ᐅ Insulation Between Ceilings (or Floor/Ceiling Assembly)

Hello,

I have a question regarding the insulation of my intermediate ceiling, as I’m not completely sure if everything is correct with the vapor barrier, etc.

It is a beam ceiling, with both sides of the ceiling being occupied and heated. The construction from top to bottom is as shown in the drawing:

- 38mm (1.5 inch) chipboard subflooring
- 1cm (0.4 inch) air gap
- 5cm (2 inch) loose mineral wool in a protective fleece
- 19mm (0.75 inch) chipboard subflooring
- 5x3 cm (2x1.2 inch) battens as supports
- 120mm (4.7 inch) Isover Ultimate wood construction insulation board (thermal conductivity 0.035 W/mK)
- Vapor barrier / vapor retarder
- Counter battens
- Wood ceiling / drywall ceiling

Now to my question...

In the regular living rooms, I installed a vapor barrier film. I know it’s generally not necessary since both sides are heated, but I’m concerned that mineral wool dust might eventually penetrate the ceiling. So I installed it mainly as a health precaution.

Do I need a vapor barrier film or a vapor retarder above the bathroom? The ceiling in the bathroom will be made of moisture-resistant drywall.

Thanks and best regards,

Christoph

You can install a humidity-variable vapor retarder below the ceiling battens, with an sd-value between 0.03 and 5, which allows for drying back; joints must be carefully sealed. The vapor retarder must also be securely attached to the vertical walls using the system-compatible cartridge adhesive provided by the manufacturer and then sealed airtight with plaster. Convection of warm, moist air into the ceiling structure, especially in the bathroom, must be strictly avoided.

Thanks for the response! So, an Isover Vario climate membrane would be the right choice? I actually meant to write vapor barrier and vapor retarder before, sorry...

Thanks and best regards, Christoph