BLD2021-0910_Structural_Calculations_7.1.2021_1.28.45_PM_2279808SOLGrzN
P O W E R
July 01, 2021
Subject: Proposed Solar Panel Installation
Craig Likkel Residence, 1230 6th Ave. S, Edmonds, WA 98020
To Whom it May Concern,
Our engineering department has reviewed information, gathered by our field crews, related to the proposed solar
panel installation at the above -referenced address. The purpose of our review was to determine the structural
adequacy of the existing roof. Based on our review and analysis of the available information, and in accordance with
governing building codes, it is our professional opinion that the existing structure is permitted to remain unaltered
for the proposed solar installation.
Some superficial mold was observed on the attic trusses. We do not consider it to affect the integrity of the roof
structure at this time. However, it is incumbent upon the homeowner to ensure the mold does not grow throughout
the life of the panels. Solgen accepts no responsibility for future structural damage resulting from any possible mold
growth.
Design Parameter Summary
Governing Building Code: 2018 Washington Building Code (2018 IBC)
Risk Category: II
Design Wind Speed: 97 mph (per ASCE 7-16)
Ground Snow Load: 20 psf
Roof Information
Roof Structure: 2x4 Manufactured Trusses @ 24" O.C.
Roofing Material: Asphalt Shingles (1 layer)
Roof Slope: 18 degrees
Roof Connection Details
Lag Screws: 5/16" diameter min., with min. 2.5" embedment into framing members, at 48" O.C. min, staggered
Locations per design drawings
Note: Required embedment length excludes the tapered tip of the screw, and embedment into sheathing.
Analysis
The proposed installation - including weight of panels, racking, and mounts - will be approximately 2.57 psf. In the
areas where panels are installed, roof live loads will not be present. The reduction of roof live load is adequate to
fully or partially compensate for the addition of the panel installation. Because the member forces in the area of the
solar panels are not increased by more than 5%, the stresses in the members are not increased by more than 5%, and
so per section 807.4 of the International Existing Building Code (IEBC), the structure need not be altered for gravity
loading.
The proposed installation will be 6" max. above the roof surface (flush mounted) and parallel to the roof surface.
Therefore, any increase in wind loading on the building structure from the solar panel installation is expected to be
negligible. Wind is the governing lateral load case. Because the increase in lateral loading is not increased by more
than 10%, per section 807.5 of the adopted IEBC, the structure need not be altered for lateral loading.
Wind uplift on the panels has been calculated in accordance with the relevant provisions of ASCE 7-16. This loading
has been used to verify the adequacy of the connection specified above. Connection locations should be in
accordance with design drawings.
Conclusion
The roof structure need not be altered for either gravity or lateral loading. Therefore, the existing structure is
permitted to remain unaltered. Connections to the roof must be made per the "Roof Connection Details" section
above. Copies of all relevant calculations are enclosed.
Limitations and Disclaimers
The opinion expressed in this letter is made in reliance on the following assumptions: the existing structure is in good
condition (with the exception of the superficial mold noted previously); the existing structure is free from defects in
design or workmanship; and the existing structure was code -compliant at the time of its design and construction.
These assumptions have not been independently verified, and we have relied on representations made by the
property owner and his or her agents with respect to the foregoing. The undersigned has not inspected the structure
for patent or latent defects.
Electrical engineering is beyond the scope of this analysis. Solar panels must be installed per manufacturer
specifications. Structural design and analysis of the adequacy of solar panels, racks, mounts, rails, and other
components is performed by each component's respective manufacturer and the undersigned makes no statement
of opinion regarding such components. This letter and the opinions expressed herein are rendered solely for the
benefit of the permitting authority (city or county building department), and may not be utilized or relied on by any
other party.
If you have any questions or concerns, please contact our office at (509)-931-1663, or email me directly at
Trevor.Jones@solgenpower.com.
Sincerely,
Trevor A. Jones, P.E.
7/1/2021
SOLGrzN
P O W E R Note: All calculations per ASCE 7
Load Comparison
This calculation justifies the additional solar load by comparing existing to proposed gravity loads
in the location of the solar panels.
Dead Load
Asphalt Shingles
1/2" Plywood
Framing
Insulation
1/2" Gypsum Ceiling
M,E, & Misc
Solar Panel
Total Dead Load
Snow Load
Ground Snow Load, Pg
Exposure Factor, Ce
Thermal Factor, Ct
Importance Factor, IS
Flat Roof Snow Load
Slope
Unobstructed Slippery Surface?
Slope Factor, C,
Sloped Roof Snow Load
Live Load
Roof Live Load
Load Combination
D+Lr
D + S
Max. Load
% of original
U/i+hniif Qnlor %A/i+h CnInr
3
3
psf
1
1
psf
3
3
psf
1
1
psf
2
2
psf
1.5
1.5
psf
0
2.57
psf
11.5 1 14.07 psf
20
1
1.1
1
15.4
18
No
No
1.00
1.00
15.4
15.4
psf
Eqn. 7.3-1 orjurisdiction min.
degrees
psf
20 1 0 psf
31.5
14.1
psf
26.9
29.5
psf
31.5
29.5
psf
94%
Result: Because the total forces are decreased, per the relevant code
provisions stated in the body of the letter, the existing roof
structure is permitted to remain unaltered.
SOLGr-N
P O W E R
Lag Screw Calculation (per ASCE 7-16 Ch. 30 and NDS)
This calculation justifies the connection of the solar panels to existing roof members, by showing the
connection capacity is equal to or greater than the uplift force demands.
Connection Demand
Spacing perpindicular to rail
Spacing parallel to rail
Effective Wind Area on each connection
Roof Angle
Wind Speed
Exposure Coefficient, KZ
Topographic Factor, KZt
Directionality Factor, Kd
Elevation Factor, Ke
Velocity Pressure, qZ
Prying Coefficient
GCp (max)
Exposed Panels? (yE = 1.5)
Pressure Equalization Factor, ya
Uplift Force
Max. Uplift Force / Connection (0.6 WL)
Solar Dead Load (0.6 DL)
Max. Uplift Force (0.6 WL - 0.6 DL)
Connection Capacity
Fastener Type
Fastener Diameter
Embedment Length, min
Lumber Species & Grade
Lumber Specific Gravity
Nominal Withdrawal Capacity, W
# of Screws
Load Duration Factor, CD
32.5
in 1/2 panel length
48
in Max spacing
10.8
ftz
18
degrees
97
mph
0.94
1
0.85
0.99
19.1
psf
1
Zones 1, 2e
Zones 2n, 2r, 3e Zone 3r
1.5
2.5
3.6
No
Yes
Yes
0.79
0.79
0.79
22.5
56.3
81.0
psf
146.3
365.7
526.7
Ibs
16.7
16.7
16.7
Ibs
129.6
349.0
510.0
Ibs
Lag Screw
0.3125 in
2 in
DFL #2 (Assumed)
0.5
532.0 Ibs
1
1.6
(Note: CM = Ct = Ceg = 1.0)
Adjusted Withdrawal Capacity, W' 851.2 Ibs
Compare Adjusted Withdrawal Capacity to ASD Factored Demand
Zones 1, 2e Zones 2n, 2r, 3e Zone 3r
O. K. O. K. O. K.
NDS 12.2-1