ᐅ Laminate Flooring Installed on OSB Boards over Concrete

Hello everyone,

I am currently working on installing a floor covering in the attic (above this is an insulated pitched roof attic, below is a living space with a bathroom and several bedrooms). For this, I first laid and screwed 24 mm (1 inch) high wooden battens on the concrete floor. Now, OSB panels are to be installed on these battens. On top of that, laminate flooring will be laid. The house is 18 years old.

I was recently advised that this approach might not be a good idea because the OSB panels act as a vapor barrier, and moisture could accumulate under the OSB over time. The keyword here was ventilation space. This advice came from a trained carpenter.

Do I need to install a vapor retarder, and if so, directly on the concrete floor? Do I need to apply any other sealing elsewhere?

If I understand correctly, moisture could settle if there are significant temperature differences. What would be the proper installation build-up in this case?

Thanks in advance!

Hello questioner.
According to your information, the wood-based panels (OSB boards) are installed on battens. Just make sure there are sufficient edge gaps to allow ventilation behind the assembly and to prevent any moisture buildup (the term “moisture accumulation” is somewhat exaggerated in the context of this construction method).
OSB boards actually act as a vapor retarder, but not as a vapor barrier.
However, since no excess moisture from the old concrete slab’s construction is likely to escape (which is very unlikely), you don’t need a vapor barrier foil between the concrete slab and the battens.
Of course, it won’t do any harm, but it’s not really necessary. Proper ventilation of the battens and thus the wood-based panel layer is what matters—not much else!
Regards, KlaRa

KlaRa schrieb:

Hello questioner.
Based on your information, the wood-based panels (OSB panels) are installed on battens. Just make sure there are sufficient edge gaps to allow ventilation within the construction and to prevent any trapped moisture (the term is somewhat exaggerated in the context of the described build).
OSB panels indeed act as a vapor retarder but not as a vapor barrier.
However, since there will very likely be no excess moisture escaping from the old concrete ceiling from its original curing, you don’t need a vapor barrier membrane between the concrete ceiling and the battens.
Sure, it won’t harm to add one, but it’s not really necessary. Proper ventilation behind the battens and thus the wood-based panel layer is what really matters—nothing more!
Regards, KlaRa

Thank you very much for your assessment. I have taken the edge gaps into account.