# Toilet Rooms/Corridors - Nonseparated occupancies (Sec. 508.3)& Accessory occupancies



## PaulJi (May 3, 2013)

*Given:* CCB 2010 (IBC 2009):  2Story, Type III-B, Fully Sprinklered,  A-3 & B occupancy groups.

Total Gross Building Area - First Floor = 25,923 sf = A-3 occupancy + B occupancy

Total Gross Building Area - Second Floor = 25,923 sf = B occupancy

At = 9,500sf  for A-3 with area increases for frontage and sprinklers the Allowable area is 35,625 sf.

The situation on the first floor is:

Hallways = 941 sf

Toilets = 2,429 sf

B-Occupancy = 1,760 sf

A-3 Occupancy= 20,793 sf

I'd like to use the *Sec. 508.3 Nonseparated occupancies method.*

My question or confusion is how to handle "accessory areas" (*that do not count toward occupant load *)such as hallways and toilet rooms. I realize occupant type is different from occupant load.

The Hallways and Toilets appear to be "accessory or occupancies that are ancillary to the main occupancy* (A-3)* of the building" however when I look at Sec. 508.2.1  Accessory occupancy area limitations it limits the aggregate accessory occupancies to 10% of the building area of the story At value. In my case, that would be *950 sf.*   As noted above toilets and hallways exceed 950 sf.  Hallways and Toilets are not specific to any Occupancy classification as referenced in in Sec 508.2.2 to Section 302.1.

I understand the requirement to limit accessory occupancies such as those listed in Sec. 302.1 ... ie F, B, I, H, etc as they carry with them occupant loads but toilets to my knowledge are not specific to these groups and in the case of A classification types do not have an occupant load.

It seems to me that area required for the toilets (that the Mechanical Code requires) should be considered accessory occupancies that are not restricted by Section 508.2.  That Section 508.3 should be sufficient to classify these (non-occupant load contributing spaces) as A-3 occupancy classifications.

This is probably as clear as mud ... it is to me...but I'd appreciate if anyone could clarify the classification of these "ancillary" "non-load" spaces and whether Sec. 508.2.1 applies if at all?


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## kilitact (May 3, 2013)

Assembly use (A-3) would be calculated at net square foot, excluding toilet rooms, hallways. These areas don't factor into calculation for accessory use calculation.


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## north star (May 3, 2013)

*: + :*

PaulJi,

Agree with **kilitact** !

Also, ...Welcome to The Building Codes Forum!   

*: + :*


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## RLGA (May 3, 2013)

Assembly occupancies are not determined by net area; however, assembly functions per Table 1004.1.1 for determining occupant load are.

Here's how I do it, and I have had no problem with building departments on this method.  Hallways (i.e. corridors) are assigned to the occupancy they support.  Therefore, if a hallway is located within a Group B, it is part of the Group B (and should be included in the gross floor area for determining the occupant load for functions that use gross floor area).  If they are shared, I would assign the building area for that portion to the main occupancy group, which, in your case, would be Group A-3.  Restrooms are handled similarly. However, with assembly groups, occupant load is only determined by the spaces with actual assembly functions using net floor area factors and/or number of fixed seats.

However, what I covered above has nothing to do with determining nonseparated occupancies.  There are four methods in handling separation of occupancies: 1) Separated, per Section 508.4; 2) nonseparated, per Section 508.3; 3) accessory, per Section 508.2; or 4) a combination of two or more of the previous three.

Since the allowable area per story per your calculation is 35,625 sq. ft. for the most restrictive occupancy group (i.e. A-3) and the largest floor area is 25,923 sq. ft., you can use the nonseparated method--determination of accessory area does not factor into the situation.  The building does not exceed the height per Table 503 for Group A-3 (the CBC only allows an increase in floor area or in height for the sprinkler system, but not both).

Regarding accessory occupancies (if using that method), the 10% applies to the *actual story* *floor area *and not the allowable floor area for the main occupancy.  Therefore, your first story could have accessory spaces with an aggregate area up to 2592 sq. ft. and not 950 sq. ft.


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## PaulJi (May 3, 2013)

Sawhorse,

Your comments cleared my confusion.  I was misreading Sec. 508.2.1.   Reading the section again I see my error. Thanks much.

BTW I've enjoyed reading articles on the RLGA website.

Thanks also to north star and kilitact.


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