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.
G
garfunkel4 Feb 2018 23:16What I’m curious about here is the following.
There is a general rule of thumb that mold is unlikely to occur below 70% indoor humidity, but can this also be applied to the insulation layer? The rule mainly applies to the typical case of an exterior wall, cold surface, and mold growth.
But if there is a leak in the insulation layer, more precisely in the vapor barrier or vapor retarder, can mold still develop within the layer at, for example, 50% indoor humidity (at normal room temperature), or can it really be assumed that no mold will form because too little moisture is being introduced?
How does a climate membrane that works in both directions behave in this context? Does the relative humidity control the direction of moisture flow?
There is a general rule of thumb that mold is unlikely to occur below 70% indoor humidity, but can this also be applied to the insulation layer? The rule mainly applies to the typical case of an exterior wall, cold surface, and mold growth.
But if there is a leak in the insulation layer, more precisely in the vapor barrier or vapor retarder, can mold still develop within the layer at, for example, 50% indoor humidity (at normal room temperature), or can it really be assumed that no mold will form because too little moisture is being introduced?
How does a climate membrane that works in both directions behave in this context? Does the relative humidity control the direction of moisture flow?
In the best case, yes, through expansion and thus enlargement of tiny holes on the nanometer scale or even smaller. However, I believe that apart from the manufacturer and a few others, no one could confirm whether and how all of this is supposed to work.
I also think that the values could vary significantly depending on the region and environment.
I also think that the values could vary significantly depending on the region and environment.
T
tomthomson5 Feb 2018 09:35Thank you for your effort. I have also contacted the manufacturer about this and will keep you updated.
T
tomthomson5 Feb 2018 11:32Here is the feedback from the manufacturer:
"Indoor relative humidity levels around 70% can be considered safe in terms of damage risk. At this humidity, the mentioned hazards are only expected after a longer exposure period.
Depending on the duration and intensity of moisture load, the risk of damage increases. Mineral-based materials are generally less prone to mold growth compared to organic materials.
Therefore, moisture in freshly installed wet building materials such as concrete, masonry, plaster, and screed should be quickly removed from the building or extracted from the materials.
DIN 4108-7:2011-01 (Thermal insulation and energy saving in buildings – Part 7: Airtightness of buildings – Requirements, planning and execution recommendations, and examples) includes the following note under section 5 'Planning and execution':
'... Building materials must not be unnecessarily exposed to excessively high humidity during the construction phase. Therefore, sufficient dehumidification (e.g., ventilation) must be ensured.'
Ideally, "dry living in" of the building is not required, and interior finishing can proceed immediately and without a ventilation gap to the exterior components.
Below are some practical implementation examples, as well as tips and recommendations. These should be adapted as necessary to the specific project conditions and follow the sequence of construction activities.
The 60/2 and 70/1.5 rule (Building physics)
To protect constructions even during temporarily increased relative humidity (RH), a vapor retarder
Planning phase – Trade sequence – Construction process
Trapped construction moisture in dry building materials or components (e.g., insulated rafter spaces) can lead to mold growth later on.
Material drying times – Choice of building materials
Too rapid drying of wet building materials can cause cracking or deformation. The recommended "curing periods" or resting times vary greatly and must be confirmed with the respective manufacturer. Common market reference values are: cement screed: ~7 days, calcium sulfate screed: ~2 days, fast-drying screed: ~1 day.
During the "curing period," exceeding an average RH of 70% is unavoidable. Active dehumidification should begin no later than 14 days after installation.
Using drying screeds is an effective method to reduce construction moisture to a minimum and therefore minimize risk.
Dry and absorbent materials, such as gypsum fiberboard or gypsum plasterboard, can buffer humidity peaks. Materials used for buffering must be suitable for this purpose.
Planning adapted to the construction situation, coordination with the plasterer, and scheduling of the work are recommended. Construction management plays a key role here."
"Indoor relative humidity levels around 70% can be considered safe in terms of damage risk. At this humidity, the mentioned hazards are only expected after a longer exposure period.
Depending on the duration and intensity of moisture load, the risk of damage increases. Mineral-based materials are generally less prone to mold growth compared to organic materials.
Therefore, moisture in freshly installed wet building materials such as concrete, masonry, plaster, and screed should be quickly removed from the building or extracted from the materials.
DIN 4108-7:2011-01 (Thermal insulation and energy saving in buildings – Part 7: Airtightness of buildings – Requirements, planning and execution recommendations, and examples) includes the following note under section 5 'Planning and execution':
'... Building materials must not be unnecessarily exposed to excessively high humidity during the construction phase. Therefore, sufficient dehumidification (e.g., ventilation) must be ensured.'
Ideally, "dry living in" of the building is not required, and interior finishing can proceed immediately and without a ventilation gap to the exterior components.
Below are some practical implementation examples, as well as tips and recommendations. These should be adapted as necessary to the specific project conditions and follow the sequence of construction activities.
The 60/2 and 70/1.5 rule (Building physics)
To protect constructions even during temporarily increased relative humidity (RH), a vapor retarder
- should achieve a minimum diffusion resistance (sd-value) of 2 m at 60% average RH (e.g., new buildings or temporary conditions such as kitchens and bathrooms)
- should achieve an sd-value of at least 1.5 m at 70% average RH (e.g., during construction phase, see above)
Planning phase – Trade sequence – Construction process
- Building envelope closed, no insulation and no airtight layer, with unfinished masonry, roof sealed but uninsulated. Initially, wet materials are installed (e.g., plaster, screed). After a 2–3 week drying period: installation of insulation and vapor retarder, step by step. This creates a mold risk for organic surfaces and increases initial moisture content in hygroscopic materials.
- Building envelope closed, insulation installed and airtight layer sealed, unfinished masonry, roof sealed and insulated. Wet materials are installed (e.g., plaster, screed). After a maximum of 2 weeks resting period, active dehumidification of the building.
- Ventilation This means continuous, day and night ventilation. A cross-flow of air through the entire building must be created. Ventilation through tilted windows or short bursts is insufficient to remove enough moisture.
- Technical drying Dehumidifiers perform active drying of the building. Typically, one to two dehumidifiers of average capacity are sufficient in the attic of a residential building to maintain an average maximum relative humidity of 70%. The number of dehumidifiers needed depends on the moisture present, building volume, and the drying capacity of the units.
Supplementary heating supports the drying process during ventilation. Heating increases the release of moisture from wet building materials, which can then be ventilated out of the building. Heating without continuous ventilation should therefore be avoided.
Disadvantages of ventilation: a) At very low outside temperatures, there is a risk that fresh plaster or wet screeds will be damaged and/or b) drying occurs too quickly, as outdoor air, especially on cold days, is very dry.
Trapped construction moisture in dry building materials or components (e.g., insulated rafter spaces) can lead to mold growth later on.
Material drying times – Choice of building materials
Too rapid drying of wet building materials can cause cracking or deformation. The recommended "curing periods" or resting times vary greatly and must be confirmed with the respective manufacturer. Common market reference values are: cement screed: ~7 days, calcium sulfate screed: ~2 days, fast-drying screed: ~1 day.
During the "curing period," exceeding an average RH of 70% is unavoidable. Active dehumidification should begin no later than 14 days after installation.
Using drying screeds is an effective method to reduce construction moisture to a minimum and therefore minimize risk.
Dry and absorbent materials, such as gypsum fiberboard or gypsum plasterboard, can buffer humidity peaks. Materials used for buffering must be suitable for this purpose.
Planning adapted to the construction situation, coordination with the plasterer, and scheduling of the work are recommended. Construction management plays a key role here."
K
Knallkörper5 Feb 2018 12:57This has nothing to do with the humidity inside the insulation. Here, the relative humidity naturally increases significantly from the inside to the outside through the cross-section when it is warm inside and cold outside. The important thing is to prevent the dew point from being reached and to ensure that the upper covering is relatively vapor-permeable. Apparently, this is not the case with your setup.
T
tomthomson5 Feb 2018 14:08@Knallkörper
Yes, it’s not directly related to my original question, but even after I asked again specifically, the manufacturer refers me back to the same information. I suspect they don’t want to take any risks or make a definitive statement... unfortunately.
Exactly, the OSB probably acts more as a barrier or even a vapor retarder in my case, since we installed the boards with tongue and groove nearly perfectly and screwed them every 8 cm (3 inches). That’s why I came up with the idea to deliberately drill holes or mill slots to allow some “breathing.” (Considering through which small pores the moisture must have come in through the membrane, just 4 to 6 holes of 10 mm (0.4 inches) diameter on a 2.50 x 1.25 m (8.2 x 4.1 ft) board should be enough.)
I assume it will be a mix of measures after the screed is in place, the heating program is running, and the bulk of the moisture is gone. Open the vapor retarder, check the moisture, replace insulation in spots if necessary for safety, and run construction dryers as soon as possible. Once the moisture levels are right at the bottom and the wet construction phases are complete, the membrane should work correctly.
Yes, it’s not directly related to my original question, but even after I asked again specifically, the manufacturer refers me back to the same information. I suspect they don’t want to take any risks or make a definitive statement... unfortunately.
Exactly, the OSB probably acts more as a barrier or even a vapor retarder in my case, since we installed the boards with tongue and groove nearly perfectly and screwed them every 8 cm (3 inches). That’s why I came up with the idea to deliberately drill holes or mill slots to allow some “breathing.” (Considering through which small pores the moisture must have come in through the membrane, just 4 to 6 holes of 10 mm (0.4 inches) diameter on a 2.50 x 1.25 m (8.2 x 4.1 ft) board should be enough.)
I assume it will be a mix of measures after the screed is in place, the heating program is running, and the bulk of the moisture is gone. Open the vapor retarder, check the moisture, replace insulation in spots if necessary for safety, and run construction dryers as soon as possible. Once the moisture levels are right at the bottom and the wet construction phases are complete, the membrane should work correctly.
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