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Home My WebLink AboutMiscellaneous - 30 LEANNE DRIVE 4/30/2018m I 1e-- r Y T R E n 9 1 n E E R S VSE Project Number: U2246-0108-171 May 4, 2017 Boston Solar 55 Sixth Road Woburn, MA 0 1801 REFERENCE: Michael Lis Residence: 30 Leanne Drive, North Andover, MA 01845 Solar Array Installation To Whom It May Concern: We have reviewed the panel layout and photographs provided by Boston Solar 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. Design Parameters Code: Massachusetts State Residential Code (780 CMR Chapter 51, 8th Edition (2009 IBQ Occupancy Category: II Design wind speed: 100 mph (3 -sec gust) per ASCE 7-05 Wind exposure category: C Ground snow load: 50 psf Existine Roof Structure Roof Framing and Material: Per plans prepared for Michael Lis (Dated 05/01/17) Connection to Roof Mounting connection: (1) 5/16" lag screw w/ min. 2.25" embedment at max. 5 1 " O.C. Use (4) #10 wood screws at rail ends as required. Racking system: Unirac 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 Massachusetts State Building Code (780 CMR Chapter 16, 8th Edition (2009 IBQ 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: U2246-0108-171 Michael Lis Residence TR 5/4/2017 E NY nsin E E R S 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 51" maximum. Because lateral loads are increasing by less than 10%, the installation of the solar panels meets the requirements in Section 3403.4 of the Massachusetts State Building Code (780 CMR Chapter 16, 8th Edition (2009 IBQ and the structure is permitted to remain unaltered. Any non-structural changes to the plans will not affect the conclusions of this letter. Limitations Installation of the solar panels must be performed in accordance with manufacturer recomendations. 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 05/04/2017 Roger Alworth, P.E. MA License: 47740 - Expires: 06/30/2018 Principal Enclosures RTA/tirn 651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com JOB NO.: U2246-0108-171 TSUBJECT: WIND PRESSURE E Y nr=in E E R S PROJECT: Michael Lis Residence 1components and Cladding Wind Calculations Label: ISolar Panel Array Note: Calculations per ASCE 7-05 SITE-SPECIFIC WIND PARAMETERS: Basic Wind Speed [mph]: 100 Notes: Exposure Category: C Occupancy Category: 11 Importance Factor, 1: 1.0 ADDITIONAL INPUT & CALCULATIONS: Height of Roof, h [ft]: � 25 - (Approximate) Comp/Cladding Location: Gable Roofs 27* < 0:5 45* Enclosure Classification: Enclosed Buildings Zone 1 GCP:: 1.0 Figure 6-11 D (enter largest abs. value) Zone 2 GCP 1.2 (enter largest abs. value) Zone 3 GCP: i� 1.2 (enter largest abs. value) a: 9.5 Table 6-2 zg MI.: 900 Table 6-2 Kh: 0.95 Table 6-3 K,t: 1 Equation 6-3 Kd: 0.85 Table 6-4 Velocity Pressure, qh [Psfl: 20.6 Equation 6-15 GCpi: 0 Figure 6-5 (largest abs. value) OUTPUT: I p---':qh[(GCP)—(GCPj)jj Equation6-4 Zone 1 Pressure, p [psfl: 20.6 psf (1.0 W, Interior Zones*) Zone 2 Pressure, p [psfl: 24.7 psf (1.0 W, End Zones*) Zone 3 Pressure, p [psfl: 24.7 psf (1.0 W, Corner Zones* within a) (a= 3 ft) 14 JOB NO.: U2246-0108-171 TSUBJECT: CONNECTION E NY n G i n E E R S PROJECT: Michael Lis Residence Lag Screw Connection Capacity: Demand: Lag Screw Size [in]: 5/16 Cd: 1.6 NDS Table 2.3.2 Pressure Max Max. Trib. Max. Uplift (1.0 Wind) Spacing Area Embedment [in]: 2.25 (psf) (ft) (ft) Force (Ibs) Grade: SPF (G = 0.42) Zone Capacity [lbs/in]: 205 NDS Table 12.2A 1 20.6 4.3 11.7 240 Number of Screws: 1 2 24.7 4.3 11.7 288 Prying Coefficient: 1.4 3 24.7 3.1 8.6 212 Total Capacity [lbs]: 527 Demand< Capacity: CONNECTION OKAY T E NY nei n E=- E R S PROJECT: Michael Lis Residence CALCULATE ESTIMATED GRAVITY LOADS DEAD LOAD (D) Roof Pitch/12 Composite Shingles 1/2" Plywood Framing Insulation 1/2" Gypsum CIg. M, E & Misc JOB NO.: U2246-0108-171 SUBJECT: GRAVITY LOADS Increase due to Original pitch loading 2.4 8.1 1.2 34 3.0 psf 0.0 psf 0.0 psf 0.0 psf DL 7 psf PV Array DL 3 psf 1.21 2.0 psf 1.21 1.0 psf ROOF LIVE LOAD (Lr) Existing Design Roof Live Load [psf] 20 JASCE 7-05, Table 4-1 Roof Live Load With PV Array [psfl 0 w/ Solar Panel SNOW LOAD (S): Existing Array Snow Ground Load, pg [psfl: Roof Slope [*]: Snow Ground Load, pg [psfl: Terrain Category: Exposure of Roof: Exposure Factor, C,: Thermal Factor, Ct: Risk Category: Importance Factor, 1,: Flat Roof Snow Load, pf [psfl: Minimum Roof Snow Load, pm [psfl: Unobstructed Slippery Surface? Slope Factor Figure: Roof Slope Factor, Cs: Sloped Roof Snow Load, pr, [psfl: Design Snow Load, S [psfl: 8.1 8.1 34 34 50 50 C C Fully Exposed Fully Exposed 0.9 0.9 1.1 1.1 11 11 1.0 1.0 35 35 0 0 No Yes Figure 7-2b Figure 7-2b 1.00 0.60 35 21 35 21 ASCE 7-05, Section 7.2 ASCE 7-05, Table 7-2 ASCE 7-05, Table 7-2 ASCE 7-05, Table 7-2 ASCE 7-05, Table 7-3 ASCE 7-05, Table 1-1 ASCE 7-05, Table 7-4 ASCE 7-05, Equation 7-1 ASCE 7-05, Section 7.3.4 ASCE 7-05, Section 7.4 ASCE 7-05, Section 7.4 ASCE 7-05, Figure 7-2 ASCE 7-05, Equation 7-2 T E n s i n E E R 8 PROJECT: Michael Lis Residence Summary of Loads Maximum Gravity Loads: JOB NO.: U2246-0108-171 SUBJECT: LOAD COMPARISON Existing With PV Array D [psfl 7 10 Lr [psfl 20 0 S 1pfsq 35 21 Existing With PV Array D + Lr [psfl 27 10 ASCE 7-05, Section 2.4.1 D + S [psfl 41 30 ASCE 7-05, Section 2.4.1 Maximum Gravity Load [psfl:1 41 1 3 Ratio Proposed Loading to Current Loading: 1 74% 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 Massachusetts State Building Code (780 CMR Chapter 16, Sth Edition (2009 IBC)) are met and the structure is permitted to remain unaltered.