Balcony Loads - IBC 2012 vs. ASCE 7-10

[manstrom]

IBC 2012 states "Balconies and Decks - Same as occupancy served". e.g. 40 psf for an apartment balcony

ASCE 7-10 states "1.5 times the live load for the occupancy served. Not required to exceed 100 psf" e.g. 60 psf for an apartment balcony

Has anyone come across this before? Which one should govern? Conservatively, I could use the heavier load but this seems excessive. I am surprised that there is a conflict.

 

[steellion]

Hmm... ASCE 7-05 has 100 PSF live load for balconies except 60 PSF for 1-2 family residences < 100 ft^2. It looks like they scaled it back for 2010. IBC is the law, but personally I would go with the ASCE recommendations. Balconies are a critical design item best served with a bit of caution.

 

[manstrom]

Right. It used to be 60 psf for balconies in 1 and 2 family residences (cantilevered balconies, not supported on 2+ sides - a deck). IBC 2009 (iirc) revised balconies to "same as occupancy served" and now I see ASCE 7 is essentially going back to 60.

I don't mind beefing up a balcony design, but I am surprised at the error between the two.

 

[steellion]

It is probably not an "error" so much as a difference of opinion. Some things are different between the IBC and ASCE7, most notably some of the R, Cd values for seismic FRS (at least it used to be that way). I wish IBC would just adopt ASCE7 by reference for all structural engineering matters. Maybe it will go that way for the next code cycle.

 

[briancpotter]

This is strange, but I don't see any reason to ignore the reasoning behind the choice of 1.5 * Occupancy:

"Balconies and decks are recognized as often
having distinctly different loading patterns than most
interior rooms. They are often subjected to concentrated
line loads from people congregating along the
edge of the structure (e.g., for viewing vantage
points). This loading condition is acknowledged in
Table 4-1 as an increase of the live load for the area
served, up to the point of satisfying the loading
requirement for most assembly occupancies."

Anyone happen to know of the IBC Commentary mentions balcony loading at all?

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[msquared48]

I have always agreed with a higher load for balconies due to the tendency for psople to congregate there when partying or relaxing.

I was shocked to hear af few years ago that the code was changed to 40 psf for balconies. Now I know why some use that lower value.

Perhaps someone should bring this up to the IBC / ASCE7 committees...

Mike McCann
MMC Engineering

 

[RareBugTX]

Whenever I come across a code discrepancy like this i always go with the conservative one. Also, I try to cross reference with real life and I would clearly see people jammed the coming summer in a balcony drinking, eating hotdogs and even kegs full of beer on such balcony. 40 psf is clearly unacceptable.

 

[efsinc]

Balconies always get special attention from me, and especially the handrails, for precisely the reasons stated above. For awhile there, it seemed like every year or so the news carried a story of a balcony coming down with people craning there necks to see a parade, a sunset, an ambulance.... The heavier load does not seem excessive to me either. But I thank you for pointing out this unobserved discrepancy.

 

[dcarr82775]

In colder parts of the country/world firewood gets stacked on decks and balconies as well. I will use 40psf on a deck in some instances just because of the redundancy, but never on a balcony

 

[manstrom]

This is what I got from the ICC

"Chapter 16 of the 2012 IBC does not reference the ASCE 7 -10 live load table for determination of minimum live loads. Therefore, IBC Table 1607.1 always governs for live loads."

 

[lexpatrie]

Bear in mind that collapse does not (and frankly speaking usually does not) involve a problem with the code or application of the code.

It's the install.

And from what I've seen, engineering of such is usually never applied, let alone deficient. It simply was never done.

--Brian.

 

[msquared48]

In my opinion, decks, with their support system producing less rotation at the building face as opposed to balconies, with proper flashing and sealing, the chance of structural degredation of the framing members from water intrusion at the building interface is less. For that reason alone, outside of the possibility of a reasonably higher occupant loading, I would use the 60 psf value, if not more, to limit the rotation at the interface. The price difference between a 2X6 and 2X8 or 10 is not that much...

I assume that ALL sealed balconies are adequately vented too - every joist space front and rear. They just have to be.

Mike McCann
MMC Engineering