# New Build - Floor insulation Qs



## Birroc (4 Nov 2008)

Hi,

Whats involved in putting down floor insulation before the screed is laid ?
I presume I have to sweep up all the dirt/dust, put down the Kingspan (100mm) and cut around the plumbing pipes. Should I tape the Kingspan sheets together ? Anything else ?

What plastic do I put on top of the Kinspan ? Just normal polythene ?


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## jmrc (4 Nov 2008)

No need for plastic on top of your Kingspan. might tape together if you think it will be windy but the screed will soon take care of that. A few blocks maybe too just to weigh it down so the screed doesn't move it..

Best of luck


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## Jorus (4 Nov 2008)

Hi Birroc,

We are putting down our floor insulation this weekend -going to scrape and clean the floor first and then put down the insulation - we are going to put plastic cover over it - the screed can react with the insulation and most screed companies will ask you to put plastic down over the insulation and under the underfloor heating pipes!

We are putting clear 500 gauge ploythene over the insulation.


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## rmdt (4 Nov 2008)

There is no need to tape the joints. However the insulation should be tightly butted together. If there are any gaps such as around pipes or where a sheet got damaged fill these with expanding foam. You should also use perimeter strips at the edges where the slab meets external walls (some people recommend the same for internal walls, depending how serious you are about the job). These strips are about 6 inches high and 1 inch thick.

It is not standard practice to place plastic over the insulation. However, it is now increasing common to hear people recommending this as it prevents the foil lining/insulation/concrete from reacting over time. Normal polythene sheeting should do, but I have also heard of some type of paper being used which wouldn't cause problems with condensation later.


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## builder ed (4 Nov 2008)

Birroc, I have been advised by the screed company to make sure the pipes are well secured with galvaband otherwise they will rise to the top of the screed.  (That is if you are using the liquid screed) Taping the joints is not enough and you need to use minimum 500 guage polythene to prevent reaction with the foil and to prevent the Kingspan from "floating" if the concrete gets between the joints. Cold bridging will be prevented also.


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## Birroc (4 Nov 2008)

rmdt said:


> You should also use perimeter strips at the edges where the slab meets external walls (some people recommend the same for internal walls, depending how serious you are about the job). These strips are about 6 inches high and 1 inch thick.


 
Thanks for all the prompt replies. 500 gauge polythene - good to know.

rmdt, what are the perimeter strips made from ? Do Kingspan do them ?

Jorus, what do you mean by "going to scrape and clean the floor first" -how will you scrape a concrete raft floor ?


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## sydthebeat (4 Nov 2008)

Birroc said:


> Thanks for all the prompt replies. 500 gauge polythene - good to know.
> 
> rmdt, what are the perimeter strips made from ? Do Kingspan do them ?
> 
> Jorus, what do you mean by "going to scrape and clean the floor first" -how will you scrape a concrete raft floor ?


 

birroc.. are you going to slab the internal of the external walls with insulated plasterboard?


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## Birroc (5 Nov 2008)

sydthebeat said:


> birroc.. are you going to slab the internal of the external walls with insulated plasterboard?


 
No Syd, external walls already plastered. No insulated plasterboard at all, never liked the idea. Went instead for 150mm cavity full fill of ecobeads.
Why do you ask ?


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## sydthebeat (5 Nov 2008)

Birroc said:


> No Syd, external walls already plastered. No insulated plasterboard at all, never liked the idea. Went instead for 150mm cavity full fill of ecobeads.
> Why do you ask ?


 

because if you were its adviseable to put wider perimeter strip insulations around the floor to touch the insulation on the insulation backed plasterboard, it forms a much better thermal barrier.


anyway, your not so...

i would incorporate at least a 25mm strip around all the external (and internal!!) rising walls.

on the 500 gauge ploythene 'slipping sheet'... this is definitely a good idea.... but if budget allows id try to use a 1200 gauge.

if you want to do a better job, but with a bit extra work... lay two sheets of 50mm instead of one sheet of 100mm.... when doing this stagger and tape the joints.... 100mm boards can tend to buckle and rise...


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## Birroc (5 Nov 2008)

sydthebeat said:


> i would incorporate at least a 25mm strip around all the external (and internal!!) rising walls.


 
Thanks for the info Syd. I dont understand what a 'strip' is - where do I find this and what does it look like ?


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## sydthebeat (5 Nov 2008)

birroc:

[broken link removed]

look at this little vid....

pay attention to the strip insulation thats installed just as the floor board insulation drops into place...

its located at the external walls to create a thermal barrier between the block and the concrete floor.

also....
look at page 4 of this document: http://www.environ.ie/en/Publicatio...g/BuildingStandards/FileDownLoad,18751,en.pdf

you can see the strip insulation at the wall...

let these details be your bible!!!


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## Birroc (5 Nov 2008)

Thanks Syd, I think I understand it now.

Would 30mm of Kingspan floor insulation be enough to use as a strip ?

I notice in the video that the floor insulation rests against the strip insulation (which stands on the concrete raft) but in the document the strip sits on top of the floor insulation (which touches the block wall direct).

Which would you recommend ?


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## sydthebeat (5 Nov 2008)

i recommend the strips sit on the board...

your cavity insulation should start 225mm below finished floor level as well.


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## builder ed (5 Nov 2008)

I used the xtratherm strips that Sydthebeat mentions.  They are 25mm X 150mm X 1400mm and are really handy.  It saves cutting strips from full board and have foil on both sides.  I put in 75mm xtratherm and will be putting in 75mm screed once the plumber finishes the pipework.


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## wexford dude (5 Nov 2008)

Birroc,

On


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## wexford dude (5 Nov 2008)

Birroc,

On the point of starting your cavity wall insulation 225 below FFL.If you are going to do this make sure that you fix this to the inside leaf.Your wall ties will only start at FFL so if you don't fix the insulation below this it will be loose and may lie across the cavity.Any mortar droppings can build up and allow water to seep across your cavity.

Personally I would not put the insulation below FFL for this reason as you will inevitably have a certain amount of mortar dropping and this provides a space for it to accumulate without causing any harm - once it doesnt build up above FFL.


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## Birroc (5 Nov 2008)

builder ed said:


> I used the xtratherm strips that Sydthebeat mentions. They are 25mm X 150mm X 1400mm and are really handy. It saves cutting strips from full board and have foil on both sides. I put in 75mm xtratherm and will be putting in 75mm screed once the plumber finishes the pipework.


 
Oh ok, so these strips are a seperate product. I was going to cut the Kingspan boards to make them.

Is this xtratherm better than the Kingspan equivalent ?

A friend told me that aeroboard would be just as effective given that I am pouring concrete screed on top of it. What do ye think ?


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## rmdt (5 Nov 2008)

Kingspan and xtratherm are both pretty much the same stuff.  However aeroboard isn't.  There is no problem using aeroboard, but you will need to use a greater thickness of it to give the same u value.


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## Slates (5 Nov 2008)

wexford dude said:


> Birroc,
> 
> On the point of starting your cavity wall insulation 225 below FFL.If you are going to do this make sure that you fix this to the inside leaf.Your wall ties will only start at FFL so if you don't fix the insulation below this it will be loose and may lie across the cavity.Any mortar droppings can build up and allow water to seep across your cavity.
> 
> Personally I would not put the insulation below FFL for this reason as you will inevitably have a certain amount of mortar dropping and this provides a space for it to accumulate without causing any harm - once it doesnt build up above FFL.


Would you not just build in a set of wallties one block down for FFL.............


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## sydthebeat (5 Nov 2008)

wexford dude said:


> Birroc,
> 
> On the point of starting your cavity wall insulation 225 below FFL.If you are going to do this make sure that you fix this to the inside leaf.Your wall ties will only start at FFL so if you don't fix the insulation below this it will be loose and may lie across the cavity.Any mortar droppings can build up and allow water to seep across your cavity.
> 
> *Personally I would not put the insulation below FFL for* this reason as you will inevitably have a certain amount of mortar dropping and this provides a space for it to accumulate without causing any harm - once it doesnt build up above FFL.


 

you NEED to do this now to comply with building regulations.

Its easy to do.... just put in small pieces of insulation in the cavity to hold it in palce.

Its bad practise to allow mortar to fall into the cavity.


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## wexford dude (5 Nov 2008)

Slates you would not have wall ties below FFL as your dpm laps over your inside leaf goes down the cavity face of the inside leaf and then out to the external face of the outside leaf.Therefore your wall ties would have to protrude thru the dpm and that wouldnt be great.

Syd - your theory as always is spot on.In order to avoid mortar falling down the cavity the blocklayer would have to use cavity boards.I have never seen them used.The blocklayer on my own house was v. tidy but even then some mortar ends up slipping down the cavity.

If you can get the blocklayer to use cavity boards then by all means put the insulation below FFL.If not personally I would leave that small section of insulation out - just my opinion.


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## Slates (5 Nov 2008)

wexford dude said:


> Slates you would not have wall ties below FFL as your dpm laps over your inside leaf goes down the cavity face of the inside leaf and then out to the external face of the outside leaf.Therefore your wall ties would have to protrude thru the dpm and that wouldnt be great.
> 
> Syd - your theory as always is spot on.In order to avoid mortar falling down the cavity the blocklayer would have to use cavity boards.I have never seen them used.The blocklayer on my own house was v. tidy but even then some mortar ends up slipping down the cavity.
> 
> If you can get the blocklayer to use cavity boards then by all means put the insulation below FFL.If not personally I would leave that small section of insulation out - just my opinion.


it depends what way you detail the dpm, I've got radon in and ties without breaking the radon membrane


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## wexford dude (5 Nov 2008)

Did you use an alternative dpm detail.I would be interested to see it.


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## builder ed (5 Nov 2008)

Birroc said:


> Oh ok, so these strips are a seperate product. I was going to cut the Kingspan boards to make them.
> 
> Is this xtratherm better than the Kingspan equivalent ?
> 
> A friend told me that aeroboard would be just as effective given that I am pouring concrete screed on top of it. What do ye think ?



The xtratherm and Kingspan gives you much the same uVal but if you use Aeroboard Platinum Floor insulation you would have to use 100mm where 75mm of Kingspan/xtratherm woud suffice.  You will need a miniumum 100mm of Aeroboard just satisfy the minimum requirement in the current building regs


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## wexford dude (6 Nov 2008)

If you have built up your FFL significantly above the existing ground level you will have a bigger build up under your concrete floor slab.You only require 150mm of stone so it may well be cheaper in this instance to use 100mm or even 150mm of aeroboard than place the additional stone and use the thinner Kingspan/Xtratherm insulation.
Just depends on the site layout.


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## baldyman27 (11 Nov 2008)

Just wondering why everyone is so keen on Kingspan insulation? There are others that are every bit as good, and sometimes better, for far less.


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## Birroc (11 Nov 2008)

baldyman27 said:


> Just wondering why everyone is so keen on Kingspan insulation? There are others that are every bit as good, and sometimes better, for far less.


 
I priced Kingspan and Xtratherm and they were the same.


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## sydthebeat (11 Nov 2008)

baldyman27 said:


> Just wondering why everyone is so keen on Kingspan insulation? There are others that are every bit as good, and sometimes better, for far less.


 
like whom??

'kingspan' has become a name synonymous with Polyurethane board insulation... much the same way 'hoover' is used for vaccuum cleaners.

on this board its more often than not used to describe Pu or PIR insulation....

There is also brands such as Xtratherm and Ballytherm... what others are there?


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## baldyman27 (11 Nov 2008)

Quinntherm would be another, if its still available. I do a lot of house bases as a contractor and it just seems that engineers always spec Kingspan. When pricing, I always ring my builders providers and ask them if there's an alternative giving the same u-value and more often than not there is and for a considerable amount less. And, yes, I do pass on the saving!


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## sydthebeat (11 Nov 2008)

baldyman27 said:


> Quinntherm would be another, if its still available. I do a lot of house bases as a contractor and it just seems that engineers always spec Kingspan. When pricing, I always ring my builders providers and ask them if there's an alternative giving the same u-value and more often than not there is and for a considerable amount less. *And, yes, I do pass on the saving*!


 
you dont have to if the supplier is specified....

but fair dues!!!


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## Birroc (1 Dec 2008)

sydthebeat said:


> birroc:
> 
> [broken link removed]
> 
> ...


 
Should I put the strip insulation on internal walls too ? I mean, the internal blocks also rest on the cold raft foundation so that acts as a thermal bridge to the screed - yes/no ?


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## sydthebeat (1 Dec 2008)

Birroc said:


> Should I put the strip insulation on internal walls too ? I mean, the internal blocks also rest on the cold raft foundation so that acts as a thermal bridge to the screed - yes/no ?


 

for a better job... yes....

every little helps!


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## Birroc (1 Dec 2008)

Thanks Syd, I am using 30mm of Kingspan for the exteranl 'strip perimeter' but I will use this other product that is only 10mm of foam (comes in 50m rolls, plumber told me about it) for the internal walls.

Nearly finished now. Only a few sheets left to put down. Nasty business !!


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## sydthebeat (1 Dec 2008)

Birroc said:


> Thanks Syd, I am using 30mm of Kingspan for the exteranl 'strip perimeter' but I will use this other product that is only 10mm of foam (comes in 50m rolls, plumber told me about it) for the internal walls.
> 
> Nearly finished now. Only a few sheets left to put down. Nasty business !!


 
whats that product called birroc.. is it like pipe lagging foam??

oh, and if you think floor is tough, wait until you hit the roof!!..


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## Birroc (1 Dec 2008)

sydthebeat said:


> whats that product called birroc.. is it like pipe lagging foam??
> 
> oh, and if you think floor is tough, wait until you hit the roof!!..


 
Just bought 2 rolls. Its 'Unitherm'. 8mm * 160mm * 50m. Used a lot when putting in underfloor heating it seems. It feels a bit like pipe lagging foam yeah. €40 a roll.

I wont be insulating the roof as such (I have 2 story), just rockwool in the joists. Dont mind that so much.


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