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Home My WebLink AboutBLD2021-00693 - 07 STRUCTURAL CALCULATIONSSubject: Proposed Solar Panel Installation Gary Lester Residence, 620 Duckabush Rd, Brinnon, WA To Whom it May Concern, 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: 30 psf Roof Information Roof Structure: 2x6 Rafters @ 24" O.C. Roofing Material: Corrugated Metal Roof Slope: 27.84 degrees Note: Required embedment length excludes the tapered tip of the screw, and embedment into sheathing. (1) S-5! SolarFoot to existing member with (2) 1/4"-14x1-1/2 wood screws @ 48" O.C. along rails 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. 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. Locations per design drawings November 15, 2021 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 806.2 of the International Existing Building Code (IEBC), the structure need not be altered for gravity loading. Sincerely, Trevor A. Jones, P.E. Limitations and Disclaimers 11/15/2021 If you have any questions or concerns, please contact our office at (509)-931-1663, 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. Conclusion 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. Note: All calculations per ASCE 7 Load Comparison Without Solar With Solar Dead Load Corrugated Metal 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 2.57 psf Total Dead Load 11.5 14.07 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?Yes Yes Slope Factor, Cs 0.70 0.70 Sloped Roof Snow Load 16.2 16.2 psf Live Load Roof Live Load 20 0 psf Load Combination D + Lr 31.5 14.1 psf D + S 27.7 30.3 psf Max. Load 31.5 30.3 psf % of original 96% 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. 30 1.1 27.84 1 1 23.1 SolarFoot Connection 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 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 27.84 degrees Wind Speed 97 mph Exposure Coefficient, Kz 0.9 Topographic Factor, Kzt 1 Directionality Factor, Kd 0.85 Elevation Factor, Ke 1.00 Velocity Pressure, qz 18.4 psf Zones 1, 2e Zones 2n, 2r, 3r Zone 3e GCp (max)1.5 2.5 3.6 Exposed Panels? (γE = 1.5)No Yes Yes Pressure Equalization Factor, γa 0.79 0.79 0.79 Uplift Force 21.7 54.2 78.1 psf Max. Uplift Force / Connection (1.0 WL)235.0 587.5 846.0 lbs ASD Factored (0.6 WL)141.0 352.5 507.6 lbs Solar Dead Load (0.6 DL)16.7 16.7 16.7 lbs Max. Uplift Force (0.6 WL - 0.6 DL)124.3 335.8 490.9 lbs Connection Capacity Connection Type S-5 SolarFoot Ultimate Capacity 1229 lbs Factor of Safety 2.5 Qty. of Connectors 1 Total Capacity 491.6 lbs Compare ASD Factored Demand to Capacity Demand 490.9 lbs Capacity 491.6 lbs Result Capacity exceeds demands. Therefore, connection passes.