Good evening,
it's me again...
But I’m really impressed with the help here, no matter the topic.
One more question, this time about insulation between rafters:
- Rafters are 220mm (9 inches) thick
- Can / should / must I fill the entire rafter thickness?
- So, do I use 220mm (9 inches) insulation with a thermal conductivity of 0.035 W/(m·K)
- Or 200mm (8 inches) insulation with 0.032 W/(m·K) and leave 20mm (1 inch) of air space?
Thanks,
Regards and stay healthy!
it's me again...
But I’m really impressed with the help here, no matter the topic.
One more question, this time about insulation between rafters:
- Rafters are 220mm (9 inches) thick
- Can / should / must I fill the entire rafter thickness?
- So, do I use 220mm (9 inches) insulation with a thermal conductivity of 0.035 W/(m·K)
- Or 200mm (8 inches) insulation with 0.032 W/(m·K) and leave 20mm (1 inch) of air space?
Thanks,
Regards and stay healthy!
Lumpi_LE schrieb:
...someone really botched itThis can happen in older buildings. In some cases, bitumen membranes were also used. Simply omitting the ventilation behind could lead to moisture problems.
Appel2000 schrieb:
Okay, I just meant that I read somewhere that you shouldn’t completely fill the rafter depth to avoid direct contact between the insulation and the vapor barrier.How is that supposed to work? Gravity will cause the insulation to rest directly on the membrane.Tassimat schrieb:
How is that supposed to work? Gravity will cause the insulation to rest on the membrane.Valid point. They probably mean the underlay membrane above the insulation, not the vapor retarder below. If ventilation of the mineral wool is intended, it would be between the underlay membrane and the insulation, either as partial rafter insulation or full rafter insulation without an air gap.A
Appel20004 May 2020 17:22No, the vapor retarder was actually what I meant.
So, when I think of insulation between rafters, it is installed between the rafters.
It should stay in place on its own and not be "held" by the vapor retarder….
And I have not planned an additional layer "behind the insulation" towards the attic…. what purpose would that serve?
So, when I think of insulation between rafters, it is installed between the rafters.
It should stay in place on its own and not be "held" by the vapor retarder….
And I have not planned an additional layer "behind the insulation" towards the attic…. what purpose would that serve?
Appel2000 schrieb:
No, it was actually the vapor retarder that was meant.
So when I think of insulation between rafters, it is installed between the rafters.
It should hold in place by itself and not be "held" by the vapor retarder....
And I have not planned an additional membrane "behind the insulation" towards the attic... what would that be for? Well, that’s pointless. You are skipping ventilation of the insulation layer without fully utilizing it. So either with an air gap between the insulation and the underlay membrane or not at all.
An additional membrane towards the attic is the insulation below the rafters. This is used when the rafter depth is insufficient, insulating the area of the counter battens for the drywall or gypsum boards. This also insulates the rafters themselves, which often act as thermal bridges when they extend all the way to the exterior.
Viewed from the inside:
2 layers of gypsum board (2x gypsum board)
Counter battens
Batten
Vapor barrier (climate membrane)
Insulation
Underlay membrane
Batten or sheathing
If applicable, ventilation space via counter battens
Roof covering
The insulation is responsible for the U-value.
The membranes determine the Sd-value.
The air cavity facing the interior can serve as a “pre-wall installation layer.”
2 layers of gypsum board (2x gypsum board)
Counter battens
Batten
Vapor barrier (climate membrane)
Insulation
Underlay membrane
Batten or sheathing
If applicable, ventilation space via counter battens
Roof covering
The insulation is responsible for the U-value.
The membranes determine the Sd-value.
The air cavity facing the interior can serve as a “pre-wall installation layer.”
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