Digging up solid floors

[Nozzle]

I'm in two minds about fitting wet UFH downstairs. I've started this thread in the building section rather than plumbing, as it's about the technicalities of cutting up the floor, more than anything to do with the UFH installation.

It's a 1970's challet type house, the floor downstairs is solid, and I was intending to dig up the tiles and floor one room at a time, then get the floor re-poured (by a contractor) leaving a length of tail pipe for later connection. Not very tidy, but would work.

The plan was to use 9" angle grinder to slice a margin near each of the walls, be it an external (double skin) or internal (cinder block) wall and cut out the resultant "island" of floor, dig it all out, then get a UFH guy to clip it all down etc.

I did some googling, and I think my plan might fall down at the first stage..

It would all look a bit like this:
http://oxfordgreenhouse.co.uk/blog/can-super-insulate-floor-part-one-digging/

But how can I be sure the house isn't relying on a concrete floor slab to keep it up?!

I might assume the external walls and inner structural walls are built on trench fill foundations with a concrete floor poured later - so in principle cutting out a hole shouldn't make any difference... but then I might come accross some rebar?! The house is built on level, poorly drained soil. Is it okay to just start cutting and digging and see what crops up??

I'm not refering to hazards from cables, gas pipes, water pipes or other services - those are in my mind "a given". It's also not an option to have wet UFH retro fit on top of the existing floor for reasons I wont bore you with.The final FFL must be the same as what it currently is.

Nozzle

 

[bluebaron]

hi Nozzle,

I was planning exactly the same thing but looking at it closer I have decided against the extra work/risk/cost.

IMO it didn't make sense digging up a perfectly good, if uninsulated floor, just to put is all back again with UFH. I'll do the extension and blend it in with the old and add a radiator in the old part.

BB

 

[Lower]

Have you got the ceiling height to cope with raising the floor? Would probably end up being cheaper and easier to put the underfloor heating down on the existing slab and then raise the floor on the rooms that you are not putting UFH to the same height.

 

[Nozzle]

Part of the house has already been layed with UFH and tiled so it is finished and not to be touched again - the "old bit" and "new bit" need to finish at the same FFL.

Nozzle

 

[Nozzle]

Well, the 70 quid Aldi breaker has done a great job and it's still going strong.



I've dug up 40mm depth of tiles and screed and now down to the concrete sub floor. I'm unsure if it's right/safe to cut up the concrete floor. I know the external walls aren't built over the sub-floor as I can see the dpm layer:



A question to those who get involved with footings:

Do internal load-bearing block walls also have their own footings, or are they built onto of the subfloor?

Nozzle

 

[Doggit]

Unless you're on a raft slab, then all the wall will have their own foundations.

Stick at the depth you've got to, and have a look at Nu Heat Lo pro 10, and put down Celotex rather than EPS underneath it.

 

[endecotp]

Stick at the depth you've got to, and have a look at Nu Heat Lo pro 10, and put down Celotex rather than EPS underneath it.

Nuheat say you need a layer of chipboard between insulation and their UFH boards.
Or you can use something stronger than celotex, like insulated tile backer boards.

(I don't know anything about this subject, but I was curious and looked at thr nuheat website.)

 

[Doggit]

There are several methods of fixing the LowPro system, and it depends on the sub floor, and the subsequent top layer. Unlike EPS, Celotex is very stable, so isn't going to deflect when the Nuheat boards are laid on top.

I forgot to mention earlier, that you need to work progressively towards the manifold if you're doing a room at a time, as you don't want any joints in the pipework that may leak at some point. The manifold would normally be in the centre of the house, but if you have to run the pipes across one room to get to another (not a good way to do it) then they've got to be set in as you go.

 

[Nozzle]

Hi Doggit and andecotp,

Many thanks for contirbuting to my thread, I'll take a look at the Nuheat Lo pro product later on today, I'm quite sceptical about the claims some of these manufacturers make about their thin insulation products, though I'm willing to consider one if it means avoiding digging up the sub floor too. I plan to leave capped-off tail pipes routed to a cupboard under the stairs, (coiled up so there is enough lenght to get to final destination without needing a joint) and once there, it can stay there as long as needed until I get the chance to move the Rayburn and dig up the kitchen floor too. I'd always go celotex over EPS as it is nice and strong structurally, and also holds the pipe clips better.

Nozzle

 

[Doggit]

What are you putting on top of the UFH Nozzle. I take it you know to test the pipe before you overlay it.

 

[Nozzle]

I do know to test the pipe before the screed is poured over it. I'm probably going to get a firm in to do it anyway, but I want to make sure what they fit is suitable, long lasting and reliable, rather than "just good enough to get the job done". Hence not being keen on the micro-bore type piping. Not only that, I can see difficulty trying to get microbore piping reliably attached to the spare ports on the manifold already installed (which takes standard size piping). Underlay and carpet with LOW TOG is going on top, there will also be a radiator in the room. If it works in this room, it'll work in the kitchen (coming to that job next year) and that will have tiles down.

Nozzle

 

[endecotp]

It sounds like you're going to have very thin screed.

 

[Nozzle]

As Doggit has said, there are a couple of type of LoPro which might still be an option, a 10mm pipe version and a normal version which both have low build-up. I do think either are a compromise though, and digging up the floor, if safe to do so, is my preferable option. I've been in touch with a local concrete cutting firm who say either of my two suggestions are possible. Fly in the ointment might be rebar though. Is it normal to have rebar in a domestic floor?

Nozzle

 

[Doggit]

You wouldn't normally find rebar unless it's a raft, in which case, leave well alone. But looking at the pictures, although the job would't quite be right, levelling the subfloor off, putting down between 25 and 50mm of PIR, and then the UFH and then a thin self leveling compound on top, might just be okay.

 

[Nozzle]

I'm pretty sure it's not a raft as I can see where the floor meets the external wall there is a DPM which curves up the wall. Also, the soil here is quite clay and flat and I think the raft type is for very sandy soil?? I think if it were a raft the external wall would sit on top of the concrete, rather and the concrete butt up to the wall. I can see the internal wall that is structural is also the same, but the internal wall that is not structural (but still block), sits straight on the concrete with a damp membrane wedged in there.

I used a stud finder on the floor, on the off chance it might pick up some rebar.. but really I don't think it penetrates deep enough to show even if there was some there.

UFH guy coming over on Friday, I hope he'll have some smart ideas.

Nozzle