BSOL2015-0033 Structural CalcsSTRUCTURAL NOTES: WIND RESISTANCE OF SUNPOWER
COMPOSITION MOUNTING SYSTEM P/N 1505-735
No. c020843
Document Number: 1507-586 Exp. sea 20n
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REV.
EO#
DESCRIPTION
DATE
AUTHOR
A
1186
RELEASE
3/11/08
A. Friesen
B
1407
Update IBC load combination
06.24.09
A. Friesen
C
8253
Minor Editorial Changes/Current Seal
.02.22.2010
A. Friesen
1507-586 Rev C
SUNPOWER CORPORATION, SYSTEMS
1414 Harbour Way South
Richmond,, CA
94804
PH; 510.540.0550
FAX: 510.540.0552
Page 1 of 10
02.22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540.0550
Richmond, CA 94804 USA www.Sunpowercorp.com F: 1.510.540.0552
I. INTRODUCTION
The SunPower Composition. Mounting System's mounting pad is, desigaed' primarily for connection of.PV modules
directly to roof sheathing, without the need for additional backing or blocking. The°mounts are to be placed
symmetrically from 3" to 12" from the ends, of each module along the long sides of the module.
This document is intended to provide background, rationale, and calculations supporting the,installation
requirements presented in the. SunPower Composition Mounting System mounting detail, of the,drawing,package.
The conclusion of these calculations is as follows:
1) In jurisdictions using the International Building Code' (IBC), the SunPower Composition Mounting System
may be installed without the use of blocking up to 120 mph basic wind speed' in all .roof zones (1,'2, and 3)' and
Exposures B or C. except as follows:
a. 85 mph basic wind speed or greater, Exposure C, blocking must'be installed to supporta mount where
any portion of a module supported by that'mount is in zone 3, and the roof slope is 2;12 — 6:12.
b. 100 mph basic wind speed or greater, Exposure B, blocking must be installed to suppot a mount where
any portion of a module supported by that mount:is in zone 3 ani, the roof slope is 2:12-- 6:12.
C. 110 mph basic wind speed or greater, Exposure C, blocking must be installed to support a mount where
any portion of a module supported by that mount is in zones 2 or 3 and the.roof slope is 2:12 — 6:12.
d. 120 mph.basic wind speed or greater, Exposure B, blocking must be installed to support. a mount where
any portion of a module supported by that mount is in zones 2 or 3nand the -roof slope is 2:12 — 6:,12,
2) These calculations apply for use with SunPower.photovoltaic modules measuring approximately 32" x 62" -and
mounted. in compliance with Document 001-14158 rev E•.
' The Caldomia Building Code (CBC) is considered to be identical'to the IBC for the purposes of this document.
2 All basic wind speeds are as.defined in ASCE 7-05; that is, nominal design 3 second gust at 33 feet, Exposure C. UBC wind
speed is determined on a different basis (fastest mile) and is not equivalent. Above 120 mph basic wind speed, securement must
be evaluated on a case by case basis.
3 zones as defined in ASCE 7-05. For most residences, zone;3 can conservatively be taken to be that region within four(4) feet of
two perpendicular roof edges, including the ridge in the case of gable roofs.
1507-586 Rev C Page 2 of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1:510.540.0550
Richmond, CA 94804 USA www.sunpowercorp.com F: 1.510.540.0552
Structural Notes: Wind Resistance of SunPower Composition Mounting System P/N 1505-735
III. SUNPOWER COMPOSITION MOUNTING SYSTEM CAPACITY
Ot�
While the uplift pressure due to wind on the l'V modules will be less than on the structural sheathing, the loads will
be concentrated at discrete locations, in -this case the mounting pads, through the reaction of the fasteners. See
FIGURE 1 and -FIGURE 2 for a.schematic,of the Composition Mounting System mounting pad.
Note that the mounting pad will normally have eight (8) screws engaged. For the purpose° of the calculations,
however, it is assumed that only four (4) screws are engaged'. This assumption is made to allow for those cases
where the remaining screws are driven in or adjacent to an unblocked seam between deck sheets.
Failure can occur through several modes either individually or in combination:
a Withdrawal ofthe.mounting pad screws.
b. Sheathing point -load capacity
c. Sheathing nail pullout.
Based on a comparison of these failure modes, shown below, screw pullout is most critical at an allowable pullout
capacity per Composition Mounting System device of 250 pounds.
The required number (4' each) of rIV-Buildex Trugrip GT #9 x 1-1/2" screws necessaryto anchor a mount is
determined as follows:
APA Form TT -051B (November 2008), Screw Wlthdrawal from.the Face ofAPA=Trademarked.Structural Panels,
on page 2 of 3 recommends the capacity of a screw in withdrawal from OSB: (the weaker of the altemative.,sheathing
materials) be determined using NDS ,(2005) formula 11.2-2 (Table 11.2B) with a specific gravity value, G = .45. For
a.#9 screw, this yields a value for W = 102 lb flinch of thread- in the sheathing.
For a single screw°with threads in 7/16" of OSB, W = 102 x7/16 = 45 lb f per. screw.
Adjusted for wind duration of load, W'= CD x W = 1.6 x 45 = 72 lb. f per screw.
The required number of screws, based on the.capacity of the sheathing itself (see Section III.C., below) is:
250 lbF721bf per screw= 3.5, 4 screws.
The screws must be positioned symmetrically to the axes of the mount and must be 1-1/2" long in order to assure the
3/8" tapered tip of this screw fully protrudes from the backside of the sheathing, taking into account the washer,
mount and :sheathing thicknesses. Because the screws may coincide with seams in the sheathing and thereby be
ineffective, all 8 screws holes must be utilized.
In those cases where ;attaching to the sheathing is insufficient for the required uplift, the SunPower Composition
Mounting System is installed with the use of blocking. Approved blocking is a 2x6 flatwise between rafters or
trusses. See Section III.E. below and the associated detail
1507-586 Rev C Page 3of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540.0550
Richmond, CA. 94804 USA Www..sunpowercorp com F: '1.510.540.0552
Structural Notes: Wind Resistance of SunPower Composition Mounting System P/K 1505-735
Uplift..from. PV module
Resistance to
uplift provided
by #9 ITW
Buildex Trugrip
GT Metal -to -
Wood
fasteners. 8
installed, 5
required to be
secure.
FIGURE 1: Schematic of the SunPower Composition
Mounting System(P/N 1505-753)
F1/4 - 2D TAPPED THRU
80'.CSINK0.08 DEEP
IR Od
�
t
38
1.5(
8X 0 250
FIGURE 2: Plan View of Composition Mounting System Base
1507-586 Rev C Page.4 of 10 03:22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540.0550
Richmond, CA 94804 USA www.sunpowercorp.com F: 1.510.540.0552
Structural Notes:: Wind Resistance of SunPower Composition Mounting System P/N 1505-735
C. Structural Sheathing Point -Load Canaci
All calculations are carried out using ASD�for convenience of use with the NDS.
From NIST Voluntary Product Standard 2-04 (PS -2) for OSB, Table 1, the minimum ultimate point -load capacity
(static) = 400 lb f for 24" roof span rating.
Convert this to an ASD'value.by use of NDS 2005 (Table NI), K = 2.16/0. where 0 is selected as a:Bending
Resistance Factor = _85.
P = 400 x .85/2.16 = 157
P' (for wind load combinations) = P x CD where CD = 1.6 per NDS:
P'= 157x1.6=252
The conclusion taken from the, preceding is that the wind capacity (ASD/IBC 2006) of the anchorage of the
SunPower Composition mount device in, sheathing can be safely taken as 250 lb f.
D. Sheathing Nail Capacity
A final possible failure mode would be that the wind uplift that is concentrated at the mount could cause the nails
local to the device to withdraw and a localized roof failurecould result.
Sheathing is assumed edge nailed at 6" and 12" inches in the field with 8d box nails.
Before failure (disconnection of the sheathing from the roof), at least five (perhaps as many as 16) nails
would be in active withdrawal.
Per 2005 NDS, Table 11.2C, 8d.box nails, (0.113" diameter) have withdrawal capacity (ASD) of 28 Ib/in
penetration.
Pa, (IBC) = 5 (nails) x 1.6 (wind) x 1.5" (penetration) x 28 lb/in = 336 lb. ASD
(Note regarding ,failuremode: The implication of the assumption of multiple nail participation is that a nail local to
the device will begin to pull out and may pull out: completely; but the nearest'5 nails will be intact. This isnot a
failure.)
E. Blocking
In those cases where attaching to -the sheathing, is insufficient for the; required uplift, the SunPower Composition
Mounting System must be installed_ with the use of blocking. Approved blocking is a 2x6 placed flatwi'se between
rafters or trusses. The toe -nailing required is 3 —16d sinkers. each end of the;block. Altematively, the blocks can be
end nailed through 2x.rafters or trusses with 3 —16d sinkers each end:
1. From the SunPower Safety and Installation Instructions:.. for 72 cell module&(measuring
approximately 32" x 62" (Document 001-14158 Rev *E):
"5.1 Site Considerations ... SunPower modules aredesigned to meet a maximum positive
(or upward, e.g., wind) ... design pressure of 50 lb/fe .:."
This,is taken as the.Nominal wind pressure a panel can resist. Le., it incorporates a safety factor.
Accordingly the blocking connections may conservatively be designed.for this worst case without concern
for wind exposure.
1507-586 Rev C Page 5 of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540.0550
Richmond, CA 94804 USA www.sunpowercorp.com F: 1:510.540.0552
Area of Panel x 50 psf = 1-3:4 sf x 50 psf = 670 lb f..
Each mount will be exposed,to 50% of this or 3351b f
Deducting .6D (=.6 x 33/2 lb f)„ P' = 335 + 10 = 345 lb f..
It: must be assumed amount will be located, at or near one end of a'block.
System P/N 1505-735
The wind (lateral) resistance of 16d toe -nailed sinkers is calculated as follows:
From the 2005 NDS Table .11N, Z = 115 lb f for a 16d sinker (.148e x.3-1/4")
The 2005 NDS adjustment fora short duration load is Ca= 1.6
The adjustment for toe -nail is Cm = .83; based on the 2005 NDS 11.5.4.2
Z'= 115x 1.6 x.83 = 153 lb f
_> 316d sinker toenails. are required each. end, for a total capacity 459 lb f
The wind (lateral) resistance of 16d end -nailed sinkers is, calculated as follows:
The values 'from above are identical except. C., = .67 per NDS 11.5.2.2 must be substituted for C,,.
Making this substitution,' Z' =124-lbf
_> alternatively 316d sinker end=nails.may be,used each end, for a total capacity of 372 Ib f.
2. Splitting of the blocking is, an issue since the screws securing the -blocking may be used as self
drilling/self tapping. No more than three screws should be used and two are preferable, #9 x 2-1/2" ITW
Buildex Trugrip screws with bonded washers should be used.wsecure'the mounts in a blocked condition.
Note that pre -drilling is inquired. The screws should be placed (a) in a diagonal pattern on two opposite
comers of the mount for two total screws, or (b) two screws on opposite sides of the mount centered omits
major or minor axis for a total of two screws. Note the latter can be more prone to splitting.
The effective length of these screws into the blocking is 1" after deduction for the roofing, tip, sheathing,
washer and the mount. The capacity of the threaded length in the blocking would be:
W = 121 lb f/inch from NDS(2005) Table 11.2B
W" = CD x W = 1.6 x 121= 1941b flinch (and per screw).
With'two effective screws'P;& =-2 x 194 = 387 Ib f, the -required capacity of 345 Ib f is exceeded. Note this
requirement isindependent of wind exposure as long as the panels are approved.
The above connections/altematives.are reflected in the sketch on the following page.
1507-586 Rey C Page 6 of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540.0550
Richmond, CA 94804 USA www.sunpowercorp.com F: 1.510.540.0552.
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1507-586 Rev C
1414 Harbour Way South
Richmond, CA 94804 USA
Mounting System P/N 1505-735
Page_ 7 of 10
SUNPOWER
www.sunpowercorp.com
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02.22.2010
P: 1.510.540.0550
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Structural Notes: Wind Resistance of SunPower Composition Mounting System PLN 1505-735
IV. WIND LOADS AND INSTALLATION TABLE
A. Wind Forces
For purposes of these notes and this product, the wind pressures are calculated by use of ASCE 7-05, Chapter 6.
ASCE 7.05 provides: the most recent; and best available generally recognized authority for determination of wind
forces.
B. Critical Load Combination and Analysis
The Allowable Stress Design (ASD) Method, Load Combination. Equation 16-14 of the 2006113C -- .6D
+ W + H — is most critical to assure the capacity of the SunPower Composition Mounting, System is
adequate. This critical load combination simplifies to
0.6D + W
in the absence of earth pressure. The calculations for the anchorage load demand are based on a photovoltaic module
of dimensions 31.4" x 61.4" with a weight of33 .lbs.
85 mph
Exposure B
Exposure C
Zone 1. (Feld)
U lift— Ibf
Zone 2 (Edge) Zone 3 (Comer) Zone i (Field)
Uplift — Ibf — Uplift — Ibf
Zone 2 (Edge)
lit
U — lbf
Zone 3 (Comer)
Uplift — Ibf
2-12-6-12. 81
1 123 194 87 1
172
1 269
7:12- 12:12 79
1 95 95 108 1
130
1 130
90 mph
Exposure B
Exposure C
Zone 1 (Feld)
uplift — Ibf
Zone 2 (Edge) Zone 3 (Comer) Zone,1 (Field)
Uplift —.Ibf Uplift —1bf uplift — Ibf
Zone 2 (Edge_)
Uplift — Ibf
Zone 3 (Comer)
Uplift = Ibf
212 -8:12139
139 218 99
194
303
T:12 -12:12 79
97 1 97 111 1
138
1 136
100 mph
Exposure 8
Exposure C
Zone 1 (Field)
U lift —1
Zone 2 (Edge) Zone, 3 (Comer) Zone (Feld)
Uplift — Ibf Uplift — Ibf Uplift — Ibf
Zone 2 (Edge)
U r t — Ibf
Zone 3 (Comer)
U lift — Ibf
112-6:12 88
174 1 272 125 1
242
377
7:12 -12:12 99
122 1 122 140 1
170
1 170
110 m h
Exposure B
Exposure C
Zone 1 (Feld)
U lift— Ibf
Zone 2 (Edge) Zone3 (Comer) Zone 1 (Field)
Uplift — Ibf Uplift — Ibf Uplift — Ibf
Zone (Edge)
Uplift — Ibf
Zone 3 (Comer)
Uplift, — IV2-12-6:12
109
212 331 153 1
296
1 468
7:12-12:12 122
149 1 149 171 1
208 ji
208
120 mph
osure B
Exposure C
Zone 1 (Feld)
Uplift Ibf
Zone 2 (Edge) Zone 3 (Comer) Zone 1 (Feld)
Uplift — Ibf Uplift — IV. Uplift — Ibf
Zone 2 (Edge)
Uplift — Ibf
Zone 3 (Comer)
Uplift — Ibf
212 - 6:12 131
1 284 1 396 184 1
363
1 647
7:12- 12-12 147
1 179 1 179 208 1
250
1 250
See example calculations following for highlighted conditions'.
TABLE 2: Wind Load 'Table Used for Installation
Environmental Constraints:
1. 1. Basic wind speed per
ASCE 7-05
21. Building height <=40 ft.
3. TopographicFactor= l
4. Importance Factor =l
5. Directionality Factor = 0.85
6. Module Area. 13.4 ft
7.
Module Mass 33 IN
8. GCp from Tables 6-11Cand 6-11'D
9. GC, r= 0 because modules are not
enclosed.
10. Values in bold red indicate that
blocking : is• required.
1507-586 Rev C Page 8 of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1.510.540:0550
Richmond, CA 94804 USA www.sunpowercorp.com F: 1.510.540.0552
Structural Notes: Wind Resistance of SunPower Composition Mounting, System P/N 1505-735
Example I
Basic wind speed V = 85 mph
Exposure Category = B
Building height = 40,ft:
Gable roof, 2:12 — 6:12
Zone 3 (Comer)
Module Area A = 13.4 W2.
Module mass D = 33 lbf
Topographic factor K, = 1 (Section 6.5:7.2)
Directionality Factor Kd = 0.85 (Section 6.5.4:4, Table 6-4, Components and Cladding)
Importance factor I = 1 (Table 6-1, Category.Il)
Velocity Pressure Exposure Coefficient Ks = 0.76 (Section 6.5.6:6, Table 6-3)
Velocity Pressure qh= 0.00256(Kj(K. d)(VZ)(I) (Equation 6-13)
Velocity Pressure qh= 0.00256(0.76)(1)(0.85)(85^2)(1)
Velocity Pressure qh= 11.961bIW2
Design Wind Pressure p = gh[(GCP) — (GCpJ] (Equation 6-22, Components and Cladding, Low Rise)
GC, Acting away from surface = -2:54 (Figure 6-11C, interpolated.for module area)
GCpi, = 0 (Figure 6-5; modules are open)
Design Wind Pressure p = (11.96)[(-2.54) — (0)]
Design Wind Pressure p = -30.4 lb/ft^2
Uplift Force on module (W) = pA = -407.4 lbf
Total Force on module =.6D + W = -387.6
Uplift demand force per mount (2 mounts per module) = -387:6 / 2 = 194 lbf
1507-586 Rev C Page 9 of 10 02.22.2010
1414 Harbour Way South SUNPOWER P: 1.530.540.0550'
Richmond, CA, 94804 USA WWW.sunpowercorp.com F: 1.510.540.0552
4 lb
Structural Notes: Wind Resistance of SunPower Composition Mounting System P/N .1505-735
Example 2.
Basic wind speed V = 110 mph
Exposure Category = C
Building height = 40 ft.
Gable roof, 7:12 —12:12
Zone 2 (Edge)
Module Area.A = 13.4 ft^2
Module mass D = 33 lbf
Topographic factor K. = 1 (Section 6.5:7.2)
Directionality Factor Ka = 0.85 (Section 6.5.4.4; Table 6-4, Components and. Cladding)
Importance factor I = 1 (Table 6-1, Category In
Velocity Pressure Exposure Coefficient K. = 1.04 (Section 6.5.6.6; Table 6-3)
Velocity Pressure qh= 0.00256(KE)(Kn)(Ka)(VZ)(I) (Equation. 6-15)
Velocity Pressure qh= 0.00256(1.04)(1)(0.85)(110^2)(1)
Velocity Pressure qh= 27.38 IbIW2
Design Wind Pressure p = gh[(GC,)— (GC,;)] (Equation 6-22, Components and Cladding, Low Rise)
GC,.AcOng away from surface =-1.19 (Figure 6-111), interpolated for module area)
GC,; = 0 (Figure 6-5; modules are open)
Design Wind Pressure p = (27:38)[(-1..19) — (0)]
Design Wind Pressure p = -32.6 lb/ft^2
Uplift Force on module=-pA = -436.6 lbf
Total .Force on module =.6D + W = -416.8
Uplift demand force per mount (2 mounts per module) = -416.8 / 2 = 208 lbf
1507-586 Rev C Page 10 of 10 02.22.2010
1414. Harbour Way°South SUNPOWER P: 1.510.540.0550
Richmond, CA 94804 USA www.Sunpowercorp.com F: 1.510.540.0552