We want to add a bathroom on the outside of our house. There is an existing roof over about 5x3 1/2 feet of the house so I was hoping to build it in that space.
My question is teo fold... can I do it in that amount of room and what kind of foundation do I have to do

The size sounds a little small,you say 5 foot by 3 1/2 foot?

Is that 5' long and 3 1/2 ' wide?

Where would a door be?

Placing a toilet and sink in a room this small might prove difficult, but not out of the question,if you can squeeze in.

The floors would have to be up high enough to allow access for the plumbing ,plus the problem of where the main stack is as you will need to tie into it for the stool and sink.

Where do you live and are you trying to build this to any building code? It sounds like I would not like to be seen sitting on this throne.

Balllengerbl1 Has some excellent points.

I would also add RIP up the roof and do a real bathroom. It's a lot cheaper to do all new and what did you lose? Tiny roof. A lot of costumers think of saving and that's fine but many times it cost WAY more than to go new. How old are the shingles on your little roof. How about its height can you get 9" or more insulation under it.. Now make the bathroom bigger. The foundation should be full depth footers/block walls/ and either a on slab concrete floor insulated and water radiant heat. Or crawl space and better access for mechanicals. drainage etc. I personally put a bathroom for a customer in a X area on second floor. Pedestal sink 30"shower and toilet, and even built in some shelves it worked better than we all expected. You probably didn't want to hear this but do it right and no problems later and the house has a lot more value no by having a real bathroom or big powder room.

The space , 5 X 3 1/2', is just about a little bit bigger then a regular bath tub, (60 X 31") You may be able to cram a toilet and small wall hung lavatory in there but that's about it. N Good luck, Tom

csilksnzy I was at my pluming supply house and new you can get smaller tubs/showers but wasn't sure of the exact measurements. As speed ball pointed out the 60x31 is a basic tub. I know your are in inches. I checked and the smallest tub I found with out paying a fortune is 54x29x16 which was about $225.00 my price. Its not much difference from Cox but 6" is 6" you need to add 2 inches to the 29" because of the nailing flange to install. That is tub only price. Have you thought building your own shower with all tile or a Neo angle shower to get some more inches. Hope this helps Good Luck!

No, you cannot install bathroom in 5'x 3 1/2' space. Period. Don't let anybody else tell you otherwise.

Foundations for a single story structure is to be about 18" deep and 12" wide. However, this depends on your soil composition and geo-location. I would call Building Dept. or ask any contractor. It is a basic information.

Just to specify... I was just thinking a powder room, not a full bathroom

Locate a Mobile Home Supply House and check out their space saving fixtures. This will be a very tight fit. Going to be like going tyo the putty in a closet. Good luck, Tom

Ok, for powder room you may be able to do it. Use Porcher wall hung sink. They are only about 6 to 8" narrow. See the sketch...

... or this way:

Maybe the poster could check out those fixtures they currently use in prisons: sink/toilet combo.