Internal wall insulation, what now?

Hello everyone,

I am new here and would like to ask you something:
We have now bought a little house, built in 1977, and want to start renovating.
The facade is not insulated, but the exterior walls are covered on the inside with 2cm of Styrofoam and drywall. This measure was planned by the architect at the time and is also stated in the original building description. After 40 years, there are no signs of mold or moisture in/on the walls in the house. Now we are wondering: should we leave it all inside or rather remove it?
In addition, we want to install new electrical wiring, so we will have to chase the boards. Can this simply be done without any problems? Afterwards, just fill the chases with plaster again?! Can/should one maybe put a new drywall panel over it?

Thank you in advance

Hello "BoBeLe". 2cm of Styrofoam as internal insulation. I could hardly believe my eyes. Internal insulation is not necessarily complex in terms of building physics mechanisms, but you have to know what you are doing. For internal insulation to be effective at all, among other things, the insulation must be sufficiently thick. But 2 cm?? That is never functional, even as a rough estimate. Wall surface temperature in relation to the outside temperature provides an indication of the approximate temperature gradient in the wall cross-section. The insulation thickness must be adjusted accordingly, together with a vapor barrier (which is usually applied as a paintable seal for internal insulation). I'll put it this way: The 2cm insulation thickness certainly had little effect. Except that it may have shifted the dew point into the room. That is why there is no mold, because the moisture did not condense on a building component. Slotting the board and putting gypsum on it belongs in the same category as the execution of the 2cm insulation layer: With all due respect: that is rubbish. Either you let internal insulation be planned and executed by someone who understands their profession, or you will experience surprises. No offense intended: my suspicion will probably be correct that you will be overwhelmed by the subject. At this point, I deliberately do not want to give a tip because with "half measures + internal insulation" more damage is caused than benefit can be gained! ------------------------ KlaRa

Thank you, you are probably right! The insulation topic is clearly not my area of expertise! Nevertheless, I would be grateful for a tip

So what should we do now? If the 2cm don't have any effect anyway, except moving the dew point into the room, then out with it?!

If the house was granted a building permit before 01.11.1977, there is only one requirement for minimum thermal protection according to DIN 4108 from 1952. From 01.11.1977 onwards, the 1st Thermal Insulation Ordinance specified the thermal insulation value of heat-transferring exterior components. Either the architect acted somewhat more foresighted in the first case, within the possibilities at that time, or he complied with the requirements of the 1st Thermal Insulation Ordinance with the interior insulation in the second case.

Without precise knowledge of the structural conditions, without knowledge of the building construction and the planned renovation and conversion measures, no qualified statement can be made about an energetic building renovation. Which insulation and heating concept is appropriate or possible in your case can only be decided in the context of the entire building. Uncoordinated individual measures and spontaneous decisions without a professionally sound background must be absolutely avoided to prevent building damage.

Especially interior insulation is quite complex in terms of building physics. What is on your wall does not correspond to a building-physically functional structure. Interior insulation must either be absolutely vapor-tight — practically impossible under real construction conditions — or diffusion-open, installed without cavities, and capillary-active with moisture being transported away to the interior.

The materials used so far do not meet either of these two requirements. They may appear harmless at first glance; more details become apparent when the interior insulation has been partially removed. It is very likely that condensate and mold have formed over the years in the transition between the polystyrene and the cold interior side of the exterior wall.

I would recommend that you completely remove this interior insulation, as chasing for electrical installations is also inadvisable. A new insulation concept should only be developed with an architect or civil engineer experienced in old buildings and renovations, who can also advise you on material selection and the construction of components if you do the work yourself. I advise against so-called energy consultants who are not capable of viewing such a project holistically.

The facade is not insulated, but the exterior walls are covered from the inside with 2cm styrofoam and drywall.

I am currently renovating as well with an architect and a construction supervisor. You can forget about that; the insulation effect is really poor. What’s important is that you have to separate both materials, drywall boards go into mixed construction waste and styrofoam separately. The latter costs quite a bit to dispose of properly these days. Although with 2cm it doesn’t add up to much.