Thomson, Sydney Letter SS ®
VSE Project Number: U1932.1364.241
July 3, 2024
Bright Planet Solar
ATTENTION: Mikey Heinz
103A Millbury St.
Auburn, MA 01501
REFERENCE: Thomson, Sydney Residence: 114 Woodland Drive, Northampton, MA 01062
Bright Planet Solar Project: BPS380710
Solar Array Installation
To Whom It May Concern:
We have reviewed the existing structure at the above referenced site.The purpose of our review was to determine the
adequacy of the existing structure to support the proposed installation of solar panels on the roof as shown on the panel
layout plan.
Based upon our review, we conclude that the existing structure is adequate to support the proposed solar panel installation.
Design Parameters
Code: Massachusetts State Residential Code (780 CMR Chapter 51, 9th Edition (2015 IRC))
Risk Category: II
Design wind speed, Vult: 117 mph (3-sec gust)
Wind exposure category: C
Ground snow load, Pg: 40 psf
Flat roof snow load, Pf: 35 psf
Existing Roof Structure
Roof structure: 2x8 rafters @ 16" o.c.
Roofing material: asphalt (composite) shingles
Roof slope: 37°
Connection to Roof
Mounting connection: (1) Ecofasten Rockit Smartslide w/(2) #12 screws into framing at max. 48" o.c. along panel edges
This installation uses a rail-less system. Panel Orientation: Portrait
Maximum panel dimension: 76.4x41 in
Connections shall be staggered so as not to overload any existing structural member
Conclusions
Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation.
The gravity loads,and thus the stresses of the structural elements,in the area of the solar array are either decreased or
increased by no more than 5%.Therefore,the requirements of Section 807.4 of the 2015 IEBC as referenced in 780 CMR
Chapter 34, 9th Edition are met and the structure is permitted to remain unaltered.
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
®
VSE Project Number: U1932.1364.241
Thomson, Sydney Residence
7/3/2024
The solar array will be flush-mounted (no more than 10"above the roof surface)and parallel to the roof surface.Thus,we
conclude that any additional wind loading on the structure related to the addition of the proposed solar array is negligible.
The attached calculations verify the capacity of the connections of the solar array to the existing roof against wind (uplift),
the governing load case.Increases in lateral forces less than 10%are considered acceptable.Thus the existing lateral force
resisting system is permitted to remain unaltered.
Limitations
Installation of the solar panels must be performed in accordance with manufacturer recommendations.All work performed
must be in accordance with accepted industry-wide methods and applicable safety standards.The contractor must notify
Vector Structural Engineering,LLC should any damage,deterioration or discrepancies between the as-built condition of the
structure and the condition described in this letter be found.The use of solar panel support span tables provided by others is
allowed only where the building type,site conditions,site-specific design parameters,and solar panel configuration match
the description of the span tables.The design of the solar panels,solar racking (mounts,rails,etc.)and electrical engineering
is the responsibility of others.Waterproofing around the roof penetrations is the responsibility of others.Vector Structural
Engineering assumes no responsibility for improper installation of the solar array.Vector Structural Engineering shall be
notified of any changes from the approved layout prior to installation.
VECTOR STRUCTURAL ENGINEERING, LLC
07/03/2024
_______________________________________________________
Wells Holmes, S.E.
MA License: 54240 - Expires: 06/30/2026
Project Engineer
Enclosures
WLH/thp
07/03/2024
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
JOB NO.:U1932.1364.241
SUBJECT:WIND PRESSURE
®
PROJECT:Thomson, Sydney Residence
Label:Note: Calculations per ASCE 7-10
SITE-SPECIFIC WIND PARAMETERS:
Basic Wind Speed [mph]:117 Notes:
Exposure Category:C
Risk Category:II
Importance Factor, I:
ADDITIONAL INPUT & CALCULATIONS:
Height of Roof, h [ft]:25 (Approximate)
Comp/Cladding Location:Yes
Enclosure Classification:
Zone 1 GCp:0.9 Figure 30.4-2C (enter negative pressure coefficients)
Zone 2 GCp:1.2
Zone 3 GCp:1.2
α:9.5 Table 26.9-1
zg [ft]:900 Table 26.9-1
Kh:0.95 Table 30.3-1
Kzt:1 Equation 26.8-1
Kd:0.85 Table 26.6-1
Velocity Pressure, qh [psf]:28.2 Equation 30.3-1
GCpi:0 Table 26.11-1
PRESSURES:Equation 30.9-1
Zone 1, p [psf]:25.9 psf (1.0 W, Interior Zones, beyond 'a' from roof edge)
Zone 2, p [psf]:33.2 psf (1.0 W, End Zones, within 'a' from roof edge)
Zone 3, p [psf]:33.2 psf (1.0 W, Corner Zones, within 'a' from roof corner)
(a= 3 ft)
Solar Panel Array
Gable Roofs 27° < θ ≤ 45°
Enclosed Buildings
Components and Cladding Wind Calculations
piphGCGCqp
JOB NO.:U1932.1364.241
SUBJECT:CONNECTION
®
PROJECT:Thomson, Sydney Residence
Calculate Uplift Forces on Connection
Pressure
(0.6 Dead -0.6 Wind)
(psf)
Max Trib. Width1
(ft)
Max Trib.
Area2
(ft2)
Max Uplift
Force
(lbs)
Zone 1 13.7 4.0 25.5 349
Zone 2 18.1 4.0 12.7 231
Zone 3 18.1 4.0 12.7 231
Calculate Connection Capacity
Connection Description:
Ultimate Capacity3 [lbs]:1590
Factor of Safety:3
Quantity per Connection:1
Prying Coefficient:1
Connection Capacity [lbs]:530
Determine Result
Maximum Demand [lbs]:349
Connection Capacity [lbs]:530
Result:Capacity > Demand, Connection is adequate.
Notes
1. 'Max Trib. Width' is the width along the panel seams tributary to the connection.
3. Ultimate capacity values are from manufacturer testing.
2. 'Max Trib Area' is the product of the 'Max. Trib Width' and the panel width/height perpendicular to the
direction of the connection spacing. Tributary area on connections at array edges are reduced by 50% as they
Ecofasten Rockit Smartslide w/(2) #12 screws into framing
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U1932.1364.241
SUBJECT:GRAVITY LOADS
®
PROJECT:Thomson, Sydney Residence
GRAVITY LOADS Roof Pitch: 9.0 :12
ROOF DEAD LOAD (D)
Increase due to
pitch
Material weight
[psf]
Asphalt (Composite) Shingles 1.25 2.0
1/2" Plywood 1.25 1.0
Framing 1.00 3.0
Insulation 1.00 0.0
1/2" Gypsum Clg.1.25 0.0
M, E & Misc 1.00 0.0
Total Existing Roof DL
PV Array DL 1.25 3
DL:1.25
ROOF LIVE LOAD (Lr)
Existing Design Roof Live Load [psf]20 ASCE 7-10 Table 4-1
Roof Live Load With PV Array [psf]20
SNOW LOAD (S):w/ Solar Array
Roof Slope [x:12]:9.0
Roof Slope [°]:37
Ground Snow Load, pg [psf]:40 ASCE 7-10, Section 7.2
Terrain Category:C ASCE 7-10, Table 7-2
Exposure of Roof:Fully Exposed ASCE 7-10, Table 7-2
Exposure Factor, Ce:0.9 ASCE 7-10, Table 7-2
Thermal Factor, Ct:1.1 ASCE 7-10, Table 7-3
Risk Category:II ASCE 7-10, Table 1.5-1
Importance Factor, Is:1.0 ASCE 7-10, Table 1.5-2
Flat Roof Snow Load, pf [psf]:35 ASCE 7-10, Equation 7.3-1
Minimum Roof Snow Load, pm [psf]:0 ASCE 7-10, Section 7.3.4
Unobstructed Slippery Surface?No ASCE 7-10, Section 7.4
Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4
Roof Slope Factor, Cs:1.00 ASCE 7-10, Figure 7-2
Sloped Roof Snow Load, ps [psf]:35 ASCE 7-10, Equation 7.4-1
Design Snow Load, S [psf]:3535
9.0
37
40
C
Fully Exposed
0.9
1.1
II
1.0
35
0
No
Figure 7-2b
1.00
35
Design material
weight [psf]
2.5
1.3
3.0
0.0
0.0
0.0
6.8
3.8
#VALUE!
Existing
JOB NO.:U1932.1364.241
SUBJECT:LOAD COMPARISON
®
PROJECT:Thomson, Sydney Residence
Summary of Loads
Existing With PV Array
D [psf]7 11
Lr [psf]20 20
S [psf]35 35
Maximum Gravity Loads:
Existing With PV Array
(D + Lr) / Cd [psf]21 24 ASCE 7-10, Section 2.4.1
(D + S) / Cd [psf]36 40 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:36 40
Maximum Member Forces:
GEOMETRY
Span(ft)15.7 (Approximate)
Solar Panel Array Start, a (ft)0.0 (Approximate)
Solar Panel Array Length, b (ft)5.1 (Approximate)
Framing Spacing (ft)1.3
MEMBER FORCES
Existing With PV Array
Vertical Reaction, V1 (lbs)380 399 OK
Vertical Reaction, V2 (lbs)380 384 OK
Existing With PV Array
Moment @ Center, M (lbs-ft)1493 1521 OK
Ratio
The gravity loads, and thus the stresses of the structural elements, in the area of the
solar array are either decreased or increased by no more than 5%. Therefore, the
requirements of Section 807.4 of the 2015 IEBC as referenced in 780 CMR Chapter 34,
9th Edition are met and the structure is permitted to remain unaltered.
(Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr)
Ratio
102%
105%
101%