Confused about 25mm upstand insulation

[gwebstech]

Hi all

 

Im coming to concrete the slab on my new build. so 1500mm type 1, 50mm sand, visqueen, 125mm insulation , reinf, and then 4 inches concrete

 

I understand the concrete floor needs a 25mm upstand around the perimeter. This upstand needs to be as low as the bottom of the floor insulation - correct?

 

My main query is - ive read that the 25mm upstand should be as low as the cavity insulation too - that cant be right as the cavity is infilled with concrete to 225mm lower than damp course and i thought you only started putting cavity insulation in, when you have got the slab down and are building the actual walls of the house (not the substructure).

 

So  i guess that i also need to put insulation down in the substructure cavity under the visqueen overlap? is that what i misunderstood?

 

 

thanks

Edited September 12, 2019 by gwebstech

[Mr Punter]

The perimeter insulation goes on top of the floor insulation.  You can make it higher than the proposed concrete level and trim it later.

[Russell griffiths]

It depends on what standard you are building to, you can fill the cavity below dpc with a lean concrete mix, or a better choice would be insulation, have you got a cross section of your wall floor build up, what did you submit to building control. 

[Declan52]

Are you sure your measurement of 1.5m of hardcore is correct???

And type 1 for this as well???

[gwebstech]

1 hour ago, Russell griffiths said:

It depends on what standard you are building to, you can fill the cavity below dpc with a lean concrete mix, or a better choice would be insulation, have you got a cross section of your wall floor build up, what did you submit to building control. 

 

its got to be concrete infill, to stop the ground collapsing the blockwork

56 minutes ago, Declan52 said:

Are you sure your measurement of 1.5m of hardcore is correct???

And type 1 for this as well???

lol 150mm - my bad

[gwebstech]

A builder i know has just told me he puts - stone/sand then insulation then visqueen and then reinf

 

which is correct? ill ring the BI tomo to check

 

thanks

[Oz07]

You use more if putting to bottom of insulation. I always sit 25mm ontop of main insulation and have it ripped to whatever the slab thickness is i.e. 4", Tape it to main insulation by time polythene over it doesn't go anywhere

[gwebstech]

30 minutes ago, Oz07 said:

You use more if putting to bottom of insulation. I always sit 25mm ontop of main insulation and have it ripped to whatever the slab thickness is i.e. 4", Tape it to main insulation by time polythene over it doesn't go anywhere

 

so you DO put the visqueen over the insulation then?? i had it in my head the visqueen went under the insulation but it makes more sense to put the insulation then the visqueen

[PeterW]

Depends ...!! Visqueen or DPM under and a then a slip membrane over the top of the EPS/PIR to stop the concrete getting under it and floating it up is usual. 

[gwebstech]

5 minutes ago, PeterW said:

Depends ...!! Visqueen or DPM under and a then a slip membrane over the top of the EPS/PIR to stop the concrete getting under it and floating it up is usual. 

 

thanks

 

and does the reinf have to be laid on cradles or something?

[PeterW]

Just now, gwebstech said:

 

thanks

 

and does the reinf have to be laid on cradles or something?

 

You should use chairs or risers to put it into the centre of the slab depth. Has the engineer specified mesh..? For a 100mm slab you may get away with fibres which is cheaper and quicker than mesh. 

[gwebstech]

no engineer specified, the notes show 2 ways of doing floor, one says screed with light mesh which i assumed was a142 reinf and the other was just use mesh over drains but im sure th BI said id got to use mesh all over the floor