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Home My WebLink AboutENGINEER LETTER - 22-00024 - 64 S 3rd E - Solar PanelsDate: 16 February 2022 Big Dog Solar Energy 620 Pheasant Ridge Dr Chubbuck, ID 83202 Sarah Avila Residence: 64 South 3rd East, Rexburg, ID 83440 Dear Sir/ Madam, Conclusion Page 1 of Sarah Avila letter Structural Letter of Approval Terra Engineering Consulting (TEC) has performed a structural analysis for the existing framing and load conditions and determined that the structure can support the additional load of the proposed solar panel system. TEC has reviewed the site survey, photographs of the existing framing, and the proposed PV array. The attached calculations are based off the assumptions that the existing structural components are in good condition, that they meet industry standards, and that the site survey provided by the client is accurate. The design assumptions 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. 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 structural evaluation shows that existing framing is able to withstand the additional load while meeting current standards, allowing the structure to remain unaltered; see calculations and span table attached. 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 connection hardware is pre-engineered by manufacturer, and designed for metal roofs installations. 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, PE President Installation and waterproofing shall be performed within accepted industry standards. Page 2 of Sarah Avila letter 2/16/2022 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 References Design Parameter Risk Category: II Ground Snow load: 45 psf Roof Snow load: 31.2 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: 2x6 Rafters at 24” O.C. Roof material: Metal seam Roof slope: 30° Roof type: Gable Solar Panels Weight: 2.8 psf Code: 2018 International Building Code/ International Existing Building Code, ASCE 7-16, and National Design Specification for Wood Construction (NDS) 2015 Edition Connection: Pre-engineered clamps Page 3 of Sarah Avila letter 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 Date:2/16/2022 Client:Sarah Avila Subject:Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°):30 30 Ground snow load, pg (psf):45 45 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):31.2 31.2 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: Unobstructed Slippery surface Unobstructed slippery surface ASCE 7-16, C7.4 Roof slope factor, Cs:0.67 0.67 ASCE 7-16, C7.4 Sloped roof snow load, ps [psf]:20.9 20.9 Roof dead load (D) Roof pitch/12 6.9 Metal seam 0.8 psf 1/2" Gypsum clg.0.5 psf 1/2" plywood 1 psf Insulation 0.5 psf Framing 2.5 psf M, E & Misc 1 psf Roof DL without PV arrays 7.3 psf PV Array DL 2.8 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]7.3 10.1 ASCE 7-16, Section 2.4.1 D+L [psf]7.3 10.1 ASCE 7-16, Section 2.4.1 D+[Lr or S or R] [psf]28.2 31.0 ASCE 7-16, Section 2.4.1 23.0 25.8 ASCE 7-16, Section 2.4.1 Maximum gravity load [psf]:28.2 31.0 ASCE 7-16, equation 7.4-1, Design Snow Load (S) D+0.75L+0.75[Lr or S or R] [psf] Date:2/16/2022 Client:Sarah Avila Subject:Beam calculator Beam Design (Roof)2x6 Rafters at 24 in o.c., span 11 ft max. Load Combination Combo DL LL W SL LLR E Sum 1 1.4 10.1 0 0 0 0 0 20.9 0 0 0 14.14 2 1.2 10.1 1.6 0 0 0 0.5 20.9 0 0 0 22.57 3 1.2 10.1 1 0 1 0 1.6 20.9 0 0 0 45.56 4 1.2 10.1 1 0 1 0 0.5 20.9 0 0 0 22.57 5 1.2 10.1 0 0 0 0 0.2 20.9 0 1 0 16.3 6 0.9 10.1 0 0 1 0 0 20.9 0 0 0 9.09 7 0.9 10.1 0 0 0 0 0 20.9 0 1 0 9.09 Roof DL 10.1 psf (see Gravity load roof DL) S 20.9 psf W E LL 0 psf RLL 0 psf (see Gravity load LL with PV arrays) U 45.56 psf beam spacing 2 ft o.c. uniform load 91.12 plf span 11 ft Mu = w(l^2)/8 1378.19 lb-ft Number of joists 1 Flexure design Cr 1.15 (2015 NDS Supp, p32) Timber grade DFL#2 (2015 NDS Supp, table 4A) Fb 900 psi (set SPF#2 as default) Kf 2.54 (2015 NDS, table 2.3.5) bending fact.0.85 (2015 NDS, table 2.3.6) dimension Cf (table 4A, NDS supp 2015, p32) S in^3 (table1B, NDS supp 2015) Fbu = Mu/S (psf)Fbu (psi) moment of inertia in^4 (table 1B, NDS supp) 2x6 1.3 7.56 315014.9 2187.603 20.8 purlin size λ (Table N3, NDS 2015 p184)F'bn (psi) Fbu Fbu < F'bn 2x6 0.8 2323.9476 2187.603 Works Design for deflection we going to assume these calculations for U1 only since its clearly higher we use the following equation to calculation max deflection, minimum interia, and deflection service load combination:D+S U 31 lb Uniform load 62 plf *convert all the units in the equaion to inch max def. (ft) E psi(Table 4A)w (plf)l (ft) I (min) (in^4) Imin< Ipurlin 0.055 1600000 62 11 19.34109 Works Design for Shear fvu = 1.5V/A V is shear Vu, and A cross sectional area of purlin found in table 1B uniform load 91.12 plf Vu 501.16 lb Vu = wl/2 Framing cross section 8.25 in^2 fvu 91.12 psi Fv 180 psi (for DFL#2) F'vn 311.04 psi F'vn > fvu Works Beam works