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RE: Roof Deck Live Loads

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We can’t second guess whether people **might** do dumb things.  Someone **might** use their living room for a fireplace showroom.  Should we design a living room for 100 psf because of the possibility?  Should 30 million home buyers pay an extra 5% for their homes because some bonehead might load CMU blocks to the ceiling in the spare bedroom?


What does it take to get 100 psf moved up to a roof deck?  Think about it.  What is a parking garage designed for?  A file room.?  It would take an extreme act of idiocy to overstress this deck to failure.  We’ve got stress factors in there looking over it, too 


Not to say that **someone**, **somewhere** won’t do it.  But that’s not our responsibility to account for it.  Providing sound engineering to our clients, is. 


If there’s good reason to believe something WILL be overloaded, or if I client requests it, use experience and engineering judgment and go.  But if I overdesigned to that extent as a general course, I’d lose my clients.


We’ve got people writing building codes that have (presumably) taken our concerns into consideration.  Take it and run with it.  I’m often asked if my designs are “real” or did I beef them unnecessarily like “all structural engineers do”  Now I see why. “Just making sure” has another term.  It’s called good, sound, engineering.




Jerry D. Coombs, P.E.
Coombs Engineering Services



From: Drew Morris [mailto:dmorris(--nospam--at)]
Sent: Monday, February 01, 2010 7:25 PM
To: seaint(--nospam--at)
Subject: Re: Roof Deck Live Loads


Do people actually read the posted LL limits?  If you directing the message to the general public, wouldn't a maximum number of people be better?

David Topete wrote:

Yes, way conservative.  But, don't put it past the tenants of unit 3A to have some friends over for a Tiki lounge party, complete with sand and faux palms...  Unless, you are designing an assisted living facility.  


Be safe and design for 100 psf LL, otherwise, post signs all around so that folks are aware of allowable LL limits..

On Fri, Jan 29, 2010 at 2:54 PM, Larry Hauer <lhauer(--nospam--at)> wrote:

Sorry if this message has already been posted, but I didn't see it so, so here it is again

I am designing a 3 story Type V apartment building which has a “Roof Terrace” above the top floor which is accessible from 2 stairways located outside the units, (i.e.- I guess anyone could access the roof terrace). The old code, (’97 UBC), would allow the roof to be designed for 40 psf live load, (Roof Decks, Item 15 of Table 16_A, ’97 UBC), but the current code, (’07 CBC or ’06 IBC), Table 1607.1 doesn’t have this category in it, (Roof Decks). Is considering this area a “Deck”, (Item 9 of Table 1607.1), appropriate, or should it be considered a possible “Assembly Area” due to it’s access from both exterior stairs? I feel 100 psf assembly live load is way to conservative for it’s use, but I guess anything is possible.

Any comments would be appreciated.

Thanks in advance,

Larry Hauer, S.E.

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David Topete, SE