BLD2022-0248_Structural_Calculations_2.25.2022_2.02.18_PM_2703657nhEngineering Alliance, Inc
https://www.eng-alliance.com
15 February 2022
UNIRAC
1411 Broadway Blvd. NE
Albuquerque, NM 87102
REFERENCE: ROBERT BERNHOFT: 8219 TALBOT RD, EDMONDS, WA 98206 USA
Solar Array Installation
To Whom It May Concern:
Per your request, we have reviewed the existing structure at the above referenced site. The purpose of our review was to determine the
adequacy of the existing structure to support the proposed installation of solar panels on the roof as shown on the panel layout plan.
Based upon our review, we conclude that the existing structure is adequate to support the proposed solar panel installation.
Design Parameter
Code: International Building Code 2018 (IBC 2018)
Risk Category: II
Design wind speed: 98 MPH
Wind exposure category: B
Ground snow load: 25 PSF
Seismic design category: *null
Existing Roof Structure
Existing Roof Structure: RAFTERS 2"X4" @ 24" O.0
Roofing material: ASPHALT SHINGLES
Connection to Roof
Mounting connection: (1) 5/16 in lag screw w/ min. 2.5 in embedment into framing at max. 48 in o.c. along rails
(2) rails per row of panels, evenly spaced; panel length perpendicular to the rails not to exceed 67.8 in
Conclusions
Based upon our review, we conclude that the existing structure is adequate to support the proposed solar panel installation. In the area of
the solar array, other live loads will not be present or will be greatly reduced (2018 IBC, Section 1607.13.5). The glass surface of the solar
panels allows for a lower slope factor per ASCE 7, resulting in reduced design snow load on the panels. The gravity loads and; thus, the
stresses of the structural elements, in the area of the solar array are either decreased or increased by no more than 5%. Therefore, the
requirements of Section 503.3 of the 2018 IEBC are met and the structure is permitted to remain unaltered.
4603 April Meadow Way, Sugar Land, TX 77479. Ph: 832 865 4757
M:
J
Engineering Alliance, Inc
https://www.eng-aIIiance.com
The solar array will be flush -mounted (not more than 5 in 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. Regarding
seismic loads, we conclude that any additional forces will be small. Conservatively neglecting the weight of existing wall materials, the
installation of the solar panels represents an increase in the total weight (and resulting seismic load) of 1.57%. Because the increase in
lateral forces is less than 10%, this addition meets the requirements of the exception in Section 503.4 of the 2018 IEBC. Thus the existing
lateral force resisting system is permitted to remain unaltered.
Limitations
Installation of the solar panels must be performed in accordance with manufacturer recommendations. All work performed must be in
accordance with accepted industry -wide methods and applicable safety standards. The contractor must notify Engineering Alliance, Inc
should any damage, deterioration or discrepancies between the as -built condition of the structure and the condition described in this letter
be found. Connections to existing roof framing must be staggered, except at array ends, so as not to overload any existing structural
member. The use of solar panel support span tables provided by others are allowed only where the building type, site conditions, site -
specific design parameters, and solar panel configuration match the description of the span tables. The design of the solar panel racking
(mounts, rails, etc.) and electrical engineering is the responsibility of others. Waterproofing around the roof penetrations is the
responsibility of others. Engineering Alliance, Inc assumes no responsibility for improper installation of the solar array.
Engineering Alliance, Inc
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SS�ONAL
President and Lead Structural Engineer
Engineering Alliance, Inc 15-FEB-2022
Phone: 832 865 4757 EXP.:15-DEC-2023
4603 April Meadow Way, Sugar Land, TX 77479. Ph: 832 865 4757
--J
Engineering Alliance, Inc
Project:
ROBERT BERNHOFT
Location:
8219 TALBOT RD, EDMONDS, WA 98206 USA
Designer:
'A
I Date:
115 February 2022
Calculations per ASCE 7-16
International Building Code 2018 (IBC 2018)
ROOF DEAD LOAD (D):
Material
Design material
weight (psf)
Increase due
to pitch
Material weight
(psf)
ASPHALT SHINGLES
2.10
1.05
2
1/2" Plywood
1.1
1.05
1
Framing
3
3
Insulation
0.5
0.5
1/2" Gypsum Clg.
2.1
1.05
2
M, E & Misc
1.5
1.5
Total Dead Loadl
10.3
PV Array Dead Load
1 3.2
1.05
3
ROOF LIVE LOAD (1-0:
Existing Design Roof Live Load [psf] 20 ASCE 7-16, Table 4.3-1
Roof Live Load With PV Array [psf] 0 --d2018 IBC, Section 1607.13.5
SEISMIC LOAD, (E):
Risk category:
II
Seismic Design Category:
*null
IP:
1
Site Class:
D
RP:
1.5
SS:
1.311
SI:
0.465
ap:
1
z:
1
h:
1
z/h:
1
Fa:
1
F,,:
*null
SMs:
1.311
SMI:
*null
SDs:
0.874
SDI:
*null
Table 1.5-1
Table 11.6-2
Table 1.5-2
Table 13.6-1
Table 13.6-1
ft
ft
Table 11.4-1
Table 11.4-2
Eqs. 11.4-1
Eqs. 11.4-2
Eqs. 11.4-3
Eqs. 11.4-4
*See Sec. 11.4.8
--J
Engineering Alliance, Inc
Project:
ROBERT BERNHOFT
Location:
8219 TALBOT RD, EDMONDS, WA 98206 USA
Designer:
SA
I Date:
115 February 2022
SITE -SPECIFIC WIND PARAMETERS:
Basic Wind Speed [mph]:
98
Exposure Category:
B
Risk Category:
II
Height of Roof, h [ft]:
15
Roof Slope [°]:
18
Site Elevation [ft]:
49
Comp/Cladding Location:
Gable Roofs, 7° < 6
Enclosure Classification:
Enclosed Buildings
Zone 1, 2e
2.0
Zone 2n, 2r, 3e
3.0
Zone 3r
3.6
a:
7
zg [ft]
1200
Kh:
0.57
Ke:
1.00
KZt:
1
Kd:
0.85
Velocity Pressure, qh [psf]:
11.99
YE:
1.5
Ya:
0.8
PRESSURES:
Sec. 26.7.3
Table 1.5-1
(Approximate)
20' FIGURE_3032B
(enter largest abs. value)
(enter largest abs. value)
(enter largest abs. value)
Table 26.11-1
Table 26.11-1
Table 26.10-1
Table 26.9-1
Equation 26.8-1
Table 26.6-1
Equation 26.10-1
Figure 29.4-8
p = gh(GCp)(YE)(Ya) (Ib/ft) Equation 29.4-7
Zone 1, 2e : psf (1.0 W)
psf (1.0 W)
psf (1.0 W)
28.8
Zone 2n, 2r, 3e :
43.2
Zone 3r :
51.8
(a= 3 ft)
--J
Engineering Alliance, Inc
Project:
ROBERT BERNHOFT
Location:
8219 TALBOT RD, EDMONDS, WA 98206 USA
Designer:
'A
I Date:
115 February 2022
COMPARE WIND & SEISMIC LOADS FOR CONNECTION (1 Sq. Ft. Section)
Wind Load, W:
Wind pressure, p:
17.3
Height, h:
1
Width, w:
1
Fperp:
17.3
Seismic Load, E:
0.7 * FP,min:
0.551
0.7 * FP ,max:
2.937
0.7 * FP ,vert:
0.367
0.7 * FP ,long:
1.468
0.7*Fp ,perp:
0.803
Wind (uplift) Controls Connection Design
CHECK INCREASE IN OVERALL SEISMIC LOADS
CFICMIr•
Array Area (Sq. Ft.)
188.33
Roof Area (Sq. Ft.)
3518.3
Estimated Roof Dead Load
10.26
Solar Dead Load
3
Total Dead Load
10.42
Coverage
5.35
Addt'I Seismic Weight
1.57
psf (Zone 1: 0.6 W from wind pressure calculation)
Ft
I't
lb (Uplift)
lb
Equation 13.3-2
lb
Equation 13.3-3
lb
Sec 13.3.1.2
lb
Equation 13.3-1
lb (uplift)
psf
psf
psf
of solar coverage on the roof
OK
Conservatively neglecting the weight of existing wall materials, the installation of the solar panels represents an increase
in the total weight (and resulting seismic load) of 1.57%. Because the increase is less than 10%, this addition meets the
requirements of the exception in Section 503.4 of the 2018 IEBC. Thus the existing structure is permitted to remain
unaltered.
--J
Engineering Alliance, Inc
Lag Screw Connection
Project:
ROBERT BERNHOFT
Location:
8219 TALBOT RD, EDMONDS, WA 98206 USA
Designer:
'A
I Date:
115 February 2022
Tributary Length (in):1 67.8
Max Tributary Width (in): 1 48
Capacity:
Lag Screw Size[in] :
5/16
Cd:
1.6
Embedment' [in]:
2.5
Grade:
SPF (G = 0.42)
Capacity [Ibs/in]:
205
Number of Screws in tension:
1
Prying Coefficient:
1.4
Total Capacity [Ibs]:
586
Demand:
NDS Table 2.3.2
NDS Table 12.2A
Pressure
Max
Max. Trib.
Max. Trib.
Max. Uplift
Zone
(0.6 Wind)
Tributary
Length
Areal
Force (Ibs)
(psf)
Width (ft)
(ft)
(ft2)
Zone 1, 2e :
14.3
4.0
2.8
11.3
161
Zone 2n, 2r, 3e :
22.9
4.0
2.8
11.3
259
Zone 3r :1
28.1
4.0
1 2.8
1 11.3
1 317
Total Tension Force(lbs): 1 317
Demand< Capacity: 54.2%, OK
Notes
1. Embedment is measured from the top of the framing member to the beginning of the tapered tip of the lag screw.
Embedment in sheathing or other material is not effective. The length of the tapered tip is not part of the embedment
length.
2. 'Max. Trib Area' is the product of the 'Max. Tributary Width' (along the rails) and 1/2 the panel width/height
(perpendicular to the rails).
--J
Engineering Alliance, Inc
SNOW LOAD (S):
Project:
ROBERT BERNHOFT
Location:
8219 TALBOT RD, EDMONDS, WA 98206 USA
Designer:
'A
I Date:
115 February 2022
Existing
w/ Solar Panel
Array
Roof Slope [x:12]:
3.9
3.9
Roof Slope [°]:
18
18
Snow Ground Load, pg [psf]:
25
25
Surface Roughness Category:
B
B
Exposure of Roof:
Fully Exposed
Fully Exposed
Exposure Factor, Ce:
0.9
0.9
Thermal Factor, Ct:
1.1
1.1
Risk Category:
II
II
Importance Factor, Is:
1
1
Flat Roof Snow Load, pf [psf]:
17
17
Minimum Roof Snow Load, pm [psf]:
0
0
Unobstructed Slippery Surface?
NO
YES
Slope Factor Figure:
Figure 7-2b
Figure 7-2b
Roof Slope Factor, Cs:
1.00
0.87
Sloped Roof Snow Load, ps [psf]:
17
15
Design Snow Load, S [psf]:
17
15
Summary of Loads
D [psf]
Lr [psf]
S [psf]
Maximum Gravity Loads:
Existing
With PV Array
10
13
20
0
17
15
Existing
With PV Array
(D + Lr) / Cd [psf]
24
15
(D + S) / Cd [psf]
24
25
(Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr)
Maximum Gravity Load [psf]:1 24 1 25
Section 7.2
Sec. 26.7.2
Table 7.3-1
Table 7.3-1
Table 7.3-2
Table 1.5-1
Table 1.5-2
Equation 7.3-1
Section 7.3.4
Section 7.4
Section 7.4
Figure 7.4-1
Equation 7.4-1
4SCE 7-16, Section 2.4.1
4SCE 7-16, Section 2.4.1
Ratio Proposed Loading to Current Loading: 102% OK
The gravity loads and; thus, the stresses of the structural elements, in the area of the solar array are either decreased or increased
by no more than 5%. Therefore, the requirements of Section 503.3 of the 2018 IEBC are met and the structure is permitted to
remain unaltered.