HomeMy WebLinkAboutBaker LetterVSE Project Number: U3232.0221.201
November 4, 2020
My Generation Energy
ATTENTION: Nathaniel Blois
100 Independence Drive, Suite 10
Hyannis, MA 02601
REFERENCE: Baker Residence: 62 Beacon Street, Yarmouth, MA 02664
Solar Array Installation
To Whom It May Concern:
Per your request,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: 140 mph (3-sec gust) per ASCE 7-10
Wind exposure category: C
Ground snow load: 30 psf
Flat roof snow load, Pf: 25 psf
Existing Roof Structure
Roof structure: 2x8 rafters @ 16" O.C.
Roofing material: composite shingles
Roof pitch: 5:12
Connection to Roof
Mounting connection: (1) 5/16" lag screw w/ min. 2.5" embedment into framing
Maximum mounting spacing along rails:
Zone 1: 48" O.C. (Beyond 4' from roof edge or ridge)
Zone 2: 48" O.C. (Within 4' of roof edge parallel or perpendicular to slope)
Zone 3: 24" O.C. (Within 4' of roof eave-eave corner or eave-ridge corner)
(2) rails per row of panels, evenly spaced; panel length perpendicular to the rails not to exceed 67 in
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: U3232.0221.201
Baker Residence
11/4/2020
The solar array will be flush-mounted (no more than 6"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.Because the increase in lateral forces is less than 10%,this addition meets the requirements of the
exception in Section 807.5 of the 2015 IEBC as referenced in 780 CMR Chapter 34,9th Edition.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.Connections to existing roof framing must be staggered,except at
array ends,so as not to overload any existing structural member.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 panel 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, LLC
11/04/2020
_______________________________________________________
Wells Holmes, S.E.
MA License: 54240 - Expires: 06/30/2022
Project Engineer
Enclosures
WLH/brw
11/04/2020
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
JOB NO.:U3232.0221.201
SUBJECT:WIND PRESSURE
PROJECT:Baker Residence
Label:Note: Calculations per ASCE 7-10
SITE-SPECIFIC WIND PARAMETERS:
Basic Wind Speed [mph]:140 Notes:
Exposure Category:C
Risk Category:II
Importance Factor, I:
ADDITIONAL INPUT & CALCULATIONS:
Height of Roof, h [ft]:15 (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:2.6
α:9.5 Table 26.9-1
zg [ft]:900 Table 26.9-1
Kh:0.85 Table 30.3-1
Kzt:1 Equation 26.8-1
Kd:0.85 Table 26.6-1
Velocity Pressure, qh [psf]:36.2 Equation 30.3-1
GCpi:0 Table 26.11-1
PRESSURES:Equation 30.9-1
Zone 1, p [psf]:32.6 psf (1.0 W, Interior Zones, beyond 'a' from roof edge)
Zone 2, p [psf]:61.5 psf (1.0 W, End Zones, within 'a' from roof edge)
Zone 3, p [psf]:94.1 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.:U3232.0221.201
SUBJECT:CONNECTION
PROJECT:Baker Residence
Calculate Uplift Forces on Connection
Pressure
(0.6 Dead -0.6 Wind)
(psf)
Max Connection
Spacing1
(ft)
Max Trib.
Area2
(ft2)
Max Uplift
Force
(lbs)
Zone 1 19.6 4.0 11.2 197
Zone 2 36.9 4.0 11.2 391
Zone 3 56.5 2.0 5.6 304
Calculate Connection Capacity
Lag Screw Size [in]:5/16
Cd:1.6 NDS Table 2.3.2
Embedment3 [in]:2.5
Grade:
Nominal Capacity [lbs/in]:205 NDS Table 12.2A
Number of Screws:1
Prying Coefficient:1.4
Total Capacity [lbs]:586
Determine Result
Maximum Demand [lbs]:391
Lag Screw Capacity [lbs]:586
Result:Capacity > Demand, Connection is adequate.
Notes
1. 'Max Connection Spacing' is the spacing between connections along the rails.
2. 'Max Trib Area' is the product of the 'Max Connection Spacing' 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 67".
SPF (G = 0.42)
3. Embedment is measured from the top of the framing member to the beginning of the tapered tip of the lag
screw. Embedment in sheathing or other material is not effective. The length of the tapered tip is not part of the
embedment length.
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U3232.0221.201
SUBJECT:GRAVITY LOADS
PROJECT:Baker Residence
CALCULATE ESTIMATED GRAVITY LOADS Roof Pitch: 5.0 :12
ROOF DEAD LOAD (D)
Increase due to
pitch
Material weight
[psf]
Composite Shingles 1.08 2.0
1/2" Plywood 1.08 1.0
Framing 1.00 3.0
Insulation 1.00 0.0
1/2" Gypsum Clg.1.08 0.0
M, E & Misc 1.00 0.0
Total Original Roof DL
PV Array DL 1.08 3
DL:1.08
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]:5.0
Roof Slope [°]:23
Snow Ground Load, pg [psf]:30 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]:25 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:0.79 ASCE 7-10, Figure 7-2
Sloped Roof Snow Load, ps [psf]:20 ASCE 7-10, Equation 7.4-1
Design Snow Load, S [psf]:20
1.00
25
Design material
weight [psf]
2.2
1.1
3.0
0.0
0.0
0.0
6.3
3.3
#VALUE!
Existing
25
5.0
23
30
C
Fully Exposed
0.9
1.1
II
1.0
25
0
No
Figure 7-2b
JOB NO.:U3232.0221.201
SUBJECT:LOAD COMPARISON
PROJECT:Baker Residence
Summary of Loads
Existing With PV Array
D [psf]6 10
Lr [psf]20 20
S [psf]25 20
Maximum Gravity Loads:
Existing With PV Array
(D + Lr) / Cd [psf]21 24 ASCE 7-10, Section 2.4.1
(D + S) / Cd [psf]27 25 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:27 25
Ratio Proposed Loading to Current Loading:94%OK
(Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr)
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.
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U3232.0221.201
SUBJECT:SOLAR LAYOUT
PROJECT:Baker Residence