Hello everyone,
We have a tent roof with the following structure:
- Tiles
- Underlay membrane
- Insulation
- Vapor barrier
Originally, a vapor-permeable vapor barrier was supposed to be used, but the site manager mentioned that in his last training, for our roof type, a standard vapor barrier, meaning not vapor-permeable, was recommended.
What is your opinion? Are there any reasons why a vapor-permeable vapor barrier should not be used?
Thanks in advance.
We have a tent roof with the following structure:
- Tiles
- Underlay membrane
- Insulation
- Vapor barrier
Originally, a vapor-permeable vapor barrier was supposed to be used, but the site manager mentioned that in his last training, for our roof type, a standard vapor barrier, meaning not vapor-permeable, was recommended.
What is your opinion? Are there any reasons why a vapor-permeable vapor barrier should not be used?
Thanks in advance.
…and here my cousin, a carpenter by profession, did this with me. He said it’s better to use them because moisture can escape to some extent.
The construction here: concrete roof tiles, pitched at 30 degrees, then a thick vapor barrier, overlapped and sealed. Between the rafters, glass wool insulation, followed by the climate membrane. This is how it looked before the insulation was installed.
The construction here: concrete roof tiles, pitched at 30 degrees, then a thick vapor barrier, overlapped and sealed. Between the rafters, glass wool insulation, followed by the climate membrane. This is how it looked before the insulation was installed.
I am quite experienced in this and happy to help. The choice of membrane depends on your insulation. There are also online vapor diffusion calculators and U-value tools where you can calculate this.
A vapor retarder requires a 100% airtight seal. It is essential to perform a blower door test afterward. In a friend’s case, it was so leaky that the test could not be completed.
With a climate membrane, the advantage is that installation errors are less critical compared to a vapor barrier. However, these membranes are not universally recommended either. Therefore, the exact construction details need to be carefully considered.
A vapor retarder requires a 100% airtight seal. It is essential to perform a blower door test afterward. In a friend’s case, it was so leaky that the test could not be completed.
With a climate membrane, the advantage is that installation errors are less critical compared to a vapor barrier. However, these membranes are not universally recommended either. Therefore, the exact construction details need to be carefully considered.
Bookstar schrieb:
I am quite experienced in this area and happy to help you. Thank you!
The current build-up is as follows:
- Clay roof tile
- Underlay membrane, sealed airtight against wind
- Mineral wool insulation (Klemmrock 035, 240mm (9.4 inches))
- Vapor barrier
- Gypsum fiberboards
Regarding the floor: The attic has two rooms – a bedroom and a bathroom. Above the bathroom, there is an attic space, while the bedroom has an open ceiling. A controlled residential ventilation system is also installed.
Is this information sufficient for you?
I am a bit confused now. A vapor retarder requires 100% clean sealing. So what exactly is a climate membrane? We currently have a vapor barrier.
@Nordlys
I had also assumed that a vapor retarder would be better, and we initially planned for that. Maybe Bookstar can soon clarify why a vapor barrier might have been recommended in our case.
The above is actually a typo; I meant vapor barrier regarding proper installation.
A climate membrane works in both directions depending on the demand. Some doubt the reliability of these membranes since they have not been around for very long.
Your construction method is completely correct and has been implemented many times before. The catch is that absolutely no vapor passes through it. If you have a leak, condensation will accumulate there and cause mold. That is why it must be 99.9% airtight and properly sealed.
Hopefully, your underlay membrane has an sd value of 0.02 or similar, meaning it is highly vapor-permeable.
In that case, you could also use a climate membrane, but choose one with a slightly higher sd value. For example, Pro Clima Intello.
A standard vapor retarder would be wrong! It has a fixed sd value of 2, which might be too low, and your insulation could become saturated.
A climate membrane works in both directions depending on the demand. Some doubt the reliability of these membranes since they have not been around for very long.
Your construction method is completely correct and has been implemented many times before. The catch is that absolutely no vapor passes through it. If you have a leak, condensation will accumulate there and cause mold. That is why it must be 99.9% airtight and properly sealed.
Hopefully, your underlay membrane has an sd value of 0.02 or similar, meaning it is highly vapor-permeable.
In that case, you could also use a climate membrane, but choose one with a slightly higher sd value. For example, Pro Clima Intello.
A standard vapor retarder would be wrong! It has a fixed sd value of 2, which might be too low, and your insulation could become saturated.
Ah, okay, thanks for the clarification!
So that means the vapor barrier is correct, and a regular vapor retarder would have been the wrong choice. When you mention a leak, do you mean a hole, or for example if the insulation isn’t perfectly fitted? What about the battens? They do penetrate the membrane at that point, but the battens should provide sealing.
The underlay used was Braas Ecotec.
What advantage would a climate membrane offer? The membrane is already installed, but I could replace it if it’s worthwhile.
So that means the vapor barrier is correct, and a regular vapor retarder would have been the wrong choice. When you mention a leak, do you mean a hole, or for example if the insulation isn’t perfectly fitted? What about the battens? They do penetrate the membrane at that point, but the battens should provide sealing.
The underlay used was Braas Ecotec.
What advantage would a climate membrane offer? The membrane is already installed, but I could replace it if it’s worthwhile.
Basically, the rule is: airtight on the inside, breathable on the outside. This applies to walls, windows, and similar elements.
You want to prevent warm, moist air from the interior from reaching your insulation, as it could condense there and cause mold. Therefore, a vapor barrier must be installed on the interior side, and it needs to be applied carefully. There are adhesives, nail sealing tapes, and similar products for this purpose.
A leak could be something like a nail hole if no sealing tape was applied underneath. The insulation behind it is less affected in this case but should of course still be installed properly.
On the exterior side, you want the moisture to be able to escape, so a vapor-permeable (breathable) layer should be installed there.
You want to prevent warm, moist air from the interior from reaching your insulation, as it could condense there and cause mold. Therefore, a vapor barrier must be installed on the interior side, and it needs to be applied carefully. There are adhesives, nail sealing tapes, and similar products for this purpose.
A leak could be something like a nail hole if no sealing tape was applied underneath. The insulation behind it is less affected in this case but should of course still be installed properly.
On the exterior side, you want the moisture to be able to escape, so a vapor-permeable (breathable) layer should be installed there.
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