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Home My WebLink AboutSTRUCTURAL LETTER - 21-00387 - 154 Elm Ave - Solar Panels.pdf 55 WEST 500 SOUTH, HEBER CITY, UT 84032 T 925.787.3067 U RIGHTANGLEENG.COM May 24, 2021 Horizon PWR 166 Valley Street Providence, RI 02909 RE: Structural Roof Evaluation for the Parkinson Residence: 154 Elm Avenue, Rexburg, Idaho As per your request, we have evaluated the roof structure under the proposed solar panel array. The information used to evaluate this structure was gathered by Horizon PWR on behalf of Right Angle Engineering. The roof structure consists of 2x6 rafters spaced at 24” on center. The roof material consists of asphalt shingles. The design criteria used to analyze this structure are listed above and included with this letter. The adopted building codes in this jurisdiction are: the 2018 International Building Code, the 2018 International Existing Building Code, and ASCE 7-16. International Existing Building Code (IEBC) 2018 section 806.2 indicates that alterations to an existing building that results in less than a 5% increase in the total stress may be performed without a structural evaluation of the existing building. As demonstrated in the attached calculations, the additional weight of the solar panels will be less than 5% increase in the gravity loading and the stress on the existing roof framing. Based on our assessment we have determined that the existing roof framing will safely and adequately support the additional loads imposed by the solar panels without reinforcement. In order for the loads to be evenly distributed, the roof attachments should be staggered and spread evenly throughout the panel array. Attachment points should be spaced at a maximum of 48” on center. The racking system should be installed per the manufacture’s specifications. There should be a minimum of 18 Unirac Flashloc attachment points to the roof. Each attachment should have a 5/16” or 18/8 SS lag screw with 2.5” minimum penetration centered on each truss top chord or rafter. Waterproofing around the roof penetrations is the responsibility of others. Right Angle Engineering assumes no responsibility for improper installation of the solar panels. Regards, Robert D Smythe, P.E. Right Angle Engineering 5/24/21 Design Criteria: Design Wind Speed (ASD)- 115 mph Ground Snow Load- 50 psf Risk Category- II Exposure category- C 2 Design Criteria: Design Wind Speed (3 second gust) 115 mph Exposure Category C Risk Category 2 Mean Roof Height 30 ft Roof Type Gable Roof Building Type enclosed Roof Dead Load- ASCE Table C3-1 Asphalt Shingles 2 psf 5/8" Plywood Sheathing 2 psf Roof Framing 4 psf Insulation 0 psf Gypsum sheathing 0 psf Solar Panel Array 3 psf Dead Load Without Panels 8 psf Dead Load With Solar panels 11 psf Roof Live Load Existing Roof Live Load 20 psf ASCE 7-16 Table 4.3-1 Roof Live Load with Solar Panels 0 psf 2018 IBC 1607.13.5.1 Roof Snow Load-ASCE 7-16 Ground Snow Load (pg) 50 psf Section 7.2 Exposure Factor (Ce) 0.9 Table 7.3-1 Thermal Factor (Ct) 1.1 Table 7.3-2 Importance Factor (Is) 1 Table 1.5-2 Flat Roof Snow Load (Pf) 35 Equation 7.3-1 Slippery surface Slope Factor (Cs) 0.85 Figure 7-2 Nonslippery Surface Slope Factor (Cs) 1 Figure 7-2 Roof Snow Load 35 psf Equation 7.4-1 Reduced Roof Snow Load (Slippery Surface) 29 psf Equation 7.4-1 Load Combinations - ASCE 7-16 Section 2.4.1 Without Solar Panels With Solar panels D + Lr 28 psf 11 psf D + S 42.7 psf 40.5 psf 3 Solar Array 1- East Roof Slope 19 degrees Number of panels 8 Panel Area 140 ft^2 Wind Calculations- ASCE 7-16 GCp Zone 1 -1 Figure 30.3-(2A-5B) GCp Zone 2 -1.8 Figure 30.3-(2A-5B) GCp Zone 3 -2.8 Figure 30.3-(2A-5B) Gcpi 0.18 Table 26.13-1 Velocity Pressure (qh) 28.2 psf qh= .00256KhKhtKdV^2 Equation 26.10-1 Kh 0.98 Table 26.10-1 Kht 1 Equation 26.8-1 Kd 0.85 Table 26.6-1 Designed wind pressure (P) psf Equation 30.8-1 P= qh(GCh) - (GChi)) Zone 1 Pressure (P) -33.3 psf Zone 2 Pressure (P) -55.8 psf Zone 3 Pressure (P) -84 psf Roof Connection Shear Capacity 190 lbs NDS 2015 Table 12K Shear tributary area 18 ft^2 Pullout Capacity 266 lbs/in Lag screw embedment 2.5 in Total pullout capacity 665 lbs NDS 2015 Table 12.2A Pullout max tributary area 11.9 ft^2 Factor of Safety 1.41 Minimum number of connections 15 Beam Stress IEBC 2018 Section 806.2 Beam Span 15 ft Spacing 2 ft Roof Framing type 2x6 rafters Panel Orientation portrait Number of Panels per rafter 2 Panel distance from eave 2 Without Solar Panels With Solar Panels Percent Increase Bending Moment 2399.1 ft-lbs 2228.1 ft-lbs 92.9% Less than 105% Vertical Reaction (V1) 639.8 lbs 646.8 lbs 101.1% Less than 105% Vertical Reaction (V2) 639.8 lbs 506.03 lbs 79.1% Less than 105% 4 Solar Array 2- South Roof Slope 19 degrees Number of panels 2 Panel Area 35 ft^2 Wind Calculations- ASCE 7-16 GCp Zone 1 -0.9 Figure 30.3-(2A-5B) GCp Zone 2 -1.7 Figure 30.3-(2A-5B) GCp Zone 3 -2.6 Figure 30.3-(2A-5B) Gcpi 0.18 Table 26.13-1 Velocity Pressure (qh) 28.2 psf qh= .00256KhKhtKdV^2 Equation 26.10-1 Kh 0.98 Table 26.10-1 Kht 1 Equation 26.8-1 Kd 0.85 Table 26.6-1 Designed wind pressure (P) psf Equation 30.8-1 P= qh(GCh) - (GChi)) Zone 1 Pressure (P) -30.5 psf Zone 2 Pressure (P) -53 psf Zone 3 Pressure (P) -78.4 psf Lag Screw Connection Shear Capacity 190 lbs NDS 2015 Table 12K Shear tributary area 18 ft^2 Pullout Capacity 266 lbs/in Lag screw embedment 2.5 in Total pullout capacity 665 lbs NDS 2015 Table 12.2A Pullout max tributary area 12.5 ft^2 Factor of Safety 1.41 Minimum number of connections 3 Beam Stress IEBC 2018 Section 806.2 Beam Span 14 ft Spacing 2 ft Roof Framing type 2x6 rafters Panel Orientation portrait Number of Panels per rafter 1 Panel distance from eave 3.5 Without Solar Panels With Solar Panels Percent Increase Bending Moment 2089.9 ft-lbs 2180.4 ft-lbs 104.3% Less than 105% Vertical Reaction (V1) 597.1 lbs 573.7 lbs 96.1% Less than 105% Vertical Reaction (V2) 597.1 lbs 573.7 lbs 96.1% Less than 105%