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Home My WebLink AboutENGINEER LETTER - 18-00147 - 2360 W 960 S - Solar Array___________________________________________________________________________________________ Domus Structural Engineering, LLC P.O. Box 6986 Broomfield, CO 80021 530‐864‐7055 Domusstructural@gmail.com To: Blue Raven Solar 1220 S. 630 E. Ste. 430 American Fork, UT. 84003 Subject: Certification Letter Milner Residence 2360 West 960 South Rexburg, ID. 80537 To Whom It May Concern, Design Criteria: ● Applicable Codes = 2012 IBC/IRC, ASCE 7‐10, and NDS‐12 ● Roof Dead Load = 7 psf (MP1) ● Roof Live Load = 20 psf ● Wind Speed = 115 mph, Exposure C, Risk Category II ● ● Attachments: (1) 5/16" dia lag screw with 2.5" min embedment depth, at spacing shown above. Sincerely, John Calvert, P.E. Project Engineer March 21, 2018 The roof structure of (MP1) consists of composition shingle on roof plywood that is supported by pre‐manufactured trusses that are spaced at @ 24"o.c.. The top chords, sloped at 27 degrees, are 2x4 sections, the bottom chords are 2x4 sections and the web members are 2x4 sections. The truss members are connected by steel gusset plates. The max unsupported projected horizontal top chord span is approximately 6'‐3''. The existing roof framing system of (MP1) is judged to be adequate to withstand the loading imposed by the installation of the solar panels. No reinforcement is necessary. Ground Snow Load = 50 psf ‐ Roof Snow Load = 35 psf The spacing of the solar standoffs should be kept at 48" o.c. for landscape and 48" o.c. for portrait orientation, with a staggered pattern to ensure proper distribution of loads. A jobsite observation of the condition of the existing framing system was performed by an audit team of Blue Raven Solar as a request from Domus Structural Engineering. All review is based on these observations and the design criteria listed below and only deemed valid if provided information is true and accurate. On the above referenced project, the roof structural framing has been reviewed for additional loading due to the installation of the solar PV addition to the roof. The structural review only applys to the section of the roof that is directly supporting the solar PV system and its supporting elements. The observed roof framing is described below. If field conditions differ, contractor to notify engineer prior to starting construction. The scope of this report is strictly limited to an evaluation of the fastener attachment, underlying framing and supporting structure only. The attachment's to the existing structure are required to be in a staggered pattern to ensure proper distribution of loading. All panels, racking and hardware shall be installed per manufacturer specifications and within specified design limitations. All waterproofing shall be provided by the manufacturer. Domus Structural Engineering assumes no responsibility for misuse or improper installation of the solar PV panels or racking. Please contact me with any further questions or concerns regarding this project. Milner Residence, Rexburg, ID 1 ____________________________________________________________________________________ Domus Structural Engineering, LLC P.O. Box 6986 Broomfield, CO 80021 530‐864‐7055 Domusstructural@gmail.com 50 psf (ASCE7 - Eq 7-1) 1 (ASCE7 - Table 7-2) 1 (ASCE7 - Table 7-3) 1 35.0 psf (ASCE7 - Eq 7-2) 1 35.0 psf 3.0 psf 4.00 ft 2.67 ft 10.68 sft 32 lb 4.00 2.00 0.73 0.00 (Ceiling Not Vaulted) 0.27 7.0 psf 7.9 psf Gravity Loading PV System Weight Weight of PV System (Per Blue Raven Solar) X Standoff Spacing = Y Standoff Spacing = Note: PV standoffs are staggered to ensure proper distribution of loading 2x4 Top Chords @ 24"o.c. I = Importance Factor = Cs = Slope Factor = Standoff Tributary Area = ps = Cspf ps = Sloped Roof Snow Load = pf = Flat Roof Snow Load = Roof Snow Load Calculations pg = Ground Snow Load = Ce = Exposure Factor = pf = 0.7 Ce Ct I pg Ct = Thermal Factor = Roof Live Load = 20 psf Roof Plywood Roof Dead Load (MP1) Composition Shingle Note: Roof live load is removed in area's covered by PV array. DL Adjusted to 27 Degree Slope Point Loads of Standoffs Miscellaneous Vaulted Ceiling Total Roof DL (MP1) PV Dead Load = 3 psf (Per Blue Raven Solar) Milner Residence, Rexburg, ID 2 ___________________________________________________________________________________________ Domus Structural Engineering, LLC P.O. Box 6986 Broomfield, CO 80021 530‐864‐7055 Domusstructural@gmail.com 115 mph C Gable/Hip 27 degrees 20 ft 19.3 ft (Eq. 30.3-1) 0.9 (Table 30.3-1) 1 (Fig. 26.8-1) 0.85 (Table 26.6-1) 115 mph (Fig. 26.5-1A) II (Table 1.5-1) qh = 25.90 15.54 Zone 1 Zone 2 Zone 3 Positive GCp = -0.86 -1.51 -2.37 0.42 (Fig. 30.4-1) Uplift Pressure = -13.40 psf -23.47 psf -36.86 psf 11.0 psf X Standoff Spacing = 4.00 4.00 2.67 Y Standoff Spacing = 2.67 2.67 2.67 Tributary Area = 10.68 10.68 7.12 Footing Uplift = -143 lb -251 lb -262 lb Zone 1 Zone 2 Zone 3 Positive GCp = -0.86 -1.51 -2.37 0.42 (Fig. 30.4-1) Uplift Pressure = -13.40 psf -23.47 psf -36.86 psf 10.0 psf (Minimum) X Standoff Spacing = 4.00 4.00 2.67 Y Standoff Spacing = 1.67 1.67 1.67 Tributary Area = 6.68 6.68 4.45 Footing Uplift = -89 lb -157 lb -164 lb -262 lb 450 lb Therefore, OK Fastener =1 - 5/16" dia Lag Number of Fasteners = 1 Embedment Depth = 2.5 Pullout Capacity Per Inch = 250 lb Fastener Capacity = 625 lb w/ F.S. of 1.5 & DOL of 1.6= 667 lb Therefore, OK Wind Calculations Maximum Design Uplift = Standoff Uplift Capacity = 450 lb capacity > 262 lb demand Fastener Capacity Check Standoff Uplift Check Kz (Exposure Coefficient) = Kzt (topographic factor) = Kd (Wind Directionality Factor) = V (Design Wind Speed) = Risk Category = qh = 0.00256 * Kz * Kzt * Kd * V^2 Wind Pressure P = qh*G*Cn Exposure Category Per ASCE 7‐10 Components and Cladding Mean Roof Height Roof Slope 667.2 lb capacity > 262 lb demand 0.6 * qh = Standoff Uplift Calculations-Landscape Input Variables Wind Speed Effective Wind Area Design Wind Pressure Calculations Roof Shape Standoff Uplift Calculations-Portrait Milner Residence, Rexburg, ID 3 ___________________________________________________________________________________________ Domus Structural Engineering, LLC P.O. Box 6986 Broomfield, CO 80021 530‐864‐7055 Domusstructural@gmail.com (MP1)PASS Dead Load 7.9 psf PV Load 3.0 psf Snow Load 35.0 psf Governing Load Combo = DL + SL Total Load 45.9 psf Fb (psi) = f'b x Cd x Cf x Cr (NDS Table 4.3.1) 900 x 1.15 x 1.5 x 1.15 Allowed Bending Stress = 1785.3 psi (wL^2) / 8 = 447.815 ft# = 5373.78 in# Actual Bending Stress = (Maximum Moment) / S = 1754.8 psi L/180 (E = 1600000 psi Per NDS) = 0.416 in Deflection Criteria Based on = (w*L^4) / (185*E*I) = = L/491 > L/180 Therefore OK Allowed Deflection (Live Load) =L/240 0.312 in (w*L^4) / (185*E*I) L/642 > L/240 Therefore OK Member Area = Fv (psi) = 180 psi (NDS Table 4A) Allowed Shear = Fv * A = Max Shear (V) = w * L / 2 = 287 lb Framing Check 2x4 Top Chords @ 24"o.c. Member Span = 6' - 3" 5.3 in^2 Check Shear w = 92 plf (True Dimensions) 945 lb Allowed > Actual -- 30.4% Stressed -- Therefore, OK DF#2 Member Spacing @ 24"o.c. Maximum Moment = Check Deflection I (in^4) 5.36 Lumber Sp/Gr Actual Deflection (Live Load) = Allowed Deflection (Total Load) = Actual Deflection (Total Load) = Allowed > Actual -- 98.3% Stressed -- Therefore, OK Member Properties Member Size 2x4 S (in^3) 3.06 0.117 in Check Bending Stress Continuous Span 0.153 in Milner Residence, Rexburg, ID 4 ___________________________________________________________________________________________ _ Domus Structural Engineering, LLC P.O. Box 6986 Broomfield, CO 80021 530‐864‐7055 Domusstructural@gmail.com Level Area Weight (psf) Weight (lb) Roof 2413 sf 7.9 psf 18957 lb Ceiling 2413 sf 6.0 psf 14478 lb Wood Siding 150 ft 5.0 psf 3000 lb (8'-0" Wall Height) Int. Walls 150 ft 6.4 psf 3840 lb 40275 lb 3.0 psf 405 sf 1215 lb 4028 lb 1215 lb 3.0% Lateral Check 4028 lb > 1215 lb, Therefore OK Per 2012 IBC Chapter 34 Existing Weight of Effected Building Existing Weight of Effected Building Proposed Weight of PV System Weight of PV System (Per Blue Raven Solar) Approx. Area of Proposed PV System Approximate Total Weight of PV System 10% Comparison 10% of Existing Building Weight (Allowed) Approximate Weight of PV System (Actual) Percent Increase Milner Residence, Rexburg, ID 5