Levitt, Sam Letter SS ®
VSE Project Number: U6045.0020.241
June 11, 2024
Current Energy LLC
305 Wells Street
Greenfield, MA 01301
REFERENCE: Levitt, Sam Residence: 69 Lyman Road, Northampton, MA 01060
Current Energy LLC Project: 379
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: 2x6 rafters @ 24" o.c.
Roofing material: asphalt (composite) shingles
Roof slope: 27°
Connection to Roof
Mounting connection: (1) Ironridge HUG w/(2) screws to framing at max. 48" o.c. (portrait and landscape) along rails
• Install (2) rails per row of panels, evenly spaced from panel center
• Maximum panel dimension: 74x44 in
• Rail cantilever shall not exceed the lesser of 50% of the connection spacing or max cantilever allowed by manufacturer
• 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 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.
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
®
VSE Project Number: U6045.0020.241
Levitt, Sam Residence
6/11/2024
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
06/11/2024
_______________________________________________________
Wells Holmes, S.E.
MA License: 54240 - Expires: 06/30/2026
Project Engineer
Enclosures
WLH/bpp
06/11/2024
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
JOB NO.:U6045.0020.241
SUBJECT:WIND PRESSURE
®
PROJECT:Levitt, Sam 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)Hip?
Comp/Cladding Location:No
Enclosure Classification:
Zone 1 GCp:0.9 Figure 30.4-2B (enter negative pressure coefficients)
Zone 2 GCp:1.7
Zone 3 GCp:2.5
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]:25.1 psf (1.0 W, Interior Zones, beyond 'a' from roof edge)
Zone 2, p [psf]:46.6 psf (1.0 W, End Zones, within 'a' from roof edge)
Zone 3, p [psf]:71.6 psf (1.0 W, Corner Zones, within 'a' from roof corner)
(a= 3 ft)
Solar Panel Array
Gable/Hip Roofs 7° < θ ≤ 27°
Enclosed Buildings
Components and Cladding Wind Calculations
()()piphGCGCqp−=
JOB NO.:U6045.0020.241
SUBJECT:CONNECTION
®
PROJECT:Levitt, Sam 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 13.3 4.0 12.3 164
Zone 2 26.2 4.0 12.3 323
Zone 3 41.2 4.0 12.3 508
Calculate Connection Capacity
Roof Connector:
Additional Connection Info:
Ultimate Capacity3 [lbs/in]:3011
Factor of Safety:3
Qty. of Connectors:1
Prying Coefficient:1
Total Capacity [lbs]:1004
Determine Result
Maximum Demand:508
Connection Capacity:1004
Result:Capacity > Demand, Connection is adequate.
Notes
1. 'Max Trib. Width' is the width along the rails tributary to the connection.
3. Ultimate capacity values are from manufacturer testing.
4. Install metal roof connector per manufacturer's written instructions with recommended fasteners when
indicated.
2. 'Max Trib Area' is the product of the 'Max. Trib Width' and 1/2 the panel width/height perpendicular to the
rails. (2) rails per row of panels. Length of panels perpendicular to the rails shall not exceed 74".
Ironridge HUG
w/(2) screws to framing
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U6045.0020.241
SUBJECT:GRAVITY LOADS
®
PROJECT:Levitt, Sam Residence MP1-MP3
GRAVITY LOADS Roof Pitch: 6.1 :12
ROOF DEAD LOAD (D)
Increase due to
pitch
Material weight
[psf]
Asphalt (Composite) Shingles 1.12 2.0
1/2" Plywood 1.12 1.0
Framing 1.00 3.0
Insulation 1.00 0.0
1/2" Gypsum Clg.1.12 0.0
M, E & Misc 1.00 0.0
Total Existing Roof DL
PV Array DL 1.12 3
DL:1.12
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]:6.1
Roof Slope [°]:27
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:0.72 ASCE 7-10, Figure 7-2
Sloped Roof Snow Load, ps [psf]:25 ASCE 7-10, Equation 7.4-1
Design Snow Load, S [psf]:2535
6.1
27
40
C
Fully Exposed
0.9
1.1
II
1.0
35
0
No
Figure 7-2b
1.00
35
Design material
weight [psf]
2.2
1.1
3.0
0.0
0.0
0.0
6.4
3.4
#VALUE!
Existing
JOB NO.:U6045.0020.241
SUBJECT:LOAD COMPARISON
®
PROJECT:Levitt, Sam Residence MP1-MP3
Summary of Loads
Existing With PV Array
D [psf]6 10
Lr [psf]20 20
S [psf]35 25
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 30 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:36 30
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.:U6045.0020.241
SUBJECT:GRAVITY LOADS
®
PROJECT:Levitt, Sam Residence MP4
GRAVITY LOADS Roof Pitch: 6.1 :12
ROOF DEAD LOAD (D)
Increase due to
pitch
Material weight
[psf]
Asphalt (Composite) Shingles 1.12 2.0
1/2" Plywood 1.12 1.0
Framing 1.00 3.0
Insulation 1.00 0.0
1/2" Gypsum Clg.1.12 0.0
M, E & Misc 1.00 0.0
Total Existing Roof DL
PV Array DL 1.12 3
DL:1.12
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]:6.1
Roof Slope [°]:27
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
6.1
27
40
C
Fully Exposed
0.9
1.1
II
1.0
35
0
No
Figure 7-2b
1.00
35
Design material
weight [psf]
2.2
1.1
3.0
0.0
0.0
0.0
6.4
3.4
#VALUE!
Existing
JOB NO.:U6045.0020.241
SUBJECT:LOAD COMPARISON
®
PROJECT:Levitt, Sam Residence MP4
Summary of Loads
Existing With PV Array
D [psf]6 10
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 39 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:36 39
Maximum Member Forces:
GEOMETRY
Span(ft)12.6 (Approximate)
Solar Panel Array Start, a (ft)5.8 (Approximate)
Solar Panel Array Length, b (ft)5.5 (Approximate)
Framing Spacing (ft)2.0
MEMBER FORCES
Existing With PV Array
Vertical Reaction, V1 (lbs)454 464 OK
Vertical Reaction, V2 (lbs)454 476 OK
Existing With PV Array
Moment @ Center, M (lbs-ft)1433 1498 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
105%
102%
105%