Wood Balcony Analysis

[WiSEiwish]

Hello,

I'm working on a project that involves the analysis of existing wood balconies. There were some flashing issues that lead to water entering the residences, so the balconies have to be removed, flashed, then re-installed. I'm a bit confused as to what the design loads should be. The balconies are for condominiums and they are single level balconies (no stairs). The American Forest and Paper Association has construction guide for residential wood decks and says that it references the 2009 International Residential Code, but the design loads used in the tables call for a 40psf live load compared to 60psf from ASCE 7-05.

I have no experience with the International Residential Code, nor do I have access to it. Does anybody have any experience or knowledge as to what the appropriate design loading is for residential wood balconies?

Thank you.

 

[frv]

There was a post on here a few days ago relating to the same issue. I believe the consensus was, and I agree, that you really ought to design it for 100 psf. The balcony is probably never going to see it, but every year you hear about a few of those things coming down during a party. I think it's definitely worthwhile to go conservative on non-redundant structures.

 

[msquared48]

And make sure you slope the surface 1/4"/ft or so away from the residence, also providing adequate screened venting of the joist spaces.

Mike McCann
MMC Engineering

 

[WiSEiwish]

Thanks for the input. Just to clarify the scope a bit, the balconies are already designed, and I just need to make sure they are up to code. If I were to design them from scratch then I completely understand that over designing them to around 100psf is a great idea. I guess my question is what is code compliance? I saw two conflicting values and wanted to make sure that I was using the correct one.

Thanks.

 

[focuseng]

2009 IRC:

http://publicecodes.cyberregs.com/icod/irc/2009/index.htm?bu=IC-P-2009-000002&bu2=IC-P-2009-000019

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MAP

 

[dhengr]

I wouldn’t use the IRC for condo or condo deck design, I would use the IBC & ASCE 7. However, the AF&PA Deck Construction Guide #6 that you mention is a good guide for the thought process and details involved in deck construction. And, I don’t have the latest copies of the various codes. But, don’t they generally talk about private deck LL of 40#/sf, plus the potential of some snow loading and drifting, plus due consideration of lateral loading potential. Or, a LL equal to the adjoining interior floor loading. Look at the fine print on the difference btwn. a private deck, a public deck at a restaurant or bar for example, and a public balcony at a theater or event venue for example and the exact definitions of each. Then consider the potential for lateral loading and how the deck is braced and/or tied into the bldg. floor diaphragm. Obviously, I would be more concerned about a drunken crowd swaying back and forth to the music at the bar, and out near the handrail, than I would be at a fine dinning establishment. And, most deck failures have had more to do with this lateral load problem, or a weak column condition, than a few pound gravity overload.

You’re pretty short on the actual details here; deck size, framing direction, actual framing and details, the outer support system. Imagine the difference btwn. three stories of decks, all supported on the same two continuous posts to a found., vs. different length posts supporting each individual deck. You know this, we can’t see it from here. The flashing and counter flashing and ledger attachment details are every bit as important as the exact LL, and are also big contributors to deck problems and failures. So, meeting code and doing a really good design involves a lot more than just the live load.

 

[RareBugTX]

I use 100 psf min. I imagine you have patio doors leading to them, so check for snow drift if your location deems it necessary. Not only design your joists. Girders and columns, but analyze your connections too. Pretty much all of porch and balconies tragedies fail at those connections.

 

[WiSEiwish]

Thanks guys.

Since the balconies are already built, I will be checking them with compliance with ASCE 7-05. Thus I will be using a 60psf live load rather than the 40psf noted in the AF&PA design guide. However, I will do a check to see if they also work for 100psf. Humans are unpredictable, so that seems like a pretty good idea.

 

[woodman88]

Here is a free link to the 2012 IRC. See TABLE R301.5 MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS for 40 psf on the Balconies (exterior) and decks. Footnote e. states "See Section R502.2.2 for decks attached to exterior walls."

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[RareBugTX]

Oops! Got carried away by the main structure, but guardrails to be checked too. 200 lb concentrated at any point of guardrail and/or 150 plf along the full length of the guardrail system.

 

[Ron]

Pe2012...a condominium is not a "residential" structure. The residential code is limited to 1 and 2 family structures. A condominium is a commercial structure, governed by the full building code, not the residential code.

 

[MJB315]

Pay special attention to the connection to the building. All too often, deck joists are attached to a ledger board that is poorly fastened to the structure (i.e. nailed through siding to rim joists that are poorly secured themselves). Bad bad.

"We shape our buildings, thereafter they shape us." -WSC

 

[woodman88]

Per the 2009 IBC Table 1607.1
1 Apartments (see residential)
5 Balconies (exterior) and decks - Same as occupancy served
12 Dwellings (see residential)
21 Hotels (see residential)
27 Residential
All other areas - 40 psf
Hotels and multifamily dwellings private rooms - 40 psf
Public rooms - 100 psf

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.