BPS417337 - CAROL CAHILLANE - CALCULATIONS - 10.31.24ENGINEER WAS RETAINED IN A LIMITED CAPACITY FOR THIS PROJECT. DESIGN IS BASED UPON INFORMATION PROVIDED BY THE CLIENT WHO IS SOLELY RESPONSIBLE FOR ACCURACY OF SAME. NO RESPONSIBILITY
AND/OR LIABILITY IS ASSUMED BY, OR IS TO BE ASSIGNED TO THE ENGINEER FOR ITEMS BEYOND THAT SHOWN ON THESE SHEETS.Project #: BPS417337October 31, 2024103A Millbury St. Auburn, MA 01501STRUCTURAL CALCULATIONSCahillane Residence Solar Module Addition336 Ryan Road, Florence, MA 01062LIMITATIONS
PROJECT NO.BPS417337PROJECTDATECahillane Residence Solar Module Addition10/31/2024SUBJECTBYGeneral InformationHKBuilding Code Conformance (Meets Or Exceeds Requirements)2021 International Building Code (IBC) w/ local ordinances2021 International Residential Code (IRC) w/ local ordinances2021 International Existing Building Code (IEBC) w/ local ordinancesASCE 7-10DESIGN PARAMETERS:Risk Category: IIWind Speed (3-Second Gust): 117 mphWind Exposure Category: CImportance Factor: 1.0Ground Snow Load: 40 psfFlat Roof Snow Load: 35 psfEXISTING ROOF STRUCTURE:Roof Structure: 2x6Framing Spacing:16" o.c.Roofing material: Composition ShinglesRoof Slope: 5/12LIMITATIONS:The following structural calculations enclosed pertain to the structural evaluation for the solar module addition to the existing structure located at the site referenced on the coversheet. The calculations presented are to determine the adequacy of the existing structure to support the proposed installation of solar modules and their attachment to the roof as shown on the module layout plan. The connection to the existing roof consists of mounting hardware tested and designed by SnapNrack solar mounting. The solar array will be mounted either flush or with variable tilt hardware as shown on the construction drawings (no more than 18" above the roof surface). Installation parallel to the roof surface is required in order to achieve a low tilt angle between the modules and the roof surface.Installation of the solar modules and any electrical equipment must be performed in accordance with the manufacturers recommendations and all work performed is to follow accepted industry-wide methods and applicable safety standards. The contractor is to notify the engineer of record should any damage, deterioration, or discrepancies between the as-built conditions of the structure and the conditions described in this letter are found. Connections to the existing roof framing must be staggered, except at array ends, so as not to overload any existing structural member. The use of the manufacturers anchor span tables are permitted where the building type, site conditions, site specific design parameters, and solar module orientation match the description of the span tables. The design of the solar module mounts, rails, etc. and any associated engineering with said systems is the responsibility of the manufacturer. Waterproofing around solar penetrations is also the responsibility of others. The engineer of record assumes no responsibility for the improper installation of any solar array.STRUCTURAL NARRATIVE:APPLICABLE CODES:
PROJECT NO.BPS417337PROJECTDATECahillane Residence Solar Module Addition10/31/2024SUBJECTBYComponants and Cladding Wind CalculationsHKRooftop Solar Wind PressureBased on the International Building Code and the ASCE 7-10Vult =117 mph Ultimate Wind Speed 3-Second Gust [Figures 26.5-1A, B, C, & D]IIRisk Category (I), (II), or (III and IV)[IBC Table 1604.5]CExposure Category[Section 26.7.3]z =20ftzg =900 ft Nominal Ht. of Atmospheric Boundary Layer [Table 26.11-1]α = 9.53-Sec. Gust-Speed Power Law Coefficient[Table 26.11-1]Kh =0.90 Velocity Pressure Exposure Coefficient [Table 26.10-1]Kzt =1.0 Topographic Factor [Figure 26.8-1]Kd =0.85 Wind Directionality Factor [Table 26.6-1]Roof Inputs:Roof type =GableSlope = >7 to 27Roof SlopeA =10sq. FtEffective area tributary to an individual anchor [Section 26.2]a =3ft[Section 26.3]GCPi =0.18 Internal Pressure Coefficient (±) [Table 26.11-1]Wind Zone =1 2 3GCP =0.91.72.6[Figure 30.4-2B]ANALYSISDesign Wind Velocity Pressure:[Equation 30.3-1]qh =26.9 PSF Velocity Pressure 1.0W (ULT)Design Solar Module Wind Pressure: Wind Zones =123P =29.0psf50.5psf74.7psfVelocity Pressure 1.0W (ULT)0.6P =17.4psf30.3psf44.8psfVelocity Pressure 0.6W (ASD)SOLAR MODULE ATTACHMENT CHECKSAnchor =2.67 ft Anchor SpacingLModule =74 in Length of ModuleDL = 2.8 psf Solar Dead LoadNumber of Screws = 1[Section 2.4.1]Tmax,1 =259lbsTmax,2 =235lbsTmax,3 =177lbsTpry =259lbsTallow = 530lbsResult = Pmin = 16.0psf (C & C minimum design wind load per Section 30.2.2.)0.6P = 44.8psf (Worst Case Wind Loading)OKNote:Minimum Design Wind Pressure:SAnchor /2 : Anchors at the edge of the array experience half of the tributary area compared to an anchor in the array interior.Connection is Adequate, Tpry < Tallow[0.6P - 0.6DL] * SAnchor /2 * LModule /2[0.6P - 0.6DL] * SAnchor * LModule [0.6P - 0.6DL] * SAnchor * LModule /2[Equation 30.4-1]DESIGN INPUTWidth of pressure coefficient zone[Negative pressure coefficients]Mean Roof Height
PROJECT NO.BPS417337PROJECTDATECahillane Residence Solar Module Addition10/31/2024SUBJECTBYGravity LoadsHKRooftop Solar AdditionBased on the International Building Code and Local Code OrdinancesMaterials:2.5x=2.72.3x=2.4Mechanical and Electrical = 0.5x=0.5Miscellaneous = 0.5x=0.51.4x=1.5=7.7psfDesign Solar Loads (psf):Module Weight =2.3 x=2.5Racking Weight =0.5 x=0.5=3.0psf10.8psfROOF LIVE LOAD (Lr)Existing Roof Live Load =20psfRoof Live Load = in Array Locations =0psfin Array Locations ROOF SNOW LOAD (SL)With Solar ArrayGround Snow Load (Pg, psf) =Min. Flat Roof Snow Load (Pf, psf) = Flat Roof Snow Load (Pf, psf) = Terrain Category = Exposure Factor (Ce) = Thermal Factor (Ct) = Importance Factor (Is) = Min. Roof Snow Load (Pm, psf) = Unobstructed Slippery Surface = Roof Slope = Slope Factor (Cs) = Sloped Roof Snow Load (Ps, psf) = Design Snow Load (SL, psf) = Composition Shingles =3/4" Plywood Sheathing =2x6 Rafters at 16" o.c. =ROOF DEAD LOADS (DL)0 0 [ASCE 7-10, Section 7.3.4]35 35 [Per local requirements]27.7 27.7 [ASCE 7-10, Equation 7.3-1]1.0 1.0 [ASCE 7-10, Table 1.5-2]1.1CNo Yes5/12 5/121.00 0.79 [ASCE 7-10, Figure 7-2]35.0 27.635.00.927.61.11.1[ASCE 7-10, Table 4-1][2021 IBC Section 1607.14.4.1]40 40 [ASCE 7-10, Section 7.2]ExistingΣ Solar Array LoadsΣ Total Roof Loads =Material Weight (psf):Load increase due to Roof Pitch:Design Roof Loads (psf):1.11.11.11.11.1Σ Existing Roof Load[ASCE 7-10, Equation 7.4-1][ASCE 7-10, Section 7.4][ASCE 7-10, Table 7-3]1.10.9 [ASCE 7-10, Table 7-2]C [ASCE 7-10, Table 7-2]Pf= 0.7(Ce)(Ct)(Is)(Pg)Ps = (Cs)(Pf)
PROJECT NO.BPS417337PROJECTDATECahillane Residence Solar Module Addition10/31/2024SUBJECTBYGravity LoadsHKRooftop Solar AdditionBased on the International Building Code and Local Code OrdinancesExisting Loads (psf)DL =7.7Lr =20SL =35(DL + Lr) / Cd22.2Cd = 1.25 (Roof Live Load)(DL + SL) / Cd37.2Cd = 1.15 (Roof Snow Load)Cd = 0.90 (Roof Dead Load)37.2psfpsfNew and Existing Design Load Ratio = RESULTSWorst Case Design Load = 33.490%Existing Structure is Adequate!12.0LOAD COMBINATIONS:33.4Based on this review the existing structure is adequate to support the proposed solar module installation. It can be concluded that any additional wind loading on the structure related to the addition of the proposed solar array is negligible due to the small distance between the roof surface and the top of the solar module. The capacity of the solar arrays connection to the existing roof structure against wind uplift, the governing load case, is adequate. Seismic loading is negligible due to the low seismic weight of the solar modules. The gravity loads and therefore bending stresses in the existing roof members will not be increased past the allowed 5% per 2021 IEBC section 502.4, due to the roof live load in the area of the solar array is either not present or greatly reduced per the 2021 IBC section 1607.14.4.1 exception. In areas where snow loading is present, the slope of the roof and glass surface of the solar module allows for a lower slope factor (ASCE 7-10) resulting in a reduced design snow load. Due to these reductions in the gravity loads the existing structure is allowed to remain unaltered. The increase in lateral forces from the solar addition are less than 10%, therefore as stated in the 2021 IEBC section 502.5, the existing lateral force resisting system also is permitted to remain unaltered.[2018 NDS Table 2.3.2]LOAD COMPARISONLoads With Solar (psf)10.8027.6