Insulating external walls internally

[DaveH]

For various reasons I need to put some additional insulation internally on my external blockwork walls. What is the preferred method of doing this (using PIR)? The obvious way would be to dot and dab insulated plasterboard but I'm not a huge fan of dot and dab. I was thinking of using sheets of PIR and then battening over the top to act as a service void and then screwing the plasterboard to the battens. Am I running the risk of thermal bridging by screwing the battens through the insulation and into the blockwork? Or alternatively battening onto the blockwork to create a service void and then screwing insulated plasterboard to the battens. It's a cavity wall with 50mm PIR insulation in the 100mm cavity. Am I overthinking this?

 

Thanks

 

[PeterW]

You can either use 25mm between the battens, and 25mm under to get 50mm, or just use 25mm as it will be good enough to improve the fabric. 

[Onoff]

I set 47mm studs off the wall with a minimum 5mm gap on plastic shims. Fixed the studs at 5 points with concrete screws. Foam gunned behind the battens. PIR in between the studs.

 

(I had/have v.little idea of what I'm doing btw ? ).

 

 

Edited November 1, 2019 by Onoff

[DaveH]

This is what I was thinking of doing (or alternately having the battens fixed directly to the blockwork and screwing insulated plasterboard on top). I will take the PIR right to the slab before additional floor insulation, UFH and screed is installed to ensure continuous insulation wall to floor to wall.

 

Am I overthinking things by worrying about the spots where the fixings for the battens will be? Am I likely to create a load of small cold spots on the wall by breaking the 25mm PIR element? There is still 50mm PIR in the cavity so it's not like it's uninsulated or a solid wall.

 

Your thoughts would be appreciated. Thanks.

 

 

[Onoff]

Think you need a vcl in the make up of that section?

[DaveH]

15 minutes ago, Onoff said:

Think you need a vcl in the make up of that section?

 

The PIR sheets will be foil backed and all joints taped. I understood that this was all I needed but happy to be proved otherwise (before it's too late!)

[eandg]

An interested observer as planning on doing much the same (albeit foil-backed insulation onto a sips panel so thermal bridging may be a bit less of an issue). The big concern for me is breaking the VCL when screwing the batten in. 

[Onoff]

3 minutes ago, eandg said:

An interested observer as planning on doing much the same (albeit foil-backed insulation onto a sips panel so thermal bridging may be a bit less of an issue). The big concern for me is breaking the VCL when screwing the batten in. 

 

Blob of silicone.

[eandg]

22 minutes ago, Onoff said:

 

Blob of silicone.

On the joins before screwing in?

[jayc89]

On 01/11/2019 at 20:29, Onoff said:

I set 47mm studs off the wall with a minimum 5mm gap on plastic shims. Fixed the studs at 5 points with concrete screws. Foam gunned behind the battens. PIR in between the studs.

 

(I had/have v.little idea of what I'm doing btw ? ).

 

 

 

How are you getting on with this @Onoff. Was this on a solid or cavity wall? Any problems with moisture?

[Pocster]

3 hours ago, jayc89 said:

Any problems with moisture?

He has lots of issues with that after 4 yrs 

[Onoff]

3 hours ago, jayc89 said:

 

How are you getting on with this @Onoff. Was this on a solid or cavity wall? Any problems with moisture?

 

None at all on the fully tiled walls. It's a wet room in regular use. Only issue is some black mould (?) On the painted ceiling. That was done in Dulux Trade Diamond Matt. 

 

I think that's because there is no heating in the bathroom still. Towel rail and UFH aren't connected yet. 

 

[Pocster]

4 minutes ago, Onoff said:

 

None at all on the fully tiled walls. It's a wet room in regular use. Only issue is some black mould (?) On the painted ceiling. That was done in Dulux Trade Diamond Matt. 

 

I think that's because there is no heating in the bathroom still. Towel rail and UFH aren't connected yet. 

 

I meant in your pants