I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

On Apr 19, 7:44*pm, andrew wrote:
I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

I would think the insulation value of the air-gap will be
insignificant compared to 65mm celotex.

However with celotex, you pay pretty much for thickness - so not much
price-difference between 25mm plus 40mm, and 65mm. But two layers
would mean you can install a continuous layer behind the studs (or
ideally, the whole lot, if you can afford the loss of room-space).

(I'm assuming you're insulating a solid masonry wall).

Extra space in the depth of the studs also useful for cable routing.

In article , andrew
writes
I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this.

Sounds good.

This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

Nope, air movement undermines insulation. Make sure there is no path for
air from the cold (brick) side of the insulation to warm (plasterboard)
side. This is normally done with wide foil tape to cover joints and
small gaps with expanding foam to fill larger gaps.

Def don't do what some hired 'friends' did to a chum's installation,
used misc offcuts to make up insulation in panels, free to rattle and
with nothing sealing the gaps. Air was free to move around the whole
lot, negating the insulation.

Watch out for any gaps top and bottom that might allow cold air to pass
to the inevitable small (hopefully tiny gap) between the insulation PB.

Make sure that the insulation is well fixed in place, you don't want to
use a plasterboard fixing in the future for a shelf and find yourself
pushing the insulation backwards.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

On Apr 19, 7:44*pm, andrew wrote:
I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

Thinner than what?
You get far more resulting insulation with no gaps for air to blow
through. If you're using rigid boards, use foam to fill any little
gaps.


NT

On Apr 19, 7:44 pm, andrew wrote:
I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

I wouldn;t have bothered with the studs and just attached insulated pb
to the walls...

Jim K

On Apr 20, 12:15*pm, Jim K wrote:
On Apr 19, 7:44 pm, andrew wrote:

I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

I wouldn;t have bothered with the studs and just attached insulated pb
to the walls...

Jim K

Is celotex rigid enough to simply glue PB onto it, no studs? I assume
polystyrene isnt.


NT

On Apr 20, 5:36 pm, Tabby wrote:
On Apr 20, 12:15 pm, Jim K wrote:



On Apr 19, 7:44 pm, andrew wrote:

I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

I wouldn;t have bothered with the studs and just attached insulated pb
to the walls...

Jim K

Is celotex rigid enough to simply glue PB onto it, no studs? I assume
polystyrene isnt.

NT

yup bought it readymade loads of times - Kingspan usually onto 12.5mm
pb 8X4s.

Expect you could do it homebrew as long as you get the celotex dead
plumb. The premade stuff appears to use that spray-on "spiders web"
contact adhesive stuff, plus you;ll use mechanical fixings too to add
to security.

Expect the PB itself adds a lot to strength thinner thicknesses of
whichever insulation sheet.

(Polystyrene not vapour proof so probly a non-starter (burns quick n
nasty too))

Jim K

Tabby wrote:

On Apr 19, 7:44Â*pm, andrew wrote:
I'm just about to embark on this, builder has fabricated the stud wall
with 3 x 2 set just off the 13" brick wall. Perceived wisdom is to
squeeze the 65mm celotexlike boards in between the studs and flush with
them and fix plasterboard over this. This makes sense in that the
plasterboard gains some support and is what the insulation manufacturer
recommends. From an insulation point of view wouldn't it make sense to
have an thinner air gap either side of the insulation as the thinner gap
would be less likely to transfer heat by convection currents?

AJH

Thinner than what?
You get far more resulting insulation with no gaps for air to blow
through. If you're using rigid boards, use foam to fill any little
gaps.

I was not meaning gaps front to back, this will all be well sealed.

The recommended method is Brick : airspace : insulation : plasterboard.

In my case there will be a 10mm air space.

I was wondering if better insulation effect would be had by

brick : 5mm airspace : insulation : 5mm air space : plasterboard.

The builder insisted on the stud work because the old brick wall was so
badly pocked and spalled that the time truing each plasterboard with dot
and dab would have increased labour cost more than the cost of the stud
wall.

AJH

On Apr 20, 9:50*pm, andrew wrote:
Tabby wrote:
On Apr 19, 7:44*pm, andrew wrote:
I'm just about to embark on this, builder has fabricated the stud wall
with 3 x 2 set just off the 13" brick wall. Perceived wisdom is to
squeeze the 65mm celotexlike boards in between the studs and flush with
them and fix plasterboard over this. This makes sense in that the
plasterboard gains some support and is what the insulation manufacturer
recommends. From an insulation point of view wouldn't it make sense to
have an thinner air gap either side of the insulation as the thinner gap
would be less likely to transfer heat by convection currents?

AJH

Thinner than what?
You get far more resulting insulation with no gaps for air to blow
through. If you're using rigid boards, use foam to fill any little
gaps.

I was not meaning gaps front to back, this will all be well sealed.

The recommended method is Brick : airspace : insulation : plasterboard.

In my case there will be a 10mm air space.

I was wondering if better insulation effect would be had by

brick : 5mm airspace : insulation : 5mm air space : plasterboard.

The builder insisted on the stud work because the old brick wall was so
badly pocked and spalled that the time truing each plasterboard with dot
and dab would have increased labour cost more than the cost of the stud
wall.

AJH

Ah! Yes, your way would give more insulation, but the amount of
difference it makes is fairly trivial once you've got a good layer of
celotext in there. I'd do as you suggest only if it doesnt increase
labour.

Celotex around R=1 per inch, so maybe R2 if you put 2" up. Air
cavities, I forget, 0.12 or something, so about 6% difference.


NT

On Apr 20, 5:47*pm, Jim K wrote:
On Apr 20, 5:36 pm, Tabby wrote:



On Apr 20, 12:15 pm, Jim K wrote:

On Apr 19, 7:44 pm, andrew wrote:

I'm just about to embark on this, builder has fabricated the stud wall with
3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the
65mm celotexlike boards in between the studs and flush with them and fix
plasterboard over this. This makes sense in that the plasterboard gains
some support and is what the insulation manufacturer recommends. From an
insulation point of view wouldn't it make sense to have an thinner air gap
either side of the insulation as the thinner gap would be less likely to
transfer heat by convection currents?

AJH

I wouldn;t have bothered with the studs and just attached insulated pb
to the walls...

Jim K

Is celotex rigid enough to simply glue PB onto it, no studs? I assume
polystyrene isnt.

NT

yup bought it readymade loads of times - Kingspan usually onto 12.5mm
pb 8X4s.

Expect you could do it homebrew as long as you get the celotex dead
plumb. The premade stuff appears to use that spray-on "spiders web"
contact adhesive stuff, plus you;ll use mechanical fixings too to add
to security.

Expect the PB itself adds a lot to strength thinner thicknesses of
whichever insulation sheet.

(Polystyrene not vapour proof so probly a non-starter (burns quick n
nasty too))

Jim K

Right cheers, I might try that at some point.

FWIW baking ali foil stuck on with PVA makes a very effective VB. And
polythene a not great one.


NT