BLD2023-0142_Structural_Calculations_2.2.2023_3.55.46_PM_3348422SOLGr- N
P O W E R
February 02, 2023
Subject: Proposed Solar Panel Installation
Robert Hinds Residence, 8418 191st St SW, 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: 25 psf
Roof Information
Roof Structure: 2x4 Rafters @ 24" O.C.
Roofing Material: Asphalt Shingles (1 layer)
Roof Slope: 22 degrees
Roof Connection Details
RT Minis. Install generally into 2x rafters/chords, but up to 50% may be installed into decking only. 48" O.C.. Install
Locations per design drawings
Note: Required embedment length excludes the tapered tip of the screw, and embedment into sheathing.
Analysis
The proposed installation complies with the requirements of WAC Section 51-51-03240 R324.4 (Exception) and is
therefore deemed adequate to support the load of the rooftop solar system.
Specifically: 1) the system is designed for the local wind speed; 2) the ground snow load does not exceed 70 psf; 3)
the total dead load of all items is less than 4 psf (actual value is approximately2.74 psf); 4) Modules are not
mounted more than 18" off the roof; and 5) Supports are installed such that the dead load is spread across roof -
framing members and does not exceed 50 Ibs at any point.
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 (855)-709-1181, or email me directly at
Trevor.Jones@solgenpower.com.
Sincerely,
Trevor A. Jones, P.E.
2/2/2023
SOLGr- N
P O W E R
WA State Exception Criteria - Calculation
This calculation justifies the additional solar load by showing the solar dead load at each
attachment is less than 50 Ibs (WAC 51-51-03240, R324.4, Exception Criteria).
Connection Demand
Spacing perpendicular to rail
Spacing parallel to rail
Solar Dead Load
Solar DL Point Load
32.5 in
48 in
2.74 psf
29.68333333 Ibs
OK
1/2 panel length
Max spacing
SOLGr- N
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. Minimum embedment is 1.5 inches,
Connection Demand
Spacing perpendicular to rail
Spacing parallel to rail
Effective Wind Area on each connection
Roof Angle
Wind Speed
Exposure Coefficient, K,
Topographic Factor, K,
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
32.5
in
in
ftz
degrees 30LAR PAI
ROOT
Imph
ROOFTEC
MINI
48
10.8
22
115
0.91
1
0.85
0.98
1/2 panel length
Max spacing
25.8
psf Mount thmugh roof sheathing
h' into existing rafters
Zone 1
Zone 2r
Zone 3
1.90
1.97
No
No
No
0.79
0.79
0.79
38.5
40.0
40.0
psf
416.6
433.5
433.5
Ibs
250.0
260.1
260.1
Ibs
17.8
17.8
17.8
Ibs
232.2
242.3
242.3
Ibs
RT Mini (50/50 Deck and Rafter Mounts)
313.5 Ibs (per manufacturer)
Compare ASD Factored Demand to Capacity
Demand 242.3 Ibs
Capacity 313.5 Ibs
Result Capacity exceeds demands. Therefore, connection passes.