Regarding vapor barrier in insulated heated parts in garage?

[Ludde L]

Hello
I have a garage building where a storage room (1) and a sunroom (2) are insulated and heated (frost-free) during the colder months. I now also want to insulate the garage (3). I also have a bike storage (4) that will remain uninsulated. Where do I need to install a vapor barrier? I realize it's needed on walls A, B, and C. But should a vapor barrier also be installed on the garage side of walls D and E? Should I have a vapor barrier on the storage room side of wall F as well?
Yellow = insulation
Blue = Vapor barrier

 

[klaskarlsson]

Hi
I have a garage building where a storage (1) and a conservatory (2) are insulated and heated (frost-free) during the colder months. I now also want to insulate the garage (3). I also have a bike shed (4) that will remain uninsulated. Where do I need to place a vapor barrier? I realize it is needed on walls A, B, and C. But should there also be a vapor barrier on the garage side of walls D and E? Should I have a vapor barrier on the storage side of wall F?
Yellow = insulation
Blue= Vapor barrier

Actually, you should only barrier between warm and cold, i.e., walls between warm-warm should not be barred, as it rather increases risks if for some reason you don't have it 100% tight and happen to get moisture there (as there are barriers on both sides)

I would have used a vapor brake, which allows moisture to migrate out of the wall if it gets in, which is good if you, for example, want to cool down the garage in the future or just have it frost-free. And I would only have installed this new one against cold spaces/exterior walls.
If it's a lot of work to redo, I would have left the walls that now end up between warm-warm - it should at least allow some moisture to migrate out if one side is open, so it should be fine.

So in your case, A+B+C would be covered with a vapor brake (not barrier). Absolutely not D, E, F.

If you tend to switch which spaces are colder/warmer and so on, you might consider changing to a vapor brake in all walls and possibly hygroscopic insulation too. On the other hand, the sensitivity of this seems to be somewhat exaggerated. I haven't seen many disaster examples, and it's probably mainly so important because modern houses have very thick insulation. You probably won't insulate a garage as much (maybe just 95-145 mm?)