cellotex insulation around edge of floor?

[kazandoz]

Hi all

Can any of you wise ones advise on this...

Our building inspector is saying he wants to see a 25mm strip of cellotex around the edge of our new extension floor, against the internal wall, over the concrete slab, which the 75mm screed will come up to and then cover. We can't understand what on earth this is supposed to do - can any of you shed light on this for us? Many thanks!

 

[freddiemercurystwin]

Reduces the cold bridging through the blockwork into the edge of the slab. Standard construction for years now.

 

[kazandoz]

Sorry - to clarify, there is going to be 75mm cellotex over the concrete slab, which this cellotex 'rim' will sit on before the whole lot is screeded.
Oh and while i'm here, if the polythene between cement slab and cellotex is to do with a reation between cement and foil cover, then why do they not insist on another polythene sheet between cellotex and screed?

 

[kazandoz]

thank you! And mightily speedy too!

 

[freddiemercurystwin]

It may be less of an issue as you have continuous insulation over the slab but he's trying to minimze the cold bridge beneath your 75mm layer. Some would say overkill, some would say it is beneficial.

Your first layer of polythene is your damp proof membrane, some (including myself) specify an additional thinner sheet above the insulation to stop any screed being seeping into the gaps between the boards. Some manufacturers say you should have an additional membrane some don't.

 

[kazandoz]

At the risk of sounding thick (and working from my knowledge of roof insulation and the need to prevent rafters transferring the cold), if the walls are fully insulated, how are they creating a cold bridge?

 

[kazandoz]

thanks - you keep getting in there before i'v posted my question - answerin it before i've asked it! cheers!

 

[freddiemercurystwin]

Your inner skin of blockwork is connected to the ground, the ground is cold and will try to absorb any heat via the inner skin. Hence the efforts to try and keep both sides of the wall insulated to minimize the heat loss.

 

[^woody^]

If the cavity insulation is taken down past the DPC level, then there is no need for any additional insulation upstand around the floor perimeter, as there is no thermal bridge

 

[freddiemercurystwin]

Well there is ^woody^, unless you are sitting your inner skin on a chunk of insulation?

 

[^woody^]

What, the same cold wall that is forming the entire inner leaf?

And even with aerated blocks?

 

[freddiemercurystwin]

Every little helps!