UFH Retrofit on concrete slab

[willmo]

I'm looking to fit UFH and just can't work out the best solution. We're going to fit it in to a 60m² extension that was build in the 90's (knocking two 30m² rooms in to one to create a nice big open plan kitchen living room). Luckily we were left the drawings from when the extension was installed. The current floor set up is:

 

- 150mm compacted hardcore

- DPM

- 100mm concrete

- 40mm EPS insulation  - is it worth changing this to more efficient PIR insulation whilst we're at it?

- 22mm T&G chipboard

- Underlay

- Carpet

 

The maximum that we'd be able to raise our floor is by an additional 30mm, due to external door thresholds etc. I'm looking for ideas on what would be the best way to install UFH. Obviously the most efficient way is to dig everything out, have a 100mm concrete slab, 125mm PIR insulation, then the UFH in a 75mm screed. However I reckon that the cost of this will be much greater than the additional heating costs by leaving the current level of insulation as is.

 

For this reason, I'm looking at the various retrofit options out there.

 

- Replace this chipboard with this pre routed chipboard. At £30/m² this looks like a very expensive way of doing it, and doesn't add any additional insulation, however will not raise the floor.

- Low profile UFH on top of chipboard, with self leveling compound. This would be quite an easy job, and would fit within the 30mm of extra floor height we can afford. However I don't know if it's worth upgrading the EPS insulation.

- Low profile EPS/Aluminium spreader plate hybrid - Install this on the existing chip board. Adds a little extra insulation, not too expensive. Keep the exisiting PIR insulation?

I just keep going round in circles. Our goal is to have a room that is efficient as possible with a nice warm floor that we can walk on in bare feet, with maybe a laminate or LVT floor finish. I'm happy to accept that this system may not meet the 4000Wish power requirement for the room, so we may need to keep a few radiators.

 

Any help/guidance or additional ideas will be really appreciated.

 

[Russell griffiths]

Forget it and fit radiators, you will spend more money heating the ground under the house. 

[Oldsteel]

5 minutes ago, Russell griffiths said:

Forget it and fit radiators, you will spend more money heating the ground under the house. 

With the specified insulation, yes. 100mm minimum in the slab if you dont want to lose heat into the ground.

[willmo]

I'm fully aware that there will be heat loss to the ground. So am more than happy to include radiators in the room. However we want to get away from having a freezing floor.

 

As far as I'm aware, keeping the UFH to a lower temperature will reduce heat loss to the floor, whilst keeping the floor warm. I guess then it's the trade off of the cost of install of the wet system, vs running costs of an electric mat. I think given the area, wet might win the cost comparison.

 

Unless there is a better way to achieve a warmer floor?

[Onoff]

How high are the ceilings? Raise the door heights?

[willmo]

Unfortunately, given the front door threshold, 30mm is the maximum we can increase Going any higher would mean moving the front door, back door, and two sets of french doors, which I assume would mean moving the lintels up etc.

 

If we were to get stuck in to that amount of work, I think digging the slab out would also become an option.

[PeterW]

49 minutes ago, willmo said:

As far as I'm aware, keeping the UFH to a lower temperature will reduce heat loss to the floor, whilst keeping the floor warm

That's not correct - Heat loss is increased by the temperature but you will need to put more heat into the building anyway to heat the room so the floor temperature will become irrelevant and your losses will be near identical. 
 

What is your plan for the floor finish for the new room as that will affect the options. 

[JFDIY]

Couldn't you do 70mm PIR then used the grooved t+g structural  chipboard flooring that takes the UFH pipes?

[Mr Punter]

If you have the money you could change your EPS for Kingspan Optim-R which is a vacuum panel insulation board.

 

The 40mm thickness will be equivalent to 195mm of your current EPS.

[willmo]

1 hour ago, PeterW said:

That's not correct - Heat loss is increased by the temperature but you will need to put more heat into the building anyway to heat the room so the floor temperature will become irrelevant and your losses will be near identical. 
 

What is your plan for the floor finish for the new room as that will affect the options. 

I probably should have been clearer, I'm thinking we'll also need a couple of radiators in the room too - which would allow the UFH to run colder.

 

We're thinking of a herringbone wood effect, however are not tied to wood. So tile, engineered wood or LVT are still all on the cards. I believe tile would be the best for UFH performance?

 

1 hour ago, JFDIY said:

Couldn't you do 70mm PIR then used the grooved t+g structural  chipboard flooring that takes the UFH pipes?

That's probably the most sensible option isn't it, even if it is slightly more expensive due to the routed T&G, it will probably pay off in the future. Especially as we've got polystyrene under there at the minute, it would be good to switch that out for something more efficient.

 

I remember seeing a post of someone who tried to route out their own T&G and said it was a nightmare. I've got a nice beefy router, but am thinking it might not be worth doing it myself.

 

45 minutes ago, Mr Punter said:

If you have the money you could change your EPS for Kingspan Optim-R which is a vacuum panel insulation board.

 

The 40mm thickness will be equivalent to 195mm of your current EPS.

Oh wow, I've not come across that. The lack of prices online makes me think it's super expensive (looks maybe around £70 a square meter?). I'm just drawing the house up on autocad so can send it over to get a quote. Thanks!

[Mr Punter]

If you cannot afford the VIPs, 40mm PIR will give you an extra 50%, so like having 60mm EPS.  50mm PIR would be like 75mm EPS.

[PeterW]

21 minutes ago, willmo said:

We're thinking of a herringbone wood effect, however are not tied to wood. So tile, engineered wood or LVT are still all on the cards. I believe tile would be the best for UFH performance?

So this is a “depends” answer ..!!
 

Wood will insulate and be thicker - you could use engineered wood but that would be 14mm thick on the assumption that you float it over a backer board system of around 15mm. That leaves 60mm for PIR which isn’t enough. 

 

Tile would need a similar - if not slightly thicker - panel system and more rigid. Ideally onto a screed but you don’t have the thickness for a minimum 50mm liquid screed, plus 10mm tile and adhesive. That’s going to be probably 55mm insulation at best 

 

LVT (depending on brand) ideally goes onto a screed system, so 5mm for LVT and then 50mm screed is leaving you with 45mm insulation which isn’t enough. 
 

You say about “cold floor” but only tiles really feel cold underfoot. You could do something like LVT on 6mm ply on 22mm T&G and float it all on 60mm of PIR. It won’t feel warm but neither will it feel cold. 
 

To be honest if you’re going to the hassle of ripping out walls then I would be taking out the floor too. 100mm concrete isn’t that thick and assuming it’s not got loads of rebar in it a decent jigger breaker will take it out no problem. You’ll be left with 130mm for insulation with a 50mm flow screed over the top, a perfectly flat new floor and UFH too, with no compromises. 

[joth]

3 hours ago, willmo said:

[...] However we want to get away from having a freezing floor.

 

 

 

2 hours ago, willmo said:

[..]I think digging the slab out would also become an option.

 

If the goal is solving a freezing floor, digging it out and insulating it properly is the best choice by far, so if that is an option then go for it.

 

The add on benefit then is you can run the UFH at a much lower temperature which will allow much more freedom in selecting floor finishes.

 

 

 

[Onoff]

@Jeremy Harris made a comment in the thread below, that even with his 300mm of EPS below his slab he's losing around 8% to keeping the worms warm.

 

 

You only pay for insulation once. 

[willmo]

8 hours ago, PeterW said:

So this is a “depends” answer ..!!
 

Wood will insulate and be thicker - you could use engineered wood but that would be 14mm thick on the assumption that you float it over a backer board system of around 15mm. That leaves 60mm for PIR which isn’t enough. 

 

Tile would need a similar - if not slightly thicker - panel system and more rigid. Ideally onto a screed but you don’t have the thickness for a minimum 50mm liquid screed, plus 10mm tile and adhesive. That’s going to be probably 55mm insulation at best 

 

LVT (depending on brand) ideally goes onto a screed system, so 5mm for LVT and then 50mm screed is leaving you with 45mm insulation which isn’t enough. 
 

You say about “cold floor” but only tiles really feel cold underfoot. You could do something like LVT on 6mm ply on 22mm T&G and float it all on 60mm of PIR. It won’t feel warm but neither will it feel cold. 
 

To be honest if you’re going to the hassle of ripping out walls then I would be taking out the floor too. 100mm concrete isn’t that thick and assuming it’s not got loads of rebar in it a decent jigger breaker will take it out no problem. You’ll be left with 130mm for insulation with a 50mm flow screed over the top, a perfectly flat new floor and UFH too, with no compromises. 

If only they'd put a bunch more insulation in when it was build in the 90's eh, this would be so much easier. But you make a good point on how it should be easy to pull up. Hopefully in practise it would be just as easy. I've had a little research of putting insulation directly on hardcore (with DPM in between), and then a screed. It looks feasible, as there has already been a slab down everything should be sufficiently compacted. Thanks for the help. 

 

8 hours ago, joth said:

 

 

If the goal is solving a freezing floor, digging it out and insulating it properly is the best choice by far, so if that is an option then go for it.

 

The add on benefit then is you can run the UFH at a much lower temperature which will allow much more freedom in selecting floor finishes.

 

 

 

 

Yep, that would be the dream goal. Thankfully we have the room to not have to use this part of the house for a good few months for any work to be done, so time wise it's fine, however we don't want to sink a load of money in to it. Do you have any idea how much something like that would cost? 5k, 10k 15?

 

6 hours ago, Onoff said:

@Jeremy Harris made a comment in the thread below, that even with his 300mm of EPS below his slab he's losing around 8% to keeping the worms warm.

 

 

You only pay for insulation once. 

Oh wow, that's a great amount of insulation! I wish we were doing the extension from fresh, so that we could specify something just as good. The cost to add it during the build isn't a lot more, however it seems a bit wasteful to pay to rip it all out and start again. 

[Onoff]

8 hours ago, willmo said:

Oh wow, that's a great amount of insulation!

 

300mm? For new builds on this site that's pretty normal now. People's build specs (here) far exceed the regs in terms of insulation and particularly air tightness. Air tightness is critical but goes hand in hand with good ventilation in the form of MVHR so as not to get high humidity, dead air, mould etc. Couple all that together, done right and it equates to lower bills.....forever.

 

I've dug down in one 10m2 room only (by hand). Ended up with 165mm insulation. 150mm pir + 25mm eps. If I'd have known what I do now I'd have maybe dug deeper! 

 

(In fact with hindsight I might have done it all different! ?).

 

@oranjeboom on here dug down the floors in his whole (existing) house. Not sure how much insulation he ended up with. Think he went with ewi too?

 

You can only go so far with an old house. Internal walls will go through the floor insulation layer whereas in a new build you might start with a big, insulated slab. First floor joists penetrating walls create multiple cold bridge and air leakage points. Everything can be improved but it's often a time consuming, disruptive, work-around that falls short. Worse if you're living there! 

 

(In fact with hindsight I'd have knocked it down and rebuilt it! ??).

Edited January 14, 2021 by Onoff

[Onoff]

 

8 hours ago, willmo said:

 

Edited January 14, 2021 by Onoff

[daiking]

3 hours ago, Onoff said:

I've dug down in one 10m2 room only (by hand). Ended up with 165mm insulation. 150mm pir + 25mm eps. If I'd have known what I do now I'd have maybe dug deeper! 

I’m glad I had the foresight to retrofit my UFH before the slab was poured...

 

The benefit of not connecting the UFH for 4 years is that you realise that a decent amount of insulation, 100mm EPS + 100mm PIR, means a tiled floor is not the sort of chilling cold you get in an older un-insulated extension. Even without UFH, the insulation makes a discernible difference so it should be the priority.

[Onoff]

6 minutes ago, daiking said:

I’m glad I had the foresight to retrofit my UFH before the slab was poured...

 

The benefit of not connecting the UFH for 4 years is that you realise that a decent amount of insulation, 100mm EPS + 100mm PIR, means a tiled floor is not the sort of chilling cold you get in an older un-insulated extension. Even without UFH, the insulation makes a discernible difference so it should be the priority.

 

Agreed. Even in my as yet unheated bathroom the tiled floor is oddly not particulary cold underfoot.

[willmo]

3 hours ago, Onoff said:

 

You can only go so far with an old house. Internal walls will go through the floor insulation layer whereas in a new build you might start with a big, insulated slab. First floor joists penetrating walls create multiple cold bridge and air leakage points. Everything can be improved but it's often a time consuming, disruptive, work-around that falls short. Worse if you're living there! 

 

Tell me about it! The original part of the house is from the 1800s, so there's not a spot of insulation in there. It's a mix of suspended floors and solid (I assume it must just be compacted earth in the kitchen).

 

I've currently ripped the floorboards up in the suspended section for 100mm of PIR, with UFH spreader plates on top of that, and then the original floor boards on top. Along with the log burner, and 50mm insulation on the inside of the one external wall, that room should be very nice and warm. 

 

The place is draught city though, and we can't do too much about the single glazed front windows at the minute. We're currently trying to find what we allowed to do in the conservation area. Secondary glazing doesn't do a bad job though. The wooden double glazing from the 90's at the back of the house is way more draughty.

 

Our priorities are reducing draughts, improving insulation, UFH in that order I think.