Engler_Letter_SSVSE Project Number: U1898.0162.231
March 30, 2023
PV Squared
311 Wells St. Ste. B
Greenfield, MA 01301
REFERENCE: Engler Residence: 117 Olander Drive, Northampton, MA 01060
PV Squared Project: ENNO17012023R
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: 2x4 manufactured trusses @ 24" o.c.
Roof pitch: 7:12
Conclusions
Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation.
The glass surface of the solar panels allows for a lower slope factor per ASCE 7,resulting in reduced design snow load on
the panels.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.
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.
Increases in lateral forces less than 10%are considered acceptable.Thus the existing lateral force resisting system 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: U1898.0162.231
Engler - Northampton Residence
3/30/2023
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.Connections shall be staggered so as not to overload any existing structural member.The
design of the solar panels,solar racking (mounts,rails,etc.),the connection of the racking to the roof 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
03/30/2023
_______________________________________________________
Wells Holmes, S.E.
MA License: 54240 - Expires: 06/30/2024
Project Engineer
Enclosures
WLH/crs
03/30/2023
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U1898.0162.231
SUBJECT:GRAVITY LOADS
PROJECT:Engler Residence
GRAVITY LOADS Roof Pitch: 7.0 :12
ROOF DEAD LOAD (D)
Increase due to
pitch
Material weight
[psf]
Composite Shingles 1.16 2.0
1/2" Plywood 1.16 1.0
Framing 1.00 3.0
Insulation 1.00 0.5
1/2" Gypsum Clg.1.16 2.0
M, E & Misc 1.00 6.5
Total Existing Roof DL
PV Array DL 1.16 3
DL:1.16
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]:7.0
Roof Slope [°]:30
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?Yes ASCE 7-10, Section 7.4
Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4
Roof Slope Factor, Cs:0.66 ASCE 7-10, Figure 7-2
Sloped Roof Snow Load, ps [psf]:23 ASCE 7-10, Equation 7.4-1
Design Snow Load, S [psf]:2335
7.0
30
40
C
Fully Exposed
0.9
1.1
II
1.0
35
0
No
Figure 7-2b
1.00
35
Design material
weight [psf]
2.3
1.2
3.0
0.5
2.3
6.5
15.8
3.5
#VALUE!
Existing
JOB NO.:U1898.0162.231
SUBJECT:LOAD COMPARISON
PROJECT:Engler Residence
Summary of Loads
Existing With PV Array
D [psf]16 19
Lr [psf]20 20
S [psf]35 23
Maximum Gravity Loads:
Existing With PV Array
(D + Lr) / Cd [psf]29 31 ASCE 7-10, Section 2.4.1
(D + S) / Cd [psf]44 37 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:44 37
Ratio Proposed Loading to Current Loading:84%OK
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)
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U1898.0162.231
SUBJECT:SOLAR LAYOUT
PROJECT:Engler Residence