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Home My WebLink AboutSTRUCTURAL LETTER OF APPROVAL - 22-00076 - 367 Talon Dr - Solar PanelsDate: 4 February 2022 Big Dog Solar Energy 620 Pheasant Ridge Dr Chubbuck, ID 83202 Matthew Maroon Residence: 367 Talon 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 design information and assumptions that the calculations are based off are located in the attached References page. The contractor shall 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. Structural observation or construction inspections will not be performed by TEC or their representatives. This engineering analysis was performed in accordance with ASCE 7-16 design method. In general, this design method is a comparison of the roof loads before and after the solar panel installation. The attached engineering analysis is based on the before and after load comparison and it does not include structural analysis of the existing structure nor its framing members. 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 panel 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 IBC 2018. The slippery surface snow load reduction allowed in ASCE 7-16 is greater than the weight of the solar system, therefore, 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") 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 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. See the attached calculations for further details. Page 1 of Matthew Maroon letter 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 General Instructions Best Regards, Terra Engineering Consulting, PLLC Brice Somers, PE President TEC concludes that the installation of solar panels on existing roof will decrease the worst case scenario total vertical loads and will reduce stresses in the structural members. The reduction in total loads will increase the structure's existing factors of safety against failure. The calculations performed to support these conclusions are attached to this letter. Conclusions The solar array mounting system shall be connected to every other truss/rafter (48" maximum penetration spacing) in order to distribute the load evenly. The installer shall stagger the connections into the roof framing to not overload any existing structural members. Installation and waterproofing shall be performed within accepted industry standards. Page 2 of Matthew Maroon letter 2/4/2022 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: 35° Roof type: Gable Solar Panels 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 Page 3 of Matthew Maroon letter 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 Date:2/4/2022 Client:Matthew Maroon Subject:Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°):35 35 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 0.58 ASCE 7-16, C7.4 Sloped roof snow load, ps [psf]:35.0 20.3 Roof dead load (D) Roof pitch/12 8.4 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 11.4 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]11.4 14.4 ASCE 7-16, Section 2.4.1 D+L [psf]11.4 14.4 ASCE 7-16, Section 2.4.1 D+[Lr or S or R] [psf]46.4 34.7 ASCE 7-16, Section 2.4.1 37.7 29.6 ASCE 7-16, Section 2.4.1 Maximum gravity load [psf]:46.4 34.7 Ratio proposed load to existing load:74.78% 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:2/4/2022 Client:Matthew Maroon 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 0.9 (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]-25.90 -31.08 -31.08 W Pressure, (pos) [psf]23.31 23.31 23.31 W Pressure, (Abs. max) [psf]25.9 31.08 31.08 Connection Calculations Capacity Connection type:Lag screw Lag screw diameter:5/16 Embedment (in):2.5 Framing grade:SPF#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 15.5 11 170.9 2 18.6 11 205.1 3 18.6 11 205.1 (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).