Insulating concrete floor for engineered flooring

[gambo]

I live in a detached house from late 80s. At the moment the floor downstairs is some cheap carpet with rubber waffle underlay (tog of around 1.3-1.5 based on what i've found).

When it's not freezing outside I can live comfortably with temp set to 19.5-20. But after 2-3 days of very low temperatures I need to increase the temp to 20.5-21 because of the cold i get from floor in some rooms.

I've already renovated upstairs and am quite glad I didn't start downstairs before the energy crisis because I wouldn't have done it very efficiently.

I have lots of different leftovers at home and one of them is some random 9mm sheet of insulation from b&q (insulation board). I put it on top of carpet and can already feel a HUGE difference. I don't think the technical spec of the board actually proves what i feel but perhaps it also thanks to air trapped between carpet and the board.

Anyway, downstairs will be renovated and will lay engineered floor. I'm thinking about heat pump in future but I don't want to put 100m boards because the most i feel I can sacrifice in height is 50mm including wood floor. So, maybe HP won't be needed if I insulate the house properly and lower the cost of gas. What would be the best to put as underlay? 25mm eps topped with backer board?

Edited January 22, 2023 by Nickfromwales
50mm instead of 5mm

[Nickfromwales]

3 hours ago, gambo said:

I live in a detached house from late 80s. At the moment the floor downstairs is some cheap carpet with rubber waffle underlay (tog of around 1.3-1.5 based on what i've found).

When it's not freezing outside I can live comfortably with temp set to 19.5-20. But after 2-3 days of very low temperatures I need to increase the temp to 20.5-21 because of the cold i get from floor in some rooms.

I've already renovated upstairs and am quite glad I didn't start downstairs before the energy crisis because I wouldn't have done it very efficiently.

I have lots of different leftovers at home and one of them is some random 9mm sheet of insulation from b&q (insulation board). I put it on top of carpet and can already feel a HUGE difference. I don't think the technical spec of the board actually proves what i feel but perhaps it also thanks to air trapped between carpet and the board.

Anyway, downstairs will be renovated and will lay engineered floor. I'm thinking about heat pump in future but I don't want to put 100m boards because the most i feel I can sacrifice in height is 5mm including wood floor. So, maybe HP won't be needed if I insulate the house properly and lower the cost of gas. What would be the best to put as underlay? 25mm eps topped with backer board?

Hi.

So do you have a concrete floor or a floating floor with a ventilated void? Any insulation anywhere that you know of?

[gambo]

I'm afraid it's just concrete floor. I can't see any ventilation outside in bricks and when I lifted a piece of carpet I can only see concrete. It feels warmer where laminate floor is (with some sort of insulation underlay) than in living room and garage conversion. The garage conversion is the coldest room but apparently it was done during the build even though LA doesn't know about it.

[Redbeard]

You say "the most i feel I can sacrifice in height is 5mm including wood floor." but then you go on to say "What would be the best to put as underlay? 25mm eps topped with backer board".

 

25mm + backer board is a lot more than 5mm! Was the '5mm' figure meant to be '50mm'? If the latter then a vestigial flooating floor of 25 PIR, DPM as VCL, 18mm T & G OSB + finished floor may 'cut the mustard'. Not goood enough for UFH, though, IMO.

 

Remember, though, if you lift the ground floor by c50mm you put your stairs out of compliance with Bldg Regs, unless you can make the bottom stair a 'landing', in which case, IIRC, it can have a lesser riser.

[gambo]

Yes, I meant 5cm. I need to check stairs and building regs. Upstairs there already is 6mm cement board (as sound insulation) + 3-5mm underlay + 15mm floor but the stairs are not finished yet so perhaps I could adjust them accordingly. 

What would be the best solution if I wanted UFH?

btw we can ignore stairs for now, I don't like them tbh so would happily replace them if it opens us to more suitable options.

Edited January 21, 2023 by gambo

[Redbeard]

Some installers will say a 'thin solution' ('insulated mat' - type pipe trays) is OK. I am very convinced it is not. You don't want to be heating a void or a slab. A client had 75mm PIR below UFH and I still do not think this is sufficient. I would like to see 150mm. (BTW, it does not have to be PIR - other choices - including natural materials such as wood fibre or cork - exist).

[Tims]

We have 100mm PIR and 50mm perimeter insulation plus 40mm anhydrous screed with UFH it meets building regs, it works well and has a good U value, the heating goes on for about an hour in the morning and an hour in the evening and we keep the heat in the room (it is well insulated though).

 

We also have one 1 renovated ground floor bathroom with 50mm PIR, UFH and floating screed (more relevant), the total build up is 90mm however, I ummed and arred about having UFH in here and only 50mm of PIR under it for quite a while before I took the risk. The later works and keeps its heat but we are probably loosing more to the old concrete slab than we would like, as its internal the perimeter loss isn't as bad as it will be in your case. Again the heating is on for about an hour in the morning and an hour at night and room stays at around 21⁰C through out the day so something appears to be working.

 

The rest of the renovation will have 50mm PiR under 18mm floating flooring (due to height with DPM and VCL too) and no UFH this still gives a 68mm build up. Without UFH, 30mm PIR and a floating floor will get you your 50mm and be better than nothing. don't forget that you will probably need to level your existing slab with levelling compound or sand before you put PIR down if it's anything like ours. PIR's nasty stuff but if you're short on space it has excellent thermal resistance when compared to some of the less nasty alternatives.

 

I personally think that the 25mm or so EPS UFH panels on the market with routing for UFH pipes over an uninsulated concrete floor won't have the required U value for a good UFH system and will be pretty pants.

Edited January 22, 2023 by Nickfromwales
typos

[gambo]

50-60mm including wood floor is the maximum I can sacrifice. Adding T&G feels like a waste of space but I know I can't lay floor on top of PIR. Could I lay tile backer boards on PIR instead of T&G, or just backer board of let's say 40mm?

[Tims]

I considered cement T&G tile backed boards for the bathroom floating floor but as we were getting the extension screeded I went for screeding this room at the same time (I'm glad that I made this decision). If you aren't tiling and don't bother with UFH there are details (I think kingspan and celotex have one) for chipboard floating floors on PIR (you need DPM and VCL) , there are also details out there for tiling floating floors with various cement boards over T&G floating floor chip board or just T&G cement board ( I don't know how good these are and where we haven't screeded I am just going to use laminate flooring). After researching lots of solutions I came to the conclusion that if you want UFH you are best going for a much thicker build up floor than you currently want.

[gambo]

I will rather move house than reduce height by 10-15cm.

So, after more research my options I think are: PIR + T&G or marmox, perhaps PIR + marmox to achieve better U.

[MikeGrahamT21]

Not sure if I missed this above, but is there no option of digging out the old concrete and starting again with a modern buildup?

 

another option, for limited space is vacuum insulation panels. https://www.kingspan.com/gb/en/products/insulation-boards/floor-insulation-boards/optim-r-flooring-system/

 

or aerogel

https://enviroform-insulation.com/insulation/solid-floor-insulation/

Edited January 22, 2023 by MikeGrahamT21

[saveasteading]

On 21/01/2023 at 11:36, gambo said:

random 9mm sheet of insulation from b&q (insulation board).

I have an uninsulated concrete floor, and a small area of this insulation in my workshop, under carpet tiles. A fragile foam board with aluminium surface.

The benefit to comfort is immediate as it resists heat loss from feet to cold concrete but  so do shoes.

But that is not the same as insulating the room against heat loss.

It is better than nothing of course. This plus underlay plus carpet is starting to add up.

You could add however many mm you can tolerate using foam board as specified for under heated tiled floors. 

Btw the aluminium face does not assist insulation, but it makes bare feet in near contact  feel warmer and helps sell boards by looking good.

[Nickfromwales]

8 hours ago, gambo said:

50-60mm including wood floor is the maximum I can sacrifice. Adding T&G feels like a waste of space but I know I can't lay floor on top of PIR. Could I lay tile backer boards on PIR instead of T&G, or just backer board of let's say 40mm?

You could possibly get away with retro-fit overlay UFH here if the finished floor is a porcelain tile, as this will make the floor a much better emitter of heat. Carpet will always make this a no go afaic.

This will always be a very poor installation, with elevated running costs, so seriously consider sticking with rads.

[Iceverge]

Get digging I say. 

 

You'll never regret putting in too much insulation. 

 

Leveled sand binding. 

150mm EPS

DPM

150mm EPS.

Slip sheet

UFH fixed with long staples. 

100mm concrete slab. 

[gambo]

4 minutes ago, Iceverge said:

Get digging I say. 

 

You'll never regret putting in too much insulation. 

 

How much could it cost on 80s/90s build very roughly? Just for digging. Im a bit worried it will make a lot of mess.

[Iceverge]

That's a piece of string question unfortunately. 

 

Ranging from £60/m2 if you do all the work yourself and bury the spoils in the garden to maybe double that if you contract it out. 

 

Have you checked to see how thick your floor slab is? It might only be 50mm. You could save lots of digging by opting for a thinner layer of insulation and floating 2xlayers of 11mm OSB on top crossed, glued and screwed.  100mm PIR, 22mm OSB and carpet would be about 0.2W/m2K at less than 150mm total depth. Comfortable underfloor as not cold tiles or concrete.  Oversize the rads to future proof for ASHP. 

 

 

 

 

 

Yes it will be messy. 

 

 

 

[gambo]

I haven't checked the depth. I most likely stick to insulating the current slab as I think it could be too disturbing to dig it up.

[Nickfromwales]

19 minutes ago, gambo said:

I haven't checked the depth. I most likely stick to insulating the current slab as I think it could be too disturbing to dig it up.

Just remember if you insulate and lay carpet you'll need something to deal with point loading. Can you be persuaded into installing engineered floor or tiles? Will save on the depth and cost of the wooden deck board to go over the insulation.

[gambo]

1 hour ago, Nickfromwales said:

Just remember if you insulate and lay carpet you'll need something to deal with point loading. Can you be persuaded into installing engineered floor or tiles? Will save on the depth and cost of the wooden deck board to go over the insulation.

That's the plan, ie. insulation boards + engineered wood (woodpecker 15mm). Posts above suggest using T&G over insulation boards but it would reduce the insulation by 18mm. I'm thinking if I can just buy wider planks to spread the load even more.

[Temp]

We have 80mm insulation under UFH and wish we fitted more. I would stuck with rads if you only have 50mm.

 

I think Building Regs recommend minimum 18mm thick boards over joists or similar. I would look at 20 or 21mm Engineered boards and 30mm PIR insulation if you can get it?

 

Figure out which direction is best to run the boards. 

 

Fit 30mm PIR insulation between 30mm battens on 600mm centres. Battens at 90 degrees to the direction the boards will run. Battens glued and/or screwed down. Batten also around the perimeter and at doorways. 

 

Fit 21mm T&G Engineered wood boards (210mm wide?). They should be glued together and secret nailed to the battens. The glue applied by brush to the groove to make sure of really good coverage. Eg don't just run the glue bottle down it doesn't usually apply enough glue to the sides to the groove (according to our builder).

 

Should allow an expansion gap around the perimeter covered by skirting.

 

If you can afford it digging out the floor and fitting more insulation would be better.

Edited January 23, 2023 by Temp

[gambo]

22 hours ago, Temp said:

Fit 30mm PIR insulation between 30mm battens on 600mm centres. Battens at 90 degrees to the direction the boards will run. Battens glued and/or screwed down. Batten also around the perimeter and at doorways. 

 

Fit 21mm T&G Engineered wood boards (210mm wide?). They should be glued together and secret nailed to the battens. The glue applied by brush to the groove to make sure of really good coverage. Eg don't just run the glue bottle down it doesn't usually apply enough glue to the sides to the groove (according to our builder).

Wouldn't this create a significant thermal bridge (the battens)? I've just removed carpet and underlay and put: 25mm quinn therm (from someone's skip) + 6mm cement board + carpet (but no old underlay). It's just around my desk and chair to see how it feels. I'm a bit worried about thermal bridging of battens so perhaps using thin backer boards + 25mm kingspan would spread the load evenly.

 

22 hours ago, Temp said:

If you can afford it digging out the floor and fitting more insulation would be better.

I'm a bit worried that that's not well money spent. Based on my research it would cost £10-15k at least. Having a very well insulated floor would force me to start looking at other bits like insulating walls (internally), replacing windows. Now I at least have an excuse that the house is not good for ASHP anyway. Other thing is finding someone who will replace the floor without causing structural damage to the house.

[Temp]

You might get away without battens if the insulation is suitable but check with the maker.  I've heard of people having problems in high traffic areas. People walking around bend the boards slightly compressing the insulation which eventually breaks up or becomes spongy.