31B-112 39 Munroe SolarTo:Sunbug Solar
411A Highland Ave
Somerville, MA 02144
Subject:Structural Certification for Installation of Solar Panels
Lombard Residence
39 Munroe Street
Northampton, MA. 01060
To Whom It May Concern,
Design Criteria:
●Applicable Codes = Massachusetts Residential Code, 9th Edition, ASCE 7-12, and 2015 NDS
●Roof Dead Load = 8 psf (MP1 - barn) -- 12 psf (MP2 - main house)
●Roof Live Load = 20 psf
●Wind Speed = 117 mph, Exposure B
●
The spacing of the solar standoffs should be kept at 48" o.c..
I further certify that all applicable loads required by the codes and design criteria listed below were applied to the AEE
SnapNRack solar rail system and analyzed. Furthermore, the installation crews have been thoroughly trained to install
the solar panels based on the specific roof installation instructions developed by AEE SnapNRack for the racking system
and Sunmodo for the roof connections. Finally, I accept the certifications indicated by the solar panel manufacturer for
the ability of the panels to withstand high wind and snow loads.
January 24, 2019
A design check for the subject residence was done on the existing roofing and framing systems for the installation of
solar panels over the roof. From a field inspection of the property, the existing roof support structures were observed by
the client's auditors as follows:
The roof structure of (MP1 - barn) consists of composition shingle on 1x decking that is supported by true dimensioned
2x5 rafters @ 24"o.c. The rafters have a max projected horizontal span of 9'-0", with a slope of 30 degrees. The rafters
are butt joinsted at the ridge, and are supported at the eave by a load bearing wall. There are 2x4 collar ties @ 24"o.c.
for structural stability.
The roof structure of (MP2 - main house) consists of composition shingle on 1x decking that is supported by true
dimensioned 2x6 rafters @ 24"o.c.. The rafters support a vaulted ceiling and have a max projected horizontal span of 14'-
0", with a slope of 30 degrees. The rafters are supported at the ridge by a 2x8 continuous hip rafter and at the eave by a
load bearing wall. There is a knee wall that is approximately at the mid-span of the rafters to provide additional bracking
to the rafters.
The existing roof framing system of (MP1 - barn) is judged to be adequate to withstand the loading imposed by the
installation of the solar panels. No reinforcement is necessary.
The existing roof framing system of (MP2 - main house) is judged to be adequate to withstand the loading imposed by
the installation of the solar panels. No reinforcement is necessary.
Ground Snow Load = 40 psf - Roof Snow Load = 28 psf
Lombard Resisdence, Northampton 1
Sincerely,
Elaine Huang, P.E.
Project Engineer
Please contact me with any further questions or concerns regarding this project.
Lombard Resisdence, Northampton 2
40 psf
(ASCE7 - Eq 7-1)
1 (ASCE7 - Table 7-2)
1.1 (ASCE7 - Table 7-3)
1.1
35.0 psf
(ASCE7 - Eq 7-2)
0.8
28.0 psf
3.00
3.00
1.39
0.00 (Ceiling Not Vaulted)0.618.0 psf
9.2 psf
3.00
3.001.67
4.000.3312.0 psf
13.86
Gravity Loading
PV Dead Load = 4 psf (Per Sunbug Solar)
1x Decking
Vaulted Ceiling
2x5 Rafters @ 24"o.c.
2x6 Rafters @ 24"o.c.
MiscellaneousTotal Roof DL (MP2 - main house)
Total Roof DL (MP1 - barn)
Roof Dead Load (MP2 - main house)
Composition Shingle
DL Adjusted to 30 Degree Slope
DL Adjusted to 30 Degree Slope
Roof Snow Load Calculations
pg = Ground Snow Load =
Miscellaneous
1x Decking
Vaulted Ceiling
Ce = Exposure Factor =
pf = 0.7 Ce Ct I pg
Ct = Thermal Factor =
I = Importance Factor =
Cs = Slope Factor =
Roof Dead Load (MP1 - barn)
Composition Shingle
ps = Cspf
ps = Sloped Roof Snow Load =
pf = Flat Roof Snow Load =
Lombard Resisdence, Northampton 3
Per ASCE 7-12 Components and Cladding
117 mph
BGable/Hip30 degrees
20 ft40 ft
17.5 ft
(Eq_6-15)0.7 (Table 6-3)
1 (Fig. 6-4)0.85 (Table 6-4)
117 mph
1 (Table 6-1)qh = 20.85
Zone 1 Zone 2 Zone 3 Positive
GCp =-0.90 -1.10 -1.10 0.85 (Fig. 6-11)Uplift Pressure =-18.77 psf -22.94 psf -22.94 psf 17.7 psf
X Standoff Spacing =4.00 4.00 4.00
Y Standoff Spacing =2.75 2.75 2.75Tributary Area =11.00 11.00 11.00Footing Uplift =-206 lb -252 lb -252 lb
-252 lb
400 lb
Therefore, OK
Fastener =1 - 5/16" dia Lag
Number of Fasteners =1
Embedment Depth =2.5Pullout Capacity Per Inch =250 lb
Fastener Capacity =625 lbw/ F.S. of 1.5 =417 lbTherefore, OK
Wind Calulations
Input VariablesWind Speed
Effective Wind Area
Design Wind Pressure Calculations
Roof Shape
Building Least Width
Roof Slope
417 lb capacity > 252 lb demand
Maximum Design Uplift =
Standoff Uplift Capacity =
400 lb capacity > 252 lb demand
Fastener Capacity Check
Standoff Uplift Check
Kz (Exposure Coefficient) =
Kzt (topographic factor) = Kd (Wind Directionality Factor) =
V (Design Wind Speed) =
I Importance Factor =
qh = 0.00256 * Kz * Kzt * Kd * V^2 * IWind Pressure P = qh*(G*Cp)
Exposure Category
Mean Roof Height
Standoff Uplift Calculations
Lombard Resisdence, Northampton 4
PASS
Dead Load 9.2 psfPV Load 4.0 psf
Snow Load 28.0 psf
Governing Load Combo = DL + SLTotal Load 41.2 psf
Fb (psi) =f'b x Cd x Cf x Cr (NDS Table 4.3.1)975 x 1.15 x 1.3 x 1.15
Allowed Bending Stress = 1676.2 psi
(wL^2) / 8
=835.061 ft#
=10020.7 in#
Actual Bending Stress = (Maximum Moment) / S
= 1202.5 psi
L/180 (E = 1500000 psi Per NDS)=0.6 in
Deflection Criteria Based on =(5*w*L^4) / (384*E*I)=
=L/277 >L/180 Therefore OK
Allowed Deflection (Live Load) =L/240
0.45 in(5*w*L^4) / (384*E*I)
L/408 >L/240 Therefore OK
Member Area =Fv (psi) =150 psi (NDS Table 4A)Allowed Shear = Fv * A =Max Shear (V) = w * L / 2 =371 lb
Framing Check (MP1 - barn)
Simple Span
0.390 in
0.265 in
Member Properties
Member Size2x5 S (in^3)8.33 HF#1 Member Spacing@ 24"o.c.
Maximum Moment =
Check Deflection
I (in^4)20.83 Lumber Sp/Gr
Actual Deflection (Live Load) =
Allowed Deflection (Total Load) =
Actual Deflection (Total Load) =
Allowed > Actual -- 71.8% Stressed -- Therefore, OK
1500 lb
Allowed > Actual -- 24.8% Stressed -- Therefore, OK
10.0 in^2
Check Shear
w = 82 plf
(True Dimensions)
Check Bending Stress
2x5 Rafters @ 24"o.c.
Member Span = 9' - 0"
Lombard Resisdence, Northampton 5
PASS
Dead Load 13.9 psfPV Load 4.0 psf
Snow Load 28.0 psf
Governing Load Combo = DL + SLTotal Load 45.9 psf
Fb (psi) =f'b x Cd x Cf x Cr (NDS Table 4.3.1)1400 x 1.15 x 1.3 x 1.15
Allowed Bending Stress = 2406.9 psi
(wL^2) / 8
=2246.96 ft#
=26963.6 in#
Actual Bending Stress = (Maximum Moment) / S
= 2247 psi
L/180 (E = 1600000 psi Per NDS)=0.933 in
Deflection Criteria Based on =(w*L^4) / (185*E*I)=
=L/294 >L/180 Therefore OK
Allowed Deflection (Live Load) =L/240
0.7 in(w*L^4) / (185*E*I)
L/482 >L/240 Therefore OK
Member Area =Fv (psi) =150 psi (NDS Table 4A)Allowed Shear = Fv * A =Max Shear (V) = w * L / 2 =642 lb
Framing Check (MP2 - main house)
Continuous Span
0.349 in
0.572 in
1800 lb
Allowed > Actual -- 35.7% Stressed -- Therefore, OK
Check Bending Stress
Maximum Moment =
Allowed > Actual - 93.4% Stressed -- Therefore, OK Check Deflection
Allowed Deflection (Total Load) =
Actual Deflection (Total Load) =
Actual Deflection (Live Load) =
(True Dimensions)
w = 92 plf
2x6 Rafters @ 24"o.c.
Member Span = 14' - 0"
Member Properties
Member Size S (in^3)I (in^4)Lumber Sp/Gr Member Spacing2x612.00 36.00 HFSS @ 24"o.c.
Check Shear
12.0 in^2
Lombard Resisdence, Northampton 6