ᐅ Vapor retarder installed incorrectly (installed the wrong way)

Hello everyone,

we are currently converting our attic and have come across a "small" problem where I hope you can help me.

We have just installed the vapor retarder. We used the product Vario KM Duplex UV from ISOVER, which has one side with a smooth surface and one side with a felt surface. And here lies our problem: it seems we installed the vapor retarder the wrong way around. The felt side is facing the interior, while the smooth side is against the fiberglass insulation.

Now we are wondering whether we need to remove everything and start over, or if the protection is still effective as is and whether this might cause issues in the future.

I would appreciate any advice you could give me on this.

Best regards, Daniel

Hello Daniel.
What has happened, has happened.
The performance of the vapor control layer depends solely on the so-called sD value, and this remains assured even if such a layer is installed in reverse, contrary to the professional standards.
Regards, KlaRa

KlaRa schrieb:
Hello Daniel.
What has happened, has happened.
The effectiveness of the membrane depends solely on the so-called sd-value. This value is guaranteed as long as such a membrane is installed in reverse, contrary to the technical guidelines.
Regards, KlaRa

So, no problem then?

I am currently dealing with this topic as well, and in various guides, there is a strong emphasis on installing the membrane the right way around. Especially when it comes to a climate membrane, as in this case, since these usually only function correctly in one direction, particularly at low temperatures.

Based on the research I have done, I would have said the membrane needs to be removed and reinstalled properly.

But I tend to trust a professional more than unverified internet sources.

A phone call with the manufacturer might quickly clarify several things.

garfunkel schrieb:
A phone call with the manufacturer might clarify a lot quickly.

Their answer should now be crystal clear, since the manufacturer has defined a front and back side with different characteristics. They probably are not allowed to say otherwise.

So either that is the case, installing it the other way around is faulty and pointless, or the manufacturer’s response would be more or less biased. I would still be interested in KlaRa’s final say on this.

I wouldn’t necessarily say that.
It’s possible that the manufacturer gives a very clear answer, namely that it’s not allowed. It’s also possible that they say it doesn’t matter, even if you lose the manufacturer’s warranty, or...

A manufacturer being completely rigid and only stating what they consider the safest option is not necessarily the case. I have encountered this several times before, even outside the construction industry.