Under stairs loo without external walls - possible/worth investigating?

[PastaLaFeasta]

We are going to do up the kids' bedroom this summer and possibly install new flooring, move the radiator location and replaster. As its so disruptive I'm wondering if it would be worth looking into installing a compact loo and sink under the stairs - the space is next to the kids' room so I guess we'd be able to run the pip under the floorboards, just over 3m to the outside path where the drains run to the mains, there's a man hole cover about 2 meters up from where this pipe may exit. The floor under stairs seems to be concrete as there used to be tiles in the hall. It's a Victorian semi converted into two flats and we are ground floor.

The space is 93cm wide and maybe 2m long but with the slope the usable space is much less - 50cm in is 1.85cm high and 70cm in is 157cm, the entrance is 217cm. We could consider a macerator Saniflo system and we don't have a budget exactly so are prepared for it to be at least a few £k although part of the larger project. There are pipes we can box in but no meters and it would be good to have some storage at the back for suitcases etc. We can't afford to buy a bigger house here so we are trying to make the most of the space we have. We may investigate extending in future which would make a second loo very useful, especially when selling. I was thinking I'd approach a local builder we've used before but it would be good to know if it's remotely feasible and I'm not asking for something completely ridiculous.

watching with interest. A Saniflo loo has been suggested to us as the layout of our renovation/remodel is awkward due to soil pipe location. I'm not keen on a sniffle - have no idea why other than childhood memories of noise and faults!

We have a loo under our stairs and the soil pipe goes under the sitting room floor to the drains at the back. As there is no window we have an extractor fan as well which vents out the back.

rather than a poo mincer, consider a bucket in the back garden.

We've just installed a tiny downstairs loo, creating a new room to do so. We have a saniflo slim and pipes go under the floor from front to back of the house to the soil pipe. Saniflo's are known to fail because of the work needed to mash the poo (not nice sorry!!) so our downstairs loo is a "wee only" loo!

The saniflo was approx £600, we had to have a slim one because the space is very small. Finding a toilet that was able to fit a saniflo at the back was not easy and we spent £400 on the toilet rather than buy a cheaper one purely because it was the only one that had the space at the back AND was narrow enough to fit. It's been worth every penny though!

We did exactly the same as bilbodog last year. Proper soil pipe under the sitting room floor that joins up with the main drain running alongside the outside wall. Wanted to avoid a macerator at all costs.

We did exactly this in our last house. Proper soil pipe and extractor fan which vented at the front of the house. Worked brilliantly!

We did this. It was part of a bigger job because drilling through concrete to lay the pipes was quite a big deal. We put in an extractor fan which then connected up through ceiling space and out at the back of the house. The loo is tiny but it does the job!
If youre ripping up the floor and moving radiators too then you might as well do it.

Ok thanks for sharing your experiences, so not a hopeless plan potentially, but disruptive, we've had the side path excavated before which wasn't too bad and I'm pretty sure the kids' room has floorboards so perhaps a proper soil pipe is not out of the question. I may take a peek in a hidden corner as its carpeted at the moment. Sadly the conversion with small extension was a bit of a bodge job so it may not be as expected, the original tiles in the hallway were sadly butchered for the radiator plumbing.

I didn't consider the outlet for the vent, we may have to redo the ceiling in the bedroom anyway as its wallpapered and probably the original crumbling plaster underneath, the same as the walls. We could move the kids into our room and decamp to the living room during the work. If we are doing a big job anyway we should probably make the most of it and do it right. Although losing the storage space will a down side.