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Home My WebLink AboutSTRUCTURAL LETTER - 23-00375 - 249 Jill Dr - Solar PanelsDate: 12 June 2023 G3 Solar 272 W 200 N #200 Lindon, UT 84042 McKay Wise Residence: 249 Jill Dr, Rexburg, ID 83440 Dear Sir/ Madam, Design Method Results 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 existing structure information is assumed based on the survey and information provided by the client. The design information and assumptions that the calculations are based off are located in the attached References page. The design of the solar panel’s mounting hardware and electrical engineering are provided by others. This engineering analysis was performed in accordance with ASCE 7-16 and 2018 IBC/IRC design methods. In general, this design method is a comparison of the roof loads before and after the solar panel installation. The snow load in the area of the panels will be reduced due to the roof pitch and the solar panel’s slippery surface, as justified in Section 7.4 in ASCE 7-16. Due to the reduction of snow load the total roof loads and the stresses of the structural elements are decreased after the solar panels are installed. The total additional roof load of the solar panels system is 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 slippery surface snow load reduction allowed in Section 7.4 in ASCE 7-16 reduces the roof snow load in the area of the solar panels. The total combined vertical loads are reduced when considering the worse case load combination (ASD). Regarding lateral wind loads, the solar panel structure is considered to be partially enclosed due to the low profile of the panels (3 to 6 inches) and airflow restrictions below the panels caused by the pv frame, wiring, conduit, and frame brackets. Because the system is considered to be 'partially enclosed' additional wind pressure on the structure is considered negligible. 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. See the attached calculations for further details. 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 General Instructions 2. Contractor shall keep an accurate set of As-Built plans Best Regards, Terra Engineering Consulting, PLLC Ahmad Alshakargi, PE Civil Engineer 4. Connection: 5/16'' lag screws 2.5'' minimum penetration at 48'' maximum spacing. 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. The calculations performed to support these conclusions are attached to this letter. Conclusions 6. If during solar panel installation, the roof framing members appear unstable or deflect non-uniformly, our office should be notified before proceeding with the installation. 1. Contractor shall comply with all Federal, State, County, City, local and OSHA mandated regulations and requirements. The most stringent shall govern. 3. The solar panel's racking system and mounting hardware shall be mounted in accordance with the manufacturer's most recent installation manual. 5. Panel supports connections shall be staggered to distribute load to adjacent trusses. 7. Structural observation or construction inspections will not be performed by TEC, Engineer-of-Record (EOR) nor their representatives. 6-12-2023 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 References Design Parameter 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 with at 24” O.C. Roof material: Composite shingles Roof slope: 30° Solar Panels Module: VSUN405-108BMH 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: 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 C Date:6/12/2023 Client:McKay Wise Subject:Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°):30 30 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):0 0 ASCE 7-16, equation 7.3-4 Roof Surface type:Other Unobstructed slippery surface ASCE 7-16, C7.4 Roof slope factor, Cs: 1 0.67 ASCE 7-16, C7.4 Sloped roof snow load, ps [psf]: 35.0 23.5 Roof dead load (D) Roof pitch/12 6.9 Composite shingles 3 psf 1/2" Gypsum clg.0 psf 1/2" plywood 1 psf insulation 0.8 psf Framing 3 psf M, E & Misc 1.5 psf Roof DL without PV arrays 10.7 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]10.7 13.7 ASCE 7-16, Section 2.4.1 D+L [psf]10.7 13.7 ASCE 7-16, Section 2.4.1 D+[Lr or S or R] [psf]45.7 37.2 ASCE 7-16, Section 2.4.1 37.0 31.3 ASCE 7-16, Section 2.4.1 Maximum gravity load [psf]:45.7 37.2 Ratio proposed load to existing load:81.29% The stresses due to gravity load in the area of the solar panels is reduced, allowing the structure 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: 6/12/2023 Client: McKay Wise Subject: Wind Pressure Calculations 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) -1 -1.2 -1.2 GCp (pos) 0.9 0.9 0.9 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 0.94 (ASCE 7-6 Table 26.10-1) Kd 0.85 (ASCE 7-16 Table 26.6-1) Velocity Pressure,qh (psf) 27.05 (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] -27.05 -32.46 -32.46 W Pressure, (pos) [psf] 24.35 24.35 24.35 W Pressure, (Abs. max) [psf] 27.05 32.46 32.46 Connection Calculations Lag screw diameter: 5/16 Capacity Connection type: Lag screw Embedment (in): 2.5 Framing grade: DFL#2 G: 0.5 Capacity [lbs/in]: 266 (2015 NDS table 12.2A) Number of screws: 1 Total capacity [lbs]: 665.00 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 16.2 11 178.5 2 19.5 11 214.2 3 19.5 11 214.2 (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).