Insulated plasterboard on ceiling or..

keano25 wrote: »

normal plasterboard with attic insulation, which would you choose and why?

House is a bungalow.

Insulation between joists and insulated board under the joists.
Gives you less depth in attic and allows flooring for storage.

keano25

kceire wrote: »

Insulation between joists and insulated board under the joists.
Gives you less depth in attic and allows flooring for storage.

So both?

BryanF

kceire wrote: »

Insulation between joists and insulated board under the joists.
Gives you less depth in attic and allows flooring for storage.

Where is the air-tightness layer?

BryanF wrote: »

Where is the air-tightness layer?

Good question. Not so easy answer with my set up.
If this is a new build then the details should be different to my option. I assumed it was a retro fit job and there was no other A/T barrier in place.

keano25

Mine is retro fit.

B-D-P--

kceire wrote: »

Good question. Not so easy answer with my set up.
If this is a new build then the details should be different to my option. I assumed it was a retro fit job and there was no other A/T barrier in place.

But for a new build its better to put where?

B-D-P-- wrote: »

But for a new build its better to put where?

Keep it in the same plane then and design the joists to hold the required amount of insulation. Allow for AT layer and don't penetrate with spot lights.

screw 6mm ply to underside of joists, insulation above the ply-between the joists, tack ATM to underside of ply, insulated board under that ATM, fixed up to joists

if no ATM, still go with insulated board & insulate between joist

chillit

Charlie Charolais wrote: »

screw 6mm ply to underside of joists, insulation above the ply-between the joists, tack ATM to underside of ply, insulated board under that ATM, fixed up to joists

if no ATM, still go with insulated board & insulate between joist

Can I ask what is the purpose of the ply in this arrangement? Could you not tack the atm to the joists and then just fix the insulated board to the joists also. And the atm needs to be taped to walls below the insulated board level I suppose and plastered over.

Charlie Charolais wrote: »

screw 6mm ply to underside of joists, insulation above the ply-between the joists, tack ATM to underside of ply, insulated board under that ATM, fixed up to joists

??

your ATM is then punctured at every electrical outlet, and worse still, probably circle drilled for spots which woudl destroy your ATM

a better construction is to fix ATM to underside of joists. Then counter batten with 2 x 1's to create service cavity for electrics.

The either foil back plasterboard or insulated plasterboard

sydthebeat wrote: »

??

your ATM is then punctured at every electrical outlet, and worse still, probably circle drilled for spots which woudl destroy your ATM

a better construction is to fix ATM to underside of joists. Then counter batten with 2 x 1's to create service cavity for electrics.

The either foil back plasterboard or insulated plasterboard

I assume with this arrangement Syd, there's no insulation between the rafters/joists?

From memory, this is what the Saint Gobain Technical Acadamy detail too.

listermint

Would air gap breathing membrane and foam between joists not be a better approach at rafter level ?

And easier...

kceire wrote: »

I assume with this arrangement Sydney, there's no insulation between the rafters/joists?

From memory, this is what the Saint Gobain Technical Acadamy detail too.

with my arrangement?
you certainly can insulate between the ceiling joists if you want.
The insulated plasterboard option is there if you want to make it easier to floor out attic for storage

chillit

My engineer has asked/speced the following.
1. Rockwool between the joists - 200mm deep
2. ATM tacked onto joists and taped onto walls below the level of the finished plaster board ceilng
3. 2x1 counter battens for the electrics
4. insulated plasterboard with minimum 60mm of PIR insulation

This makeup is supposed to get a u-value of 0.12 according to the engineers calcs.
The engineer has also suggesting using more rockwool in the attic in the areas behind the small walls. I think you call these small walls knee walls.

kieran.

chillit wrote: »

My engineer has asked/speced the following.
1. Rockwool between the joists - 200mm deep
2. ATM tacked onto joists and taped onto walls below the level of the finished plaster board ceilng
3. 2x1 counter battens for the electrics
4. insulated plasterboard with minimum 60mm of PIR insulation

This makeup is supposed to get a u-value of 0.12 according to the engineers calcs.
The engineer has also suggesting using more rockwool in the attic in the areas behind the small walls. I think you call these small walls knee walls.

I would prefer not to have a service cavity between the two insulation layers especially not foil backed PIR

1. Rockwool between the Rafters/Ceiling joists
2. PIR insulation
3. ATM tacked onto rafters and taped onto walls below
4. 2x1 counter battens for the electrics
5. plasterboard

chillit wrote: »

Can I ask what is the purpose of the ply in this arrangement? Could you not tack the atm to the joists and then just fix the insulated board to the joists also. And the atm needs to be taped to walls below the insulated board level I suppose and plastered over.

Hi,

our case if slightly different, we suspended the plasterboard to accommodate the MHRV ducting, so the ply was to hold the insulation between the joists

sydthebeat wrote: »

??

your ATM is then punctured at every electrical outlet, and worse still, probably circle drilled for spots which woudl destroy your ATM

a better construction is to fix ATM to underside of joists. Then counter batten with 2 x 1's to create service cavity for electrics.

The either foil back plasterboard or insulated plasterboard

hi Syd,
the wall chases were filled & plastered prior to the ATM, so the ATM was sealed flat to walls, the ceiling was suspended so spots just bored in PB, ATM is 200mm above PB

Charlie Charolais wrote: »

hi Syd,
the wall chases were filled & plastered prior to the ATM, so the ATM was sealed flat to walls, the ceiling was suspended so spots just bored in PB, ATM is 200mm above PB

that situation is not applicable to the posters one which you replied to above

why did you suggest fixing ply board to the underside of the rafters?

sydthebeat wrote: »

that situation is not applicable to the posters one which you replied to above

why did you suggest fixing ply board to the underside of the rafters?

the situation is different, and I acknowledged this

The ply protected the ATM & its fixings from the insulation weight above, making it easier to install the ATM below the ply

Charlie Charolais wrote: »

the situation is different, and I acknowledged this

The ply protected the ATM & its fixings from the insulation weight above, making it easier to install the ATM below the ply

yes but it doesnt make sense when you consider the works that have to be done to second fix electrics