VCL for lean-to roof

[Cognis0]

I've removed the ceiling in our lean-to extension to form a nice airy/open kitchen/family space. I plan to insulate between the rafters with 140mm flexible wood-fibre and then over the top with 60mm wood-fibre t&g.

On top of this, for VCL/airtightness, I was thinking of using Passive Purple liquid membrane in white which would also provide a decorative finish. This should avoid the need to scim plaster and paint.

Does anyone have any comments/see flaws in this plan?

[Conor]

Can't see that looking good at all, I'm afraid. And you've the issue of penetrations for lights etc that won't be sealed. You could use PIR under the joists , tape, the. Batten out and board under. Gives you a void to run your wiring etc.

[Iceverge]

If you have no penetrations I would rather render directly to the woodfiber as an airtightness layer rather than purple passive. A a clay or lime render may be needed if you wish to retain the  breathability of the wood fiber. 

 

Having used a fair few tubs of the Soudal airtight paint it yellows in sunlight and has a texture a bit like fiberglass so I don't think it's a suitable final finish. 

 

Caution of blocking any airflow gaps with the batts if you have under sarking ventilation in the roof. 

 

 

 

 

[Cognis0]

That's helpful, thanks Iceverge... 

10 hours ago, Iceverge said:

If you have no penetrations I would rather render directly to the woodfiber as an airtightness layer rather than purple passive. A a clay or lime render may be needed if you wish to retain the  breathability of the wood fiber. 

 

Having used a fair few tubs of the Soudal airtight paint it yellows in sunlight and has a texture a bit like fiberglass so I don't think it's a suitable final finish. 

 

Caution of blocking any airflow gaps with the batts if you have under sarking ventilation in the roof.