Insulating existing concrete floor - your experiences?

[firenze13574]

Hi all,

We have a flat roof extension (built in late 1970s) at the back of our house that contains the kitchen and dining area. This is a concrete floor covered by a thin layer of chipboard and then lino (see pic).

The extension including the floor is noticeably colder than in the rest of the house. I am looking at getting the roof insulation upgraded but as we are planning on installing a new kitchen also looking at floor insulation options.

Where the existing lino connects to the carpet in the main part of the house there is a rise of approx 10mm (see pic). This could be used for insulation board, plus perhaps another 5-10mm if new lino can be laid without the chipboard.

I would be interested to hear a) anyone's experiences with adding 10-20mm of insulation board onto a concrete floor - did it make any difference or was it a waste of time?

Also, b) is it worth putting down the insulation board after ripping out the old kitchen but before installing the new one, so that it covers the whole concrete floor? I am wondering if it is possible to isolate the new kitchen units from the concrete floor, or if this will cause more problems than it solves.

Thanks for your advice.

 

[motorbiking]

have you thought about laminate on double insulated underlay?

To make a big difference will probably need 50mm

 

[endecotp]

Your picture looks more like hardboard than chipboard.

Most insulation boards (e.g. celotex) need reasonably sturdy floating wooden flooring over the top; I think 20mm T&G is the minimum recommended, but in practice that means 22mm chipboard. An alternative is to put down wooden battens and insulation between them; if the battens are close enough together then you can use thinner wood over the top, maybe only 12mm. Still, it wil be much thicker than you seem to have space for.

One option might be something like Marmox Multiboard. This has a stronger surface than other boards - fibreglass & cement. You can tile directly over marmox; for vinyl I think you'd need a layer of something, e.g. thin ply (thoughts anyone?). So you could have 10mm marmox, 5mm plywood, then vinyl. 10mm isn't very much though. Ideally you'd have a lot more.

There are other "tile backer" boards and "underfloor heating" boards with similar properties.

The kitchen units should probably be supported using battens off the concrete.

 

[^woody^]

Waste of time

 

[mikeey84]

Aerogel could be an option, but it's eye-wateringly expensive so payback would be measured in centuries.

 

[endecotp]

Aerogel could be an option

Not really. It's compressible, so you need battens and a layer of reasonably thick ply over the top. There isn't space for that.

The "stupidly expensive" solution that would work in this case would be vacuum panels - but it would be cheaper to use 50mm of celotex and raise the floor level through the rest of the house.

 

[oldbutnotdead]

Do you know if there's any insulation in your flat roof- if there isn't (and there's enough depth on the joists or scope to lower the ceiling by 150mm or so) then you'd get a much better ROI by dropping the ceiling & insulating up there

EDIT Oops- yes you're already looking at that

 

[Doggit]

As already spotted, you've got hardboard on the floor, and that's doing nothing whatsoever. It's going to depend on how much height you're prepared to lose, and would you accept a step up into the kitchen. You also haven't mentioned the construction of the walls etc, as this could also be contributing to the cold area.

Firstly, if you don't insulate under the kitchen units, then you'll have a cold space that will seep out into the kitchen, so reckon to do the floor, and then install the kitchen. But you can't put down insulation, and then lino, as it'll just sink through, so you'd need to add 18mm T&G chipboard on top of it, glued along the edges, and then the lino, and that's going to add about 30mm at least (assuming 10mm UFH insulation). Alternatively, either glue down a wooden floor, or put down 5mm fibreboard, and then a floating floor. You could use laminate, but it gets cold in the winter, so hardwoods better, and for a kitchen, engineered wood is more stable.

I've just done a floor with 5mm fibreboard, and then a floating 18mm engineered oak floor on top of it, and it's way warmer than the old tiles were.

 

[mikeey84]

Not really. It's compressible, so you need battens and a layer of reasonably thick ply over the top. There isn't space for that.

The "stupidly expensive" solution that would work in this case would be vacuum panels - but it would be cheaper to use 50mm of celotex and raise the floor level through the rest of the house.

You can get aerogel boards designed for floors that don't need ply over the top. 13mm in total according to a website I've seen.

Whilst aerogel is eye-wateringly expensive, vacuum panels are arse clenchingly expensive!

 

[tomfe]

Areogell is only twice as efficient as pir, so 13mm panel is the same as 26mm kingspan....

 

[endecotp]

Areogell is only twice as efficient as pir, so 13mm panel is the same as 26mm kingspan....

It's not even as good as that:

Spacetherm aerogel: 0.015 W/mK
Phenolic insulation board: 0.018 W/mK
PIR board: 0.022 W/mK

It's only useful if you need something that's vapour-permeable, where you'll be comparing it with mineral wool, wood fibre etc. They are typically around 0.038 W/mK so it's about 2.5 times better.

 

[firenze13574]

Cheers for the feedback.

@endecotp, you are right it is hardboard not chipboard.

@Doggit, the walls are double leaf brick with some form of cavity insulation (a kind of foam that turns to powder as soon as you touch it). Agree 100% it would be better to insulate under units too.

@mikeey84, the thermablock website mentions "Aerogel Blanket Insulation of 10mm or 20mm, with a 3mm high impact board". Forgive my ignorance but this means you can place lino directly on the "high impact board", right ? Any idea how much aerogel would cost roughly per m2? (extension is about 3.5m x 5.5m)

Thanks again.

 

[endecotp]

thermablock website mentions "Aerogel Blanket Insulation of 10mm or 20mm, with a 3mm high impact board". Forgive my ignorance but this means you can place lino directly on the "high impact board", right ?

No. The aerogel will be crushed when you walk on it.

Any idea how much aerogel would cost roughly per m2?

Very roughly £100 per square meter for 10mm thick.

It's not the solution in this case.

 

[endecotp]

I noticed some 5mm extruded polystyrene underlay boards in b&q yesterday that said you could lay vinyl tiles directly on top. I don't know if vinyl tiles are significantly stiffer than vinyl on a roll, but maybe a couple of layers of those would be best.