gross and net load's accessory spaces for plumbing calcs

hey gang, got one for you. 2009 IBC and IPC.

let's say we have a bank. it has a teller line, offices, and meeting rooms.

when working out the occupant load, all the general areas and offices we're using a factor load of 100 (gross).

for the board room (conference room) we are using a factor load of 15 (net). and for the teller queuing area, we are using a factor load of 5 (net).

since this is not california, we are using just the 2009 IBC and IPC. on the conservative side, we started out counting all the accessory spaces (stairs, restrooms, corridors, etc.), since we have a 'gross' load factor. but now it's requiring additional fixtures (existing facility, built it the late 60's).

so i had a thought. if the net load occupants are greater than the gross load occupants (not including accessory spaces), can we then not include the accessory space occupants? keep in mind, we are only doing this for plumbing fixture counts. for egress, i'm going the conservative route.

functionally, this bank has been in operation for along time. they don't need any more toilets than they already have. but per the new codes, if we apply a conservative view of occupant loading to the plumbing fixture counts, we have to add more.

also, because of the code requirement that fractional numbers will ALWAYS be rounded up (for plumbing fixture counts), it seems that with the gross occupant loading numbers (where you have to count restrooms), there's a double wammy going on here.

in this case, including all the gross areas, we need 2.16 toilets for men and the same for women. they have two for each right now and are happy with that. that's why i'm trying to justify a net area application to the accessory spaces to get below the +2 number.

so, let me know what you think? let me know if i'm all flush up? Smile

Original Post
i considered that (as we are an Alteration-Level 1 or 2). but it is vague as to what code was used at the time of construction.

there are no documents that go back that far, to show what code was applied. imperatively i'm confident that we have not increased the number of occupants significantly. but i can't prove it.

but, comparing the previous floor plan to the current floor plan, using the current code, and the number of occupants is increased by only a handful, well below the 20% level. so if this application of section 710 is acceptable, then we are in good shape.

but since we are remodeling the interior, including the restrooms to make them accessible, won't this get kicked out of the IEBC for this issue? i'm not too familiar with the IEBC, so i'm not completely clear on it's application. if it is a minimum standard, i would think we could always exceed that standard. but at some point, i would think we can't cherry pick which sections we want to apply.

and even if we can do this, solving my immediate problem, my question above becomes more theoretical. what do you think?
but since we are remodeling the interior, including the restrooms to make them accessible, won't this get kicked out of the IEBC for this issue?

No. It is an existing building and you're altering it, which is exactly what the IEBC is for. If your project affects more than 50% of the building's total area, then you need to comply with Level 3 Alteration requirements. If not, it sounds like a Level 2 alteration, which means you'll need to also comply with the requirements for Level 1.

The Exception to Section 101.5 allows you, with approval of the building official, to use the same code requirements applicable at the time the building was built.

If not, look at the prescriptive compliance method in Chapter 3. In Section 303.1, it states that alterations shall comply with the requirements for new construction, but the alterations shall be such that the existing building is no less conforming with the provisions of the code than it was prior to the alteration.

If that is not applicable, or interpretation of the above does not work in your favor, then look at the "classification of work" method. If the work only qualifies as a Level 1 alteration, then, per Section 601.2, as long as you don't make it less safe, then maintaining the "status quo" is all that is required, except that materials and methods need to comply with codes for new construction.

If Level 2 is applicable, then all new work needs to comply with the IBC, and the section on plumbing that I mentioned earlier applies. To determine if the occupant load increases, I would calculate the occupant load of the building before the alterations using the current IBC and then do a calculation for the configured space and compare the two. If the difference is more than 20%, then comply with the IPC fixture counts. If the number of fixtures have been sufficient for the number of occupants based on the current code for all these years, if you don't increase it much under the current code, then the same number of fixtures should continue to be sufficient.

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