solar permitting initiative - structural 2013-04-08

8/12/2019 Solar Permitting Initiative - Structural 2013-04-08

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Streamlining Structural Permittingfor Residential PV Installations

04/08/2013


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Builds on East Bay Green Corridor's Solar Permitting Initiative's

work:

Spearheaded by:

Carla Din Director, East Bay Green Corridor Structural Guidelines: Giyan

Senaratne, SE

Emeryville Sr. Plans Reviewer & CEO, WC3


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Why streamline,whats the problem?

Code Officials dont know if the proposed PVinstallation will be structurally sound. Contractors & Home Owners

dont want added

cost of unneeded structural engineering.

Solar Support Components Manufacturers

take responsibility for the array above the roof,but leave it to others to determine if the roof

framing can support the array.


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"These are electricians, putting PV panels

on roofs, being asked to figure out

structural support issues."

Ellie Leard, Building Inspector City of Berkeley


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Can we define a

PREQUALIFIED system?80/20 rule

What does it look like?


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Pre-qualified System1) Flush-Mounted2) Wood-Framed Roof3) Code Compliant Roof

4) Anchor SpacingDownward Limits Wind Uplift Limits

Archaic Modern (Post-1930)

Simple Worksheet Format

Over-the-Counter Approval

span tables


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1. Flush-Mounted (ICC Acceptance Criteria AC-428)

10 max min


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Flush-Mounted PV Examples


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Wind Catchers dont prequalify (special uplift loads)


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Especially with raised arrays,

Failures can occur..


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2. Wood-Framed Roof

S. K. Ghosh

Associates Inc.


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Wood-Framed Construction = Resilient, Robust


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3. Roof is Code Compliant -

Reasonably sound, no evidence of decay

= visual inspection -

Complies with 1927 or later UBC

= built after 1930, or = if earlier, complies with archaicconstruction span table

- No second overlay reroofs Innocent unless proven otherwise !


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"Archaic" Construction

horizontal span

roughsawn

2x4s at

32" o.c.


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Archaic Construction 1. Pre-1930, or2. Any vintage rough sawn @ 32 o.c.


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"Carpenter Trusses"

horizontal span


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Context: PV Modules ( 2.4 to 2.7 psf ) + support frame = 4 psf

max.

Wood-framed roofs: 10 psf +/- ( 40% increase in load ?? !! )


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Why Code Compliant ? Because code compliant roofs have RESERVE LOADCARRYING CAPACITY Modern Roof Live Load = 12 to 20 psf Re-roof Overlays = 2 to 4 psf


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Re-Roof Overlays Allowed:

Explicit in code from 1979 to now (example: 1997, Appendix Chapter 15)


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Roof Live Load = Construction Load


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Roof Live Load has been in Code a long time..Older Codes'

Roof Live Load:

Low Slopes:

30 psf

Steeper Slopes:20 psf

Berkeley 1911Berkeley 1922

Berkeley 1928

UBC 1927


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With all that Reserve Capacity, whats the problem? No problem, IF you anchor to EVERY rafter !


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CONCENTRATED Loads: (a few rafters do all the work!)


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CONCENTRATED Loads: (a few rafters do all the work!)


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One Option: Stagger the anchors !


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The Other Option: Do the math ! - Roof live load decreases at steeper slopes - Load duration correction: 0.9/1.25 - Slope correction factor: cosine of slope


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Rafter Load Sharing:

Load sharing is affected by roof sheathing thickness andrafter size spacingStrength Increase:Every 2nd

rafter = 1.50

factorEvery 3rd

rafter = 1.75

factor

(based on 2x6 at 24 o.c. with plywood)


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Analysis Considers Two Load Combos: PV Dead Load alonePV Dead Load + Wind Down


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Demand/ Capacity Ratios

Roof SLOPE No. of RAFTER Spaces

X : 12 degrees 1 2 3

0: to 6:12 (0o

to 26o

) 0.63 0.71 0.80

7: to 9:12 (27o

to 36o

) 0.70 0.81 0.95

10: to 12:12 (37o

to 45o

) 0.74 0.86 1.01

13: to 17:12 (46o

to 55o

) 0.85 1.00 1.18

18: to 24:12 (56o

to 63o

) 0.89 1.06 1.27


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Rules of Thumb for Downward Loads: Anchor every third

joist

(for 24o.c. = 6 ft max) Exceptions: Up to 6:12 and 16 o.c.: every fourthjoist (5-4) Steeper than 9:12: every second

joist

18:12 or steeper: every joist If anchors are staggered:

spacing may be twice

the

above limits, but 6'-0" max.


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Wind Exposure Category

B C D


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Hillcrest Wind Speed-up Effects

Translate to Equivalent Exposure C or D


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Maximum Anchor Spacing (Number of Rafter Spaces)Roof SLOPE Wind Exposure

X : 12 degrees B C D

0: to 6:12 (0o

to 26o

) 3* 3 3

7: to 9:12 (27o

to 36o

) 3 3 2

10: to 12:12 (37o

to 45o

) 2* 2 2

13: to 17:12 (46o

to 55o

) 2 1 1

18: to 24:12 (56o

to 63o

) 1 1 1* For 16 spacing, one more rafter space is allowed.


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Industry Workhorse: 5/16" diam. lag screw


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Solar Support Component Manufacturers' Guidelines


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Wind Uplift Anchor Tributary Areas:

Bottom Edge

Middle / Field

Side Edge

Corner


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Wind Uplift Anchor Tributary Area Limits Use

Manufacturers' Guidelines

or Table Below:Roof SLOPE Trib

Area, Sq. Ft.

X : 12 degrees Middle Edge

flat to 6:12 (0o to 26o

) 36 187: to 9:12 (27o

to 36o

) 26 26

10: to 12:12 (37o to 45o ) 22 22


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Wind Uplift Anchor Tributary Area Limits:


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Pre-qualified System1) Flush-Mounted2) Wood-Framed Roof3) Code Compliant Roof

4) Anchor SpacingDownward Limits Wind Uplift Limits

Archaic Modern (Post-1930)span tables

Next Step: Make Simple Structural Worksheet


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Special thanks for help & thoughtful comments !

Joe Cain & Amir Massoumi, Solar City Shon Fleming, Sun Light & Power Jeremy Rogelstad

& Chad Medcroft, Zep

Solar

Ron Jones & Stuart Wentworth, Quick Mount PV

Ron LaPlante, Div. of State Arch. & Chair, SEAOC Solar Systems Comm.Jason Ericksen, S.K. Ghosh

Assoc., Member, SEAOC Solar Systems Comm.

Giyan

Senaratne, Sr. Plans Review Consultant, Emeryville, & CEO, WC3

Alex Roshal, Chief Building Official, BerkeleyEllie Leard,

Building Inspector, Berkeley

David Lopez, Sr. Bldg. Plans Examiner, Berkeley

Jeff Thomas, Sr. Bldg. Plans Examiner, Berkeley

Val Dizitser, Sr. Bldg. Plans Examiner, Berkeley

Sam Law, Fire & Safety Plans Examiner, Berkeley

Neal DeSnoo, Sustainability Division Mgr., Berkeley Billi Romaine,

Sustainability Coordinator, Berkeley

Alex Wagner,

Structural Designer, Tipping Mar

Carla Din, Director, East Bay Green Corridor


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Goal: Happy Installers, Homeowners & Code OfficialsSolar Richmond


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For questions or requests to copy,please contact:Carla Din,

DirectorEast Bay Green Corridor

1221 Oak St., Suite 555

Oakland, CA 94612

(510) 272-3889

[email protected]

www.ebgreencorridor.org

John Wolfe, SE

Associate

IPPING MAR1906 Shattuck Ave, Berkeley CA 94704(510) 549-1906 ext [email protected]

www.tippingmar.com

solar permitting initiative - structural 2013-04-08

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