodating future solar at 3 lbs per square foot into the dead load since solar panels were assumed to be eventually ‘fixed’ to the building.  The live load allocation to the roof was approximately 20 lbs per square foot. In the case of Edna Maguire, live load and dead load are close to equal. Dead load is important as there is a part of the current building code (CBC Chapter 34) that allows for a post-construction increase in dead load of 5% of the dead load allocation. So, in essence, there is latitude to increase the fixed or dead load by approximately 1 lb per square foot assuming approximately 20 lbs per square foot of dead load. The governing codes traditionally are updated every 3 years and therefore are continually subject to changing these allowances.
 
DESIGN MODIFICATIONS TO EDNA MAGUIRE ORIGINAL DESIGN:
 
During the bidding of Edna Maguire there were dramatic construction price increases occurring throughout the Bay Area.  As a result, the bids for Edna came in approximately $5 million over the target price. In response to high bid results, the District and construction managers initiated ‘value engineering’ (VE) exercises to reduce cost from many elements of the building design. This VE exercise included modifying the design of the ceilings from an architecturally appropriate exposed “acoustical steel deck” to basic (non-aesthetic) structural steel deck with the inclusion of the suspended acoustical grid ceiling that you now see throughout the Edna interiors. This design change resulted in approximately 2-1/2 to 3 lbs of additional weight for the ’suspended ceiling' that was not foreseen in the original design. The post-design inclusion of the suspended acoustical ceilings depleted the 3 lbs of allocation for future solar panels for Edna’s roofs.
 
FEASIBILITY OF ACCOMMODATING FUTURE SOLAR PANELS ON EMS ROOFS:
 
The current consideration of solar panels at Edna has been reported to require approximately 3 to 4 lbs per square foot of potential additional dead load. Placing this additional load onto the existing structure would require a complete re-analysis and re-justification of the entire structural system with an improbable outcome that all the members and all the connections would accommodate it, including all the factors of safety in the most recent code. The 2010 code is no longer in effect.  The most current building code would be in effect for this analysis.  The entire structural system would include all the steel members and connections from the roof through, and including, the concrete foundations. In addition, the State of California (DSA) may feel compelled to include re-analysis of facility components beyond the structural system, such as the fire alarm system, etc. All of this provides no assurance that the State will approve the addition of solar panels without structural or other upgrades. The chances would be very high that the State would require upgrades to portions of the structure after all the cost of re-engineering and review fees are paid. The District needs to assess the value of this risk, the associated upfront costs without assurance of approvals and the payback of the solar panels in the context of these costs and the improbability of unchallenged approvals from the State.