Airtight tape that can be plastered

Nisio

Hi,

I've a dormer bungalow build under way at the moment and I'm looking at ways to airtight the upstairs rooms (construction is slates, battens, breathable membrane, air gap, rigid insulation between joists, insulated plasterboard over joists).

I was hoping to find some airtightness tape that I could use to seal the joints between the insulated plasterboards (and between these plaster boards and the wall/floor where they meet).

Could anyone recommend a tape/method?

Thanks,

Oisin

sas

Nisio wrote: »

Hi,

I've a dormer bungalow build under way at the moment and I'm looking at ways to airtight the upstairs rooms (construction is slates, battens, breathable membrane, air gap, rigid insulation between joists, insulated plasterboard over joists).

I was hoping to find some airtightness tape that I could use to seal the joints between the insulated plasterboards (and between these plaster boards and the wall/floor where they meet).

Could anyone recommend a tape/method?

Thanks,

Oisin

You should be installing an airtightness membrane under the rafters before you apply the insulated plasterboard.

There is an issue however with your dew point that you'd need to consider here before doing this. There is a rule of thumb that says that you must have minimum 2/3 of your insulation on the cold side of an airtightness membrane. That's 2/3 of your insulation value, not necessarily thickness i.e. this assumes you are using insulating materials with equivalent thermal conductivity.

What you are suggesting is not something that is typically done so I wouldn't expect it to deliver any meaningful results.

Is there a reason you are not asking about using a membrane?

Nisio

sas wrote: »

Nisio wrote: »

Hi,

I've a dormer bungalow build under way at the moment and I'm looking at ways to airtight the upstairs rooms (construction is slates, battens, breathable membrane, air gap, rigid insulation between joists, insulated plasterboard over joists).

I was hoping to find some airtightness tape that I could use to seal the joints between the insulated plasterboards (and between these plaster boards and the wall/floor where they meet).

Could anyone recommend a tape/method?

Thanks,

Oisin

You should be installing an airtightness membrane under the rafters before you apply the insulated plasterboard.

There is an issue however with your dew point that you'd need to consider here before doing this. There is a rule of thumb that says that you must have minimum 2/3 of your insulation on the cold side of an airtightness membrane. That's 2/3 of your insulation value, not necessarily thickness i.e. this assumes you are using insulating materials with equivalent thermal conductivity.

What you are suggesting is not something that is typically done so I wouldn't expect it to deliver any meaningful results.

Is there a reason you are not asking about using a membrane?

I've asked the guy doing our ber/sign off about the need for a vapour membrane and his opinion was that given the roof construction (detailed above) and the thickness of insulation (150 mm between rafters and 40 mm foil-backed insulation stuck to the plasterboard and a 50 space between the breathable felt and the insulation) that a separate layer wasn't required.

MicktheMan

Nisio wrote: »

I've asked the guy doing our ber/sign off about the need for a vapour membrane and his opinion was that given the roof construction (detailed above) and the thickness of insulation (150 mm between rafters and 40 mm foil-backed insulation stuck to the plasterboard and a 50 space between the breathable felt and the insulation) that a separate layer wasn't required.

Vapour control is one thing, air tightness is something else. What air tightness target are you aiming for?

What stage is the roof at?
A better specification might be to make your roof a warm roof where insulation is above and between rafters rather than between and below. This way there is no issue with dew point location as sas has referred to above.

Nisio

MicktheMan wrote: »

Nisio wrote: »

I've asked the guy doing our ber/sign off about the need for a vapour membrane and his opinion was that given the roof construction (detailed above) and the thickness of insulation (150 mm between rafters and 40 mm foil-backed insulation stuck to the plasterboard and a 50 space between the breathable felt and the insulation) that a separate layer wasn't required.

Vapour control is one thing, air tightness is something else. What air tightness target are you aiming for?

What stage is the roof at?
A better specification might be to make your roof a warm roof where insulation is above and between rafters rather than between and below. This way there is no issue with dew point location as sas has referred to above.

Our roof is finished so it's fixed to a cold roof design. On the airtightness we haven't been working to a target more looking at joints/boundaries in the house and ways to airtight them