ᐅ Breathable underlayment membrane, yes or no???

Created on: 1 Feb 2013 11:46
S
sebi0809
S
sebi0809
1 Feb 2013 11:46
Hello

I have a question because I have heard many different opinions from my friends and colleagues.
We just bought a house and want to fully convert the attic.

The roof (clay tiles sealed with mortar on the inside) still looks good, so we don’t plan to replace it for now. However, it will need to be redone in 5-10 years.

When I am in the attic, I see the bare clay tiles. Do I now need to install a vapor-permeable underlay membrane, then insulation, plus a vapor barrier?
Or can I skip the underlay membrane?
If so, does my insulation need an air gap to the tiles, or should it fit tightly against them?

There are always very different opinions on this!

Afterwards, drywall will be installed since the space will be used as living area.

In 5-10 years, when the roof is replaced, an underlay membrane would be installed from the outside anyway.

I hope I have explained my question clearly enough.

Thank you for your answers.

Best regards

Sebi
€uro
1 Feb 2013 13:00
Hello,
sebi0809 schrieb:
...We just bought a house and want to fully convert the attic.
Will the attic be heated?
sebi0809 schrieb:
...When I stand in the attic now, I see the bare clay tiles. Do I need to install a vapor-permeable underlay membrane, then insulation plus a vapor barrier?
There is already a certain problem here. How can a vapor-permeable underlay membrane be properly installed without being secured under the roof covering?
sebi0809 schrieb:
... Or can I skip the underlay membrane?
Hardly!
sebi0809 schrieb:
... If yes, does my insulation need to have an air gap to the tiles or should it be tightly pressed against them?
Ventilation above the insulation is always an advantage, never a disadvantage!
sebi0809 schrieb:
... There are many different opinions on this!
That’s true!
sebi0809 schrieb:
... Afterwards, drywall will be installed since the room is going to be used as living space.
Install a vapor barrier behind the drywall!

Best regards
A
Atschi
17 Jul 2013 17:59
Hello everyone!

I am facing the same issue, but part of my attic is finished while another part is not. The builder constructed one section as follows, from outside to inside: roof tiles, battens (no counter-battens), battens screwed directly onto the rafters, then wooden boards for ventilating behind the tiles, 10 cm (4 inches) of cellulose insulation, wooden boards, 2 cm (0.8 inches) of rigid foam board (Herathan), and 4 cm (1.6 inches) of wood wool boards (Heraklith).

Since I installed a roof window in this area, I was able to inspect the structure and was surprised that the entire insulation is dry and the finished area stays relatively cool even at an outside temperature of 30°C (86°F). My question is: I would like to add battens on the outside of the rafters, then attach an OSB board for ventilation behind the tiles, followed by 18 cm (7 inches) of insulated cavity wool, and a vapor barrier. Is it possible to use OSB boards for this, or are wooden boards better, since the joints are not completely airtight and may affect the insulation ventilation?