BLD2022-0229_Structural_Calculations_2.21.2022_11.27.23_AM_2692775SOLGEN
P O W E R
February 21, 2022
Subject: Proposed Solar Panel Installation
Peter Maskiell Residence, 22606 105th Ave. W, Edmonds, WA
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.
Design Parameter Summary
Governing Building Code: 2018 Washington Building Code (2018 IBC)
Risk Category: II
Design Wind Speed: 110 mph (per ASCE 7-16)
Ground Snow Load: 20 psf
Roof Information
Roof Structure: 2x6 Rafters @ 24" O.C.
Roofing Material: Asphalt Shingles (2 layers)
Roof Slope: 18 degrees
Roof Connection Details
RT Minis into 2x rafters or truss top chords at 48" O.C., install per design drawings and manufacturer specs
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 2.76 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 806.2 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 806.3 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; 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.
2/21/2022
SOLGN
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
Withniif Cnl-mr \A/ith Cnlnr
5
5
psf
1
1
psf
3
3
psf
1
1
psf
2
2
psf
1.5
1.5
psf
0
2.76
psf
13.5 1 16.26 psf
20
1
1.1
1
15.4
18
No
No
1.00
1.00
15.4
15.4
psf
Eqn. 7.3-1 or jurisdiction min.
degrees
psf
20 1 0 psf
33.5
16.3
psf
28.9
31.7
psf
33.5
31.7
psf
95%
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.
SOLGN
P O W E R
RT Mini Connection Calculation
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 perpendicular to rail
Spacing parallel to rail
Effective Wind Area on each connection
Roof Angle
Roof Type
Wind Speed
Exposure Coefficient, K,
Topographic Factor, K,t
Directionality Factor, Kd
Elevation Factor, Ke
Velocity Pressure, q,
GCp (max)
Exposed Panels? (YE = 1.5)
Pressure Equalization Factor, ya
Uplift Force
Max. Uplift Force / Connection (1.0 WL)
ASD Factored (0.6 WL)
Solar Dead Load (0.6 DL)
Max. Uplift Force (0.6 WL - 0.6 DL)
Connection Capacity
Connection Type
Total Allowable Capacity
Compare ASD Factored Demand to Capacity
Demand
Capacity
Result
32.5
48
10.8
18
Gable
110
0.87
1
0.85
1.00
in 1/2 panel length
in Max spacing
ft,
degrees 'OLARIN"I
ROOFOFINGG
mph
ROOFTECH
MINI
Mount through roof:
into existing rafters
22.9 psf
Zones 1, Zones 2n,
2e 2r, 3r Zone 3e
1.5
2.5
3.6
No
No
No
LFOOT
6
7
CHIKO
7# Rail
i
0.79
0.79
0.79
27.0
45.0
64.8
psf
292.6
487.7
702.3
Ibs
175.6
292.6
421.4
Ibs
17.9
17.9
17.9
Ibs
157.6
274.7
403.4
Ibs
RT Mini into 2x Rafter
447.0 Ibs (per manufacturer)
403.4 Ibs
447.0 Ibs
Capacity exceeds demands. Therefore, connection
passes.