ᐅ Moisture – Roof Structure – Walls and Timber

Happy Sunday

I am new to the forum and not really a building expert (but I can paint, wallpaper, etc.).

New build: Construction started November 2011 – move-in December 2012

Roof:
- Insulation is located in the attic; under the insulation is a blue vapor barrier foil, so everything stays dry.
- The roof itself is not insulated from above. It only has a grey membrane on top, and on both sides of the roof slope, there are two ventilation openings each.
- The loft space is very cold in winter. You can feel a constant draft.
(sorry for the amateur description)

Problem:
- On the wall (north side), the brick (Bisotherm) is slightly damp around the horizontal beam running along the wall.
- There is a gap of about 0.5 cm (0.2 inches) between the wall and the beam.
- The beam itself is also slightly damp (no visible signs of mold yet).
- Otherwise, no moisture detected elsewhere. Insulation (glass wool? rock wool?) in this area is dry (it rests on the wood, not on the wall), as is the membrane.
(this also ends at the beam)
- The room below the roof is dry in the affected area (no visible moisture damage).

Question:
- Is this normal and part of residual moisture (condensation), or
- should one be concerned?

Thank you very much for your answers and help.

Hello, please send a photo. However, the first beam should be at least 6cm (2.5 inches) away from the wall to allow space for 6cm (2.5 inches) of insulation wool. Was a ring beam (concrete) poured there? If so, it could be residual moisture.

Here you can see the roof structure in the shell stage.
This is not a ring beam.
The roof is designed as a cold roof.
The insulation is placed on the floor of the attic.
There is no insulation between the masonry and the beam.
Is it possible that warm air from the room condenses on the cold wall in the attic area?
A vapor barrier, in the form of a blue foil, is installed up to the beam (the insulation lies on top of this foil).
The ceilings of the rooms below the attic are about 5cm (2 inches) thick but are not designed as load-bearing ceilings, meaning the attic cannot be converted into living space.

Here is another view from a different room.

Hello Johnny,

Actually, there shouldn’t be any thermal bridge issues there (bisotherm), although I generally find this solution with the collar beam level rather unappealing. My guess is holes in the vapor retarder, but more likely: the vapor retarder was not properly sealed or plastered over! This allows warm, moist air to condense on the cold surface. Tip: open a small area of plaster and take a look. According to DIN standards, the foil must be glued (using a special flexible adhesive, not acrylic) and the plaster should be reinforced with fabric mesh or expanded metal...

Homis’ comment sounds very reasonable: I also believe that the vapor retarder was not installed properly.