ᐅ Structure of Ceiling Between Living Space and Unheated Attic
Created on: 16 Jan 2020 21:32
H
hans_dampfH
hans_dampf16 Jan 2020 21:32Hello everyone,
I urgently need help with this ceiling assembly (see image).
Outside: unheated attic, but it will be converted into living space in a few years
Inside: living area
According to the above assembly, there is 0.22 kg/m² (0.045 lb/ft²) of condensation. If I replace the variable climate membrane with a vapor retarder that has a high sd value, the calculation shows no condensation.
However, based on statements in various forums, it is almost impossible for vapor retarders and climate membranes to remain airtight over the years, and a significant amount of condensation could enter the structure through convection. Due to the sealed OSB board on top and the sealed vapor retarder below, the moisture could no longer escape and would cause damage to the structure.
Which option carries fewer risks? The variable climate membrane with low diffusion and potential for drying back out, or the vapor retarder while hoping everything remains airtight?
Or are there other possible solutions?
Current unchangeable condition of the ceiling:
- 25 mm (1 inch) OSB boards
- KVH beams 220/100 mm (8.7 x 3.9 inches)
- Glass wool 035, 260 mm (10.2 inches)
Best regards
I urgently need help with this ceiling assembly (see image).
Outside: unheated attic, but it will be converted into living space in a few years
Inside: living area
According to the above assembly, there is 0.22 kg/m² (0.045 lb/ft²) of condensation. If I replace the variable climate membrane with a vapor retarder that has a high sd value, the calculation shows no condensation.
However, based on statements in various forums, it is almost impossible for vapor retarders and climate membranes to remain airtight over the years, and a significant amount of condensation could enter the structure through convection. Due to the sealed OSB board on top and the sealed vapor retarder below, the moisture could no longer escape and would cause damage to the structure.
Which option carries fewer risks? The variable climate membrane with low diffusion and potential for drying back out, or the vapor retarder while hoping everything remains airtight?
Or are there other possible solutions?
Current unchangeable condition of the ceiling:
- 25 mm (1 inch) OSB boards
- KVH beams 220/100 mm (8.7 x 3.9 inches)
- Glass wool 035, 260 mm (10.2 inches)
Best regards
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