HomeMy WebLinkAboutSTRUCTURAL LETTER - 23-00159 - 1000 Westwood Dr - Solar PanelsDate: 4 April 2023
Big Dog Solar Energy
620 Pheasant Ridge Dr
Chubbuck, ID 83202
Jonathon Egan Residence: 1000 Westwood Dr, Rexburg, ID 83440
Dear Sir/ Madam,
Conclusion
Structural Letter of Approval
Terra Engineering Consulting (TEC) has performed a structural analysis for the existing roof
based on the existing and proposed load conditions, and determined that the structure can
support the additional weight of the proposed solar panel system. The attached calculations are
based off the assumptions that the existing structural components are in good condition and that
they meet industry standards. The existing structure information is assumed based on the survey
and information provided by the client. The design information and assumptions that the
calculations are based off are located in the attached References page. The design of the solar
panel’s mounting hardware is to be provided by others.
This engineering analysis was performed in accordance with ASCE 7-16 and 2018 IBC/IRC
design methods. The total additional roof load of the solar panels system is 3 psf, and the typical
20 psf live load will not be present in the area of the panels, as defined per Section 1607.13.5.1
in 2018 IBC. The structural evaluation shows that existing framing is able to withstand the
additional load while meeting current standards, allowing the structure to remain unaltered; see
calculations and span table attached. Regarding lateral wind loads, the solar panel structure is
considered to be partially enclosed due to the low profile of the panels (3 to 6 inches) and
airflow restrictions below the panels caused by the pv frame, wiring, conduit, and frame
brackets. Because the system is considered to be 'partially enclosed' additional wind pressure on
the structure is considered negligible. The addition of total PV system weight result in an
increase under 10% of the total roof weight, and meets the seismic requirements in Section 502.5
of 2018 IEBC. See the attached calculations for further details.
TEC concludes that the installation of solar panels on existing roof will not affect the structure,
and allows it to remain unaltered under the applicable design standards. The calculations
performed to support these conclusions are attached to this letter.
1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204
General Instructions
2. Contractor shall keep an accurate set of As-Built plans
Best Regards,
Terra Engineering Consulting, PLLC
Ahmad Alshakargi, PE
Civil Engineer
1. Contractor shall comply with all Federal, State, County, City, local and OSHA
mandated regulations and requirements. The most stringent shall govern.
3. The solar panel's racking system and mounting hardware shall be mounted in
accordance with the manufacturer's most recent installation manual.
4. Connection: 5/16'' lag screws 2.5'' minimum penetration at 48'' maximum spacing.
5. Panel supports connections shall be staggered to distribute load to adjacent
trusses.
6. If during solar panel installation, the roof framing members appear unstable or
deflect non-uniformly, our office should be notified before proceeding with the
installation.
7. Structural observation or construction inspections will not be performed by TEC,
Engineer-of-Record (EOR) nor their representatives.
4/4/2023
1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204
References
Design Parameter
Risk Category: II
Ground Snow load: 50 psf
Roof Snow load: 35 psf
Design Wind Speed: 115 mph (3 sec gust) per ASCE 7-16
Seismic Design Category: D
Wind Exposure Category: C
Existing Roof Structure
Roof framing: 2x4 Pre-fab Trusses at 24” O.C.
Roof material: Metal seam
Roof slope: 15°
Solar Panels
Weight: 3 psf
Code: 2018 International Building Code/ International Existing Building Code, ASCE 7-16, and
National Design Specification for Wood Construction (NDS) 2015 Edition
1863 GOLDENROD WAY / NORTH SARATOGA SPRINGS, UT 84045 / T (801)-616-6204
Date:4/4/2023
Client:Jonathon Egan
Subject:Gravity load
Gravity load calculations
Snow load (S)Existing w/ solar panels
Roof slope (°):15 15
Ground snow load, pg (psf):50 50 ASCE 7-16 C7.2
Terrain category:C C ASCE 7-16 table 7.3-1
Exposure of roof:Fully exposed Fully exposed ASCE 7-16 table 7.3-1
Exposure factor, Ce:0.9 0.9 ASCE 7-16 table 7.3-1
Thermal factor, Ct:1.1 1.1 ASCE 7-16 table 7.3-2
Risk Category:II II ASCE 7-16 table 1.5-1
Importance Factor, Is:1 1 ASCE 7-16 table 1.5-2
Flat roof snow load, pf (psf):35.0 35.0 ASCE 7-16, equation 7.3-1
Minimum roof snow load, pm (psf):0 0 ASCE 7-16, equation 7.3-4
Roof Surface type:
Unobstructed
Slippery surface
Unobstructed
slippery surface ASCE 7-16, C7.4
Roof slope factor, Cs:0.92 0.92 ASCE 7-16, C7.4
Sloped roof snow load, ps [psf]:32.2 32.2
Roof dead load (D)
Roof pitch/12 3.2
Metal seam 0.8 psf 1/2" Gypsum clg.0 psf
1/2" plywood 1 psf insulation 0.8 psf
Framing 3 psf M, E & Misc 1.5 psf
Roof DL without PV
arrays 7.4 psf
PV Array DL 3 psf
Roof live load (Lr)Existing w/ solar panels
Roof Live Load 20 0 2018 IBC, Section 1607.13.5.1
ASD Load combination:
Existing With PV array
D [psf]7.4 10.4 ASCE 7-16, Section 2.4.1
D+L [psf]7.4 10.4 ASCE 7-16, Section 2.4.1
D+[Lr or S or R] [psf]39.6 42.6 ASCE 7-16, Section 2.4.1
31.6 34.6 ASCE 7-16, Section 2.4.1
Maximum gravity load [psf]:39.6 42.6
Max Applied Load (2x4 Pre-fab trusses at 24" o.c. 3.2/12 pitch, 32' span)42.6 psf
Max Allowable Load (2x4 Pre-fab trusses at 24" o.c. 3/12 pitch, 34' span)55 psf OK
See attached span table
ASCE 7-16, equation 7.4-1 Design
Snow Load (S)
D+0.75L+0.75[Lr or S or R] [psf]
Date:4/4/2023
Client:Jonathon Egan
Subject:
Wind Pressure Calculations
Basic wind speed (mph)115
Risk category II
Exposure category C
Roof type Gable
Figure for GCp values ASCE 7-16 Figure 30.3-2A-I
Zone 1 Zone 2 Zone 3
GCp (neg)-0.9 -1.7 -2.6
GCp (pos)0.5 0.5 0.5
zg (ft)900 (ASCE 7-16 Table 26.11-1)
α 9.5 (ASCE 7-16 Table 26.11-1)
Kzt 1 (ASCE 7-16 Equation 26.8-1)
Kh 0.94 (ASCE 7-6 Table 26.10-1)
Kd 0.85 (ASCE 7-16 Table 26.6-1)
Velocity Pressure,qh (psf)27.05 (ASCE 7-16 Equation 26.10-1)
Gcpi 0 (ASCE 7-16 Table 26.13-1)(0 for enclosed buildings)
Zone 1 Zone 2 Zone 3
W Pressure, (neg) [psf]-24.35 -45.99 -70.33
W Pressure, (pos) [psf]13.53 13.53 13.53
W Pressure, (Abs. max) [psf]24.35 45.99 70.33
Connection Calculations Lag screw diameter:5/16
Capacity
Connection type:Lag screw
Embedment (in):2.5
Framing grade:DFL#2 G:0.5
Capacity [lbs/in]:266 (2015 NDS table 12.2A)
Number of screws:1
Total capacity [lbs]:665.00
Demand
Anchor spacing:48 in
Anchor spacing in roof corners:48 in
Zone
( 0.6 W
Pressure,
psf), see
Note 1
Max.
tributary
area (ft^2)Max Uplift force (lbs)
1 14.6 11 160.7
2 27.6 11 303.5
3 42.2 11 464.2
(only changes if structure located
on a hill or ridge)
Connection Meets Demand
Wind load and
Connection
Note 1: 0.6W results from dominant ASD combo [0.6D+ 0.6W] (ASCE 7-16 2.4.1).
Roof Truss Span Tables
15Alpine Engineered Products
Top Chord 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6
Bottom Chord 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6
2/12 24 24 33 27 27 37 31 31 43 33 33 46
2.5/12 29 29 39 33 33 45 37 38 52 39 40 55
3/12 34 34 46 37 39 53 40 44 60 43 46 64
3.5/12 39 39 53 41 44 61 44 50 65 47 52 70
4/12 41 43 59 43 49 64 46 56 69 49 57 74
5/12 44 52 67* 46 58 69* 49 66 74* 53 66 80*
6/12 46 60* 69* 47 67* 71* 51 74* 76* 55 74* 82*
7/12 47 67* 70* 48* 72* 72* 52* 77* 77* 56* 80* 83*
2/12 24 24 33 25 27 38 27 31 41 29 32 44
2.5/12 28 29 40 29 32 43 31 37 46 33 37 49
3/12 30 33 45 31 37 47 34 42 50 36 42 54
3.5/12 33 37 49* 34 41 51* 36 46 54* 39 46 58*
4/12 35 41 52* 36 45* 54* 39 50* 58* 42* 49* 62*
‡ Other pitch combinations available with these spans
For Example, a 5/12 - 2/12 combination has approx. the same allowable span as a 6/12 - 3/12
Top Chord 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6 2x4 2x6 2x6
Bottom Chord 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6 2x4 2x4 2x6
16" 23 24 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 § 25 §
18" 25 27 28 27 27 29 § 29 § 29 § 29 § 29 § 29 § 29 §
20" 27 28 30 28 28 32 31 30 33 § 32 31 33 §
24" 29 30 33 31 31 35 34 33 38 35 34 40
28" 32 32 36 34 33 39 37 36 42 38 37 44
30" 33 33 38 35 35 40 38 37 44 40 39 45
32" 34 34 39 36 36 42 39 39 45 41 40 47
36" 36 36 42 39 38 45 42 41 48 43 43 50
42" 39 39 45 41 41 48 44 44 52 45 46 54
48" 40 42 49 43 44 52 46 47 56 46 49 58
60" 44 47 55 46 49 58 48 53 63 49 55 65
72" 45 51 60 48 54 64 51 57 68 51 59 69
§ = Span Limited by length to depth ratio of 24
Pitch
Depth
Spans in feet to out of bearing
Spans in feet to out of bearing
5/12 38* 47* 57* 39* 51* 59* 42* 56* 63* 45* 54* 68*
6/12 - 2/12 ‡ 40 43 59* 42 49 62* 45 56* 66 48 57* 71*
6/12 - 2.5/12 ‡ 37 38 52 38 44 57* 41 50 61* 44 52 66*
6/12 - 3/12 ‡ 33 33 45 35 38 52 38 43 56* 40 46 60*
6/12 - 3.5/12 ‡ 28 28 38 32 32 44 34 37 50 36 39 54
6/12 - 4/12 ‡ 22 22 31 26 26 36 30 30 41 32 32 44
Alpine truss designs are
engineered to meet specific
span, configuration and load
conditions. The shapes and
spans shown here represent
only a fraction of the
millions of designs produced
by Alpine engineers.
Total load(PSF)
Duration factor
Live load(PSF)
Roof type
55
1.15
40 snow
shingle
55
1.15
30 snow
tile
47
1.15
30 snow
shingle
40
1.15
20 snow
shingle
40
1.25
20 **
shingle
**construction
or rain,
not snow load
55
1.15
40 snow
47
1.15
30 snow
40
1.15
20 snow
40
1.25
20 rain or constn.
Total load(PSF)
Duration factor
Live load(PSF)
NOTES:These overall spans are based on NDS
‘01 with 4" nominal bearing each end, 24" o.c.
spacing, a live load deflection limited to L/240
maximum and use lumber properties as follows:
2x4f =2000psif=1100psiE=1.8x10 2x6f =1750
psi f=950 psi f =1900 psi E=1.8x10 . Allowable
spans for 2x4 top chord trusses using sheathing
other than plywood (e.g. spaced sheathing or 1x
boards) may be reduced slightly. Trusses must
be designed for any special loading such as
concentrated loads from hanging partitions or air
conditioning units, and snow loads caused by
driftingnearparapetorslide-offfromhigherroofs.
To achieve maximum indicated spans, trusses
may require six or more panels. Trusses with an
asterisk (*) that exceed 14' in height may be
shipped in two pieces. Contact your local Alpine
trussmanufacturerorofficeformoreinformation.
bt b
tc
6
6
Common --Truss configurations for the
most widely designed roof shapes.
Mono --Used where the roof is required to
slope only in one direction. Also in pairs
with their high ends abutting on
extremely long spans with a
support underneath
the high end.
Scissors --Provides a cathedral or
vaulted ceiling. Most economical when the
difference in slope between the top and
bottom chords is at least 3/12 or the bottom
chord pitch is no more than half the top chord
pitch.
Flat --The most economical flat truss for a
roof is provided when the depth of the truss in
inches is approximately equal to 7% of the
span in inches.