Vapor Retarder in the Basement
I am renovating a single-family house built in 1976. The basement (only about 1/4 underground) is constructed of 20 cm (8 inches) concrete, while the ground floor is a timber frame build.
The finished rooms in the basement have an interior insulation of 6 cm (2.5 inches) mineral wool (very loose, allowing excellent air circulation), plus 8 cm (3 inches) gypsum board with textured wallpaper, and no vapor retarder. The mineral wool looks accordingly affected.
Now, I have directly applied 15 cm (6 inches) rigid mineral wool insulation on the concrete with PU foam adhesive, followed by a 1.5 cm (0.6 inches) OSB board also glued with PU foam. (The new calcium silicate windows have a Uw value of 0.7). Everything was pressed firmly during installation so there is no air gap, and the OSB joints are sealed. The interior wall adjoining the concrete, made of calcium silicate blocks, was routed out by 15 cm (6 inches) along the concrete and filled with mineral wool. This way, I avoid thermal bridges everywhere.
The vapor diffusion equivalent (Sd) values from outside to inside are therefore 16 / 0.15 / 3.4.
To prevent moisture problems, I might need to install an additional interior vapor retarder. I am uncertain what the optimal Sd value for this interior layer would be to ensure proper performance both in winter and summer. Question: Could someone assess whether the above assembly can work without an additional vapor retarder?
(I plan to apply a synthetic plaster on top of the OSB board).
I am renovating a single-family house built in 1976. The basement (only about 1/4 underground) is constructed of 20 cm (8 inches) concrete, while the ground floor is a timber frame build.
The finished rooms in the basement have an interior insulation of 6 cm (2.5 inches) mineral wool (very loose, allowing excellent air circulation), plus 8 cm (3 inches) gypsum board with textured wallpaper, and no vapor retarder. The mineral wool looks accordingly affected.
Now, I have directly applied 15 cm (6 inches) rigid mineral wool insulation on the concrete with PU foam adhesive, followed by a 1.5 cm (0.6 inches) OSB board also glued with PU foam. (The new calcium silicate windows have a Uw value of 0.7). Everything was pressed firmly during installation so there is no air gap, and the OSB joints are sealed. The interior wall adjoining the concrete, made of calcium silicate blocks, was routed out by 15 cm (6 inches) along the concrete and filled with mineral wool. This way, I avoid thermal bridges everywhere.
The vapor diffusion equivalent (Sd) values from outside to inside are therefore 16 / 0.15 / 3.4.
To prevent moisture problems, I might need to install an additional interior vapor retarder. I am uncertain what the optimal Sd value for this interior layer would be to ensure proper performance both in winter and summer. Question: Could someone assess whether the above assembly can work without an additional vapor retarder?
(I plan to apply a synthetic plaster on top of the OSB board).
The OSB boards themselves can act as a vapor barrier if their edges are properly sealed with airtight adhesive. Otherwise, you can use a standard vapor retarder membrane.
However, I would be cautious and have a dew point analysis done for the wall. That way, it will be clear where and how you need to install the vapor retarder.
Of course, it would have been better to do this beforehand. But it probably can’t be changed now.
However, I would be cautious and have a dew point analysis done for the wall. That way, it will be clear where and how you need to install the vapor retarder.
Of course, it would have been better to do this beforehand. But it probably can’t be changed now.
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