Kingspan over existing plaster

[rreanor]

I have a double skin/no cavity/no external render victorian semi, and i want to insulate some of the bedroom external walls.

I dont want to have to remove the plaster as it'll cause major disruption. It seems dot and dab is not advisable unless there is a cavity, however can i mechanically fix it instead i.e. install a baton frame over the existing plaster (screwed into the brick behind) and then screw the board onto the batons?

 

[noseall]

can i mechanically fix it instead i.e. install a baton frame over the existing plaster (screwed into the brick behind) and then screw the board onto the batons?

Yes.

 

[Dereekoo]

Yes

 

[rreanor]

Yes

Do you know is his was a recommended method by the manufacturer, or did you just assume it would be ok? I suppose my only concern would be the plaster behind eventually blowing

 

[noseall]

I suppose my only concern would be the plaster behind eventually blowing

Fit 25mm insulation between the (25mm deep) battens first. It'll trap any plaster behind.

 

[Dereekoo]

Do you know is his was a recommended method by the manufacturer, or did you just assume it would be ok? I suppose my only concern would be the plaster behind eventually blowing

Yeas, see Kingspan K118 brochure. No reason why plaster should blow if its in a solid state now.

 

[mattylad]

Do you need to put a vapour barrier of any sort when doing this?
If so is this before the battens are fitted?

 

[Dereekoo]

Do you need to put a vapour barrier of any sort when doing this?
If so is this before the battens are fitted?

Yes.
No.

 

[rreanor]

Yes.
No.

Doesn't there need to be a cavity behind?

 

[Dereekoo]

Doesn't there need to be a cavity behind?

Depends on your view and proposed U target , mines a cavity as per K118 brochure, some will infill with insulation for higher U value or to save on space

 

[rreanor]

Depends on your view and proposed U target , mines a cavity as per K118 brochure, some will infill with insulation for higher U value or to save on space

What does the cavity created actually achieve? Is it to prevent cold moist air hitting the final internal wall, or to provide ventilation?

 

[Dereekoo]

Its not there to achieve anything, its there because you have battened the wall and is either infilled or left empty.

 

[robinbanks]

Is it to prevent cold moist air hitting the final internal wall

That's the insulation's job

Do you need to put a vapour barrier of any sort when doing this?

You don't need a separate sheet membrane for vapour control if you're using foil-faced board and happy with the performance of the tape you've chosen to join adjacent board edges to each other

 

[Dereekoo]

Not if you're using foil-faced board and happy with the performance of the tape you've chosen to join adjacent board edges to each other

I thought that was a vapour barrier of some sort

 

[robinbanks]

It is; my take away from mattylad's post was whether a sheet membrane like visqueen or some more high tech alternative was needed. Edited for clarity