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Home My WebLink AboutENGINEERING LETTER REDLINED - 21-00442 - 1093 Arctic Willow Dr - Solar PanelsDescription : 1093 Arctic Willow Dr - Solar PanelsAddress : 1093 Arctic Willow DrRecord Type : Solar PanelsDocument Filename : Kelly Thompson Letter - ID.pdf Comment Author Contact Information: Corrections in the following table need to be applied before a permit can be issued Review Report Approved # 21-00442 Solar Panels Approval of plans does not constitute approval of variance from code Powered by TCPDF (www.tcpdf.org) Date: June 14, 2021 Big Dog Solar Energy 620 Pheasant Ridge Dr Chubbuck, ID 83202 Kelly Thompson (shop structure): 1093 Arctic Willow Dr, Rexburg, ID 83440 Dear Sir/ Madam, Conclusion Structural Letter of Approval Terra Engineering Consulting (TEC) has performed a structural load comparison for the existing roof based on the existing and proposed load conditions, and determined that the structure can support the additional weight of the proposed solar panel system. The attached calculations are based off the assumptions that the existing structural components are in good condition and that they meet industry standards. The design information and assumptions that the calculations are based off are located in the attached References page. The contractor must notify TEC of any damage to the roof system encountered at the time of installation. The design of the solar panel’s mounting hardware is to be provided by the manufacturer or installer. This engineering analysis was performed based off the ASCE 7-16 design method. In general, this design method is a comparison of the roof loads before and after the solar panel installation. Snow load in the area of the panels will be reduced due to the roof pitch and the panel’s slippery surface, as justified in section 7.4 in ASCE 7-16; and in this scenario, the total stresses of the structural elements are decreased after the solar system is installed. The total load of the solar panels is assumed to not exceed 3 psf, and the typical 20 psf live load will not be present in the area of the panels, as defined per Section 1607.13.5.1 in 2018 IBC. The total combined gravity loads result in an increase of less than 5% to the existing load, meeting Section 806.2 of 2018 IEBC, thus the structure still meets standards. Regarding lateral loads, the wind load controls, and due to the low profile of the panels (3” to 6”) as well as PV frame, wiring, conduit, and structural component below the module causing restriction in airflow which allow it to be considered as “partially enclosed structure”; thus the additional pressure on the structure is considered negligible. The attached connection calculations demonstrate the proposed connection capability to withstand the applied uplift forces. The addition of total PV system weight result in an increase under 10% of the total roof weight, and meets the seismic requirements in section 502.5 of 2018 IEBC. TEC concludes that the installation of solar panels on existing roof will not affect the structure, and allows it to remain unaltered under the applicable design standards. These conclusions are based on the attached calculations. 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 General Instructions Best Regards, Terra Engineering Consulting, PLLC Brice Somers, P.E. President The solar array mounting system must be connected to every other truss/rafter (48" maximum penetration spacing) in order to distribute the load evenly. The installer must stagger the connections into the roof framing to not overload any existing structural member. Installation and waterproofing must be performed within accepted industry standard. 6/14/2021 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 References Design Parameter Load Combination: ASD Risk Category: II Ground Snow load: 50 psf Roof Snow load: 35 psf Design Wind Speed: 115 mph (3 sec gust) per ASCE 7-16 Seismic Design Category: D Wind Exposure Category: C Existing Roof Structure Roof framing: 2x4 Pre-fab trusses at 24” O.C. Roof material: Composite shingles Roof slope: 14° Roof type: Gable Solar Panels Module: EAGLE 66TR G4 370-390 W Weight: 3 psf Code: 2018 International Building Code/ International Existing Building Code, ASCE 7-16, and National Design Specification for Wood Construction (NDS) 2015 Edition Connections: (1) 5/16” Lag screw with 2.5” min. embedment into the framing at 48” O.C. spaced along the rail 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 Date: 6/14/2021 Client: Kelly Thompson Subject: Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°): 14 14 Ground snow load, pg (psf): 50 50 ASCE 7‐16, C7.2 Terrain category: C C ASCE 7‐16, table 7.3‐1 Exposure of roof: Fully exposed Fully exposed ASCE 7‐16, table 7.3‐1 Exposure factor, Ce: 0.9 0.9 ASCE 7‐16, table 7.3‐1 Thermal factor, Ct: 1.1 1.1 ASCE 7‐16, table 7.3‐2 Risk Category: II II ASCE 7‐16, table 1.5‐1 Importance Factor, Is: 1 1 ASCE 7‐16, table 1.5‐2 Flat roof snow load, pf (psf): 35.0 35.0 ASCE 7‐16, equation 7.3‐1 Minimum roof snow load, pm (psf): 20 20 ASCE 7‐16, equation 7.3‐4 Roof Surface type:Other Unobstructed slippery surface ASCE 7‐16, C7.4 Roof slope factor, Cs: 1 0.93 ASCE 7‐16, C7.4 Sloped roof snow load, ps [psf]: 35.0 32.6 Roof dead load (D) Roof pitch/12 3.0 Composite shingles 3 psf 1/2" Gypsum clg. 2.2 psf 1/2" plywood 1 psf insulation 0.8 psf Framing 3 psf M, E & Misc 1.5 psf Roof DL without PV arrays 11.9 psf PV Array DL 3 psf Roof live load (Lr)Existing w/ solar panels Roof Live Load 20 0 2018 IBC, Section 1607.13.5.1 ASD Load combination: Existing With PV array D [psf] 11.9 14.9 ASCE 7‐16, Section 2.4.1 D+L [psf] 11.9 14.9 ASCE 7‐16, Section 2.4.1 D+[Lr or S or R] [psf] 46.9 47.5 ASCE 7‐16, Section 2.4.1 38.2 39.3 ASCE 7‐16, Section 2.4.1 Maximum gravity load [psf]:46.9 47.5 Ratio proposed load to existing load: 101.17% The increase of gravity load in the area of the solar panels does not exceed 5%, meeting the requirment of section 806.2 in the 2018 IEBC. The structure is permitted to remain unaltered ASCE 7‐16, equation 7.4‐1, Design Snow Load (S) D+0.75L+0.75[Lr or S or R] [psf] Date: 6/14/2021 Client: Kelly Thompson Subject: Wind Pressure Calculation Basic wind speed (mph) 115 Risk category II Exposure category C Roof type Gable Figure for GCp values ASCE 7‐16 Figure 30.3‐2A‐I Zone 1 Zone 2 Zone 3 GCp (neg)‐0.9 ‐1.7 ‐2.6 GCp (pos) 0.5 0.5 0.5 zg (ft) 900 (ASCE 7‐16 Table 26.11‐1) α 9.5 (ASCE 7‐16 Table 26.11‐1) Kzt 1 (ASCE 7‐16 Equation 26.8‐1) Kh 0.9 (ASCE 7‐6 Table 26.10‐1) Kd 0.85 (ASCE 7‐16 Table 26.6‐1) Velocity Pressure,qh (psf) 25.90 (ASCE 7‐16 Equation 26.10‐1) Gcpi 0 (ASCE 7‐16 Table 26.13‐1) (0 for enclosed buildings) Zone 1 Zone 2 Zone 3 W Pressure, (neg) [psf]‐23.31 ‐44.03 ‐67.34 W Pressure, (pos) [psf] 12.95 12.95 12.95 W Pressure, (Abs. max) [psf] 23.31 44.03 67.34 Connection Calculations Capacity Connection type: Lag screw Lag screw diameter: 5/16 Embedment (in): 2.5 Framing grade: SPF No. 2 G: 0.42 Capacity [lbs/in]: 205 (2015 NDS table 12.2A) Number of screws: 1 Total capacity [lbs]: 512.50 Demand Anchor spacing: 48 in Anchor spacing in roof corners: 48 in Zone ( 0.6 W Pressure, psf), see Note 1 Max. tributary area (ft^2) Max Uplift force (lbs) 1 14.0 11 153.8 2 26.4 11 290.6 3 40.4 11 444.4 (only changes if structure located on a hill or ridge) Connection Meets Demand Wind load and Connection Note 1: 0.6W results from dominant ASD combo [0.6D+ 0.6W] (ASCE 7‐16 2.4.1).