Is this feasible?

[willbish]

I'm thinking of removing the inner EPS layer of my ICF to make space for a slim concealed cistern then using a back to the wall pan for a first floor bathroom.

The joists run parallel to the wall

 

Im hoping to get a waste pipe/ pan connector to do two 90° within the space between the concrete wall and the first joist.

Position of first joist is flexible, so I am thinking 40mm from finished wall which is 135mm from concrete, is this sufficient?

 

Ive had a look at S trap toilets but they all seem ugly/old fashioned.

[Jeremy Harris]

I don't see why not.  The thin inner insulation layer does next to sod all in terms of real-world performance, and is really just there as a form for the concrete.  There's a very small risk that the cistern may end up slightly cooler, but frankly that's going to be trivial when compared to the effect of fill water at around 8°C coming into the cistern.

[willbish]

Thanks @JSHarris, I had some slight concerns about condensation on the cistern by moving it into the wall.

 

I was interested in how much space I am going to need to comfortably get 2x90° bends between the concrete and first joist. 135mm should provide some wriggle room.

 

What I should probably do is buy the pan and cistern now so that I can be sure before placing the first joist but I've very little space in my lock up at the moment.

[PeterW]

Don’t use two 90s - get a Geberit frame and they come with a 90 degree one that you can get to drop within 80mm of the frame itself. Then into a 90 and back under the floor. 

 

Just done one like this and works perfectly. 

[willbish]

@PeterW I'd like to use a Geberit frame but the toilet is situated under a window and there isnt enough vertical space to fit any of their models in. This Pura cistern will do the trick but means compromising with a back to wall pan rather than wall hung.

 

[willbish]

Also means the toilet seat will cover the flush plate when open but I can live with that

[PeterW]

39 minutes ago, willbish said:

@PeterW I'd like to use a Geberit frame but the toilet is situated under a window and there isnt enough vertical space to fit any of their models in. This Pura cistern will do the trick but means compromising with a back to wall pan rather than wall hung.

 

 

Are you sure ..? The Kappa comes with an 82cm frame for a wall hung too and is only about £40 more than the cistern alone. It would make it easier to fit a pan at a later date as the outlet pipe is locked into the wall 

 

https://www.fountaindirect.co.uk/geberit-duofix-wc-frame-82cm-prewall-111-260-00-1.html

[ProDave]

There is a type of 110mm soil pipe fitting that is a really acute sharp 90 degree bend, sharper than a normal bend. I forget what it's proper name is, but I got one from Travis Perkins when I needed to offset the stack pipe and 2 normal bends would give too much offset.

[PeterW]

9 minutes ago, ProDave said:

forget what it's proper name is,

 

Its an 87.5 degree short radius bend. 

 

There red are no real 90 degree bends anyway - all are 87.5 which means when you stack a pair you end up with a natural 5 degree fall on the soil running away from the vertical face as in @willbish picture. 

 

If you want less than 5 degrees (or 1:12 which is quite steep) then cranking the bends away from the vertical plane gives you some leeway to make the angle more shallow. 

[willbish]

19 hours ago, PeterW said:

Are you sure ..?

 

The Kappa would fit under the window but it isnt 'super' slim. I don't want to build the rest of the wall out 80mm. The Pura model I was looking at is 80mm deep so almost fits in the 70mm EPS layer. Was thinking another layer of PB over the rest of the wall to build it out.

 

If anyone knows of a super slim cistern for a wall hung toilet then Im interested.