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Confused about 25mm upstand insulation


gwebstech

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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 by gwebstech
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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

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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

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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. 

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