Hello everyone,
Today, the tongue-and-groove boards were nailed in, the retractable attic ladder was installed, and I went up to the attic for the first time in a long while. Since our insulation layer is in the ceiling between the floors, the attic was very cold.
I noticed that when the ladder is open, a rush of warm, moist air comes out near the stair opening — for a moment, I was worried that this moisture might cause damage. But that shouldn’t be possible, since the roof is basically open except for the tiles and the underlay membrane.
Then I wondered why a vapor retarder is installed under the insulation and sealed airtight at all — wouldn’t the moisture just pass through the insulation anyway? Or would there be a dew point somewhere inside the insulation because of the temperature difference, causing it to stay damp and develop mold?
I also started to think about how one would finish the attic space — not that I plan to do it, but who knows. If I add another insulation layer in the roof and seal it airtight again, wouldn’t the moisture then have no way to escape, leaving the insulation in the ceiling between floors exposed? In that case, would the insulation in the ceiling between floors need to be removed, or does it not matter since there would no longer be a temperature gradient there?
I look forward to your responses.
Today, the tongue-and-groove boards were nailed in, the retractable attic ladder was installed, and I went up to the attic for the first time in a long while. Since our insulation layer is in the ceiling between the floors, the attic was very cold.
I noticed that when the ladder is open, a rush of warm, moist air comes out near the stair opening — for a moment, I was worried that this moisture might cause damage. But that shouldn’t be possible, since the roof is basically open except for the tiles and the underlay membrane.
Then I wondered why a vapor retarder is installed under the insulation and sealed airtight at all — wouldn’t the moisture just pass through the insulation anyway? Or would there be a dew point somewhere inside the insulation because of the temperature difference, causing it to stay damp and develop mold?
I also started to think about how one would finish the attic space — not that I plan to do it, but who knows. If I add another insulation layer in the roof and seal it airtight again, wouldn’t the moisture then have no way to escape, leaving the insulation in the ceiling between floors exposed? In that case, would the insulation in the ceiling between floors need to be removed, or does it not matter since there would no longer be a temperature gradient there?
I look forward to your responses.
Hi,
the described construction is a so-called cold roof (in the attic).
It’s very good that you used tongue-and-groove boards instead of OSB as the floor covering there. We discussed this topic recently here as well. See the post at threads/spitzboden-osb-platten-messgeraet.14292/page-2#post-113799
Yes: The dew point is located around the ceiling/attic floor area. To prevent damage to the insulation and mold growth, the tongue-and-groove boards with a gap must be installed on cross battens. The whole assembly needs to be able to “breathe.”
Under the cold roof, the conditions are roughly similar to outdoor conditions.
Of course, despite insulation in the upper floor ceiling and a vapor retarder, some heat will still pass upwards into the attic (nothing is perfect in the world!).
If you want to convert or insulate this attic area under a cold roof, you definitely need to coordinate very carefully with your house manufacturer. It is possible, but it involves many considerations—in other words, it’s not something you can just do quickly.
Best regards
Thorsten
the described construction is a so-called cold roof (in the attic).
It’s very good that you used tongue-and-groove boards instead of OSB as the floor covering there. We discussed this topic recently here as well. See the post at threads/spitzboden-osb-platten-messgeraet.14292/page-2#post-113799
Yes: The dew point is located around the ceiling/attic floor area. To prevent damage to the insulation and mold growth, the tongue-and-groove boards with a gap must be installed on cross battens. The whole assembly needs to be able to “breathe.”
Under the cold roof, the conditions are roughly similar to outdoor conditions.
Of course, despite insulation in the upper floor ceiling and a vapor retarder, some heat will still pass upwards into the attic (nothing is perfect in the world!).
If you want to convert or insulate this attic area under a cold roof, you definitely need to coordinate very carefully with your house manufacturer. It is possible, but it involves many considerations—in other words, it’s not something you can just do quickly.
Best regards
Thorsten
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