expansion in concrete floor

[chrisbrick]

hi I am doing a extension and just laid the concrete slab after i done it some one said i should have put 25mm celotex or some kind of expansion joint all the way round against the exsisting house and new blockwork underneath the dpm. It was not on the drawing . However could building control make me take the slab up or is there another way round it. The floor make up is hardcore, sand , dpm ,concrete, insulation,screed Thanks for any help or advice

 

[2929twin]

Chrisbrick, the 25mm isn`t as an expansion. It`s a thermal break to stop cold bridging from the wall. I`m surprised BC didn`t spot it missing, they usually check after DPM and insul. stage, before you cast slab.

 

[chrisbrick]

ah right so what happens now then because its not in there

 

[2929twin]

Depends. How concerned are you? Will BC see it? It would be a real pain to rectify now, if you can live with it, a blind eye approach may do. We didn`t put this strip in before the new regs. regarding insulated slabs. indeed never insulated floors at all. Although I expect to be pounced on very shortly by other forum members, I suggest you get on with living.

 

[chrisbrick]

if bc did pick up on it would they have the slab out or would they see it as a minor error and why did architech not put it on drawings.

 

[2929twin]

Err.. dunno,..dunno,..and dunno.

 

[freddiemercurystwin]

if bc did pick up on it would they have the slab out or would they see it as a minor error and why did architech not put it on drawings.

That depends how pedantic your inspector is, your Arch didn't draw it cause he's a Bozo. Tell him I said so!

Did you got Full Plans Approval before you started Building? Or are you doing this on a Notice?

 

[chrisbrick]

not sure full plans i think. is this now done with all concrete slabs how serious or vital is it.

 

[freddiemercurystwin]

If you got Full Plans Approval then it will have either been noted and written into the conditions or has been missed. You may want to find out from your Architect. If you got Full Plans Approval and the plan checkers at the council have missed it then you can probably ignore it as what has been Approved is what you need to build ie no insulation at the edge on the 'Approved' drawings and no need for it on site (in theory).

It is done with all slabs yes. In reality it doesn't do an awful lot, reduces the cold bridging from the ground into the slab a little. As mentioned it would be a snotty Inspector who expected the slab to ripped up. Are you building this yourself?

 

[chrisbrick]

yes doing extension my self up untill roof so need all help i can get .

 

[noseall]

If you haven't already started the brickwork above damp, then cut some cavity insulation and fit it to the drain trough below dpc.

Obviously, you will need to fill the cavities up to 225mm below dpc first!

 

[freddiemercurystwin]

As mentioned, if they approved it without the insul at the edge you can forget about it.

If you got Full Plans Approval and the plan checkers at the council have missed it then you can probably ignore it as what has been Approved is what you need to build ie no insulation at the edge on the 'Approved' drawings and no need for it on site (in theory).

Not that it should be a show stopper anyway.

 

[theoldun]

Freddymerc makes sense in everything he has said.
However do what noseall has told you, and you will be killing two birds with one stone, as NHBC now require cavity insulation to be taken down to two course below DPC.
Most local BC have not picked up on this, but it is nearly always only a matter of time before they follow NHBC technical guidance.
oldun.