I have been burned by toilet room layouts repeatedly. Back in the day BADA (before ADA) a single occupancy toilet room layout was 4.5’ x 4.5' (20.25 SF) or maybe 2.5’ x 6’ (15 SF!). You could easily fit a 5-fixture toilet room in 8’ x 11' (88 SF).
As times changed, it became harder and harder to fit everything into the space it “ought” to take - the hours wasted trying to fit 10# in a 5# container! The problem arose over and over because too little space was allocated in the earliest phases. By the time it came to work out the toilet room layout in detail, what with the usual encroachments, all sorts of things had to be re-designed to make accommodation.
Look at my crude sketch to see what I mean. The post ADA toilet room layout is 228 SF. Pre ADA is 108 SF. Post ADA you need more than twice the area for each toilet room. (Don't think that I have anything against ADA. I don’t. 90% of ADA is an improvement. My story here is about the learning curve required to reset expectations.)
In the Schematic Design Phase allow 3’ / fixture plus 4’ for H/C stall and entrance maneuverability X 12’ width. These are enclosing dimensions that include wall thicknesses and plumbing chases.
If more than 6 fixtures are required, increase the room’s width to 16’ and place sinks opposite the water closets. Getting privacy is more difficult with fixtures on both sides of the room in this toilet room layout so you may need a screen wall at the entrance. Large toilet rooms take up a lot of space, but some occupancy types, especially Assembly, need it.
Other considerations for toilet room layouts.
Determining the required fixture count is often found in a Plumbing Code rather than the building code. And while you are working on toilet room layouts, give a thought to the Ideal Janitor’s Closet, which should also be larger than you might think.
Nowadays ALL toilet rooms must be accessible. Single occupancy rooms at 8’ x 8’ enclosing dimensions actually take slightly less space, provide more privacy, can be placed more conveniently around the building and eliminate toilet compartments. You basically give up the ’core’ concept when you use this toilet room layout; and all occupancies are not candidates for this approach. Another plus for single occupancy toilet rooms is that two master designs, one with a vanity and one with a sink, solve most of your ’potty’ problems.