I have a plain wall (no reveals) with 24mm deep p/t battens, between
which will go 20mm celotex, then 20mm celotex & 9.5mm PB on top. That
is the limit after removing architraves.

Do I have to maintain battens at 450mm centres when the insulation
braces the PB?

Just happened to notice quite a few walls on the internet have
obviously 600mm spacing with 12.5mm PB, relying on it seems the
insulation to stop the PB flapping around & joints cracking.

On 21 Sep, 16:30, "js.b1" wrote:
I have a plain wall (no reveals) with 24mm deep p/t battens, between
which will go 20mm celotex, then 20mm celotex & 9.5mm PB on top. That
is the limit after removing architraves.

Do I have to maintain battens at 450mm centres when the insulation
braces the PB?

Just happened to notice quite a few walls on the internet have
obviously 600mm spacing with 12.5mm PB, relying on it seems the
insulation to stop the PB flapping around & joints cracking.

I stick the insulation in position with canned foam an put blobs of
it here and there in the centre. Obviously nail the pb one before the
foam goes off. The joint will still need taping or scrim of it is to
be plaster skimmed.
You might need a vapour barrier. Esp. in kitchen, bathroom.

On Sep 21, 6:47*pm, harry wrote:
I stick the insulation in position with canned foam an
put blobs of it *here and there in the centre.

There is a "new" specific foam for this - "insta foam". It is low
expansion but high strength and very fast, but is gun only and tends
to trash guns quite quickly.

Obviously nail the pb one before the foam goes off.

A few hammerfix re obvious fire regs.
With expanding foam you would need them quite quick :-)

The joint will still need taping or scrim of it is to
be plaster skimmed.

I always skim, simply because wallpaper when stripped off plasterboard
can be a right mess :-)

You might need a vapour barrier. Esp. in kitchen, bathroom.

I will foil tape the joints, it is 2 layers of 20mm celotex so there
will be quite a good vapour barrier. It is a box-room so limited
moisture issues.

It just looked like a shed load of wood piled ready for the wall !!
However the second layer of celotex will minimises the cold bridging
of wood and 40mm PIR is a whole lot better than
nothing in a "2 outside wall & prevailing wind" room.

With hindsight I would "******** to the spirit of BR" and use 40mm
rough-cut eXtruded PolyStyrene, bond it to the wall, a few stainless
"giant drawing pins" re fire, and directly skim the suface.

On 21 Sep, 21:17, "js.b1" wrote:
On Sep 21, 6:47*pm, harry wrote:

I stick the insulation in position with canned foam an
put blobs of it *here and there in the centre.

There is a "new" specific foam for this - "insta foam". It is low
expansion but high strength and very fast, but is gun only and tends
to trash guns quite quickly.

Obviously nail the pb one before the foam goes off.

A few hammerfix re obvious fire regs.
With expanding foam you would need them quite quick :-)

The joint will still need taping or scrim of it is to
be plaster skimmed.

I always skim, simply because wallpaper when stripped off plasterboard
can be a right mess :-)

You might need a vapour barrier. Esp. in kitchen, bathroom.

I will foil tape the joints, it is 2 layers of 20mm celotex so there
will be quite a good vapour barrier. It is a box-room so limited
moisture issues.

It just looked like a shed load of wood piled ready for the wall !!
However the second layer of celotex will minimises the cold bridging
of wood and 40mm PIR is a whole lot better than
nothing in a "2 outside wall & prevailing wind" room.

With hindsight I would "******** to the spirit of BR" and use 40mm
rough-cut eXtruded PolyStyrene, bond it to the wall, a few stainless
"giant drawing pins" re fire, and directly skim the suface.

You can buy the foam boards with a rough thin plastic surface "paper"
intended for plaster. Takes plaster well.

On Sep 22, 9:03*am, harry wrote:
You can buy the foam boards with a rough thin plastic surface "paper"
intended for plaster. Takes plaster well.- Hide quoted text -

I only recently saw them.

It came down to what I could get cheaply as seconds for my mother. It
gives her a "super-insulated bedroom" if the heating were to say fail
or other work needs doing on her main bedroom.

PIR foam is quite a price, but seconds can be really cheap (£4 per
20mm sheet, only light edge damage).