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Home My WebLink AboutENGINEERING LETTER - 20-00801 - 129 Madison Ave - Solar PanelsVSE Project Number: U3806.0061.201 October 6, 2020 Comet Energy 13601 W McMillan Road, Ste 102 PMB 166 Boise, ID 83713 REFERENCE: Carol Wither Residence: 129 Madison Avenue, 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: 50 psf Seismic design category: D Existing Roof Structure Roof structure: 2x4 manufactured trusses @ 24" O.C. Roofing material: asphalt shingles Roof slope: 18° Connection to Roof Mounting connection: (1) 5/16" lag screw w/ min. 2.5" embedment into framing at max. 48" o.c. along rails (2) rails per row of panels, evenly spaced; panel length perpendicular to the rails not to exceed 67 in Conclusions Based upon our review,we conclude that the existing structure is adequate to support the proposed solar panel installation. The gravity loads and;thus,the stresses of the structural elements,in the area of the solar array are either decreased or increased by no more than 5%.Therefore,the requirements of Section 807.4 of the 2015 IEBC 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: U3806.0061.201 Carol Wither Residence 10/6/2020 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.Regarding seismic loads,we conclude that any additional forces will be small.Conservatively neglecting the weight of existing wall materials,the installation of the solar panels represents an increase in the total weight (and resulting seismic load)of 9.7%.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. 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 must 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.)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 10/06/2020 _______________________________________________________ Trevor Hawkes, P.E. ID License: 18683 - Expires: 12/31/2020 Project Engineer Enclosures TPH/cbw 10/06/2020 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com JOB NO.:U3806.0061.201 SUBJECT:WIND PRESSURE PROJECT:Carol Wither 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)Hip? Comp/Cladding Location:No Enclosure Classification: Zone 1 GCp:0.9 Figure 30.4-2B (enter negative pressure coefficients) Zone 2 GCp:1.7 Zone 3 GCp:2.6 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 PRESSURES:Equation 30.9-1 Zone 1, p [psf]:22.0 psf (1.0 W, Interior Zones, beyond 'a' from roof edge) Zone 2, p [psf]:41.5 psf (1.0 W, End Zones, within 'a' from roof edge) Zone 3, p [psf]:63.5 psf (1.0 W, Corner Zones, within 'a' from roof corner) (a= 3 ft) Solar Panel Array Gable/Hip Roofs 7° < θ ≤ 27° Enclosed Buildings Components and Cladding Wind Calculations ()()piphGCGCqp−= JOB NO.:U3806.0061.201 SUBJECT:CONNECTION PROJECT:Carol Wither Residence Calculate Uplift Forces on Connection Pressure (0.6 Dead -0.6 Wind) (psf) Max Connection Spacing1 (ft) Max Trib. Area2 (ft2) Max Uplift Force (lbs) Zone 1 13.2 4.0 11.2 126 Zone 2 24.9 4.0 11.2 257 Zone 3 38.1 4.0 11.2 404 Calculate Connection Capacity Lag Screw Size [in]:5/16 Cd:1.6 NDS Table 2.3.2 Embedment3 [in]:2.5 Grade: Nominal Capacity [lbs/in]:205 NDS Table 12.2A Number of Screws:1 Prying Coefficient:1.4 Total Capacity [lbs]:586 Determine Result Maximum Demand [lbs]:404 Lag Screw Capacity [lbs]:586 Result:Capacity > Demand, Connection is adequate. Notes 1. 'Max Connection Spacing' is the spacing between connections along the rails. 3. Embedment is measured from the top of the framing member to the beginning of the tapered tip of the lag screw. Embedment in sheathing or other material is not effective. The length of the tapered tip is not part of the embedment length. 2. 'Max Trib Area' is the product of the 'Max Connection Spacing' and 1/2 the panel width/height perpendicular to the rails. (2) rails per row of panels. Length of panels perpendicular to the rails shall not exceed 67". SPF (G = 0.42) VECTOR STRUCTURAL ENGINEERS JOB NO.:U3806.0061.201 SUBJECT:GRAVITY LOADS PROJECT:Carol Wither Residence CALCULATE ESTIMATED GRAVITY LOADS Roof Pitch: 3.9 :12 ROOF DEAD LOAD (D) Increase due to pitch Material weight [psf] Asphalt Shingles 1.05 2.0 1/2" Plywood 1.05 1.0 Framing 1.00 3.0 Insulation 1.00 0.5 1/2" Gypsum Clg.1.05 2.0 M, E & Misc 1.00 1.5 Total Original Roof DL PV Array DL 1.05 3 DL:1.05 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):w/ Solar Array Roof Slope [x:12]:3.9 Roof Slope [°]:18 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?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]:35 ASCE 7-10, Equation 7.4-1 Design Snow Load, S [psf]:3535 3.9 18 50 C Fully Exposed 0.9 1.1 II 1.0 35 0 No Figure 7-2b 1.00 35 Design material weight [psf] 2.1 1.1 3.0 0.5 2.1 1.5 10.3 3.2 #VALUE! 2015 IBC, Section 1607.12.5 Existing JOB NO.:U3806.0061.201 SUBJECT:LOAD COMPARISON PROJECT:Carol Wither Residence Summary of Loads Existing With PV Array D [psf]10 13 Lr [psf]20 0 S [psf]35 35 Maximum Gravity Loads: Existing With PV Array (D + Lr) / Cd [psf]24 15 ASCE 7-10, Section 2.4.1 (D + S) / Cd [psf]39 42 ASCE 7-10, Section 2.4.1 Maximum Gravity Load [psf]:39 42 Maximum Member Forces: GEOMETRY Span(ft)30.0 (Approximate) Solar Panel Array Start, a (ft)1.0 (Approximate) Solar Panel Array Length, b (ft)11.0 (Approximate) Framing Spacing (ft)2.0 MEMBER FORCES Existing With PV Array Vertical Reaction, V1 (lbs)1171 1219 OK Vertical Reaction, V2 (lbs)1171 1185 OK Existing With PV Array Moment @ Center, M (lbs-ft)8786 8982 OK The gravity loads and; thus, the stresses of the structural elements, in the area of the solar array are either decreased or increased by no more than 5%. Therefore, the requirements of Section 807.4 of the 2015 IEBC are met and the structure is permitted to remain unaltered. (Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr) Ratio 102% 104% 101% Ratio VECTOR STRUCTURAL ENGINEERS JOB NO.:U3806.0061.201 SUBJECT:SOLAR LAYOUT PROJECT:Carol Wither Residence New Array Existing Array