ᐅ Attic Conversion – Insulating a Pitched Roof from the Inside – Completely Unsure
Created on: 28 Aug 2021 23:22
W
ww_chris1984
Good evening everyone!
My girlfriend and I are currently renovating my grandparents’ house to move in this autumn. It’s a matter close to our hearts, and we are doing our very best to make the most of the existing building fabric (built in 1952, solid construction with pumice stone, originally built as housing for refugees after WWII).
The next major step is converting the attic. Since we’re both more or less beginners in this area, I’m currently quite unsure and hope to get some advice and feedback from the community.
We receive different recommendations from various parties regarding the procedure and I’m unsure about how to proceed.
It concerns the insulation of the pitched roof from the inside. The plan is to install both intermediate and counter-rafter insulation (is that the correct term?). According to the contractor, the following build-up makes sense and will be implemented by the selected company: intermediate rafter insulation, then a vapor retarder, followed by counter-rafter insulation, topped with OSB boards. Finally, drywall will be installed. The insulation material is Knauf WLG32 mineral wool. The vapor retarder is a product called Knauf Insulation LDS FlexPlus.
My main question is this: The contractors say the insulation layers need ventilation behind them. For example, if there is 14 cm (5.5 inches) of insulation, there should be 16 cm (6.3 inches) of space. However, the building materials supplier, a friend who is an architect, and another contractor in my circle of friends all said that this is no longer common practice and that 14 cm (5.5 inches) of space is sufficient for 14 cm (5.5 inches) of insulation.
What is your assessment? Is this something that can be answered generally? Are there important arguments against this overall build-up? I have read about quite different construction methods.
I don’t want to presume to tell a contractor how to do their work, but I think my uncertainty is understandable. Also, I would simply like to understand it better. Losing 4 cm (1.6 inches) of space on each side of the pitched roof amounts to quite a lot, and if it is not necessary, I would prefer to avoid it.
If you need any further information to better assess the situation, I’m happy to provide it.
Thank you very much in advance for your help!
My girlfriend and I are currently renovating my grandparents’ house to move in this autumn. It’s a matter close to our hearts, and we are doing our very best to make the most of the existing building fabric (built in 1952, solid construction with pumice stone, originally built as housing for refugees after WWII).
The next major step is converting the attic. Since we’re both more or less beginners in this area, I’m currently quite unsure and hope to get some advice and feedback from the community.
We receive different recommendations from various parties regarding the procedure and I’m unsure about how to proceed.
It concerns the insulation of the pitched roof from the inside. The plan is to install both intermediate and counter-rafter insulation (is that the correct term?). According to the contractor, the following build-up makes sense and will be implemented by the selected company: intermediate rafter insulation, then a vapor retarder, followed by counter-rafter insulation, topped with OSB boards. Finally, drywall will be installed. The insulation material is Knauf WLG32 mineral wool. The vapor retarder is a product called Knauf Insulation LDS FlexPlus.
My main question is this: The contractors say the insulation layers need ventilation behind them. For example, if there is 14 cm (5.5 inches) of insulation, there should be 16 cm (6.3 inches) of space. However, the building materials supplier, a friend who is an architect, and another contractor in my circle of friends all said that this is no longer common practice and that 14 cm (5.5 inches) of space is sufficient for 14 cm (5.5 inches) of insulation.
What is your assessment? Is this something that can be answered generally? Are there important arguments against this overall build-up? I have read about quite different construction methods.
I don’t want to presume to tell a contractor how to do their work, but I think my uncertainty is understandable. Also, I would simply like to understand it better. Losing 4 cm (1.6 inches) of space on each side of the pitched roof amounts to quite a lot, and if it is not necessary, I would prefer to avoid it.
If you need any further information to better assess the situation, I’m happy to provide it.
Thank you very much in advance for your help!
P
pagoni202029 Aug 2021 20:47Joedreck schrieb:
If there was a climate membrane under your roof tiles, the insulation could be installed directly against it. As I said, at that time we didn’t have something like a climate membrane or it was called differently (roofing underlayment 😀).
Not that it wouldn’t be correct or good, but back then we had exactly the same setup.
Tiles – roofing underlayment – 24mm (1 inch) wooden boards – full insulation with Isover – polyethylene (PE) foil – wooden paneling/drywall in the living area.
@ww_chris1984 I’m not saying you should do it that way or that it’s better, but simply that this exact recommendation was given to me by professionals at the time, and looking back, it made sense to me (and the carpenters as well), and I never had any problems with it.
W
ww_chris198429 Aug 2021 21:27If you carry out a KfW renovation with an energy consultant, is she then the primary contact person who should determine whether ventilation behind the cladding is necessary?