Raising a screeded floor

[Mutley Racers]

Hi. I am after a bit of advice. We have a house where the floor in one room is 32mm lower than the rest of the 1st floor. I would like to install some wood throughout with it all nice and flush.

I am thinking of maybe using some Marmox insulation board with some ply on top or 20mm battens on the floor and then use 12mm ply on top.

Any thoughts on the above and which would be better?

I believe the latter would be cheaper but not as quick?

Thanks guys

 

[sunnybob]

Is the lower floor solid? Are there any pipes or cables that might need future access?

 

[Mutley Racers]

Yes it is a solid floor. Pipes run around the perimeter of the room, not the middle

 

[sunnybob]

I would seriously consider a damp proof membrane and concrete.

 

[Mutley Racers]

Which it already is. It will take too long to dry. Why would you not choose a floating floor with batten and ply?

 

[sunnybob]

K.I.S.S.

(keep it simple, stupid) the more you do. the more things can go wrong.

On the other hand, thats my philosophy, other people have different ones.

 

[Lons]

sunnybob » I would seriously consider a damp proof membrane and concrete.

Not enough depth for a concrete fill IMO so would have to be a sand / cement screed and even that wouldn't be recommended on top of a DPM but rather be bonded to the existing floor, but certainly not always the simplest method for anyone not used to laying screed as it can be tricky to achieve a flat decent finish.

The existing floor is concrete and presumably already has a DPM so why install a second? Can be done in any case under a floating floor which would be my choice if I was doing it as a benefit would be additional insulation.
Don't even need the battens really, many thousands of houses were built with a concrete base, polystyrene insulation slab and glued 18 or 22mm T&G chipboard over. I've worked on many of them and laid several, they function well, until you later need to cut an access hole in to them that is!

Bob

 

[MikeG.]

I'm not sure you've got room for a floating floor. I certainly wouldn't use anything less than 18mm for the flooring, be it (t&g) chipboard or ply, which leaves room for only 14mm insulation. Well, I don't think there is such a thing. You absolutely do not need battens with a floating floor. Which leaves screed as your only viable option (concrete is not an option). This is only DIY-able for the experienced and if you've seen it done, and 32mm is too thin for an orthodox sand-cement screed anyway. Therefore, I think you are going to have to get a pro in with one of the specialist screeds.

 

[Mutley Racers]

Thanks all for your replies.

I am a plumber and do install underfloor heating with screed so not a problem laying it( but as Mike has said that is traditional sand and cement, not the other ). It is the drying time that is a tad too long to wait for as I have people moving in to the place on the 13th so need floor finished by then.

Any thoughts on the Marmox board? This can be Installed on any floor and then any floor put on top. This would add insulation and be solid. So this with 12mm tongue and groove chipboard or plywood should be fine?
Mike, why would you only use at least 18mm boarding?
Thanks again.

Regards Lee

 

[Lons]

I'd tend to agree with Mike re 18mm boards as anything thinner would be prone to flex however I don't see that as a problem as you can certainly buy 15mm rigid insulation board which is close enough to make up the 1mm difference over the other floor. I've used it but can't remember the brand name, will do a search later.

Bob

EDIT:

Here you go, just typed in 15mm poly insulation and got this. Isn't the brand I used so there are alternatives out there to choose from.
https://www.insulationshop.co/15mm_xtratherm_pir_insulation_board_thin_r.html

 

[MikeG.]

.....Mike, why would you only use at least 18mm boarding?........

Too much flex, Lee. Not quite walking on a trampoline, but nonetheless it's just too thin. Seriously, this one will come back to bite you if you install 12mm.

 

[Lons]

32mm is too thin for an orthodox sand-cement screed

Have things changed Mike?
My understanding from when I was a part time lecturer at a local college was that the optimum thickness of a standard sand and cement bonded screed is 25–40mm in which case 32mm is within limits.
Certainly those were the figures I used while in business.

Bob

 

[MikeG.]

Yeah, come to think of it, I'm wrong on this. I guess that's because I don't think I've ever done a screed straight onto a concrete slab/ oversite. Sand/ cement screed on insulation needs to be 65mm minimum, and this is what I had in mind.

 

[Lons]

Yeah, come to think of it, I'm wrong on this. I guess that's because I don't think I've ever done a screed straight onto a concrete slab/ oversite. Sand/ cement screed on insulation needs to be 65mm minimum, and this is what I had in mind.

Sounds about right Mike, isn't that classed as a type of floating floor. I know that where we laid screed on existing concrete but over a dpm we worked to a minimum 50mm but needs to be thicker over insulation.

 

[Mutley Racers]

I'd tend to agree with Mike re 18mm boards as anything thinner would be prone to flex however I don't see that as a problem as you can certainly buy 15mm rigid insulation board which is close enough to make up the 1mm difference over the other floor. I've used it but can't remember the brand name, will do a search later.

Bob

EDIT:

Here you go, just typed in 15mm poly insulation and got this. Isn't the brand I used so there are alternatives out there to choose from.
https://www.insulationshop.co/15mm_xtratherm_pir_insulation_board_thin_r.html

Thank you!!!so this and 18mm tongue and groove chipboard should be ok?

Cannot believe there is a nation wide shortage of the stuff though.

 

[Mutley Racers]

.....Mike, why would you only use at least 18mm boarding?........

Too much flex, Lee. Not quite walking on a trampoline, but nonetheless it's just too thin. Seriously, this one will come back to bite you if you install 12mm.

Hi Mike. So even with an insulation board underneath it will flex?

So 18mm it will need to be.

Thanks for replying.

 

[MikeG.]

........Cannot believe there is a nation wide shortage of the stuff though.

If you mean the rigid insulation board, this is because of a catastrophic fire at a major chemical plant in Germany, which supplied most of the precursor chemicals around Europe.

 

[MikeG.]

........Hi Mike. So even with an insulation board underneath it will flex?

So 18mm it will need to be........

Yes to both. It flexes because nothing will be absolutely perfectly flat. Not the concrete, the insulation, nor the flooring, which means somewhere there will be a couple of mm gap which will allow movement (and probably squeaks), and with movement there will be wear and damage, allowing more movement. 18mm is your minimum, and I personally, in my own home and for clients, would use 22mm.

 

[Mutley Racers]

I'd tend to agree with Mike re 18mm boards as anything thinner would be prone to flex however I don't see that as a problem as you can certainly buy 15mm rigid insulation board which is close enough to make up the 1mm difference over the other floor. I've used it but can't remember the brand name, will do a search later.

Bob

EDIT:

Here you go, just typed in 15mm poly insulation and got this. Isn't the brand I used so there are alternatives out there to choose from.
https://www.insulationshop.co/15mm_xtratherm_pir_insulation_board_thin_r.html

Thank you Bob for the link and help

 

[Lons]

Thank you Bob for the link and help

No problem, sorry I didn't realise that the material is in short supply though.