17A-003 (2) Page 2 of 2
B. Loading Criteria
10 PSF=Dead Load roofing/framing 40 PSF=Live Load(ground snow load)
5 PSF=Dead Load solar panels/mounting hardware
Total Dead Load=15 PSF
The above values are within acceptable limits of recognized industry standards for similar structures.
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.
C. Roof Structure Capacity
1. The photographs provided of the attic space and roof rafters show that the framing is in good
condition with no visible signs of damage caused by prior overstressing.
D. Solar Panel Anchorage
1. The solar panels shall be mounted in accordance with the most recent "Ecolibrium Solar
Installation Manual",which can be found on the Ecolibrium Solar website(ecolibriumsolar.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. The solar panels are 1 '/"thick and mounted 4 W off the roof for a total height off the existing roof
of 6". At no time will the panels be mounted higher that 6"above the existing plane of the roof.
3. Maximum allowable pullout per lag screw is 235 Ibs/inch of penetration as identified in the
National Design Standards (NDS) of timber construction specifications for Hem-Fir (North
Lumber) assumed. Based on our evaluation, the pullout value, utilizing a penetration depth of 2
%2", is less than the maximum 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
'/Z" with a minimum size of 5/16" lag screw per attachment point for panel anchor mounts will be
adequate with a sufficient factor of safety.
4. Section 1 (Main house): Considering the roof slopes, the size, spacing, condition of roof, the
panel supports shall be placed at and attached to no greater than every other roof rafter as panels
are installed perpendicular across rafters and no greater than the panel length when installed
parallel to the rafters (portrait). No panel supports spacing shall be greater than 2 (two) rafter
spaces or 52"o/c,whichever is less.
Section 2(Sun room): Considering the roof slopes, the size, spacing, condition of roof, the panel
supports shall be placed at and attached to no greater than every fourth roof rafter as panels are
installed perpendicular across rafters and no greater than the panel length when installed parallel
to the rafters (portrait). No panel supports spacing shall be greater than 4 (four) rafter spaces or
64" o/c, whichever is less.
5. Panel supports connections shall be staggered to distribute load to adjacent rafters.
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 based on information supplied to us at the time of this report and current industry standards and
practices.
Should you have any questions regarding the above or if you require further information do not hesitate to
contact me.
V ruly yours, '
�.,. rv1 `
Scott E.Wyssli ,PE crs
MA License No flN_
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3301 North Thanksgiving Way,Suite 500
Structural Group Lehi,UT 84043
P:(801)234-7050
Scott E. Wyssling, PE
Head of Structural Engineering scott.wyssling@vivintsoiar.com
December 16,2014
revised April 10, 2015
Mr. Dan Rock, Project Manager
Vivint Solar
150 Padgette Street, Unit A
Chicopee, MA 01022
Re: Structural Engineering Services
Wilson Residence
204 Spring Grove Ave, Florence MA
S-4053642
4.59 System
Dear Mr. Rock:
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 Vivint Solar 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 the Design Group and will
be utilized for approval and construction of the proposed system.
3. Photovoltaic Rooftop Solar System Permit Submittal identifying design parameters for the
solar system.
4. 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:
• Section 1 (Main house): 2x6 dimensional lumber at 26"on center. The attic space is unfinished
and the photos indicate that there was free access to visually inspect the size and condition of the
roof rafters.
• Section 2 (Sun room): Assumed 2x6 dimensional lumber at 16" on center. The attic space is
finished and the photos indicate that there was no access to visually inspect the size and condition
of the roof rafters.
All wood material utilized for the roof system is assumed to be Hem-Fir #2 or better with standard
construction components. Our review of the photos of the exterior roof does not indicate any signs of
settlement or misalignment caused by overstressed underlying members.
Stability Evaluation:
A. Wind Uplift Loading
1, Refer to attached Ecolibrium Solar calculations sheet for ASCE/SEI 7-10 Minimum Design Loads
for Buildings and other Structures, wind speed of 90 mph based on Exposure Category"B"and 7
and 23 degree roof slopes on the dwelling areas. Ground snow load is 40 PSF for Exposure"B",
Zone 3 per(ASCE/SEI 7-10).
2. Total area subject to wind uplift is calculated for the Interior, Edge and Corner Zones of the
dwelling.
A.
VI VIE •