How to match build materials and insulation

[Swampy]

Hi, 

 

We’re building a large extension to a 1950s semi and since most external walls will be new, have decided to fit external insulated panels to the ‘old’ external walls which will remain as external (i.e. the exiting front wall and a small part of the rear). 

of course, we’ll be rendering over the panels. 

 

My question is, what are our options for the materials we use on the completely new external walls? 
I think we’ll probably render or clad them and we would want them insulated to the same degree as the existing walls. 
 

What are our options for the construction method and materials? 
That is to say, blockwork for the internal side of the cavity, then insulation, be it rockwool or panels), followed by…what? 

We’re looking to save money where we can, but I know that insulated panels are considerably more expensive than rockwool. 

Thanks! 

 

[Mr Punter]

Could you do external wall insulation on the existing, with a thin render finish, and a 350mm cavity wall (150mm cavity with blown bead) for the new bits?  You could have some brickwork in the new bit if you like.

[Swampy]

2 hours ago, Mr Punter said:

Could you do external wall insulation on the existing, with a thin render finish, and a 350mm cavity wall (150mm cavity with blown bead) for the new bits?  You could have some brickwork in the new bit if you like.

So 2 courses of blockwork, with insulation in between, then rendered externally - for the new walls? 
Out of interest, is there any other option? 

We’d want to go for the maximum level of insulation, so I think we’d have to use panels (more expensive), or rockwool (thicker walls). 

[Miek]

If you are doing EWI on the old house you could build the extension as a solid wall ( block on flat for example) and use EWI on that also. This would make the cold bridge detailing a lot easier IMO. Then thin coat the whole lot. 

 

[joth]

15 hours ago, Miek said:

If you are doing EWI on the old house you could build the extension as a solid wall ( block on flat for example) and use EWI on that also. This would make the cold bridge detailing a lot easier IMO. Then thin coat the whole lot. 

 

 

We did something very similar to this. 200mm pavatherm EWI retrofit on existing 60s B&B cavity wall, and extension is 300mm blown cellulose TF with 80mm pavatherm EWI. 

Thermal bridge free all the way around

 

Likewise the EWI is continuous up into the roof insulation