Solid floor retro-fit insulation with UFH

[mh12]

Would welcome opinions on the following please:

Want to install underfloor heating on solid ground floor of living room and another floor space which is soon to be come the bathroom.
Current setup is living room has red quarry tiles above concrete slab and the intended bathroom has what appears to be concrete slab approx 20cm above some sort of ash and then earth.

Intention is to install underfloor heat so there will be a need to some digging :
Plan is to have some hardcore base then blinding sand then DPM then PIR board then concrete another DPM layer and UFH in screed to finish at floor level.

I understand the PIR is contraindicated for IWI on solid walls, does the same hold true for solid floors?

Thank you in advance

 

[aockenden]

Checkout insulated limecrete floor systems as an alternative to the approach you’ve mentioned above.

 

[mh12]

Thank you aockenden.
After about 6 months of educating myself on this forum and benefitting from the wealth of knowledge of experienced members and also benefitting from the shared experience of new members I have started to run with my project which has been stalled for many an age.
1st point of call, extension, work has begun and retro fitting some ground floor space for UFH. Attached is a picture of the proposed UFH.

For the existing building intentions is to retro fit with the following build up from bottom up:

Soil, Geotextile membrane, RPG, Geomembrane, Geo grid with clip rails for UFH pipes, Normal Screed (thickness? 70mm), with upstands of cork board thickness 40mm adjacent to walls.

Questions: 1 ) What thickness of RPG to select? 2) Do I need concrete in this build up ?

So the above retro fit is to go into what will become the WET room floor but also to be fitted additional into a walkaway connecting new extension to existing house/lounge and also to be retro fitted into the lounge - pictures to follow.

Finally the new extension floor will be:
225mm hardcore, 50mm sand blinding, DPM, 100 concrete, DMP, 100 or 150 mm Cellotex insulation, DMPA, 75 mm WET screed with UFH

I welcome critique of the plans for the RETRO fit bit please. Need to get the floors in within the next week or so.

 

[mh12]

Sorry forgot to add this the build up for retro fit floor minus the limescreed

 

[haf]

I am looking at something similar - though will get a architect to figure out what the best option is In parallel with my own research) .. Currently my soil is 300mm max below the floorboards so I am looking for a solution that doesn't require loads more digging.. Will be interested in how you get on as I am probably 6-9 months away from starting anything other than the LBC. I assume you are not yet at LBC stage?

 

[a twig]

I wouldn’t necessarily trust an architect as the majority won’t have experience of such solutions.

Better off talking to a specialist and working a solution out with them and then getting the architect to detail that

 

[mh12]

I am looking at something similar - though will get a architect to figure out what the best option is In parallel with my own research) .. Currently my soil is 300mm max below the floorboards so I am looking for a solution that doesn't require loads more digging.. Will be interested in how you get on as I am probably 6-9 months away from starting anything other than the LBC. I assume you are not yet at LBC stage

The knowledge I've gained from this forum beats anything from elsewhere. Simply put unless you get an architect who has dealt with heritage building they're unlikely to recommend the most optimal solutions primarily due to lack of exposure to breathable systems.
I would highly recommend trawling through this site.
I'm not the best of students but having spent hours on end on this site I think I've reached a basic grasp of what the requirements for renovating old buildings with respect to insulations etc. Still learning though.
If you have 300mm floor void you should be fine maybe dig up another 100mm for good measure but as you're 9 months away no need to rush in this regard.
Off course I will keep forum posted on my progress.
Hoping that I will become useful on this forum....
Definitely enjoy the learning curve, just wish I was talented DIYer as some of the members on this forum.
I make good non paid labourer though but want to upgrade now.
Would you believe my boys (teenagers) wanted money upfront helping me in some of labouring duties in a house that is essentially being done up for them. The cheek.
They're hard negotiators and I was desperate so I gave in.

 

[DaveG]

I’m looking into this at the moment too, being halfway through digging up a floor.
I’d initially considered going back to a slab over the RFG and then an overlay system so as I could go right through the other rooms at the same time but the problem I guess is an overlay creates a vapour barrier whereas laying the pipe into a lime finish doesn’t.
Can I ask what you plan to use as a floor finish? I really wanted to use engineered wood but the problem once again is it sacrifices breathability compared with some other options so I’m a bit stumped really unless I stick with an overlay system but rely on cork edging or something similar to be sufficient at allowing any vapour transportation.

In my previous 1980s timber framed house an overlay system over the existing uninsulated concrete floor worked exceptionally well but I realise a solid stone walled property with an altogether different foundation designed to manage moisture rather than prevent it, is an entirely different beast!

On the subject of the cork edging around the floor, how is this finished? It’s not left exposed surely?

 

[mh12]

Dave, I'll try my best to answer with the limited knowledge I have in this arena.

I'm planning on having non stained tiles at the finished floor with lime grout. Dunno if tiles are totally unbreathable but I suspect the lime grout should help.

Was thinking initially of LVT but this runs the risk of become wet/damp? from the NHL slab underneath potentially and also I think LVT would require DPM which , well which I don't know much about. I'm going to try and resurrect a similar thread which might be helpful. Other members have used DPM underneath engineered wooden floors with no issues.

I didn't quite understand what you meant by overlay systems- can you please expand?

Thanks

 

[DaveG]

I think the grout lines between the tiles would give you enough breathability as you’ve described. For wood it would be a little more difficult I think.
Here’s a link to some overlay systems:

Overlay Underfloor Heating Systems | The Floor Heating Warehouse

www.thefloorheatingwarehouse.co.uk

They are more aimed at retrofit applications where people aren’t digging up floors. It’s a thin foam type board usually with some foil in that goes directly over a concrete floor.
I did this in my last place with tiles over the top and it was very effective.
The advantage for me to do that again would be avoiding having to dig out another two rooms before I can install as that would be a huge expense and upheaval.

I guess my last option is to have a mix of the two but that would mean 2 manifolds, 2 pumps etc. It still seems quite a faff.
It seems you can hardly ever do these kinds of jobs piecemeal. You’ve got to go all in!