I have seen that the question has come up previously regarding the renovation of an old house, but now it concerns new construction.
I am in the process of building a garage and am now wondering whether I should install a vapor barrier or not. Up until very recently, I have assumed that I should not have one, but now I am starting to have doubts. The garage will only be heated to between 5 and 10 degrees during the winter.
The wall is constructed as follows from the outside in:
panel, nail battens, 9mm exterior gypsum board, 120 studs, 45 horizontal studs, interior gypsum board.
If anyone thinks I should install a vapor barrier, where should I place it? I believe I have seen all the alternatives now on different pages on the net.
Personally, I think I should not have it, as the risk is that it will condense in the wrong place on really sunny days. The garage is 12 x 5 meters in a straight east-west direction, with one long side facing directly south.
I am in the process of building a garage and am now wondering whether I should install a vapor barrier or not. Up until very recently, I have assumed that I should not have one, but now I am starting to have doubts. The garage will only be heated to between 5 and 10 degrees during the winter.
The wall is constructed as follows from the outside in:
panel, nail battens, 9mm exterior gypsum board, 120 studs, 45 horizontal studs, interior gypsum board.
If anyone thinks I should install a vapor barrier, where should I place it? I believe I have seen all the alternatives now on different pages on the net.
Personally, I think I should not have it, as the risk is that it will condense in the wrong place on really sunny days. The garage is 12 x 5 meters in a straight east-west direction, with one long side facing directly south.
I don't agree. If you heat a building to 18 degrees or more year-round, you should install a vapor barrier. And it can then be advantageously moved 1/3 of the way into the wall. So in your case, a maximum of 55 mm. However, if you don't heat to 18 degrees, you should exclude the vapor barrier due to the risk of reverse moisture migration. In a garage where high humidity can occur, you should instead ensure that there is a negative pressure controlled by a fan. The risk is then very small that moisture will penetrate the structure and condense in the wrong place.
This written by a designer with moisture and mold problems as a specialty.
Tartan
This written by a designer with moisture and mold problems as a specialty.
Tartan
I would install the moisture barrier and mount an exhaust fan to have negative pressure in the garage. Then you can basically have whatever temperature you want in the garage. It's not certain that you will always want to have 5-10 degrees in the garage.
I am jumping on this thread as I have a similar question.
We are in the process of changing the facade of our house with a lightweight concrete frame. Previously, it looked like this: Brick, glass wool, lightweight concrete (siporex), plaster, thus without a vapor barrier.
Now we will remove the brick and glass wool to make the new wall as follows: Panel, 34 mm battens, wind barrier, 2 * 45 mm with insulation, lightweight concrete, and plaster. Should a vapor barrier be installed in this construction and if so, where?!
/Per
We are in the process of changing the facade of our house with a lightweight concrete frame. Previously, it looked like this: Brick, glass wool, lightweight concrete (siporex), plaster, thus without a vapor barrier.
Now we will remove the brick and glass wool to make the new wall as follows: Panel, 34 mm battens, wind barrier, 2 * 45 mm with insulation, lightweight concrete, and plaster. Should a vapor barrier be installed in this construction and if so, where?!
/Per
Everyone except the expert says vapor barrier.
What I'm afraid of if I install a vapor barrier is that when it's winter and, say, 7 degrees inside the garage, and the sun is shining directly on the entire long side, we might get 20 degrees on the outside wall.
The risk I see is that you'll get condensation on the outside of the plastic.
Now, I don't have the Mollier diagram in my head, and I don't know how much of a temperature difference is required to get condensation in winter when the humidity is relatively low. Does anyone else know?
Gosh, this is so frustrating. Why can't all the experts and laypeople agree on what to do. :-/
What I'm afraid of if I install a vapor barrier is that when it's winter and, say, 7 degrees inside the garage, and the sun is shining directly on the entire long side, we might get 20 degrees on the outside wall.
The risk I see is that you'll get condensation on the outside of the plastic.
Now, I don't have the Mollier diagram in my head, and I don't know how much of a temperature difference is required to get condensation in winter when the humidity is relatively low. Does anyone else know?
Gosh, this is so frustrating. Why can't all the experts and laypeople agree on what to do. :-/
It will be a choice between expert and layman. But if you search for "molliere" online, you will get a result, and then it is easy to understand what is happening and that the temperature difference is not so large before condensation occurs, and in your case on the "wrong" side of the plastic. I wish more people knew what a molliere diagram is and how to interpret it, then these discussions wouldn't be so complicated to explain.
Tartan
Tartan
Negative or positive pressure in the garage does not affect moisture migration in the wall at all. It is the partial pressure of the water vapor on each side of the wall that determines the direction of moisture migration. Water will (try to) diffuse from the side with higher pressure to the side with lower pressure. A Mollier diagram can tell you at what temperature the water vapor in the indoor air will start to condense, depending on the relative humidity and temperature in the room, but it does not tell you the vapor pressure you have, at least not the Mollier diagrams I have, but you can surely calculate it if you care to.perobe said:
I actually recall that it can also be read from the diagrams I used in school...Eld said:
But when you don't heat the garage, it's the condensation, as I wrote, that is the concern if you put up plastic. So the question becomes, which is worse?
Condensation risk inside the wall or moisture movement.
And as I understand it, moisture movement is not that dangerous. Only upwards, but if you have sufficiently ventilated attic space, it should not be a problem.
no, not a vapor barrier, it’s if you heat up to 13 degrees year-round that you should have a vapor barrier, not otherwise !!!!!!
good luck.....
////the educated carpenter
good luck.....
////the educated carpenter
I would not personally put plastic in the wall; my experience when looking at houses with moisture problems is that there is plastic in the wall. I have seen many theoretical explanations both for and against vapor barriers, both here and there, and usually vapor barriers are used in new houses. Vapor barriers prevent moisture movement, usually when moisture is on its way out.
It usually also requires energy-intensive ventilation in constructions with vapor barriers.
It usually also requires energy-intensive ventilation in constructions with vapor barriers.