ᐅ Interior insulation with udiin, experiences

There are interior insulation options with better performance to improve the wall's U-value.

Even with interior insulation, a few centimeters more than the 2cm (0.8 inches) you mentioned provide greater benefits for the wall. It is important that there are no air gaps in the adhesive layer of interior insulation, as these can lead to condensation, which may cause mold.

The technical information for your product does not specify which substrates the insulation boards can be adhered to. Gypsum-based plasters are generally problematic because they are moisture sensitive.

A vapor barrier or membrane is not necessary with fully adhered interior insulation.

It is better to insulate a wall from the outside. For interior insulation, the inside walls should also be included in the insulation system.

And for external insulation, there are also insulations available that only require 10 cm (4 inches) thickness to meet the energy saving regulations.

How old is the building?

Ibaaa schrieb:
A vapor barrier/foil is not necessary with a fully bonded interior insulation.

I would be very interested in the reasoning behind this.

You are comparing 2cm (0.8 inches) of internal insulation with 14cm (5.5 inches) of external insulation, which is like comparing apples and oranges. There are also thin insulation boards with low U-values available for external use. Alternatively, if you compare 14cm (5.5 inches) inside with 14cm (5.5 inches) outside, the amount of natural light entering the space will be equally limited (poor) in both cases.

Only with external insulation are the junctions of the interior walls not thermal bridges. This saves you many problems and is more cost-effective to install, as internal insulation involves a lot of cutting work, excessively deep electrical boxes, and so on.

Counter question: What is the purpose of the membrane in the wall assembly (external wall)?

The most important rule for internal insulation, whether made of mineral materials or wood fiber, is that moisture coming from the indoor air can circulate through the insulation and adhesive layers.
A membrane or vapor retarder behind the adhesive layer would cause moisture to condense there, leading to mold growth.

Insulation prevents the exterior wall from being warmed by the indoor air, shifting the dew point from within the wall to its interior surface (regardless of whether it is plaster or adhesive). If a vapor retarder (which does not necessarily have to be a foil) is omitted, the warm indoor air cools down at the interface between the insulation and the exterior wall, causing condensation. When combined with wood fiber insulation, this creates ideal conditions for mold growth.

With a properly installed vapor retarder, indoor air cannot reach this area and therefore cannot condense on the interior surface of the exterior wall or on the inner side of the vapor retarder.