ᐅ The vapor barrier is discolored brown, and the insulation is damp.
Created on: 4 Feb 2018 17:40
T
tomthomson
Hello everyone,
Our house construction started in 2017, and we are now just before the screed stage. The interior plasterwork, underfloor heating, and so on are currently completed.
Two weeks ago, I noticed a brownish spot on the vapor retarder.
We contacted the building supervisor, cut into the vapor retarder, and the result was damp wood and insulation.
At other spots where we cut in, it was not wet but also not 100% dry—maybe around 95% dry, if that can be quantified.
The building supervisor now suggests that once the screed is poured and the heating system has run through its full cycle, the vapor retarder should be opened, the insulation removed, allowed to dry, and possibly replaced.
This may help at that location temporarily, but perhaps not permanently, since it is unclear where the moisture is coming from (the roof has been inspected, so it cannot be from above).
Construction layers:
Brick
Battens
Breathable underlay membrane
22mm OSB board with tongue and groove for structural bracing
22cm (9 inches) insulation
Pro Clima Intello Plus vapor retarder
Later, there will be a suspended ceiling with gypsum board.
I currently suspect a design issue where the moisture, which can be absorbed by the variable vapor retarder, cannot escape upwards because of the OSB board. However, we need the OSB with tongue and groove for structural bracing.
Are there any experts here who can advise how this could be ventilated? Cutting slots with a router? Or drilling holes? If so, how many slots or holes would be recommended for an area of 10 by 15 meters (33 by 49 feet)?
Or is there no solution at all?
Thank you in advance for your support.
Our house construction started in 2017, and we are now just before the screed stage. The interior plasterwork, underfloor heating, and so on are currently completed.
Two weeks ago, I noticed a brownish spot on the vapor retarder.
We contacted the building supervisor, cut into the vapor retarder, and the result was damp wood and insulation.
At other spots where we cut in, it was not wet but also not 100% dry—maybe around 95% dry, if that can be quantified.
The building supervisor now suggests that once the screed is poured and the heating system has run through its full cycle, the vapor retarder should be opened, the insulation removed, allowed to dry, and possibly replaced.
This may help at that location temporarily, but perhaps not permanently, since it is unclear where the moisture is coming from (the roof has been inspected, so it cannot be from above).
Construction layers:
Brick
Battens
Breathable underlay membrane
22mm OSB board with tongue and groove for structural bracing
22cm (9 inches) insulation
Pro Clima Intello Plus vapor retarder
Later, there will be a suspended ceiling with gypsum board.
I currently suspect a design issue where the moisture, which can be absorbed by the variable vapor retarder, cannot escape upwards because of the OSB board. However, we need the OSB with tongue and groove for structural bracing.
Are there any experts here who can advise how this could be ventilated? Cutting slots with a router? Or drilling holes? If so, how many slots or holes would be recommended for an area of 10 by 15 meters (33 by 49 feet)?
Or is there no solution at all?
Thank you in advance for your support.
K
Knallkörper5 Feb 2018 15:07tomthomson schrieb:
If you consider the small pores in the membrane where moisture must have come through, nearly 4-6 holes of 10mm (0.4 inches) size on a 2.50x1.25m (8.2x4.1 ft) board should be enoughI don’t think you can compare it that way. On one hand, there are vapor-permeable membranes, such as roofing underlays, which offer almost no resistance to water vapor passing through their entire surface. On the other hand, you’re looking at an OSB board with holes in it. The holes have an SD value comparable to a vapor-permeable membrane, around 0.02m (0.07 ft), while a membrane might be around 0.1m (0.33 ft). But that applies ONLY to the holes. This means if the holes make up 0.1% of the board’s surface area, the membrane is still 100 times more permeable overall.
You can’t assume moisture escapes convectively through the holes. There is no airflow occurring!
G
garfunkel5 Feb 2018 15:51This might not be the best construction method, but it is done quite often. If it were truly problematic and frequently used, there would be more reports of damage. In fact, however, there are hardly any such cases reported.
T
tomthomson6 Feb 2018 14:00@apokolok
What exactly do you mean?
We have a house with a cold roof, so the insulation layer is not in the roof structure but in the ceiling of the top floor. The ceiling is finished with OSB boards, which are necessary as a bracing panel and to make the attic accessible.
The vapor control membrane, which is installed on the underside of the joists in the living space, is designed to absorb and release moisture from the living area depending on the situation. This works fine during everyday use once the house is occupied. However, in the current situation, due to all the construction moisture, it has absorbed too much moisture that now needs to be addressed, since the moisture was not removed quickly enough or because a vapor retarder was installed before the plaster and screed.
I have also wondered whether and how the insulation layer needs or can be ventilated with this assembly, which led to the idea of holes or slots. However, it was already pointed out here that this likely does not help, since no airflow is generated and the moisture will not convect upwards through the holes.
What exactly do you mean?
We have a house with a cold roof, so the insulation layer is not in the roof structure but in the ceiling of the top floor. The ceiling is finished with OSB boards, which are necessary as a bracing panel and to make the attic accessible.
The vapor control membrane, which is installed on the underside of the joists in the living space, is designed to absorb and release moisture from the living area depending on the situation. This works fine during everyday use once the house is occupied. However, in the current situation, due to all the construction moisture, it has absorbed too much moisture that now needs to be addressed, since the moisture was not removed quickly enough or because a vapor retarder was installed before the plaster and screed.
I have also wondered whether and how the insulation layer needs or can be ventilated with this assembly, which led to the idea of holes or slots. However, it was already pointed out here that this likely does not help, since no airflow is generated and the moisture will not convect upwards through the holes.
Ah, I was in the roof space, not on the top floor ceiling. Since it’s a cold roof anyway, I don’t see it as a big deal.
However, the construction should actually have a vapor barrier, not just a vapor retarder.
But as I said, for an unoccupied space it’s not a major issue. At first, I thought the roof was insulated and intended to be converted.
However, the construction should actually have a vapor barrier, not just a vapor retarder.
But as I said, for an unoccupied space it’s not a major issue. At first, I thought the roof was insulated and intended to be converted.
K
Knallkörper6 Feb 2018 14:46I don’t understand why a cold roof should be any less "dramatic." Moisture still cannot escape from the "intermediate ceiling." I don’t believe the construction works that way. The drying out only takes place during the summer. Regardless, everything must be opened up and dried after the screed. Depending on how many weeks pass until then, you might not have a mold problem yet.
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