ᐅ Insulation of the roof with insulation wool installed between the rafters
Created on: 26 Jan 2016 09:29
R
Robigo
Hello!
We are currently in the process of insulating our roof.
Yesterday, we partially removed the old insulation from the inside to get a better understanding of the structure.
The house is about 50 years old. The roof assembly consists of:
1. Roof tiles
2. Battens
3. Overlapping horizontal bitumen membrane
4. Currently, insulation wool directly attached to the bitumen membrane, without any ventilation gap
5. A vapor barrier foil that was not airtight
While removing the insulation wool, I noticed that the bitumen membranes are damp on the inside (this is called "not vapor-permeable" in technical terms, I believe). The insulation wool is also somewhat damp on the outer side (which is understandable). However, the rafters are still dry.
My question is: in a construction like this, do we need to install a ventilation gap, meaning a space between the bitumen membrane and the insulation wool?
I am planning to use 14 cm (5.5 inches) thick insulation with a thermal resistance of about 0.032 W/m·K. The rafters are also approximately 14 cm (5.5 inches) deep. On top of this, I was thinking of adding battens of about 3 cm (1.2 inches) in thickness to create a ventilation space.
Would this be a suitable approach?
Of course, an airtight vapor barrier foil will be installed on the inside, hopefully more effective than the current one.
Thank you for your advice.
Best regards,
Robert
We are currently in the process of insulating our roof.
Yesterday, we partially removed the old insulation from the inside to get a better understanding of the structure.
The house is about 50 years old. The roof assembly consists of:
1. Roof tiles
2. Battens
3. Overlapping horizontal bitumen membrane
4. Currently, insulation wool directly attached to the bitumen membrane, without any ventilation gap
5. A vapor barrier foil that was not airtight
While removing the insulation wool, I noticed that the bitumen membranes are damp on the inside (this is called "not vapor-permeable" in technical terms, I believe). The insulation wool is also somewhat damp on the outer side (which is understandable). However, the rafters are still dry.
My question is: in a construction like this, do we need to install a ventilation gap, meaning a space between the bitumen membrane and the insulation wool?
I am planning to use 14 cm (5.5 inches) thick insulation with a thermal resistance of about 0.032 W/m·K. The rafters are also approximately 14 cm (5.5 inches) deep. On top of this, I was thinking of adding battens of about 3 cm (1.2 inches) in thickness to create a ventilation space.
Would this be a suitable approach?
Of course, an airtight vapor barrier foil will be installed on the inside, hopefully more effective than the current one.
Thank you for your advice.
Best regards,
Robert