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Home My WebLink AboutLA193782 - Approved engineer letterVSE Project Number: U3507.0107.211 August 12, 2021 TruNorth Solar LLC ATTENTION: Donna Pickard 3735 Dunlap St. N. Arden Hills, MN 55112 REFERENCE: Preszler, Christina Residence: 16938 Fairhill Avenue, Farmington, MN 55024 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: 2020 Minnesota Building Code (2018 IBC) Risk Category: II Design wind speed, Vult: 109 mph (3-sec gust) per ASCE 7-16 Wind exposure category: C Ground snow load, Pg: 50 psf Connection to Roof Mounting connection: (1) 5/16" lag screw w/ min. 2.5" threaded 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. Rail cantilever shall not exceed 50% of connection spacing. 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 (2020 MBC,Section 1607.13.5). The glass surface of the solar panels allows for a lower slope factor per ASCE 7,resulting in reduced design snow load on the panels.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 806.2 of the 2020 Minnesota Conservation Code for Existing Buildings are met and the structure is permitted to remain unaltered. The solar array will be flush-mounted (no more than 10"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.Because the increase in lateral forces is less than 10%,this addition meets the requirements of the exception in Section 806.3 of the 2020 Minnesota Conservation Code for Existing Buildings.Thus the existing lateral force resisting system is permitted to remain unaltered. Limitations 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com VSE Project Number: U3507.0107.211 Preszler, Christina Residence 8/12/2021 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 08/12/2021 _______________________________________________________ Brett Veazie, P.E. Project Engineer Enclosures BDV/wic I hereby certify that this plan, specification or report was prepared by me or under my direct supervision and that I am a duly Licensed Professional Engineer under the laws of the State of Minnesota. Brett Veazie, License No. 56392, Expiration Date: 30-June-2022 08/12/2021 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com JOB NO.:U3507.0107.211 SUBJECT:WIND PRESSURE PROJECT:Preszler, Christina Residence Label:Note: Calculations per ASCE 7-16 SITE-SPECIFIC WIND PARAMETERS: Basic Wind Speed [mph]:109 Notes:Exposure Category:C Risk Category:II Importance Factor, I: ADDITIONAL INPUT & CALCULATIONS: Height of Roof, h [ft]:25 (Approximate) Comp/Cladding Location:Gable Roofs 27° < θ ≤ 45° Enclosure Classification: Zone 1, 2e, 2r GCp:1.75 Zone 1, 2e, 2r γa:0.78 Zone 2n, 3r GCp:1.96 Zone 2n, 3r γa:0.78 Zone 3e GCp:2.44 Zone 3e γa:0.78 γa:0.40 α:9.5 Table 26.11-1 zg [ft]:900 Table 26.11-1 Kh:0.95 Table 26.10-1 Ke:0.97 Table 26.9-1 Kzt:1 Equation 26.8-1 Kd:0.85 Table 26.6-1 Velocity Pressure, qh [psf]:23.6 Equation 26.10-1 γE:1.50 Section 29.4.4 γC:0.94 Section 29.4.4 γP:1.20 Section 29.4.4 p = q h (GC p )(γ E )(γ a ) p = q h (GC rn ), (GC rn ) = (γ p )(γ c )(γ E )(GC rn )nom Zone 1, 2e, 2r, p [psf]:48.4 psf (1.0 W) Zone 2n, 3r, p [psf]:54.3 psf (1.0 W) Zone 3e, p [psf]:67.6 psf (1.0 W) (a =3 ft) Fig. 29.4-8 WIND PRESSURES:Equation 29.4-7 Solar Panel Array Enclosed Buildings Figure 30.3-2D (negative coeff.) Components and Cladding Wind Calculations JOB NO.:U3507.0107.211 SUBJECT:CONNECTION PROJECT:Preszler, Christina Residence Calculate Uplift Forces on Connection Pressure (0.6 Dead -0.6 Wind) (psf) Max Trib. Width1 (ft) Max Trib. Area2 (ft2) Max Uplift Force (lbs) Zone 1, 2e, 2r 27.3 4.0 11.2 304 Zone 2n, 3r 30.8 4.0 11.2 344 Zone 3e 38.8 4.0 11.2 433 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]:433 Lag Screw Capacity [lbs]:586 Result:Capacity > Demand, Connection is adequate. Notes 1. 'Max Trib. Width' is the width along the rails tributary to the connection. 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. Trib Width' 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.:U3507.0107.211 SUBJECT:GRAVITY LOADS PROJECT:Preszler, Christina Residence GRAVITY LOADS Roof Pitch: 10.8 :12 ROOF DEAD LOAD (D) Increase due to pitch Material weight [psf] Composite Shingles 1.35 2.0 1/2" Plywood 1.35 1.0 Framing 1.00 3.0 Insulation 1.00 0.5 1/2" Gypsum Clg.1.35 2.0 M, E & Misc 1.00 1.5 Total Existing Roof DL PV Array DL 1.35 3 DL:1.35 ROOF LIVE LOAD (Lr) Existing Design Roof Live Load [psf]20 ASCE 7-16 Table 4.3-1 Roof Live Load With PV Array [psf]0 SNOW LOAD (S):w/ Solar Array Roof Slope [x:12]:10.8 Roof Slope [°]:42 Ground Snow Load, pg [psf]:50 ASCE 7-16, Section 7.2 Terrain Category:C ASCE 7-16, Table 7.3-1 Exposure of Roof:Fully Exposed ASCE 7-16, Table 7.3-1 Exposure Factor, Ce:0.9 ASCE 7-16, Table 7.3-1 Thermal Factor, Ct:1.1 ASCE 7-16, Table 7.3-2 Risk Category:II ASCE 7-16, Table 1.5-1 Importance Factor, Is:1.0 ASCE 7-16, Table 1.5-2 Flat Roof Snow Load, pf [psf]:35 ASCE 7-16, Equation 7.3-1 Minimum Roof Snow Load, pm [psf]:0 ASCE 7-16, Section 7.3.4 Unobstructed Slippery Surface?Yes ASCE 7-16, Section 7.4 Slope Factor Figure:Figure 7-2b ASCE 7-16, Section 7.4 Roof Slope Factor, Cs:0.47 ASCE 7-16, Figure 7.4-1 Sloped Roof Snow Load, ps [psf]:16 ASCE 7-16, Equation 7.4-1 Design Snow Load, S [psf]:1630 10.8 42 50 C Fully Exposed 0.9 1.1 II 1.0 35 0 No Figure 7-2b 0.86 30 Design material weight [psf] 2.7 1.3 3.0 0.5 2.7 1.5 11.7 4.0 #VALUE! 2020 MBC, Section 1607.13.5 Existing JOB NO.:U3507.0107.211 SUBJECT:LOAD COMPARISON PROJECT:Preszler, Christina Residence Summary of Loads Existing With PV Array D [psf]12 16 Lr [psf]20 0 S [psf]30 16 Maximum Gravity Loads: Existing With PV Array (D + Lr) / Cd [psf]25 18 ASCE 7-16, Section 2.4.1 (D + S) / Cd [psf]36 28 ASCE 7-16, Section 2.4.1 Maximum Gravity Load [psf]:36 28 Ratio Proposed Loading to Current Loading:77%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 806.2 of the 2020 Minnesota Conservation Code for Existing Buildings 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) VECTOR STRUCTURAL ENGINEERS JOB NO.:U3507.0107.211 SUBJECT:SOLAR LAYOUT PROJECT:Preszler, Christina Residence