50mm Floor Build Up in Conservatory - Floating Insulation Boards?

[ToastyToes]

Evening,

I've dug up the old floor in the conservatory as part of the renovation to remove the tiles.

I now need to make up 50mm to match the existing floorboard level in the rest of the house.

We're laying overlay underfloor heating across the whole ground floor and conservatory and wondered what would be the best way to get the 50mm level back.

I'm considering levelling the floor with self levelling compound and then floating 25mm insulation boards and then top the rest up with screed.

Could floating the insulation boards cause any issues in the future?

 

[acurachris]

I'm considering levelling the floor with self levelling compound and then floating 25mm insulation boards and then top the rest up with screed.

I'm not a builder but that sounds back to front to me. On a normal floor you'd insulate, then underfloor heating, then screed. Not sure why you're thinking of using a self levelling compound below the insulation, is it that bad? Maybe i've misunderstood!

I reckon 25mm screed on top of insulation boards is too thin, but maybe someone else will say different.

 

[ToastyToes]

I'm not a builder but that sounds back to front to me. On a normal floor you'd insulate, then underfloor heating, then screed. Not sure why you're thinking of using a self levelling compound below the insulation, is it that bad? Maybe i've misunderstood!

I reckon 25mm screed on top of insulation boards is too thin, but maybe someone else will say different.

The base is concrete, its level but not smooth as you'd expect. I thought installing insulation directly on this could cause it to be uneven and allow movement.

I guess I could install 25mm insulation, staple the UFH pipe to it, and then fill the remaining ~43mm gap with screed to meet the rest of the ground floors new UFH overlay board level..

 

[acurachris]

The base is concrete

Was there no insulation laid under the concrete already?

 

[endecotp]

25mm is not a lot of insulation for a floor, especially one with heating in it.

 

[ToastyToes]

Was there no insulation laid under the concrete already?

Yes I can see the old owner did lay some.. i think 75mm polystyrene from what I can see.

The floor isn't too cold as it stands being a concrete slab but I'd still like to use some extra insulation since I'm installing UFH

 

[endecotp]

OK, 75mm of polystyrene is not bad.

But in a conservatory... are you really going to keep it warm all the time? Insulation under a concrete floor slab means it retains heat, so it warms up slowly but also cools down slowly. How do you plan to use the space?

 

[ToastyToes]

OK, 75mm of polystyrene is not bad.

But in a conservatory... are you really going to keep it warm all the time? Insulation under a concrete floor slab means it retains heat, so it warms up slowly but also cools down slowly. How do you plan to use the space?

Breakfast room probably. It's south facing so warm even on a winters day if the sun has been out in the morning.

 

[acurachris]

What is the height difference from your conservatory to the rest of the house floor level, 50mm? You mentioned you are running UFH across the whole ground floor, so is that floor raising too?

 

[ToastyToes]

What is the height difference from your conservatory to the rest of the house floor level, 50mm? You mentioned you are running UFH across the whole ground floor, so is that floor raising too?

It's 50mm from conservatory concrete slab to the top of the floorboards across the ground floor.

18mm UFH boards will be added across the ground floor, including the conservatory.

 

[noseall]

Ideally you need 75mm of screed above UFH. If there is insulation already below the slab then adding another layer is unlikely to make much difference. Add some 25mm to the external walls perimeter if you want to do something useful.