Coe, Terence Letter SS
76 North Meadowbrook Drive
Scott E. Wyssling, PE Alpine, UT 84004
Coleman D. Larsen, SE, PE office (201) 874-3483
Gregory T. Elvestad, PE swyssling@wysslingconsulting.com
December 7, 2022
Ken Trappen
Advanced Solar Solutions
2372 Morse Avenue #912
Irvine, CA 92614
Re: Engineering Services
Coe Residence
104 Moser Street, Northampton, MA
9.720 kW System
To Whom It May Concern:
We have received information regarding solar panel installation on the roof of the above referenced
structure. Our evaluation of the structure is to verify the existing capacity of the roof system and its ability
to support the additional loads imposed by the proposed solar system.
A. Site Assessment Information
1. Site visit documentation identifying attic information including size and spacing of framing
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 will be utilized for approval and construction
of the proposed system.
B. Description of Structure:
Roof Framing: Assumed 2x8 dimensional lumber at 24” on center.
Roof Material: Composite Asphalt Shingles
Roof Slope: 45 degrees
Attic Access: Inaccessible
Foundation: Permanent
C. Loading Criteria Used
• Dead Load
o Existing Roofing and framing = 7 psf
o New Solar Panels and Racking = 3 psf
o TOTAL = 10 PSF
• Dead Load
o Existing Roofing and framing = 7 psf
o New Solar Panels and Racking = 3 psf
o TOTAL = 10 psf
• Live Load = 20 psf (reducible) – 0 psf at locations of solar panels
• Ground Snow Load = 40 psf
• Wind Load based on ASCE 7-10
o Ultimate Wind Speed = 117 mph (based on Risk Category II)
o Exposure Category C
Analysis performed of the existing roof structure utilizing the above loading criteria is in accordance
with the 2015 IRC, including provisions allowing existing structures to not require strengthening if
the new loads do not exceed existing design loads by 105% for gravity elements and 110% for
seismic elements. This analysis indicates that the existing framing will support the additional panel
loading without damage, if installed correctly.
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D. Solar Panel Anchorage
1. The solar panels shall be mounted in accordance with the most recent Roof Tech installation
manual. 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 (5) M5 x 60mm lag screws into the exis ting decking to resist uplift
forces. Contractor to verify installation to be performed in accordance with the manufacturer’s
recommendations. Pull out values per screw are based on National Design Specification values
for CDX plywood and are identified as 208 lbs/inch. Based on ½” sheathing the value per screw
would be 104 lbs providing 520 lbs uplift resistance per attachment.
3. Considering the wind speed, roof slopes, size and spacing of framing members, and condition of
the roof, the panel supports shall be placed no greater than 48” on center.
4. Panel supports connections shall be staggered to distribute load to adjacent framing members.
Based on the above evaluation, this office certifies that with the racking and mounting specified, the existing
roof system will adequately support the additional loading imposed by the solar system. This evaluation is in
conformance with the 2015 IRC, current industry standards, and is 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
12/7/2022