HomeMy WebLinkAboutENGINEER LETTER - 19-00347 - 1093 Arctic Willow Dr - Solar PanelsVSE Project Number: U2238-0290-191
June 28, 2019
Big Dog Energy
620 Pheasant Ridge Drive
Chubbick, ID 83202
REFERENCE: Kelly Thompson Residence: 1093 Arctic Willow Drive, Rexburg, ID 83440
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 Parameters
Code: International Building Code, 2012 Edition
Risk Category: II
Design wind speed: 115 mph (3-sec gust) per ASCE 7-10
Wind exposure category: C
Ground snow load: 50 psf
Existing Roof Structure
Roof structure: 2x4 manufactured trusses @ 24" O.C.
Roofing material: composite shingles
Roof pitch: 6:12
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.The member forces in the area of
the solar panels are not increased by more than 5%;thus,the stresses of the structural elements are not increased by more
than 5%.Therefore,the requirements of Section 3403.3 of the 2012 IBC are met and the structure is permitted to remain
unaltered.
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 connections to the existing roof shall be spaced at 48"maximum.Regarding seismic loads,we conclude that any
additional forces will be small.With an assumed roof dead load of 10 psf,solar array dead load of 3 psf,and affected roof
area of 33%(maximum),the additional dead load (and consequential seismic load)will be 9.6%.This calculation
conservatively neglects wall weight.Because the increase in lateral forces is less than 10%,this addition meets the
requirements of the exception in Section 3403.4 of the 2012 IBC.Thus the existing lateral force resisting system 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: U2238-0290-191
Kelly Thompson Residence
6/28/2019
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 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.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 is 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.),the connection of the
racking to the roof and 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
ID Firm License: C2269
06/28/2019
_______________________________________________________
Wells Holmes, P.E.
ID License: P-12264 - Expires: 10/31/2019
Project Engineer
Enclosures
WLH/0
06/28/2019
651 W. Galena Park Blvd., Ste. 101 / Draper, UT 84020 / T (801) 990-1775 / F (801) 990-1776 / www.vectorse.com
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U2238-0290-191
SUBJECT:GRAVITY LOADS
PROJECT:Kelly Thompson Residence
CALCULATE ESTIMATED GRAVITY LOADS
ROOF DEAD LOAD (D)
Increase due to
pitch
Original
loading
Roof Pitch/12 6.0
Composite Shingles 2.2 1.12 2.0 psf
1/2" Plywood 1.1 1.12 1.0 psf
Framing 3.0 psf
Insulation 0.5 psf
1/2" Gypsum Clg.2.0 psf
M, E & Misc 1.5 psf
DL 10 psf
PV Array DL 3 psf
ROOF LIVE LOAD (Lr)
Existing Design Roof Live Load [psf]20 ASCE 7-10, Table 4-1
Roof Live Load With PV Array [psf]0
SNOW LOAD (S):Existing
w/ Solar Panel
Array
Roof Slope [x:12]:6.0
Roof Slope [°]:27
Snow Ground Load, pg [psf]:50 ASCE 7-10, Section 7.2
Terrain Category:C ASCE 7-10, Table 7-2
Exposure of Roof:Fully Exposed ASCE 7-10, Table 7-2
Exposure Factor, Ce:0.9 ASCE 7-10, Table 7-2
Thermal Factor, Ct:1.1 ASCE 7-10, Table 7-3
Risk Category:II ASCE 7-10, Table 1.5-1
Importance Factor, Is:1.0 ASCE 7-10, Table 1.5-2
Flat Roof Snow Load, pf [psf]:35 ASCE 7-10, Equation 7.3-1
Minimum Roof Snow Load, pm [psf]:0 ASCE 7-10, Section 7.3.4
Unobstructed Slippery Surface?No ASCE 7-10, Section 7.4
Slope Factor Figure:Figure 7-2b ASCE 7-10, Section 7.4
Roof Slope Factor, Cs:1.00 ASCE 7-10, Figure 7-2
Sloped Roof Snow Load, ps [psf]:35 ASCE 7-10, Equation 7.4-1
Design Snow Load, S [psf]:3535
6.0
27
50
C
Fully Exposed
0.9
1.1
II
1.0
35
0
No
Figure 7-2b
1.00
35
JOB NO.:U2238-0290-191
SUBJECT:LOAD COMPARISON
PROJECT:Kelly Thompson Residence
Summary of Loads
Existing With PV Array
D [psf]10 13
Lr [psf]20 0
S [psf]35 35
Maximum Gravity Loads:
Existing With PV Array
(D + Lr) / Cd [psf]24 15 ASCE 7-10, Section 2.4.1
(D + S) / Cd [psf]39 42 ASCE 7-10, Section 2.4.1
Maximum Gravity Load [psf]:39 42
Maximum Member Forces:
LOCATION
GEOMETRY
Span(ft)30.2 (Approximate)
Solar Panel Array Start, a (ft)8.5 (Approximate)
Solar Panel Array Length, b (ft)8.7 (Approximate)
Truss/Rafter Spacing (ft)2.0
MEMBER FORCES
Existing With PV Array
Vertical Reaction, V1 (lbs)1181 1207 OK
Vertical Reaction, V2 (lbs)1181 1200 OK
Existing With PV Array
Moment @ Center, M (lbs-ft)8903 9182 OK
The member forces in the area of the solar array are not increased by more than 5%;
thus, the stresses of the structural elements are not increased by more than 5%.
Therefore, the requirements of Section 3403.3 of the 2012 IBC are met and the
structure is permitted to remain unaltered.
(Cd = Load Duration Factor = 0.9 for D, 1.15 for S, and 1.25 for Lr)
Ratio
House
103%
102%
102%
Ratio
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U2238-0290-191
SUBJECT:MEMBER FORCES
PROJECT:Kelly Thompson Residence
DESIGN LOADS:Load Types:Snow Live Dead
Existing Roof 35 20 10
Proposed PV Array 35 0 13
Label
Length 30.17 Existing Proposed Check
M (ft-lb)10239 10560 103%OK
Existing Proposed Check
V (lb)1358 1388 102%OK
Existing Loads
Cond
Roof
Trib (ft)
Add'l
Live
Load
(plf)
Add'l
Dead
Load
(plf)
Bm wt
(plf)wLL (plf)wDL (plf)
1 2.00 0 0 0 69.3 20.7
Proposed Loads (Distributed)
Cond
Dist to
Load
'a' (ft)
Length
of
Load
'b' (ft)
Δ wLL
(plf)
Δ wDL
(plf)
2 9 9 0.0 6.0
3 0 0 0.0 6.0
4 0 0 0.0 6.0
5 0.0 6.0
6 0.0 6.0
Proposed Loads as Point Loads
Cond
Dist 'a'
(ft)
Point
Live
Load
'PLL'
(lb)
Point
Dead
Load
'PDL'
(lb)
7
8
9
10
11
manufactured trusses
The member forces in the area of the solar panels are not increased by more than 5%; thus, the stresses of
the structural elements are not increased by more than 5%. Therefore, the requirements of Section 3403.3
of the 2012 IBC are met and the structure is permitted to remain unaltered.
0
2000
4000
6000
8000
10000
12000
0 5 10 15 20 25 30 35
MOMENT (FT-LB)
EXISTING PROPOSED
-2000
-1500
-1000
-500
0
500
1000
1500
2000
0 5 10 15 20 25 30 35
SHEAR (LB)
EXISTING PROPOSED
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
LOAD (LB)
EXISTING PROPOSED
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U2238-0290-191
SUBJECT:SOLAR LAYOUT
PROJECT:Kelly Thompson Residence
N
MT
R
MS
P
AC INV
SUB
115'