Small commercial space, is one bathroom enough?

Are you planning on a tenant improvement and looking at leasing an existing space?   Whether it is for a small office, retail, mercantile or restaurant in a small commercial space, is one bathroom enough? In a large building, may not big a big concern, as the percentage of area is minimal.  When designing for a small spaces,  Bathrooms take up valuable real estate.  Some rule of thumbs when one restroom is not enough.

 As an Architect, I interact with clients, engineers and contractors who have acquired bits of information about Building Codes.  Sometimes, those bits are misconceptions and regurgitated information.  The building codes can be intimidating and have no beginning or end. To learn the code, the best way is jumping in feet first.  

Upcoming Blog Posts

In the next series of blog posts, I will explore common Building Codes.    Each City has adopted a code but most in Arizona use the IBC (International Building Code).

The following blog posts are:

  1. Door swing direction.  Which way should the door swing, out of a room or in?
  2. Number of exits within a room?
  3. Door Size.  Who said “size doesn’t matter.”
  4. Exit corridor width.  How narrow can a hallway be?
  5. Clearances around a door?  Door arrangement between two doors.  
  6. Door fire ratings.  What is the rating?
  7. Exit Travel Distance  
  8. Do I need an elevator?
  9. Should my door have panic hardware? 
  10. Do I need a drinking fountain?
  11. Minimum size of a Bath Room?
  12. Small commercial space, is one bathroom enough?

The item in bold are addressed in this post.  As an Arizona Architect, most City’s jurisdictions work with the IBC (International Building Code).   This code analysis is based upon the IBC.

When is one Restroom enough?

When designing a building, creating an efficient plan is important.  Having extra space in an office, conference room, lobby, retail area or restaurant seating area is not a big problem.   Who wants to have wasted space in bathrooms?  It really becomes critical when designing smaller spaces.  

The number of plumbing fixtures is dependent on the number of occupants.  The code has formulas to determine the number of occupants based upon the type of occupancy.  However in smaller spaces, lets say under 2,000 s.f., one might think one restroom would be sufficient.  The code however indicates that separate restrooms are to be provided for each sex.  There are a few exceptions:

  1. Separate facilities shall not be required in structures or tenant spaces with a total occupant load, including employees and customers, of 15 or less.
  2. Separate facilities shall not be required in mercantile occupancies (Retail showrooms) in which the maximum occupant load is 50 or less per IBC (International Building Code.  Occupant Load of 100 or less in UPC (Uniform plumbing code).  Therefore, it is a good idea to check with local jurisdiction which governs the project to determine what requirement 
  3. Shopping mall – In covered mall buildings, the required public and employee toilet facilities shall be located not more than one store above or below the space and path of travel shall not exceed a distance of 300 feet.  Therefore, a central restroom facility can suffice.  However, check with landlord requirements as they may require a restroom within the suite regardless of the central restroom facility.
  4. Separate facilities (restrooms) shall not be required for dwelling units and sleeping units.  In other words, residences.

Example Scenario

A.Business area (offices) – 1,600 s.f.    Office space occupant load factor 100 sf/occupan(updated 10/2020) –   codes are ever changing and in the IBC 2018, Business area occupancy changed to 150 sf/occupant with the exception per 1004.8 Concentrated business areas.  The concentrated business areas are applied to uses such as telephone call centers, trading floors, electronic data processing or similar use business areas with a higher density of occupants.  The number of occupants would then be calculated on ‘actual occupant load’ but not less than 50 sf/occupant.

2,400 / 150 = 16 occupants.  This exceeds 15 occupants, therefore 2 restrooms are required.  “”Note – check local code ammendments as this value of 15 may differ if overruled””

B. Restaurant – 1,300 s.f.    500 s.f. – kitchen & 800 s.f. dining area.Kitchen occupant load factor 200 sf/occupant & Dining area or assembly 15 s.f/occupant.

500/200 = 3 occupants & 800/15 = 53 occupants.  Total of 56 occupants.  This exceeds 15 occupants, therefore 2 restrooms are required.

C. Retail / Mercantile – 3,000 s.f. retail & 1,000 s.f. storage   Mercantile load factor at 60 sf/occupant & Storage / Shipping area load factor at 300 s.f/occupant.

2,500/60 = 42 occupants & 1,000/300 = 4 occupants.  Total of 46 occupants.  This is less than 50 occupants, therefore 1 restroom is required.


When looking at an existing space to lease or buy that is fairly small, you may assume that 2 restrooms are most likely going to be required.  In order for one restroom to be allowed, office space must be 2,400 s.f. or less, Mercantile space ~3,700 s.f. or less and Restaurant space dining area of ~150 s.f. with a kitchen area of 1,000 s.f.   As you can see, in most scenarious, just plan on 2 restrooms.  Follow the examples above for reference but as always, refer to the local jurisdiction, the current ADA guidelines and a local professional to ensure your projects success.

Jeff Serbin

Jeff Serbin is Vice President of Serbin Studio. His responsibilities include architectural design and project management. He coordinates the work of consultants and design team members, and is involved in design from concept through construction.

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