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Home My WebLink AboutENGINEERING LETTER - 17-00114 - 323 S 3rd E - Solar9138 S. State St., Suite 101 / Sandy, UT 84070 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com UTAH OFFICES Sandy Layton St. George Project Number: U2001-0643-171 February 14, 2017 Blue Raven Solar, LLC 1220 S. 630 E., Suite 430 American Fork, UT 84003 ATTENTION: Scott Gurney REFERENCE: David Peck Residence: 323 South 3rd East, Rexburg, ID 83440 Solar Panel Installation Dear Mr. Gurney: Per your request, we have reviewed the attached layout relating to the installation of solar panels at the above- referenced site. The following materials and components are proposed in the installation of the solar panels. Roof Structure: 2x4 Manufactured trusses @ 18 in O.C. Roof Material: Composite/Asphalt Shingles Based upon our review, it is our conclusion that the installation of solar panels on th e existing roof will not adversely affect the structure of this house. The design of supporting members and connections is by the manufacturer and/or installer. The adopted building code in this jurisdiction is the 2012 International Building Code and ASCE 7-10. Appropriate design parameters which must be used in the design of the supporting members and connections are listed below:  Ground snow load: 50 psf per Utah amendments to the IBC (verify with local building department)  Design wind speed for risk category II structures: 115 mph (3-sec gust)  Wind exposure: Category C Our conclusion regarding the adequacy of the existing roof is based on the fact that the additional weight of the solar panels is less than 3 pounds per square foot. In the area of the solar panels, no 20 psf live loads will be present . Regarding snow loads, it is our conclusion that since the panels are slippery and dark, effective snow loads will likely be reduced in the areas of the panels. Regarding wind loads, we conclude that any additional forces will be negligible due to the low profile of the flush-mounted panel system. Regarding seismic loads, we conclude that any additional forces will be small. With an assumed roof dead load of 15 psf, solar panel dead load of 3 psf, and affected roof area of 40% (maximum), the additional dead load (and consequential seismic load) will be 9.4%. This calculation conservatively neglects the weight of wall dead load. Because the increase is less than 10%, this alteration meets the requirements of the exception in Section 3403.4 of the 2012 International Existing Building Code. Thus the existing structure is permitted to remain unaltered. During design and installation, particular attention must be paid to the maximum allowable spacing of attachments and the location of solar panels relative to roof edges. The use of solar panel support span tables provided by the manufacturer is allowed only where the building type, site conditions, and solar panel configuration match the description of the span tables. Attachments to existing roof trusses or rafters must be staggered so as not to overload any existing structural member. Waterproofing around the roof penetrations is the responsibility of others. Electrical engineering is beyond our scope. All work performed must be in accordance with accepted industry-wide methods and applicable safety standards. Vector Structural Engineering assumes no responsibility for improper installation of the solar panels. Please note that a representative of Vector Structural Engineering has not physically observed the roof framing of this home. Our conclusions are based upon the assumption that all structural roof components and other supporting elements are in good condition and are sized and spaced such that they can resist standard roof loads. Very truly yours, VECTOR STRUCTURAL ENGINEERING, LLC Wells L. Holmes, P.E. Project Manager Firm License No.: C2269 WLH/wsp Enclosures 02/14/2017 JOB NO.:U2001-0643-171 PROJECT:DAVID PECK (28071144) RESIDENCE SUBJECT:WIND PRESSURE 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: Enclosure Classification: Zone 1 GCp:0.9 Figure 30.4-2B (enter largest abs. value) Zone 2 GCp:1.7 (enter largest abs. value) Zone 3 GCp:2.6 (enter largest abs. value) α:9.5 Table 26.9-1 zg [ft]:900 Table 26.9-1 Kh:0.849 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: Zone 1 Pressure, p [psf]:21.99 psf (1.0W, Interior Zones*) Zone 2 Pressure, p [psf]:41.53 psf (1.0W, End Zones*) Zone 3 Pressure, p [psf]:63.52 psf (1.0W, Corner Zones* within a) (*a=assumed=3') Solar Panel Array Gable/Hip Roofs 7° < θ ≤ 27° Enclosed Buildings Components and Cladding Wind Calculations piphGCGCqp VECTOR STRUCTURAL ENGINEERS JOB NO.:U2001-0643-171 PROJECT:DAVID PECK (28071144) RESIDENCE SUBJECT:CONNECTION CAPACITY Lag Screw Connection Capacity:Demand: Lag Screw Size:5/16 Cd:1.6 Embedment:2.5 in Grade: Capacity:205 lbs/in. emb.Zone 1:13.2 4 12 158 Number of Screws:1 Zone 2:24.9 4 12 299 Total Capacity:820 lbs Zone 3:38.1 4 12 457 Demand< Capacity:CONNECTION OKAY SPF (G = 0.42) Pressure (0.6 Wind) (psf) Max Spacing (ft) Max. Trib. Area (ft2) Max. Uplift Force (lbs) VECTOR STRUCTURAL ENGINEERS JOB NO.:U2001-0643-171 PROJECT:DAVID PECK (28071144) RESIDENCE SUBJECT:GRAVITY LOADS CALCULATE ESTIMATED GRAVITY LOADS DEAD LOAD (D) Increase due to pitch Original loading Roof Pitch/12 3.9 Composite/Asphalt Shingles 4.2 1.05 4.00 psf 1/2" Plywood 1.1 1.05 1.00 psf Framing 3.0 psf Insulation 0.8 psf 1/2" Gypsum Clg.2.2 psf M, E & Misc 1.5 psf DL 12.8 psf PV Array DL 3.0 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 2015 IBC, Section 1607.12.5 SNOW LOAD (S):Existing With PV Array Roof Slope (: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?Yes ASCE 7-10, Section 7.4 Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4 Roof Slope Factor, Cs:0.867 ASCE 7-10, Figure 7-2 Sloped Roof Snow Load, ps [psf]:30 ASCE 7-10, Equation 7.4-1 Design Snow Load, S [psf]:30 1.000 35 35 3.9 18 50 C Fully Exposed 0.9 1.1 II 1.0 35 0 No Figure 7-2b JOB NO.:U2001-0643-171 PROJECT:DAVID PECK (28071144) RESIDENCE SUBJECT:LOAD COMPARISON Summary of Loads Existing With PV Array D [psf]13 16 Lr [psf]20 0 S [psf]35 30 Maximum Gravity Loads: Existing With PV Array D + Lr [psf]33 16 ASCE 7-10, Section 2.4.1 D + S [psf]47 46 ASCE 7-10, Section 2.4.1 Maximum Gravity Load [psf]:47 46 Ratio Proposed Loading to Current Loading:96.6%OK The gravity loads in the area of the solar panels 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.