To celotex or not to celotex?

[dch]

Hi all first post,

I am in the process of a self build conservatory, the base has been finished and the questions are to do with insulation of the floor which has been laid in by process of Hardcore then sand, Over the sand is a damp-proof membrane then the concrete slab.
Will it be ok to put 50mm celotex on the slab with 18mm chipboard flooring on top of the celotex? or would it be a better option to use a thinner insulation board and screed over the celotex? The final flooring will be laminate floor if this makes any difference to how its done. hope there is some suggestions for this?
cheers Dch

 

[freddiemercurystwin]

50mm insulation would be better than nothing be it under screed or timber. Don't think it will make much difference tbh, if you go the timber route use 22mm plywood instead of chipboard though.

 

[dch]

50mm insulation would be better than nothing be it under screed or timber. Don't think it will make much difference tbh, if you go the timber route use 22mm plywood instead of chipboard though.

cheers what about a extra sheet of membrane between the slab and celotex or will that be ok to leave it bare?

 

[freddiemercurystwin]

Err no need from a damp point of view if you've got a dpm under the slab and its all sealed as it should etc.

 

[theoldun]

Freddy , We have never done a floating floor with ply mate.
For floating floor over insulation, we use 18 or 22mm P5 T&G chipboard, all joints well glued to stop squeaking, 10mm expansion joint round perimeter, fill with flexible mastic on completion. Any T&G joints that have not gone quite home, fill with two part wood filler and run either palm or belt sander lightly over all joints on completion.
Note.50mm of celotex will not bring you up to current u values.
Suggest the Kardean route in preference to laminate flooring. Warmer, softer, more flexible, no moisture content worry, quieter and more easy to keep clean.
If you do want to screed over insulation you need min 65mm sand and cement screed with poly fibre reinforcement.

old un.

 

[dch]

If you do want to screed over insulation you need min 65mm sand and cement screed with poly fibre reinforcement.

old un.

with the space i have left that means taking the insulation to 25 mm to get the 65 mm screed, So which is my better option in this case 25mm insulation with screed, or 50 mm with chipboard. I am guessing leaving the screed out and putting the chipboard in will not make the floor as cold? the only thing that bothered me with the chipboard was the floor feeling like a trampoline when finished because it will be like having 3 floating floors?

 

[ban-all-sheds]

I am in the process of a self build conservatory

And the reason you didn't bother to find out how to construct and insulate the base before you did it was......?

 

[dch]

I am in the process of a self build conservatory

And the reason you didn't bother to find out how to construct and insulate the base before you did it was......?

I did look into it but was told on top would be better, just wanted to know what people thought on here and get a bit of advise

 

[ajrobb]

I thought that top insulation tends to compress in areas of heavy traffic (doors). You might want to consider FF3000 for its greater compressive strength.

 

[dch]

I thought that top insulation tends to compress in areas of heavy traffic (doors). You might want to consider FF3000 for its greater compressive strength.

Cheers I have looked into that product, it sounds like the advice I was given it was from a local builder. I did mention I wanted underfloor heating to him in the conversation but I dont think I am having that now seeing as the price from a local builders merchant came in at over a grand supply only.

 

[noseall]

It will still be a b**gger to heat no matter what you use regards floor insulation and will never meet regulations because it is a connie.

Avoiding a cold bridge is about all you will achieve. So, begs the question, why did you not insulate under the slab?

Aaanyhoo, if it were me i would go for a thinner insulation board and screed. At least you won't need any lousy chipboard and you will have a surface that will receive just about any floor covering.

 

[mac391]

You will need a damp proof membrane on top of sand blinding (if the concrete is a rough finish) before you use insulation. Bulding regs would require 100mm insulation and 70mm reinforced screed for this. i'm you have gathered by now, you havn't left enough depth to do this.



I think underfloor heating would work if you layed DPM, insulation (as much as poss) woodchip flooring and don't use a screed. It is perfectly viable as a floating floor now you have your concrete base.

 

[dch]

You will need a damp proof membrane on top of sand blinding (if the concrete is a rough finish) before you use insulation. Bulding regs would require 100mm insulation and 70mm reinforced screed for this. i'm you have gathered by now, you havn't left enough depth to do this.



I think underfloor heating would work if you layed DPM, insulation (as much as poss) woodchip flooring and don't use a screed. It is perfectly viable as a floating floor now you have your concrete base.

yep kinda getting that vibe about the depth I have left, You say another DPM bit confusing now cos a few posts back someone said not too as I had it under the slab already?

 

[guitarbonz]

Beware screed applied directly to foil faced celotex/kingspan; two independent stories of screed attacking the foil and insulation turning to mush as a result. My UFH installer/poured floor screeder insists on installing a membrane over the insulation before fixing pipes and then pouring screed. My builder has come across this problem on at least two other sites.

 

[mac391]

If you lay celotex directly onto new concrete the moisture will have an adverse effect on it.
On the other hand, a dpm on top of the new concrete will push all the moisture towards the walls, so you would have to incorporate the dpm into the dpc in the brickwork where the moisture will escape through the cavity. Or lay a liquid dpm where the moisture escapes much more slowly.

You could always leave it to dry naturally, it takes approx 1 month per 25mm.[/quote]