ᐅ Roof insulation: 40mm Styrodur C3035 instead of vapor barrier film – dew point?
Created on: 28 Mar 2013 10:25
F
Frank69Hello everyone,
We bought a house built in 1954, which was renovated by the previous owner.
During a remodeling project on the upper floor, I noticed an unusual roof insulation setup and wanted to get some opinions from others.
Regarding the roof structure:
Clay roof tiles, battens, counter battens, underlay membrane, 120 mm (5 inches) rafters – between these rafters, 120 mm (5 inches) of mineral wool insulation was installed.
So far, this seems normal to me, but then there is the following:
Instead of the usual vapor barrier, 40 mm (1.5 inches) Styrodur C3035 rigid foam boards were used. These were applied over the rafters across the entire sloped roof area and the seams between the panels were carefully sealed with green Siga Sicral tape.
At the connections to the wall, a 1 cm (0.4 inches) gap was left on each side, which was sealed flush with a silicone-like black sealing compound. This material adheres very well to both the wall and the Styrodur.
Then, a mesh fabric was applied at the transitions to the wall, coated with a kind of liquid plastic. Over this, several wide strips of the same green Sicral tape were applied extensively.
On top of the Styrodur, a substructure with battens was installed and finally Fermacell boards were fixed and neatly finished.
Does this Styrodur layer fulfill the function of the normally used vapor control layer?
Styrodur was apparently added as extra insulation, since 120 mm (5 inches) mineral wool alone is not very much.
The workmanship looks very professional. However, whether this setup is compliant with building regulations is another matter.
What about the dew point? Could the wooden structure of the roof become damp?
Unfortunately, I have no knowledge about this and would appreciate any opinions on the subject.
Best regards
Frank
We bought a house built in 1954, which was renovated by the previous owner.
During a remodeling project on the upper floor, I noticed an unusual roof insulation setup and wanted to get some opinions from others.
Regarding the roof structure:
Clay roof tiles, battens, counter battens, underlay membrane, 120 mm (5 inches) rafters – between these rafters, 120 mm (5 inches) of mineral wool insulation was installed.
So far, this seems normal to me, but then there is the following:
Instead of the usual vapor barrier, 40 mm (1.5 inches) Styrodur C3035 rigid foam boards were used. These were applied over the rafters across the entire sloped roof area and the seams between the panels were carefully sealed with green Siga Sicral tape.
At the connections to the wall, a 1 cm (0.4 inches) gap was left on each side, which was sealed flush with a silicone-like black sealing compound. This material adheres very well to both the wall and the Styrodur.
Then, a mesh fabric was applied at the transitions to the wall, coated with a kind of liquid plastic. Over this, several wide strips of the same green Sicral tape were applied extensively.
On top of the Styrodur, a substructure with battens was installed and finally Fermacell boards were fixed and neatly finished.
Does this Styrodur layer fulfill the function of the normally used vapor control layer?
Styrodur was apparently added as extra insulation, since 120 mm (5 inches) mineral wool alone is not very much.
The workmanship looks very professional. However, whether this setup is compliant with building regulations is another matter.
What about the dew point? Could the wooden structure of the roof become damp?
Unfortunately, I have no knowledge about this and would appreciate any opinions on the subject.
Best regards
Frank
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