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Home My WebLink AboutENGINEER LETTER - 17-00454 - 995 Hillview Dr - Solar PanelsVSE Project Number: U2001-1184-171 August 3, 2017 Blue Raven Solar, LLC ATTENTION: Scott Gurney 1220 S. 630 E., Suite 430 American Fork, UT 84003 REFERENCE: Lary Duque Residence: 995 Hillview Drive, Rexburg, ID 83440 Solar Array Installation To Whom It May Concern: We have reviewed the documents and photographs relating to the installation of the solar array at the above-referenced site. Based upon our review,it is our conclusion that the installation of the solar array on this existing roof will not adversely affect this structure.It is our understanding that the structural components of the existing roof framing are in good condition and free of damage.The design of the solar panel racking (mounts,rails,etc.)is by the manufacturer or contractor.Please note a representative of Vector Structural Engineering has not physically observed the roof framing. Design Parameters Code: International Building Code, 2012 Edition Risk Category: II Design wind speed: 115 mph (3-sec gust) per ASCE 7-10 Wind exposure category: C Ground snow load: 50 psf Existing Roof Structure Roof structure: 2x4 manufactured trusses @ 24" O.C. Roofing material: composite shingles Conclusions Our conclusion regarding the adequacy of the existing roof is based on the fact that the additional weight of the solar array is 3 psf or less.In the area of the solar array,other live loads will not be present or will be greatly reduced.Regarding snow loads,because the panels are slippery and unobstructed,effective snow loads will be reduced in the area of the solar array. The gravity loads in the area of the solar array are decreased;thus,the stresses of the structural elements are decreased. Therefore, the requirements of Section 3403.3 of the 2012 IBC are met and the structure 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: U2001-1184-171 Lary Duque Residence 8/3/2017 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 attached calculations verify the capacity of the connections of the solar array to the existing roof against wind (uplift), the governing load case.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 9.5%.This calculation conservatively neglects wall weight.Because lateral loads are increasing by less than 10%,the installation of the solar panels meets the requirements in Section 3403.4 of the 2012 IBC and the structure is permitted to remain unaltered. 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.Particular attention must be paid to the maximum allowable spacing of connections and the location of solar panels relative to roof edges.Connections to existing roof framing must be staggered so as not to overload any existing structural member,except at array ends.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.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 number: C2269 08/03/2017 _______________________________________________________ Wells Holmes, P.E. ID License: P-12264 - Expires: 10/31/2017 Project Engineer Enclosures WLH/kec 08/03/2017 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com JOB NO.:U2001-1184-171 SUBJECT:WIND PRESSURE PROJECT:Lary Duque Residence Label:Note: Calculations per ASCE 7-10 SITE-SPECIFIC WIND PARAMETERS: Basic Wind Speed [mph]:115 Notes: Exposure Category:C Risk Category:II Importance Factor, I: ADDITIONAL INPUT & CALCULATIONS: Height of Roof, h [ft]:15 (Approximate) Comp/Cladding Location:Hip?No Enclosure Classification: Zone 1 GCp:1.0 Figure 30.4-2C (enter largest abs. value) Zone 2 GCp:1.2 (enter largest abs. value) Zone 3 GCp:1.2 (enter largest abs. value) α:9.5 Table 26.9-1 zg [ft]:900 Table 26.9-1 Kh:0.85 Table 30.3-1 Kzt:1 Equation 26.8-1 Kd:0.85 Table 26.6-1 Velocity Pressure, qh [psf]:24.4 Equation 30.3-1 GCpi:0 Table 26.11-1 (largest abs. value) OUTPUT:Equation 30.9-1 Zone 1 Pressure, p [psf]:24.4 psf (1.0 W, Interior Zones*) Zone 2 Pressure, p [psf]:29.3 psf (1.0 W, End Zones*) Zone 3 Pressure, p [psf]:29.3 psf (1.0 W, Corner Zones* within a) (a= 3 ft) Solar Panel Array Gable Roofs 27° < θ ≤ 45° Enclosed Buildings Components and Cladding Wind Calculations piphGCGCqp VECTOR STRUCTURAL ENGINEERS JOB NO.:U2001-1184-171 SUBJECT:CONNECTION PROJECT:Lary Duque Residence Lag Screw Connection Capacity:Demand: Lag Screw Size [in]:5/16 Cd:1.6 NDS Table 2.3.2 Embedment [in]:2.5 Grade: Capacity [lbs/in]:205 NDS Table 12.2A 1 14.7 4.0 12.0 176 Number of Screws:1 2 17.6 4.0 12.0 211 Prying Coefficient:1.4 3 17.6 3.0 9.0 158 Total Capacity [lbs]:586 Demand< Capacity:CONNECTION OKAY SPF (G = 0.42) Pressure (0.6 Wind) (psf) Max Tributary Width (ft) Max. Trib. Area (ft2) Max. Uplift Force (lbs) Zone VECTOR STRUCTURAL ENGINEERS JOB NO.:U2001-1184-171 SUBJECT:GRAVITY LOADS PROJECT:Lary Duque Residence CALCULATE ESTIMATED GRAVITY LOADS ROOF DEAD LOAD (D) Increase due to pitch Original loading Roof Pitch/12 6.4 Composite Shingles 2.3 1.13 2.0 psf 1/2" Plywood 1.1 1.13 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]20 ASCE 7-10, Table 4-1 Roof Live Load With PV Array [psf]0 SNOW LOAD (S):Existing w/ Solar Panel Array Roof Slope [x:12]:6.4 Roof Slope [°]:28 Snow Ground Load, pg [psf]:50 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]:35 ASCE 7-10, Equation 7.3-1 Minimum Roof Snow Load, pm [psf]:0 ASCE 7-10, Section 7.3.4 Unobstructed Slippery Surface?Yes ASCE 7-10, Section 7.4 Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4 Roof Slope Factor, Cs:0.70 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]:2435 6.4 28 50 C Fully Exposed 0.9 1.1 II 1.0 35 0 No Figure 7-2b 1.00 35 JOB NO.:U2001-1184-171 SUBJECT:LOAD COMPARISON PROJECT:Lary Duque Residence Summary of Loads Existing With PV Array D [psf]10 13 Lr [psf]20 0 S [pfsf]35 24 Maximum Gravity Loads: Existing With PV Array D + Lr [psf]30 13 ASCE 7-10, Section 2.4.1 D + S [psf]45 38 ASCE 7-10, Section 2.4.1 Maximum Gravity Load [psf]:45 38 Ratio Proposed Loading to Current Loading:84%OK The gravity loads in the area of the solar array are decreased; thus, the stresses of the structural elements are decreased. Therefore, the requirements of Section 3403.3 of the 2012 IBC are met and the structure is permitted to remain unaltered.