HomeMy WebLinkAboutENGINEER LETTER - 21-00715 - 336 Salem Ave - Solar Panels
Wyssling Consulting
76 North Meadowbrook Drive
Alpine, UT 84004
Scott E. Wyssling, PE, PP, CME office (201) 874-3483
swyssling@wysslingconsulting.com
September 29, 2021
Current Insight P.O. Box 12924 Ogden, UT 84412
Re: Engineering Services Martin Residence 336 Salem Ave, Rexburg ID 1.820 kW System
To Whom It May Concern: 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 a Current Insight 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 Current Insight 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 2 x 4 dimensional lumber at 24” on center with Purlin support at mid-span. 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 Doug-Fir #2 or better with standard construction components. The existing roofing material consists of composite asphalt shingles. A. Loading Criteria Used • 120 MPH wind loading based on ASCE 7-16 Exposure Category “C” at slopes of 27 degrees
• 7 PSF = Dead Load roofing/framing Live Load = 20 PSF Snow Load = 50 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 2018 IRC. Analysis performed of the existing roof structure utilizing the above loading criteria indicates that the existing rafters when strengthened as calculated, 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 “Unirac Duo Installation Manual”, which can be found on the Unirac Dup website (http://Unirac.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. Connection on the roof is utilizing (2) #14 screws into the existing decking to resist uplift forces. Contractor to verify installation to be performed in accordance with the Unirac recommendations. Pull out values per screw are based on National Design Specification values for CDX plywood and are identified as 205 lbs/inch. Based on ½” sheathing the value per screw would be 104 lbs
providing 208 lbs uplift resistance per attachment. 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 with appropriate panel anchors being utilized the roof system will adequately support the additional loading imposed by the solar panels. This evaluation is in conformance with the 2018 IRC, 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 Idaho License No. 18974