Jennifer Bryan Letter SS
Wyssling Consulting
76 North Meadowbrook Drive
Alpine, UT 84004
Scott E. Wyssling, PE, PP, CME office (201) 874-3483
swyssling@wysslingconsulting.com
April 9, 2021
Ken Trappen Advanced Solar Solutions 39650 Mallard
Bass Lake, CA 93604
Re: Engineering Services Bryan Residence 705 Fairway Village, Leeds MA
10.640 kW System Dear Mr. Trappen: Pursuant to your request, we have reviewed the following information regarding solar panel installation on
the roof of the above referenced home: 1. Site Visit/Verification Form prepared by Advanced Solar Solutions representative identifying specific site information including size and spacing of rafters for the existing roof structure.
2. Design drawings of the proposed system including a site plan, roof plan and connection details for the solar panels. This information was prepared by Advanced Solar Solutions and will be utilized for approval and construction of the proposed system. 3. Photographs of the interior and exterior of the roof system identifying existing structural
members and their conditions. Based on the above information we have evaluated the structural capacity of the existing roof system to support the additional loads imposed by the solar panels and have the following comments related to our
review and evaluation: Description of Residence:
The existing residence is typical wood framing construction with the roof system consisting of truss system with all chords constructed of 2 x 4 dimensional lumber at 24” on center. The attic space is unfinished and photos indicate that there was free access to visually inspect the size and condition of the roof rafters. All wood material utilized for the roof system is assumed to be SPF #2 or better with standard construction
components. The existing roofing material consists of a composition shingles. Photos of the dwelling also indicate that there is a permanent foundation. A. Loading Criteria Used
• 116 MPH wind loading based on ASCE 7-10 Exposure Category “C” at a slope of 19 & 30 degrees
• 7 PSF = Dead Load roofing/framing Live Load = 20 PSF Snow Load = 40 PSF
• 3 PSF = Dead Load solar panels/mounting hardware
Total Dead Load =10 PSF
The above values are within acceptable limits of recognized industry standards for similar structures in accordance with the Massachusetts Uniform Construction Code (2015 IBC). Analysis performed of the existing roof structure utilizing the above loading criteria indicates that the existing rafters will support the additional panel loading without damage, if installed correctly.
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B. Solar Panel Anchorage
1. The solar panels shall be mounted in accordance with the most recent “SnapNrack Installation Manual”, which can be found on the SnapNrack website (http://snapnrack.com/). If during solar panel installation, the roof framing members appear unstable or deflect non-uniformly, our office
should be notified before proceeding with the installation. 2. Maximum allowable pullout per lag screw is 235 lbs/inch of penetration as identified in the National Design Standards (NDS) of timber construction specifications for SPF #2 assumed. Based on our evaluation, the pullout value, utilizing a penetration depth of 2 ½”, is less than what is allowable per
connection and therefore is adequate. Based on the variable factors for the existing roof framing and installation tolerances, using a thread depth of 2 ½” with a minimum size of 5/16” lag screw per attachment point for panel anchor mounts should be adequate with a sufficient factor of safety. 3. Considering the roof slopes, the size, spacing, condition of roof, the panel supports shall be placed
no greater than 48” o/c. 4. Panel supports connections shall be staggered to distribute load to adjacent trusses. Based on the above evaluation, it is the opinion of this office that the standard installation will adequately
support the additional loading imposed by the solar panels. This evaluation is in conformance with the Massachusetts Uniform Construction Code, current industry and standards, and based on information supplied to us at the time of this report.
Should you have any questions regarding the above or if you require further information do not hesitate to contact me.
Very truly yours, Scott E. Wyssling, PE MA License No. 50507