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Stability Evaluation: �dff (,, Q/_l
A. Wind Uplift Loading
1. Refer to attached MSI 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 14, 15, and 37
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.
13. Loading Criteria
10 PSF = Dead Load (roofing/framing) 40 PSF= Live Load (ground snow load)
3 PSF= Dead Load (solar panels/mounting hardware)
Total Dead Load- 13 PSF
The above values are within acceptable limits of recognized industry standards for similar structures and in
accordance with the 2009 International Residential Code with Massachusetts Amendments. Analysis performed on
the existing roof structure utilizing the above loading criteria indicates that the existing members will support the
additional panel loading without damage, 'rf installed correctly.
C. Solar Panel Anchorage
1. The solar panels shall be mounted in accordance with the most recent "Mounting System Inc.
Installation Manual", which can be found on the Mounting System Inc. website (usa.mounting-
systems.infotentsolar-mounting-systems-company). 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 W'thick and mounted 4 off the roof for a total height off the existing roof
of 6",At no time will the panels be mourned higher than 6"above the existing plane of the roof.
3. Maximum allowable pullout per lag screw is 205 Ibstnch of penetration as identified in the Nation
Design Standards (NDS) of timber construction specifications for Spruce-Pine-Fir assumed. Based
on our evaluation, the pullout value, utilizing a penetration depth of 2 W", is less than the maximum
allowable per connection and therefore is adequate.
4. Roof Sections (1, 2, and 3): Considering the roof slopes, the size, spacing, condition of the roof,
the panel supports shall be placed at and attached no greater than every fourth roof member as
panels are installed perpendicular across members and no greater than the panel length when
installed parallel to the members (portrait). No panel supports spacing shall be greater than four (4)
spaces or 64"ofc,whichever is less.
5. Panel support connections shall be staggered to distribute load to adjacent members.
6. If collar ties are not present per Massachusetts building code we recommend that 2x6 collar ties be
installed at two third of the attic height @ 48"on center.
Based on the above evaluation, 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 2009
International Residential Code with Massachusetts Amendments, current industry standards and practice, and the
information supplied to us at the time of this report.
Should you have any questions regarding the above or if you require turth: for - +n do not hest/i ri to contact
me. (zN OF \/1 r ►
v truly yours, r 777
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Scott E.Wyssling, P NO $4b50'
MA License No. 5 79 9P 1$tEpa\a4r"4
FSSIONAI te'
vivint.
vivint. 3301 North Thanksgiving Way, Suite 500
Lehi, UT 84043
Structural Group P: (801) 234-7050
Scott E Wyssling, PE
Senior Manager of Engineering scott.wyssling@vlvintsolar.com
February 10, 2016
Mr. Dan Rock, Project Manager
Vivint Solar
3301 North Thanksgiving Way, Suite 500
Lehi, UT 84043
Re: Structural Engineering Services
Wilga Residence
280 N Maple St, Florence MA
S-4773755
6.5 kW
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 VisitNerification Form prepared by a Vivint Solar representative identifying specific site
information including size and spacing of members 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 the following:
• Roof Section 1: Roof section is composed of assumed 2x6 dimensional lumber at 16" on center
and a single layer of roofing. The attic space is finished and photos indicate that there was no
access to visually inspect the size and condition of the roof members.
• Root Section 2: Root section is composed of 2x8 dimensional lumber at 16" on center and a single
layer of roofing. The attic space is unfinished and photos indicate that there was free access to
visually inspect the size and condition of the roof members.
• Roof Section 3: Roof section is composed of 2x6 dimensional lumber at 16" on center and a single
layer of roofing. The attic space is unfinished and photos indicate that there was free access to
visually inspect the size and condition of the roof members.
All wood material utilized for the roof system is assumed to be Spruce-Pine-Fir #2 or better with standard
construction components. The existing roofing material consists of composite shingle. Our review of the photos of
the exterior roof does not indicate any signs of settlement or misalignment caused by overstressed underlying
members.
vivint.