Hello everyone,
I have already read quite a bit on this topic and hope to reach a useful conclusion with your help.
Current status: We finally fulfilled a long-held wish and bought a house at the beginning of the year. We are currently working on renovating the insulation in the upper floor ourselves due to an old water damage and have now removed the old cladding as well as the insulation from the sloped ceilings. During this process, we discovered what was probably a common setup at the time, with bitumen roofing felt.
The original construction from outside to inside was as follows:
Now the reconstruction is about to begin. The solution proposed by our energy consultant includes replacing the damaged bitumen roofing felt and, under the tiles, installing an air gap followed by a wood fiberboard and adding thickness to the rafters to reach the required insulation thickness with mineral wool.
We want to comply with the energy saving regulations and achieve a U-value below 0.2. To allow any moisture that might enter to escape, a variable vapor retarder with an sd-value of 0.3m – 25m (specifically Vario XtraSafe) is to be installed.
A roofer friend came by and recommended doubling the rafters to the required height and fully insulating them, then installing a vapor barrier with an sd-value greater than 100m on the interior side. He justified this by saying that, since our roof is an old-style non-ventilated roof, ventilation would not be necessary when using a vapor barrier.
We would prefer this solution because it results in less loss of interior space. However, I am concerned about potential moisture buildup.
Regarding the planned doubling of the rafters, this has been calculated and approved by our structural engineer.
We know that re-roofing would probably be preferable, but according to the report the roof is still good for several more years and this is currently not an option due to cost.
Attached are two photos:
I have tried comparing the constructions but am unable to properly assess the results.
Thank you very much for your help.
I have already read quite a bit on this topic and hope to reach a useful conclusion with your help.
Current status: We finally fulfilled a long-held wish and bought a house at the beginning of the year. We are currently working on renovating the insulation in the upper floor ourselves due to an old water damage and have now removed the old cladding as well as the insulation from the sloped ceilings. During this process, we discovered what was probably a common setup at the time, with bitumen roofing felt.
The original construction from outside to inside was as follows:
- Concrete tiles wrapped in "roofing felt"
- 3cm (1.2 inches) battens
- 140mm (5.5 inches) rafters, very poorly dimensioned, partially unfilled without aluminum foil-coated insulation
- Gypsum board / polystyrene composite panel
- No membrane or vapor barrier was installed.
Now the reconstruction is about to begin. The solution proposed by our energy consultant includes replacing the damaged bitumen roofing felt and, under the tiles, installing an air gap followed by a wood fiberboard and adding thickness to the rafters to reach the required insulation thickness with mineral wool.
We want to comply with the energy saving regulations and achieve a U-value below 0.2. To allow any moisture that might enter to escape, a variable vapor retarder with an sd-value of 0.3m – 25m (specifically Vario XtraSafe) is to be installed.
A roofer friend came by and recommended doubling the rafters to the required height and fully insulating them, then installing a vapor barrier with an sd-value greater than 100m on the interior side. He justified this by saying that, since our roof is an old-style non-ventilated roof, ventilation would not be necessary when using a vapor barrier.
We would prefer this solution because it results in less loss of interior space. However, I am concerned about potential moisture buildup.
Regarding the planned doubling of the rafters, this has been calculated and approved by our structural engineer.
We know that re-roofing would probably be preferable, but according to the report the roof is still good for several more years and this is currently not an option due to cost.
Attached are two photos:
I have tried comparing the constructions but am unable to properly assess the results.
Thank you very much for your help.
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