HomeMy WebLinkAboutVeronica Maxey- Structural LetterSubject: Proposed Solar Panel Installation
Veronica Maxey Residence, 469 Grandey Way NE, Renton, WA
To Whom it May Concern,
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: 2x4 Manufactured Trusses @ 24" O.C.
Roofing Material: Asphalt Shingles (1 layer)
Roof Slope: 25 degrees
Note: Required embedment length excludes the tapered tip of the screw, and embedment into sheathing.
Roof Connection Details
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.
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.
Locations per design drawings
November 14, 2022
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.
RT Minis into 2x rafters or truss top chords at 48" O.C., install per design drawings and manufacturer specs
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 approximately2.73 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 lbs at any point.
Conclusion B22006057
RECEIVED
11/16/2022 lwalker
BUILDING DIVISION
Sincerely,
Trevor A. Jones, P.E.
Limitations and Disclaimers
11/14/2022
If you have any questions or concerns, please contact our office at (855)-709-1181, or email me directly at
Trevor.Jones@solgenpower.com.
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.
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.
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.
B22006057
RECEIVED
11/16/2022 lwalker
BUILDING DIVISION
Note: All calculations per ASCE 7
Load Comparison
Without Solar With Solar
Dead Load
Asphalt Shingles 3 3 psf
1/2" Plywood 1 1 psf
Framing 3 3 psf
Insulation 1 1 psf
1/2" Gypsum Ceiling 2 2 psf
M,E, & Misc 1.5 1.5 psf
Solar Panel 0 2.73 psf
Total Dead Load 11.5 14.23 psf
Snow Load
Ground Snow Load, Pg psf
Exposure Factor, Ce
Thermal Factor, Ct
Importance Factor, Is
Flat Roof Snow Load Eqn. 7.3-1 or jurisdiction min.
Slope degrees
Unobstructed Slippery Surface?No No
Slope Factor, Cs 1.00 1.00
Sloped Roof Snow Load 15.4 15.4 psf
Live Load
Roof Live Load 20 0 psf
Load Combination
D + Lr 31.5 14.2 psf
D + S 26.9 29.6 psf
Max. Load 31.5 29.6 psf
% of original 94%
Result:
This calculation justifies the additional solar load by comparing existing to proposed gravity loads
in the location of the solar panels.
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.
20
1.1
25
1
1
15.4
B22006057
RECEIVED
11/16/2022 lwalker
BUILDING DIVISION
RT Mini Connection Calculation
Connection Demand
Spacing perpendicular to rail 32.5 in 1/2 panel length
Spacing parallel to rail 48 in Max spacing
Effective Wind Area on each connection 10.8 ft2
Roof Angle 25 degrees
Wind Speed 110 mph
Exposure Coefficient, Kz 0.97
Topographic Factor, Kzt 1
Directionality Factor, Kd 0.85
Elevation Factor, Ke 1.00
Velocity Pressure, qz 25.4 psf
Zone 1 Zone 2r Zone 3
GCp (max)1.90 1.97 1.97
Exposed Panels? (γE = 1.5)No No No
Pressure Equalization Factor, γa 0.79 0.79 0.79
Uplift Force 37.9 39.5 39.5 psf
Max. Uplift Force / Connection (1.0 WL)410.8 427.5 427.5 lbs
ASD Factored (0.6 WL)246.5 256.5 256.5 lbs
Solar Dead Load (0.6 DL)17.7 17.7 17.7 lbs
Max. Uplift Force (0.6 WL - 0.6 DL)228.8 238.7 238.7 lbs
Connection Capacity
Connection Type RT Mini into 2x Rafter
Total Allowable Capacity 447.0 lbs (per manufacturer)
Compare ASD Factored Demand to Capacity
Demand 238.7 lbs
Capacity 447.0 lbs
Result
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.
Capacity exceeds demands. Therefore, connection passes.
B22006057
RECEIVED
11/16/2022 lwalker
BUILDING DIVISION