How to deal with external/internal wall.

[MarkH]

I'm worried that an external/internal wall we have might be a cold-bridge problem. It separates the two sections of our house and whilst i can work out how to deal with the external insulation well enough I'm not so sure about the bottom of the wall and loss of heat down into the ground.

 

In the image below you can see the EWI - which will extend down into the trenches about 750mm below DPC - and also the sub slab insulation. My concern is that the wall which devides the two sections of the house (whilst being insulated from the 'outside' by the ewi) is a direct path down through the floor insulation into the ground, a hole in the insulation envelope. The wall is a meter high relative to the foundation at that point so its not a short path, but still...

 

Another query: our walls are currently built up to slab level and we're waiting for materials before continuing, when I lay the DPM, how do I deal with that internal wall? Do I lay it over the wall and then build up on it (except in the doorway, what there?)? Should I have terminated that wall a course lower, DPM'd and then built up the final course?

 

As always - thanks for any and all input!

Edited September 28, 2016 by MarkH
parts made no sense...

[gravelld]

I'm not an expert but here's my opinion 

 

It is a bridge and should be designed out if possible.

 

That said, most heat loss through the slab is via the edges of the slab, particularly in many EWI cases where the plinth is left uninsulated (all those ECO and Green Deal installs...). In your case you have wisely avoided this.

 

To many, insulating the plinth down to foundations is still good enough to qualify for Enerphit (see Beattie Passive's TCosy system which does this). It might just be a case of making it up elsewhere. This suggests to me that straight-down losses are not significant, but that might depend on your ground condition, and particularly whether higher quantities of water is running through it.

 

So if possible try to find someone who knows what they are talking about and model it.

Edited September 28, 2016 by gravelld

[gravelld]

Oh here's a discussion on this I was involved in: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13530&page=1

[MarkH]

Thanks.

 

I'm thinking - given I can't come up with a practical solution - I might live with it (the bridge). The ground beneath is well drained and there is over a meter of wall (the first 350mm of which are surrounded by the slab & insulation). I'm now contemplating 300mm of EWI so really the bulk of the sub-slab stuff is going to be well insulated for over a meter below slab level.

 

I'm not that worried about small losses in overall performance, more problems from high temperature differentials from bridges - condensation and mould. It seems (I hope I'm right) that this cold bridge won't be significant to cause that.