insulation cold bridging

[grahama]

Hi all,

I am getting on with the build and am now waiting for the building inspector to see the progress before pouring the slab. My only question about what I have done is the join between the new slab and the existing house slab.



Old bay slab.



This is where I am. I have removed the old bay slab as per insprectors' instructions but the join is un even and it is hard to get insulation to sit flush against the existing house. I have put the cold bridging 25mm on the sides as shown but is it required next to the house as if I put insulation against where the old slab was there will be voids behind the new slab when poured.





Also as a side issue I have run the old visqueen under my new visqueen layer, is this ok?

Many thanks,

Graham

 

[^woody^]

You don't need insulation against the house

 

[pinenot]

Re Visqueen; how much of an overlap did you achieve and did you tape the joint of the two membranes?

I wouldn't bother over 8 feet or so of 25 mm insulation, whilst the the new slab is being built to new regs, the old slab I'm guessing, is not. But whilst I'm speculating it's simple just to miss it out at the slab edge itself I would also advise to insulate both wings either side of the slab, which formed the original ex. wall. Not only will this extend the insulated external wall/base but it will provide an expansion joint in rudimentary terms, which should be continued at the slabs/joint, only minus the insulation of course.
View media item 60357
Hope this helps...pinenot

 

[grahama]

Thanks for the replies about the insulation.

On the visqueen front, I have overlapped my main sheets for the new slab by about 3 meters as one width didn't quite fit



The old slab insulation I have laid under the new one but have used no tape.



I don't see how I can tape the old slab visqueen onto the new layers, any ideas or is it ok as I have done it??

I have a big enough overlap with the new visqueen to sandwich the old and new together which may be a better course of action, I could then tape it all together, would this be better??


Graham

 

[pinenot]

Sorry I think were're talking about different things so let me see if I can clarify; I wanted to know if the original slab/DPM (visqueen) had overlapped the new and the joint sealed with tape. If as it sounds now that is a no but you can achieve a continuity of the moisture barrier, that's the important thing.
I must admit I'm a we bit confused so could you post a horizontal sketch showing the old DPM in relationship to the new, with approx dims...pinenot

 

[grahama]

Hi,

as can be seen from my earlier reply pics, the existing house slab visqueen extends about 20" into the new extension. It is about 2M wide. I have simply, at the moment, laid the old visqueen under the new so the new slab pour will push the two visqueen layers together.

A representation of what I have done is here...



As I said earlier I have overlapped two sheets of visqueen to make the membrane fit the new extension by about 3M so I have one continuous sheet for the new slab. Where they overlap is big enough to put the old visqueen inbetween the two pieces that make up the new slab membrane.

Hope this makes it clearer.

Graham

 

[pinenot]

That's perfect Graham...pinenot

 

[grahama]

Thanks for all your help.

Graham

 

[grahama]

Well building inspector passed it so got it right in the end. To be honest he didn't even look at the visqueen or insulation on house wall, he was more interested in where my rain water was going !

Worrying for nothing !

Hey ho, it's done now so onwards and upwards as they say !

Graham