ᐅ Insulation / Vapor Retarder for Top Floor Ceiling / Collar Beams, Open Ceiling
Created on: 23 Nov 2012 12:13
K
Karsten 244
Hello, our house (built in the 1960s) is planned to get a new roof with insulation all the way up to the ridge in the next few years. But today, we need to replace the floorboards in the attic (the sloping roof sections are lightly insulated and clad with wood), and here the question arises whether a vapor retarder should be installed. 180mm (7 inches) mineral wool will be placed between the collar beams. The current ceiling construction from below is: wallpaper, plaster, straw, collar beams. From above, the ceiling is open. Since a new vapor retarder cannot be sealed airtight at the bottom to the old sloping roof, I’m unsure what purpose the vapor retarder would serve in this case. I would appreciate any tips and opinions. Looking forward to your input. Best regards, Karsten
Musketier schrieb:
A quick question related to this:
OSB boards act like an additional vapor barrier.
Is there actually a difference between sanded and unsanded?Sanded or unsanded is only a visual difference. However, there are different types of OSB boards (1, 2, 3, and 4).
OSB 3 and 4 can be used as vapor barriers; OSB 4 is additionally suitable for wet rooms.
Regards
Hello,
if you have purchased a new build, you should have received a heat demand calculation. It lists all the building components and how they need to be insulated. It also specifies the thermal conductivity classes (WLG). If you really have no experience, it won’t be easy to make the vapor barrier 100% airtight. Sealing joints, connections to walls/floor, etc.
The build-up from the bottom is gypsum board (green for bathrooms, Fermacell does not have green boards, so you can use the same board everywhere but leave a 5mm (0.2 inch) gap), then battens (ideally 23x72mm (1x3 inches), raw and dry), vapor barrier (please avoid the cheapest plastic foil—blue, blue-white; there are better products like Isover, Würth db2…), and then your insulation between the joists.
The best solution is 20cm (8 inches) of compressible mineral wool with a WLG of 0.035, raw and dry counter battens placed crosswise over the collar beams, and then another 60mm (2.4 inches) of 0.035 mats added, followed by raw, dry tongue-and-groove boards. This gives you 26cm (10 inches) of insulation, and your wallet will thank you quickly.
if you have purchased a new build, you should have received a heat demand calculation. It lists all the building components and how they need to be insulated. It also specifies the thermal conductivity classes (WLG). If you really have no experience, it won’t be easy to make the vapor barrier 100% airtight. Sealing joints, connections to walls/floor, etc.
The build-up from the bottom is gypsum board (green for bathrooms, Fermacell does not have green boards, so you can use the same board everywhere but leave a 5mm (0.2 inch) gap), then battens (ideally 23x72mm (1x3 inches), raw and dry), vapor barrier (please avoid the cheapest plastic foil—blue, blue-white; there are better products like Isover, Würth db2…), and then your insulation between the joists.
The best solution is 20cm (8 inches) of compressible mineral wool with a WLG of 0.035, raw and dry counter battens placed crosswise over the collar beams, and then another 60mm (2.4 inches) of 0.035 mats added, followed by raw, dry tongue-and-groove boards. This gives you 26cm (10 inches) of insulation, and your wallet will thank you quickly.
Homi schrieb:
...Then you have 26cm (10 inches) of insulation, and your wallet will quickly thank you. Not quite, because from an economic perspective, there is an optimal insulation thickness specific to each building component. For example, if the outside glazing only accounts for 5% of the total transmission heat losses, then “excessive” insulation measures are hardly cost-effective. Another factor comes into play: the heat generator! If, for example, it is a heat pump, the economic impact of insulation measures looks completely different than if a heat generator based on combustion principles is used.
Regards.
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