1920 mid terrace (no cavity), injected dpc, insulated plasterboard condensation?

[goconnor573]

Hello all

Apologies read several threads on this but still not 100% my scenario.

1920s mid terrace with no cavity
Injected dpc done (plaster been chipped back to brick approx 1m above floor level)
Planning to put insulated plasterboard on both outside walls (front and rear)
2500 ceiling height
1 window on rear wall 825*1630
2 windows on front wall 825*1630
Concrete floor (vent bricks closed up)

Was thinking best way was to batton the walls (dpm between batton and wall) and then screw 25 or 38mm insulated plasterboard to those and then just skim over as rest of room is being skimmed anyways. My thinking battons best way to straighten the wall aswell, 2 birds 1 stone.

With that method there will be an air gap behind the board and some say condensation might be an issue with cold outer wall then air gap and then warm board and some say not an issue, anyone any experience or docs on doong it?

Other option I was thinking was just use long fixings directly from the insulated plasterboard to the brickwork and any uneven parts plasterer could use some bonding to straighten out then skim. Would mean no air gap and less chance of condensation.

Cheers

 

[motorbiking]

Do not batten, you also don't need a vapour barrier its built in to the board. Use plaster board foam and mechanical fixings. You don't have to buy Insulated plasterboard you can go with a two layer solution (cheaper). The insulation board must have all gaps foamed and foil taped.

Celotex 50mm + plasterboard will change the U value of the walls from around 2. to <0.4

 

[goconnor573]

Cheers.
For the window revales should I get thinner insulation or will that lose be negligible?

Aye thought direct would be better option

 

[motorbiking]

It can be easier to get a couple of 25mm boards to do the windows. You can always pack them out or double them up. Typically you will need to replace window boards or add an insert.

 

[goconnor573]

So to clarify the process would be.
Plasterboard glue and mechanical fixings for PIR to the brick walls. Foil tape cut ends to ensure tight fit. I'd also assume water down PVA to clear the duct for the bricks.
Then for the plasterboard to the pir just glue?
Or glue PIR to wall then use glue and mechanical fixings through the plasterboard and pir

 

[motorbiking]

This stuff for the glue: https://www.toolstation.com/soudal-genius-gun-plasterboard-adhesive-foam/p99304?
Regular spray foam for the gaps.

1. Clean down the walls and remove any dust.
2. Apply the foam to the back of the PIR board all the way around with approx 1" gap from the edde and a zig zag in the middle.
3. leave for 2-3 minutes to cure
4 apply to wall and use a level to get it right.
5. drill some hammer fix or frame fixes e.g. 8x100 at least 4-9 per board. Tighten to get the level right.
6. Spray foam all the gaps top and bottom
7. trim down once dry and use foil tape
8. repeat steps 2-5 for the plasterboard.
9 tape and skim to finish.

Don't forget any services you might want in the walls - e.g. power, internet, tv etc.

it doesn't matter about the 5mm gap between the board and PIR due to the foam, because the PIR will be air tight.

 

[goconnor573]

Perfect
One last one.
Since injected dpc has been done, damp fellas said plasterer shouldn't go below the holes as below will be the damp line (if water does rise) which makes sense.

I'd assume same principle for the insulation?
Or since it's foil back can go below the injection holes?

Best insulation properties would be cover as much as possible but damp is the devil lol

 

[denso13]

some say condensation might be an issue with cold outer wall then air gap and then warm board

Yes, interstitial condensation can be a problem, you draw lines through a section of the wall, one the temp drop and the other the dew point. If they meet you could have an issue at that point.

 

[motorbiking]

Perfect
One last one.
Since injected dpc has been done, damp fellas said plasterer shouldn't go below the holes as below will be the damp line (if water does rise) which makes sense.

I'd assume same principle for the insulation?
Or since it's foil back can go below the injection holes?

Best insulation properties would be cover as much as possible but damp is the devil lol

I don't know, sorry