New here, have a question

[Robfosters]

Hi all, my question, I hope, is simple enough.

I am building a conservatory and the slab was laid today onto hardcore with a Dpm.

I want to use celotex insulation, but what is the way to go forward as I seem to be getting conflicting views on putting the celotex on the screed or screed on the celotex.

How should it be done for best results. Also what thickness celotex would be best to use. I'm in south east England, so extremes of weather are quite rare.

Thanks for your help.

 

[jeds]

If you screed on Celotex the screed should be minimum 70mm thick and include anti-crack mesh or fibres - or both.

If you celotex on screed you will obviously have to lay a surface finish of some description - probably 22mm chipborad flooring. You should also include a vapour barrier over the insulation.

Either will work but I would personally do whatever matches the existing. First option for masonry floor or second option for timber floors.

 

[Robfosters]

It's gonna Be a laminate floor. Can this be the surface finish or do I need Chipboard then laminate flooring?

Also, Ive heard that screed can attack the foil on celotex. Is this a myth?

Thanks

 

[jeds]

It's gonna Be a laminate floor. Can this be the surface finish or do I need Chipboard then laminate flooring?

You will need chipboard between the insulation and the laminate. I would use grade P5 moisture resistant.

Also, Ive heard that screed can attack the foil on celotex. Is this a myth?
Thanks

Yes apparently it does. But it makes no difference. The foil serves no function when enclosed within a screed. If your worried about that just cover it with a vapour layer.

 

[Robfosters]

So basically my layers should go:

DPM, concrete, screed, celotex, vapour barrier, chipboard, laminate flooring?

 

[r896neo]

if your going for the insulation above the screed unless the depths are getting silly you could happily save your money on the screed and put in more insulation.

 

[hotrod]

Just remember though that with insulation thickness you are dealing with the laws of diminishing returns and you are heating a conny

 

[mointainwalker]

Absolutely agree with Hotrod. if no UFH, then extra insulation likely to be waste of money.

 

[mointainwalker]

Deleted, as post replied to deleted

 

[r896neo]

i agree about diminishing returns and was more suggesting it in case he was planning on getting someone in to lay a screed then it will be cheaper to just buy and lay down the extra insulation to bring up the extra height in comparison to paying for the screed and labour.

 

[jeds]

So basically my layers should go:

DPM, concrete, screed, celotex, vapour barrier, chipboard, laminate flooring?

Yes. Approx 80mm insulation is max before it starts to become uneconomical.