HomeMy WebLinkAboutENGINEERING LETTER - 19-00524 - 270 Baldwin Dr - Solar PanelsVSE Project Number: U2971-0006-191
August 27, 2019
DKD Energy
ATTENTION:
7500 Rialto Blvd. Bldg. #1 Suite #250
Austin, TX 78735
REFERENCE: Russell Daines Residence: 270 Baldwin 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, 2015 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
Seismic design category: D
Existing Roof Structure
Roof structure: 2x4 manufactured trusses @ 24" O.C.
Roofing material: asphalt shingles
Roof slope: 20°
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 (2015 IBC,Section 1607.12.5).
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 807.4 of the 2015 IEBC are met and the
structure 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: U2971-0006-191
Russell Daines Residence
8/27/2019
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 attached calculations verify the capacity of the connections of the solar array to the existing roof against wind (uplift),
the governing load case.The connections to the existing roof shall be spaced at 48"maximum.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 9.7%.Because the
increase in lateral forces is less than 10%,this addition meets the requirements of the exception in Section 807.5 of the 2015
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 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.),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
08/27/2019
_______________________________________________________
Trevor Hawkes, P.E.
ID License: 18683 - Expires: 12/31/2020
Project Engineer
Enclosures
TPH/ksc
08/27/2019
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.:U2971-0006-191
SUBJECT:GRAVITY LOADS
PROJECT:Russell Daines Residence
CALCULATE ESTIMATED GRAVITY LOADS
ROOF DEAD LOAD (D)
Increase due to
pitch
Original
loading
Roof Pitch/12 4.4
Asphalt Shingles 2.1 1.06 2.0 psf
1/2" Plywood 1.1 1.06 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 2015 IBC, Section 1607.12.5
SNOW LOAD (S):Existing
w/ Solar Panel
Array
Roof Slope [x:12]:4.4
Roof Slope [°]:20
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]:35 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]:35
Figure 7-2b
1.00
35
35
4.4
20
50
C
Fully Exposed
0.9
1.1
II
1.0
35
35
No
JOB NO.:U2971-0006-191
SUBJECT:LOAD COMPARISON
PROJECT:Russell Daines 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)39.8 (Approximate)
Solar Panel Array Start, a (ft)0.9 (Approximate)
Solar Panel Array Length, b (ft)15.5 (Approximate)
Truss/Rafter Spacing (ft)2.0
MEMBER FORCES
Existing With PV Array
Vertical Reaction, V1 (lbs)1563 1627 OK
Vertical Reaction, V2 (lbs)1563 1581 OK
Existing With PV Array
Moment @ Center, M (lbs-ft)15547 15899 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 807.4 of the 2015 IEBC 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
102%
104%
101%
Ratio
VECTOR STRUCTURAL ENGINEERS
JOB NO.:U2971-0006-191
SUBJECT:SOLAR LAYOUT
PROJECT:Russell Daines Residence