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Home My WebLink AboutENGINEERING LETTER - 19-00333 - 691 Dell Dr - Solar PanelsVSE Project Number: U2238-0263-191 May 21, 2019 Big Dog Energy 620 Pheasant Ridge Drive Chubbick, ID 83202 REFERENCE: Russ Norton Residence: 691 Dell Drive, Rexburg, ID 83440 Solar Array Installation To Whom It May Concern: Per your request,we have reviewed the existing structure at the above referenced site.The purpose of our review was to determine the adequacy of the existing structure to support the proposed installation of solar panels on the roof as shown on the panel layout plan.Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation. Design Parameters Code: International Building Code, 2015 Edition Risk Category: II Design wind speed: 115 mph (3-sec gust) per ASCE 7-10 Wind exposure category: C Ground snow load: 35 psf Existing Roof Structure Roof structure: 2x4 manufactured trusses @ 24" O.C. Roofing material: asphalt shingles Roof pitch: 6:12 Conclusions Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation. In the area of the solar array,other live loads will not be present or will be greatly reduced (2015 IBC,Section 1607.12.5). The member forces in the area of the solar panels are not increased by more than 5%;thus,the stresses of the structural elements are not increased by more than 5%.Therefore,the requirements of Section 807.4 of the 2015 IEBC are met and the structure is permitted to remain unaltered. The solar array will be flush-mounted (no more than 6"above the roof surface)and parallel to the roof surface.Thus,we conclude that any additional wind loading on the structure related to the addition of the proposed solar array is negligible. The connections to the existing roof shall be spaced at 48"maximum.Regarding seismic loads,we conclude that any additional forces will be small.With an assumed roof dead load of 10 psf,solar array dead load of 3 psf,and affected roof area of 33%(maximum),the additional dead load (and consequential seismic load)will be 9.6%.This calculation conservatively neglects wall weight.Because the increase in lateral forces is less than 10%,this addition meets the requirements of the exception in Section 807.5 of the 2015 IEBC.Thus the existing lateral force resisting system is permitted to remain unaltered. 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com VSE Project Number: U2238-0263-191 Russ Norton Residence 5/21/2019 Limitations Installation of the solar panels must be performed in accordance with manufacturer recommendations.All work performed must be in accordance with accepted industry-wide methods and applicable safety standards.The contractor shall notify Vector Structural Engineering,LLC should any damage,deterioration or discrepancies between the as-built condition of the structure and the condition described in this letter be found.Connections to existing roof framing must be staggered,except at array ends,so as not to overload any existing structural member.The use of solar panel support span tables provided by others is allowed only where the building type,site conditions,site-specific design parameters,and solar panel configuration match the description of the span tables.The design of the solar panel racking (mounts,rails,etc.),the connection of the racking to the roof and electrical engineering is the responsibility of others.Waterproofing around the roof penetrations is the responsibility of others. Vector Structural Engineering assumes no responsibility for improper installation of the solar array. VECTOR STRUCTURAL ENGINEERING, LLC ID Firm License: C2269 05/21/2019 _______________________________________________________ Wells Holmes, P.E. ID License: P-12264 - Expires: 10/31/2019 Project Engineer Enclosures WLH/hub 05/21/2019 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com VECTOR STRUCTURAL ENGINEERS JOB NO.:U2238-0263-191 SUBJECT:GRAVITY LOADS PROJECT:Russ Norton Residence CALCULATE ESTIMATED GRAVITY LOADS ROOF DEAD LOAD (D) Increase due to pitch Original loading Roof Pitch/12 6.0 Asphalt Shingles 2.2 1.12 2.0 psf 1/2" Plywood 1.1 1.12 1.0 psf Framing 3.0 psf Insulation 0.5 psf 1/2" Gypsum Clg. 2.0 psf M, E & Misc 1.5 psf DL 10 psf PV Array DL 3 psf ROOF LIVE LOAD (Lr) Existing Design Roof Live Load [psf] 18 ASCE 7-10, Table 4-1 Roof Live Load With PV Array [psf] 0 2015 IBC, Section 1607.12.5 SNOW LOAD (S):Existing w/ Solar Panel Array Roof Slope [x:12]:6.0 Roof Slope [°]:27 Snow Ground Load, pg [psf]:35 ASCE 7-10, Section 7.2 Terrain Category:C ASCE 7-10, Table 7-2 Exposure of Roof:Fully Exposed ASCE 7-10, Table 7-2 Exposure Factor, Ce:0.9 ASCE 7-10, Table 7-2 Thermal Factor, Ct:1.1 ASCE 7-10, Table 7-3 Risk Category:II ASCE 7-10, Table 1.5-1 Importance Factor, Is:1.0 ASCE 7-10, Table 1.5-2 Flat Roof Snow Load, pf [psf]:24 ASCE 7-10, Equation 7.3-1 Minimum Roof Snow Load, pm [psf]:0 ASCE 7-10, Section 7.3.4 Unobstructed Slippery Surface? No ASCE 7-10, Section 7.4 Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4 Roof Slope Factor, Cs:1.00 ASCE 7-10, Figure 7-2 Sloped Roof Snow Load, ps [psf]:24 ASCE 7-10, Equation 7.4-1 Design Snow Load, S [psf]:24 1.00 24 24 6.0 27 35 C Fully Exposed 0.9 1.1 II 1.0 24 0 No Figure 7-2b JOB NO.:U2238-0263-191 SUBJECT:LOAD COMPARISON PROJECT:Russ Norton Residence Summary of Loads Existing With PV Array D [psf] 10 13 Lr [psf] 18 0 S [psf] 24 24 Maximum Gravity Loads: Existing With PV Array (D + Lr) / Cd [psf]23 15 ASCE 7-10, Section 2.4.1 (D + S) / Cd [psf]30 33 ASCE 7-10, Section 2.4.1 Maximum Gravity Load [psf]:30 33 Maximum Member Forces: LOCATION GEOMETRY Span(ft)45.4 (Approximate) Solar Panel Array Start, a (ft)8.3 (Approximate) Solar Panel Array Length, b (ft)11.0 (Approximate) Truss/Rafter Spacing (ft)2.0 MEMBER FORCES Existing With PV Array Vertical Reaction, V1 (lbs)1366 1406 OK Vertical Reaction, V2 (lbs)1366 1383 OK Existing With PV Array Moment @ Center, M (lbs-ft)15500 15897 OK Ratio (Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr) Ratio House 103% 103% 101% The member forces in the area of the solar array are not increased by more than 5%; thus, the stresses of the structural elements are not increased by more than 5%. Therefore, the requirements of Section 807.4 of the 2015 IEBC are met and the structure is permitted to remain unaltered. VECTOR STRUCTURAL ENGINEERS JOB NO.:U2238-0263-191 SUBJECT:SOLAR LAYOUT PROJECT:Russ Norton Residence MTR MSP AC INV