Toilet under stairs have a bad reputation in feng shui,
The stairs are U shapped so that on the first leg the space under the stair landing comes out 6’’8”. There, you will often find toilet compartments as small as 30” x 54”, and the partition’’s INswinging doors are as narrow as 22” wide, with the typical door being 23” wide. Having tried many times, at clients’’ requests, to squeeze a powder room or toilet under a stair, I have learned to just. Toilet under stairs https://sigmaconstruction.uk/toilet-under-stairs-.html have a bad reputation in feng shui, although it isn’t as bad as the reputations of bathrooms. Regarding the square footage and door sizes of a powder room, it may be useful to compare it to a toilet stall in a public restroom. Avoid clutter and don’t position a mirror to reflect the toilet seat. The 3 ft width isn’’t a problem going under the stair, but there isn’’t that much “run” under a normal residential stair which is that tall. Due to 36” wide stairs on both legs but I doubt I need it if I go side to side with the lav/wc. I know I’’ve done a toilet compartment 3’’x5’’, possibly smaller. Next to the lav is the toilet, maybe sunken a bit into the wall space to give me the 21” clear. Maybe you can sink that tank 8” into a wall space under the steps leaving you with about 36” so I suppose you need an area 36”x46” with a door opening not to be less then 20” to one side. They strictly enforce the 6’’-8” headroom at the required floor clearance at the front of the toilet, but don’’t enforce it over the tank or bowl, where you can’’t reasonably be standing anyway. Keep the door and toilet lid closed, and keep the bathroom clean and tidy. I’’d love to see the smallest designed bathroom under a stairs. The problem with squeezing this under a stair is finding a space 7+ ft long that has 6’’-8” headroom. If you have a bathroom located under a staircase, you’ll need to take steps to address this challenging feng shui situation. The height under the landing won’’t be anywhere near 6’’-8”, unless the landing is no more than a very few risers down from the second floor, as in a very unequal-leg U-shaped stair. If I made that 1st intermediate landing 42” wide instead of 36” like the stairs I then have my 42”x36” space. Habitable rooms, hallways, corridors, bathrooms, toilet rooms, laundry rooms and basements shall have a ceiling height of not less than 7 feet (2134 mm). Clearance from front of toilet is 21” plus toilet itself. In my first drafting job, 30 years ago, we had a standard detail showing the door location that worked in a 3 ft x 7 ft toilet with specific fixtures.