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Home My WebLink AboutENGINEER LETTER - 19-00786 - 369 W 3rd S - Solar PanelsDate: December 24, 2019 Big Dog Solar Energy 620 Pheasant Ridge Dr Chubbuck, ID 83202 Blake Willis Residence: 269 W 3RD S, Rexburg, ID 83440 Dear Sir/ Madam, Conclusion 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 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. Our conclusions are based off a structural evaluation of the existing framing under the proposed additional solar panels load. 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 1607.12.5 in 2015 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 403.4 of 2015 IEBC. TEC concludes that the installation of solar panels on existing roof will not affect the structure of this residence, 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 Installation and waterproofing must be performed within accepted industry standard. 12/24/2019 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: 34.7 psf Design Wind Speed: 115 mph (3 sec gust) per ASCE 7-10 Seismic Design Category: D Wind Exposure Category: C Existing Roof Structure Roof framing: 2x4 Pre-fab Trusses at 24” O.C. Roof material: metal seam Roof slope: 26 ° Roof type: Gable Solar Panels (8) Panels Weight: 3 psf Code: 2015 International Building Code/ International Existing Building Code, ASCE 7-10, and National Design Specification for Wood Construction (NDS) 2015 Edition Connections: Pre-engineered clamps 1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204 Date: 12/24/2019 Client: Blake Willis Subject: Gravity load Gravity load calculations Snow load (S)Existing w/ solar panels Roof slope (°): 26 26 Ground snow load, pg (psf): 50 50 ASCE 7-10, section 7.2 Terrain category: C C ASCE 7-10, table 7-2 Exposure of roof: Fully exposed Fully exposed ASCE 7-10, table 7-2 Exposure factor, Ce: 0.9 0.9 ASCE 7-10, table 7-2 Thermal factor, Ct: 1.1 1.1 ASCE 7-10, table 7-3 Risk Category: II II ASCE 7-10, table 1.5-1 Importance Factor, Is: 1 1 ASCE 7-10, table 1.5-2 Flat roof snow load, pf (psf): 34.7 34.7 ASCE 7-10, equation 7.3-1 Minimum roof snow load, pm (psf): 0 0 ASCE 7-10, equation 7.3-4 Roof Surface type: Unobstructed Slippery surface Unobstructed slippery surface ASCE 7-10, Section 7.4 Roof slope factor, Cs: 0.73 0.73 ASCE 7-10, figure 7-2b Sloped roof snow load, ps [psf]: 25.3 25.3 Roof dead load (D) Roof pitch/12 5.9 metal seam 0.8 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 10.3 psf PV Array DL 3 psf Roof live load (Lr)Existing w/ solar panels Roof Live Load 20 0 2015 IBC, Section 1607.12.5 ASD Load combination: Existing With PV array D [psf] 10.3 13.3 ASCE 7-10, Section 2.4.1 D+L [psf] 10.3 13.3 ASCE 7-10, Section 2.4.1 D+[Lr or S or R] [psf] 35.6 38.6 ASCE 7-10, Section 2.4.1 29.3 32.3 ASCE 7-10, Section 2.4.1 Maximum gravity load [psf]:35.6 38.6 Max Applied Load (2x4 pre-fab trusses at 24" o.c. 6/12 pitch, 36' span) 38.6 psf Max Allowable Load (2x4 pre-fab trusses at 24" o.c., 6/12 pitch, 47' span) 47 psf OK See attached span table ASCE 7-10, equation 7.4-1, Design Snow Load (S) D+0.75L+0.75[Lr or S or R] [psf] Roof Truss Span Tables 15Alpine Engineered Products Top Chord 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 Bottom Chord 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 2/12 24 24 33 27 27 37 31 31 43 33 33 46 2.5/12 29 29 39 33 33 45 37 38 52 39 40 55 3/12 34 34 46 37 39 53 40 44 60 43 46 64 3.5/12 39 39 53 41 44 61 44 50 65 47 52 70 4/12 41 43 59 43 49 64 46 56 69 49 57 74 5/12 44 52 67* 46 58 69* 49 66 74* 53 66 80* 6/12 46 60* 69* 47 67* 71* 51 74* 76* 55 74* 82* 7/12 47 67* 70* 48* 72* 72* 52* 77* 77* 56* 80* 83* 2/12 24 24 33 25 27 38 27 31 41 29 32 44 2.5/12 28 29 40 29 32 43 31 37 46 33 37 49 3/12 30 33 45 31 37 47 34 42 50 36 42 54 3.5/12 33 37 49* 34 41 51* 36 46 54* 39 46 58* 4/12 35 41 52* 36 45* 54* 39 50* 58* 42* 49* 62* ‡ Other pitch combinations available with these spans For Example, a 5/12 - 2/12 combination has approx. the same allowable span as a 6/12 - 3/12 Top Chord 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 Bottom Chord 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 16" 23 24 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 § 18" 25 27 28 27 27 29 § 29 § 29 § 29 § 29 § 29 § 29 § 20" 27 28 30 28 28 32 31 30 33 § 32 31 33 § 24" 29 30 33 31 31 35 34 33 38 35 34 40 28" 32 32 36 34 33 39 37 36 42 38 37 44 30" 33 33 38 35 35 40 38 37 44 40 39 45 32" 34 34 39 36 36 42 39 39 45 41 40 47 36" 36 36 42 39 38 45 42 41 48 43 43 50 42" 39 39 45 41 41 48 44 44 52 45 46 54 48" 40 42 49 43 44 52 46 47 56 46 49 58 60" 44 47 55 46 49 58 48 53 63 49 55 65 72" 45 51 60 48 54 64 51 57 68 51 59 69 § = Span Limited by length to depth ratio of 24 Pitch Depth Spans in feet to out of bearing Spans in feet to out of bearing 5/12 38* 47* 57* 39* 51* 59* 42* 56* 63* 45* 54* 68* 6/12 - 2/12 ‡ 40 43 59* 42 49 62* 45 56* 66 48 57* 71* 6/12 - 2.5/12 ‡ 37 38 52 38 44 57* 41 50 61* 44 52 66* 6/12 - 3/12 ‡ 33 33 45 35 38 52 38 43 56* 40 46 60* 6/12 - 3.5/12 ‡ 28 28 38 32 32 44 34 37 50 36 39 54 6/12 - 4/12 ‡ 22 22 31 26 26 36 30 30 41 32 32 44 Alpine truss designs are engineered to meet specific span, configuration and load conditions. The shapes and spans shown here represent only a fraction of the millions of designs produced by Alpine engineers. Total load(PSF) Duration factor Live load(PSF) Roof type 55 1.15 40 snow shingle 55 1.15 30 snow tile 47 1.15 30 snow shingle 40 1.15 20 snow shingle 40 1.25 20 ** shingle **construction or rain, not snow load 55 1.15 40 snow 47 1.15 30 snow 40 1.15 20 snow 40 1.25 20 rain or constn. Total load(PSF) Duration factor Live load(PSF) NOTES:These overall spans are based on NDS ‘01 with 4" nominal bearing each end, 24" o.c. spacing, a live load deflection limited to L/240 maximum and use lumber properties as follows: 2x4f =2000psif=1100psiE=1.8x10 2x6f =1750 psi f=950 psi f =1900 psi E=1.8x10 . Allowable spans for 2x4 top chord trusses using sheathing other than plywood (e.g. spaced sheathing or 1x boards) may be reduced slightly. Trusses must be designed for any special loading such as concentrated loads from hanging partitions or air conditioning units, and snow loads caused by driftingnearparapetorslide-offfromhigherroofs. To achieve maximum indicated spans, trusses may require six or more panels. Trusses with an asterisk (*) that exceed 14' in height may be shipped in two pieces. Contact your local Alpine trussmanufacturerorofficeformoreinformation. bt b tc 6 6 Common --Truss configurations for the most widely designed roof shapes. Mono --Used where the roof is required to slope only in one direction. Also in pairs with their high ends abutting on extremely long spans with a support underneath the high end. Scissors --Provides a cathedral or vaulted ceiling. Most economical when the difference in slope between the top and bottom chords is at least 3/12 or the bottom chord pitch is no more than half the top chord pitch. Flat --The most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7% of the span in inches.