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 I allocated too little space in the earliest phases. By the time I started 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 the toilet room work.
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.)
MY TOILET ROOM RULE OF THUMB
Eventually, enough was enough. I took a look at what I needed to change about my approach to toilet rooms. The TOILET ROOM RULE OF THUMB was born.
In the Schematic Design Phase allow 3’ / fixture plus 4’ each for H/C stall and entrance maneuverability X 12’ width. These are enclosing dimensions that include wall thicknesses and plumbing chases. This area is sacred from here on. Adding space is encouraged. In the ADA world toilet rooms cannot be too large.
If more than 6 fixtures are required, increase the room’s width to 16’ and place sinks opposite the water closets or urinals. 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. Add 3' to the length. 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. Actually, stairs fall into the category as well. Here's my rule-of-thumb for stairs.
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 concept; 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.
Toilet Rooms are a leading candidate for a standard set of details - plans, elevations, reflected ceiling plans. Select different finishes, but only change the master to improve it further.