UFH boundary - new build sup next to

[EdSt]

Hi, built a 6x3M block and beam (B&B) single story extension (new dining room) on to existing extension (old kitchen&dining room being turned in to kitchen and utility) which backs on to original stone house.
 

B&B level 26Omm below existing Finish Floor Level (FFL). Make up will be: SBR prime&self level B&B 3mm, DPM, 160mm PIR slab with 25mm insulation around perimeter, VCL/UFH Mat/grid, UFH pipes tacked down and encased in 65mm semi dry sand&cement with fibre, self level 2/3mm?, 5mm adhesive?, decoupling mat, 8mm adhesive then 15mm tumbled limestone tiles. I have 3M two pane sliding doors to go in and plan (fingers crossed) is flush threshold.
 

I also want the UFH to extend in to Exisiting part of the house. So will be hiring diamond floor saw with 18” disc to achieve 175mm cuts. Current make up of that floor is top>down is: 12mm quarry tile,60mm S&C screed, 100mm conc slab, dpm, 300+mm builders waste infil/MOT. Plan is to get down in to the infil re tamp/whack any disturbed ground, and build up with 100mm conc slab to match B&B floor height and then same build up from there.
 

Due to position of new kitchen units -a 6M ‘L’ shape run along back and side of old extension, some of the old floor might as well stay insitu with a clean cut say 650mm out from walls so around worktop kickboard depth. 

*Question* is how do I deal with the boundary of insulated &UFH built up section with old floor slab? and taking in to account the tumbled limestone tiles will span across this boundary? I was thinking 25mm perimeter PIR cut flush with FFL (?)  - but will decoupling adhesive bond to PIR and/or be ok across this 25mm gap? Will the decoupling mat  cope with movement between heated and none heated floor slabs?

 

I will have quite a bit of this interfacing old&new to deal with as also UFH will head through a trench in other part of Exisiting house which will become utility. As this small space houses the oil boiler and UFH manifold it will be plenty warm enough so hence just a 2.5M long trench for flow&return UFH pipes  (make up 100mm new con slab,160PIR,65screed, 25 Matt/adhesive/tiles) across the old slab 

 

Any observations on the plan much appreciated! Sorry it’s long winded but thought I’d tag and explain what I’m up to for benefit of anybody else on this route. 

 

Thanks!

Edited 14 hours ago by EdSt
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[nod]

At first glance You don’t need to self level Just a cement slurry to fill any gaps 8 mil isn’t enough for the tiles your using 15 mil at least 

[EdSt]

Thanks Nod. Somehow got the B&B slurry stage wrong. Don’t think I wet it down enough and have ended up with a thin uneven layer of cement&sand on top of blocks meaning an uneven finish. When I put straight edge down can see it’s not bang flush contact throughout. Would hate for any problem so was thinking self level just to be belt and braces, somebody suggested sand blind but was thinking a thin layer might be difficult (and faffy) to achieve,  again hence self level. 
 

8mm tile adhesive - thanks will check with tiler what he wants.👍

[Nickfromwales]

1 hour ago, EdSt said:

Thanks Nod. Somehow got the B&B slurry stage wrong. Don’t think I wet it down enough and have ended up with a thin uneven layer of cement&sand on top of blocks meaning an uneven finish. When I put straight edge down can see it’s not bang flush contact throughout. Would hate for any problem so was thinking self level just to be belt and braces, somebody suggested sand blind but was thinking a thin layer might be difficult (and faffy) to achieve,  again hence self level. 
 

8mm tile adhesive - thanks will check with tiler what he wants.👍

You don’t need to get the B&B so accurate, you can have a day off there   

 

The levelling is done entirely by the screeder, and if you get a good one you definitely don’t need the SLC. My guy gets the floor down so well with a dry screed that you could paint it green and play snooker on it. However, if you choose a poor screeder then expect to have to level it. 
 

12mm adhesive at least for the limestone, but it depends on how well honed the rear of the tile is, some are quite rough. Your tiler will know this, if he’s a good‘un.

 

For this situation, where you’re jumping old / new and it’s a bit of a mix I would use a decoupling membrane, as the limestone will crack over the years wherever the transitions are happening. This will virtually guarantee excellent results, and longevity.

 

You mention decoupling adhesive, which one have you looked at / has your tiler suggested?

[EdSt]

Nick from Wales. Thank you for that. I had been weighing up what the 160mm PIR would span if I put two brick under it and then stood on it on a 18mm board (simulating dissipated loading of the screed) sure it would stand a span of 600mm.I’m so paranoid about getting this wrong and the potential backtracking needed…

 

that’s the problem with DIY, you’ve no experience to know where the performance gaps are acceptable or just too anal, and so have to resort to text book (or sleeping pill! 😂)

 

need to find a tiler. But I just wanted to hear people’s thoughts on decoupler. I understand it deals with movements but just wondered if it would deal with such a stark difference in insualted&heat vs cold slab&screed. 

huge thanks for sharing your thoughts - have you any recommendations on good decoupling adhesive and decoupling membrane? Thanks

[JohnMo]

11 hours ago, EdSt said:

also want the UFH to extend in to Exisiting part of the house

Couple of things to watch for.

 

UFH works well with plenty of insulation and with zero insulation, but works very differently in both systems. Different flow temps are needed and different running regime. 

 

So don't let loops cross the two different floor build-ups, have dedicated loops in each section. You may want to to run two different manifolds and mixers for each section. They may need very different running temps.

 

The zero insulation build up will require a very low and slow running regime, if you switch it off you will have reheat the whole sub floor each time, which will use loads of energy. The way to operate is to switch on at start of heating season and off at the end of the season. If you really don't want to do that install radiators.

[JohnMo]

15 minutes ago, EdSt said:

Nick from Wales

To get a notification sent to someone type "@" and continue with no spaces to type the person's name. You will get a drop down list, choose the person - done. Comes up like this in the message 

@Nickfromwales

Edited 3 hours ago by JohnMo