ᐅ Interior and exterior insulation: How should a balcony be insulated?

No, the interior insulation does not need to be removed. Although having insulation on both sides is generally not ideal, the 2 cm (1 inch) of polystyrene on the interior is so minimal that it is absolutely insignificant. The exterior insulation just needs to be sufficiently thick (based on dew point calculation). However, due to the current energy saving regulations, you are required to install insulation of the appropriate thickness anyway.

In theory, interior insulation alone (without exterior insulation) should have caused more damage, but there are plenty of studies showing that while interior insulation does not contribute much to energy saving, it also does not cause damage because of its low thickness.

Regarding the balcony, it would likely also need to be insulated; otherwise, you would have a very cold ceiling in the living area, which would be highly prone to mold formation.

Best regards

In general, an interior insulation layer of 1 to 2 cm (0.4 to 0.8 inches) is not problematic from a building physics perspective, but this does not mean it cannot cause issues. Many factors play a role, especially since you don’t know how the indoor climate was maintained by previous occupants. Consistently high indoor humidity can lead to mold growth even with such interior insulation (presumably drywall with 2 cm (0.8 inches) of expanded polystyrene insulation) because no vapor barrier is present. In the worst case, the dew point may have shifted too close to the interior surface of the exterior wall due to the insulation. If it is not too much work, you should check this by cutting open the wall in several places (preferably in the corners of the exterior wall and at the lower meter (3 feet) and base area) creating 10 x 10 cm (4 x 4 inches) openings. If no issues are found, the openings can be re-sealed using adhesive binder.

Otherwise, I agree with S.D. regarding leaving the condition as is if sufficient exterior wall insulation is applied.

Hopegro

Hello S.D. and Hopegro,
Thank you for the quick information.
That’s a huge relief for me. Since I’m not an expert, I had a gut feeling that the interior insulation might have to be removed. For about 200 sqm (2,150 sq ft) of exterior wall, that would have meant several hours of work just for the removal. Then there are the costs and time for reinstalling the cladding...
I will definitely follow the advice about making test holes. I want to see what is behind the insulation.
Thanks for the tips... I’m sure more questions will follow.
Have a great day, everyone
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