Live Loads for Decks and Balconies

[SacreBleu]

After all the confusion about definition of "deck" versus "balcony" that endured for years under the UBC codes, the IBC supposedly cleared this up. This relates to residential and multi-family construction.

Looking at 2003 IBC Table 1607.1 (2000 IBC is similar),an exterior balcony gets a live load of 100 psf, with the exception of one or two-family residences only, not exceeding 100 sq. ft., you may use a live load of 60 psf.

I would think the OPPOSITE would make sense: a smaller balcony would have more of a chance to be crowded with people. Therefore, why isn't the live load 100 psf for 100 sq. ft or less, and 60 psf for greater than 100 sq.ft.?

Now, to make matters more confusing, read the definition of "deck" versus "balcony" - it states that "deck" is supported on at least 2 opposing sides, i.e., it is not a cantilever affair. Now the since the Code seems to consider this more "fail-safe", it allows live load same as occupancy served (40 psf for residential/multifamily). Now isn't 40 psf unconservative? I would think it should be at least 60 psf, especially for a small deck. You could easily have a party with many people on that deck. Just because it isn't cantilevered, why allow the individual joists or edge beam more of a chance to fail?

To put things in perspective, we did a load study (sort of like cramming into a VW). Assuming everyone told the truth about their weight, it came to about 73 psf.

 

[whyun]

Thanks for the insight. To put things to another perspective, consider a balcony that is 100 sf (say 5 ft by 20 ft). Assuming an average weight of 150 pounds per person, 100 psf is equivalent to about 66 people and 60 psf is equivalent to 40 people on this balcony.

I have a balcony (actually a deck) that is more than 100 sf in my home built in 1975. This is probably designed for 40 psf. I wouldn't feel comfortable having more than 20 people...

66 people in 100 sf means one person occupies 1.5 square feet (which is pretty small even for someone who is only 150 pounds).

 

[AggieYank]

Engineering Judgement. I wouldn't design a balcony or canopy for 40 or even 60 psf. I would definitely go with 100 psf.

 

[AggieYank]

EDIT for above post. canopy = deck.

basically, any place where people congregate (lobby, balcony, etc.) I design for 100 psf.