Floor insulation perimeter installation? (block build)

[JamieM]

Hi

 

I am in the middle of a block build and about lay the floor insulation.  We will have under floor pipes on top of this and then a 100mm sand/cement screed. 

 

There will be a 25mm wide piece of insulation at the side of the sand/cement at all the walls of the rooms (which I guess is there to reduce the thermal bridging).  In the plans it is just 100mm high resting on the top of the insulation but I was thinking I could make it the depth of the insulation and the depth of the screed and wedge it against the wall.  More so to make it easier when the guys are coming to do the sand/cement screed?

Anyone see any problems with doing this?

 

I have attached a picture to try and explain what I am taking about.  The first one being the way it is in the plans and the second being the way I am suggesting.

 

thanks

[A_L]

@JamieM, Why?, you appear to be putting insulation where there is already insulation. Even if not, with apparently a floor U-value of 0.13 this small amount will have a tiny/ insignificant effect.

[JamieM]

@A_L no, the insulation is between a block and the floor screed - to reduce the thermal bridge (the cold coming from below - through the blocks)

 

my question is more if it makes a difference if the piece of insulation is placed on top of the other insulation or if it is ok beling wedged in  (the yellow bits in the attached picture).

 

in my head it seems ok, just in case anyone has tried it and there is a practical reason why it may not work.

[jamiehamy]

I won't make any difference but in terms of when they come to do the screed - it will probably stay in place better if you wedge it down rather than place it on top. i.e second drawing. 

[RichS]

Can't see any problems with that, it will certainly keep it in place better.

[Oz07]

Seen it loads. 100mm rip will be fine. Merchants will do it on wall saw if you ask nicely. The polythene holds it in place. You will prob end up using a lot of 25mm otherwise and more wasteage on your thicker sheets

[Declan52]

I used of 50mm deep off cuts from insulating the roof and laid them on top of the floor insulation. I cut them at 85mm so sat 10mm high when screed was down. I put a quick squirt of foam and pushed it to the wall. None of them budged a bit.

 

[AliG]

My floor construction is exactly the same.

 

It would hold in place better the way you have suggested, but I don't think you can buy rolls of 25mm thick insulation that are 200mm wide(I might be wrong). It would be a pain to cut lots of 25mm strips from a 200mm thick board. If you can get the insulation or cut it from thick boards then your way would work.

[Oz07]

9 minutes ago, AliG said:

My floor construction is exactly the same.

 

It would hold in place better the way you have suggested, but I don't think you can buy rolls of 25mm thick insulation that are 200mm wide(I might be wrong). It would be a pain to cut lots of 25mm strips from a 200mm thick board. If you can get the insulation or cut it from thick boards then your way would work.

Are you having a laugh?

[AliG]

Sorry @Oz07 I missed your post that the merchants will cut it into strip, if so then that's all good.

 

Actually I am being daft. I was thinking it is awkward to cut 25mm strips from 200mm thick board, but cutting 200mm strips from 25mm thick board is a lot easier.

Edited April 6, 2017 by AliG

[Oz07]

No I mean you don't rip 200mm into 25 you cut 25mm gear to the desired width. You'd certainly struggle at 200mm thick 

[PeterW]

I used EPS and 25mm thick, wedged down the side of the under floor Insulation. It didn't move at all when we poured the slabs

 

out of interest what's your floor make up to get to 0.13 as it doesn't look that thick..?

[JamieM]

Cheers for the comments. I never even thought too ask the BM to cut it for us. Great idea.

 

@PeterW the 0.13 u value relates to the walls which in the plans are 150mm PIR. Think it equates to 0.1348 u value or something along them lines - just under 0.135 u value.

 

The floor in the plans is 125mm PIR and i think its around 0.17 u value but that's just from memory and i could be slightly wrong.

[PeterW]

18 minutes ago, JamieM said:

Cheers for the comments. I never even thought too ask the BM to cut it for us. Great idea.

 

Get a an offcut of OSB the width you want the insulation and lay it onto a couple of sheets of it and cut with a standard hand saw - Its there as an expansion gap more than an insulation layer so doesn't need to be perfect. I cut all of ours in 10 minutes - wedged in tight by the floor PIR.

 

What price have you had on the PIR..? I used Seconds & Co at £24 for 125/128mm and it worked fine, was £7 a board cheaper than the merchants but it does take 10 days for delivery

[JamieM]

8 minutes ago, PeterW said:

 

 

What price have you had on the PIR..? I used Seconds & Co at £24 for 125/128mm and it worked fine, was £7 a board cheaper than the merchants but it does take 10 days for delivery

 

Well clearly I've been ripped off. Mine was £12.50 a square metre which equates to about £36 a 125mm board. Think we got about 3% off that which brings it to about £35 a board. Don't know if seconds and co deliver to NI. Too late for me though as sadly i already have it waiting to be installed.

[PeterW]

TBH that was about the rates I was getting with the merchant. 

 

This is the edge detail - slight difference on mine is that as it's the structural slab the DPM is under the PIR and then there is a slip membrane and then UFH trays on top. We have full filled the cavity below ground with EPS too as additional Insulation. 

 

 

Having the EPS against the block also allows a bit of protection for the DPM. 

[Declan52]

Most BM will have 25mm *100mm by 2.4m boards that would get used for Window reveals that you can use but they will be more expensive than using a sheet you cut yourself.

[CC45]

Why 100mm sand/cement screed?  I costed this option for ours (done it myself a few times) but with extra labour costed in it was more effective to pour. 10m3 went in over about 3hrs & no one sweated much. 

 

Option 2 is what we did. I also out some expansion stuff down.

[JamieM]

9 hours ago, CC45 said:

Why 100mm sand/cement screed?

sorry, i'm not sure what you mean here?  (probably me being a numpty)

 

do you mean why sand/cement as opposed to a liquid screed?

or do you mean why 100m and not 75mm?

[CC45]

Both. 75mm liquid screed is plenty, quick, cost effective and easy.  I've done both but won't be going back to the traditional method in a hurry.

 

Neither approach is wrong but I know which I'd use again.  

[dpmiller]

Just a sanity check here- if I'm using PIR or EPS as a perimeter like this, then there's no need for the usual 8mm edge roll? 50mm poured screed if it's relevant.

[Declan52]

I just used pir as a replacement for the edge strip.  Don't see any reason why you would need both. 

[sam]

1 hour ago, dpmiller said:

Just a sanity check here- if I'm using PIR or EPS as a perimeter like this, then there's no need for the usual 8mm edge roll? 50mm poured screed if it's relevant.

EPS is more compressible than PIR so you may want EPS to allow for expansion of the screed.

[Roundtuit]

I used 40mm of pir on external walls (as I was lining the inside of the timber frame with 40mm), and the edge roll stuff on the internals with 50mm poured screed. The screening guys ok'd it (in fact, they fitted it for me).  It's been down over a year and it seems fine.  At the risk of stating the obvious, depending on how you're building, you might just need to bear in mind that the perimeter insulation thickness will limited by your internal wall/skirting finish, unless you're floor coverings will be ok laid on a strip of insulation round the edges!

[Simplysimon]

as with others, the lower insulation will hold it in place, i on the other hand, would be far more concerned with the cold bridge below the threshold. really should have had a course of marmox or similar to break it.