Insulating solid brick walls

[hairykrishna]

I am looking to take on the conversion of an old cow shed/barn in the near future. I’m currently working through various bits of the build and making sure I understand them (and get prices for them!). The existing building has solid brick exterior walls, 200 odd mm thick. We can’t change the exterior of the building to any great extent, so they have to be insulated internally.

On the plans used for the planning application (not prepared or submitted by us) it states;
“All external walls to be upgraded with 1 vertical layer tyvek breathable felt, 60mm celotex insulation, 38 x 25mm timber battens to maintain 25mm air gap, all fastened to existing brickwork. 25mm insulated plasterboard and skim”

It seemed reasonably straightforward but after reading various conflicting things online I’m no longer so sure. What’s the order of all the stuff? It reads like Felt->Insulation->Battens->Insulated plasterboard. Why two separate layers of insulation? Why are the battens (and the air gap) not immediately after the wall? Is there a “standard” way of doing it?

[moustachebandit]

hairykrishna said:

I am looking to take on the conversion of an old cow shed/barn in the near future. I’m currently working through various bits of the build and making sure I understand them (and get prices for them!). The existing building has solid brick exterior walls, 200 odd mm thick. We can’t change the exterior of the building to any great extent, so they have to be insulated internally.

On the plans used for the planning application (not prepared or submitted by us) it states;
“All external walls to be upgraded with 1 vertical layer tyvek breathable felt, 60mm celotex insulation, 38 x 25mm timber battens to maintain 25mm air gap, all fastened to existing brickwork. 25mm insulated plasterboard and skim”

It seemed reasonably straightforward but after reading various conflicting things online I’m no longer so sure. What’s the order of all the stuff? It reads like Felt->Insulation->Battens->Insulated plasterboard. Why two separate layers of insulation? Why are the battens (and the air gap) not immediately after the wall? Is there a “standard” way of doing it?

Should go external brick wall, membrane, air gap, insulation, plasterboard. The battens are fitted vertically directly to the external brick wall over the membrane. Celotex insulation batts are then slotted between the battens leaving an air gap between the wall and insulation. Then plasterboard over the top. Insulated plasterboard isn't really insulation, just plasterboard with better thermal properties than normal plasterboard. The you need the air gap between the external wall and the insulation to prevent moisture / cold coming through from the external wall.

[hairykrishna]

moustachebandit said:

Should go external brick wall, membrane, air gap, insulation, plasterboard. The battens are fitted vertically directly to the external brick wall over the membrane. Celotex insulation batts are then slotted between the battens leaving an air gap between the wall and insulation. Then plasterboard over the top. Insulated plasterboard isn't really insulation, just plasterboard with better thermal properties than normal plasterboard. The you need the air gap between the external wall and the insulation to prevent moisture / cold coming through from the external wall.

That makes some sense to me and is basically what I've seen in a few places online. Two things confused me though – what creates the air gap if I’m stuffing the gap between the battens with insulation? Do I need battens that are ‘thicker’ than the insulated sheets? The other was that the battens are effectively uninsulated cold bridges to the outside wall – does that matter?

[moustachebandit]

hairykrishna said:

moustachebandit said:

Should go external brick wall, membrane, air gap, insulation, plasterboard. The battens are fitted vertically directly to the external brick wall over the membrane. Celotex insulation batts are then slotted between the battens leaving an air gap between the wall and insulation. Then plasterboard over the top. Insulated plasterboard isn't really insulation, just plasterboard with better thermal properties than normal plasterboard. The you need the air gap between the external wall and the insulation to prevent moisture / cold coming through from the external wall.

That makes some sense to me and is basically what I've seen in a few places online. Two things confused me though – what creates the air gap if I’m stuffing the gap between the battens with insulation? Do I need battens that are ‘thicker’ than the insulated sheets? The other was that the battens are effectively uninsulated cold bridges to the outside wall – does that matter?

Set the stud frame off the wall by 25mm and secure top and bottom (rather than directly to the brick wall). If you want for extra lateral reinforcement you could run some 25mm deep roofing batten horizontally along the wall and screw the stud frame into that as well. Then just insert the celotex to sit flush with the stud timber and seal it all up with the plasterboard. By not directly mounting the stud frame to the wall you will prevent thermal bridging. I am not a builder by trade but this is how I would do it.

[FlipFlopGriff]

Is it listed then?
FFG

[hairykrishna]

moustachebandit said:

Set the stud frame off the wall by 25mm and secure top and bottom (rather than directly to the brick wall). If you want for extra lateral reinforcement you could run some 25mm deep roofing batten horizontally along the wall and screw the stud frame into that as well. Then just insert the celotex to sit flush with the stud timber and seal it all up with the plasterboard. By not directly mounting the stud frame to the wall you will prevent thermal bridging. I am not a builder by trade but this is how I would do it.

That makes sense, thanks.

FlipFlopGriff said:

Is it listed then?
FFG

Fortunately not. There are a load of planning conditions to “preserve the rural character” though which mean, aside from some tidying up and some extra roof windows, the outside has to look basically as it is now.