ᐅ Request for advice: Roof conversion and exterior wall insulation for an Okal house (breathable construction method)
Created on: 31 Jan 2026 10:54
C
CigareI am looking for expert advice regarding attic conversion and exterior wall insulation for an OKAL prefabricated house (built in 1978) with vapor-open walls and ceilings.
Current roof situation: cold roof construction
There is a continuous air gap between the ceiling and the roof. Wooden beams are about 30 cm (12 inches) thick. Air circulation currently exists all around the house.
We want to convert the roof to a warm roof construction in the future.
Our questions are:
Is additional interior insulation still advisable or necessary?
Which insulation materials would be suitable (stone wool / glass wool)?
Is there a risk of condensation with an incorrect assembly?
We were considering interior insulation of about 60-100 mm (2.4-4 inches), leaving approximately 20 cm (8 inches) of air gap. Or would it be sufficient just to convert and finish the attic space?
Our idea was roof with PIR insulation, 12-16 cm (5-6 inches), and ceiling with vapor barrier + OSB + gypsum board, while leaving the air circulation in between as it is.
Is this assumption correct or problematic from a building physics perspective?
Current facade situation:
Originally around 8 cm (3 inches) of stone wool insulation in the walls
OSB boards on both sides, about 2.2 cm (0.9 inch) inside and on the outside with a moisture-resistant cement-based layer of 4 cm (1.6 inches), followed by 1 cm (0.4 inch) of a finish similar to diamond plaster.
Our questions here:
Is exterior insulation of around 14–18 cm (5.5-7 inches) sufficient?
Or would a combination of exterior and interior insulation be more effective?
What if we only insulate from the outside, and on the inside use vapor barrier + OSB + gypsum board, similar to the ceiling?
We have several possible construction variants but are unsure which solution is the most effective, safest, and functional over the long term—especially concerning moisture protection, vapor openness, and energy efficiency.
We are seeking experience reports, professional assessments, or expert advice (preferably from those with experience in OKAL houses or prefab houses from the 1970s).
If photos would help, just ask, and I will send some.
Thank you in advance!
Current roof situation: cold roof construction
There is a continuous air gap between the ceiling and the roof. Wooden beams are about 30 cm (12 inches) thick. Air circulation currently exists all around the house.
We want to convert the roof to a warm roof construction in the future.
Our questions are:
Is additional interior insulation still advisable or necessary?
Which insulation materials would be suitable (stone wool / glass wool)?
Is there a risk of condensation with an incorrect assembly?
We were considering interior insulation of about 60-100 mm (2.4-4 inches), leaving approximately 20 cm (8 inches) of air gap. Or would it be sufficient just to convert and finish the attic space?
Our idea was roof with PIR insulation, 12-16 cm (5-6 inches), and ceiling with vapor barrier + OSB + gypsum board, while leaving the air circulation in between as it is.
Is this assumption correct or problematic from a building physics perspective?
Current facade situation:
Originally around 8 cm (3 inches) of stone wool insulation in the walls
OSB boards on both sides, about 2.2 cm (0.9 inch) inside and on the outside with a moisture-resistant cement-based layer of 4 cm (1.6 inches), followed by 1 cm (0.4 inch) of a finish similar to diamond plaster.
Our questions here:
Is exterior insulation of around 14–18 cm (5.5-7 inches) sufficient?
Or would a combination of exterior and interior insulation be more effective?
What if we only insulate from the outside, and on the inside use vapor barrier + OSB + gypsum board, similar to the ceiling?
We have several possible construction variants but are unsure which solution is the most effective, safest, and functional over the long term—especially concerning moisture protection, vapor openness, and energy efficiency.
We are seeking experience reports, professional assessments, or expert advice (preferably from those with experience in OKAL houses or prefab houses from the 1970s).
If photos would help, just ask, and I will send some.
Thank you in advance!
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