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RE: Live load / occupancy correlation

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I've been involved with several groups wanting to either upgrade existing construction or re-use a non-assembly space for assembly purposes (churches and business buying residences is popular due to either location or cost factors).  I've been the bearer of "bad news" on several occasions, and always fall back on anecdotes for my use of caution to console the owners.

One of the things I always point out, especially additions/remodels for churches with small congregations, is that although they don't have but X number of people now, they may either grow, lease, or sell to a larger group at some point in the future.  A good example for your client is holding a function where a line may form (for registration or food or whatever).  You could reasonably get 40 people lined up on a pair of joist lines in that room, and easily overload the system.  Similarly, a party with the dance floor at mid-span could reach dynamic load failure with a small fraction of the maximum occupancy rating (the wedding reception collapse in Israel a couple of years ago comes to mind).

As for 600 people in a room, I'll agree that it would be difficult to squeeze 'em in, but I live in a college town, and you'd be amazed how many kids can fit on a balcony along with a pair of kegs.   I won't design a rental balcony here for less than 100psf or 200plf on the perimeter, regardless of code minimums.  I've even seen a case where a college apartment floor sank about 16-18" at midspan during a party.  Who'd have thought you could have a live band in a 2 bedroom, 600SF place?  Political rallies will also draw that kind of crowd, and the TV crews just love to see a room packed to the gills because it looks good on film.

In your case I would likely state in a letter that the area is designed for approximately (x) pounds per square foot, which meets the code minimums for use groups (y) but not (z). If there is opportunity for easily upgrading the floor system, or not for that matter, I'll include the format of the upgrade.  As an engineer, I try to stay out of the "is/is not appropriate for your intended use" pitfall in my written communications, since there are areas of the code which I don't know by heart, though I will make a verbal recommendation to the owner as to their best course of action to get to their desired goal.

At 05:04 PM 10/25/2004 -0700, you wrote:
Thanks for the considerations - I'm walking a fine line with a client who represents a community center at a residential complex.  The building was designed as residential, but is really an assembly for "town hall" type meetings.  I'm searching for various ways to say the same thing - that the building doesn't meet code - but in terms of visualizations they can understand.  And of course in a way that covers my butt when I don't say outright that the building must be abandoned for a lesser use group.
And the maximum occupancy approach doesn't fly anyway because it would only take one small group huddled together on one beam to potentially cause a failure.  But the people density is almost an interesting tangent.  This 36'x33' room should be able to hold about 600 people weighing 200 lbs each, per current codes.  That couldn't be more unrealistic.

David Maynard <davemaynard(--nospam--at)> wrote:
I have tried to use some of the same reasoning as you, but have not found anything truly concrete.  One would think that a house should be rated for at least 100 psf, because there is always the possibility of entertaining, and the living room can easily be considered an essembly area.  But, that is getting a little too serious.
My rule of thumb has always been to assume that the average weight of a person is 200 lbs.  Some are heavier, some lighter, but on average, 200 lbs. is a good assumption.  In your example, with a room 10 ft by 10 ft (100 S.F.) at 40 PSF, that accounts for a total load of 4,000 lbs.  At 200 lbs per person, you are looking at 20 people.  Now, if the average person (I consider my self average size) takes up a space of approximately 2 ft by 2 ft, and you pack into your 100 S.F. room elbow to asshole, you can stuff in 25 people into a room the size of my office.  Can it be done?  Sure.  Is it practical, probably not.  Now, give everyone a 3 ft by 3 ft area all to themselves, and you are talking approx. 11 people in the room.  A little more reasonable, considering the size.
Now, if you are looking for an occupancy number, I believe the fire code is where to go for this number, as I believe it is a factor of square footage and certain fire protection criteria have to be met (like a sprinkler system).  If you are just looking for a "piece of mind" number, the 200 lbs. per person is probably a good rule of thumb.  However, to come up with some sort of technical data to back that up, I just can't.  Hope this helps.
Dave Maynard, PE
Gillette, Wyoming
-----Original Message-----
From: Jim Wilson [mailto:wilsonengineers(--nospam--at)]
Sent: Monday, October 25, 2004 10:32 AM
To: seaint(--nospam--at)
Subject: Live load / occupancy correlation

Is there an accepted average weight per person for purpose of correlating between a floor live load rating and a maximum occupancy number?  For example, if a 10ft x 10ft room has a floor rating of 40psf live load (assume 100% human live load), how many people could the room support?
I can't find any such reference in ASCE and Google is coming up short on this one.
Jim Wilson, PE
Stroudsburg, PA

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