Home office in the damp basement #2

Hello, I already opened the topic ( ) a year ago.

While back then it was basically about gathering information, we now want to take action soon.

We also got a second opinion, but ultimately it is simply difficult for us laypeople to really understand what can / may / should be done, and exactly for that reason I wanted to open a topic about it again.

It is about the fact that we would like to turn the basement of our house from 1987, which is currently a party room, into a home office / guest room.

The exterior walls are poured concrete and in some places connected with a kind of rubber coating, but uninsulated, just like the floor and ceiling. We were advised against insulating the walls (not possible from the outside and from the inside to avoid bringing the dew point into the living space).

Instead, we were told that the walls should best be plastered with a lime plaster because this keeps them breathable and also directly offers natural protection against mold.

We checked all the walls with a moisture meter and could not detect any moisture. Nevertheless, the humidity in the basement is rather high. Between 60 - 71% at temperatures of 15 - 17°C in May, for example.

It has now also been determined that we have radon in the basement, and we should also lay a foil on the floor so that less radon can enter the house through the floor.

The original party basement had a complete wooden cladding (interior and exterior walls) with a styrofoam ceiling. We have removed both.

1) As mentioned above, we were advised to plaster the walls with lime plaster and not to clad them at all. Actually, we would really like to clad the walls with impregnated drywall panels or similar so that we could also install electrical cables and light switches in the walls. Unfortunately, the interior walls are not deep enough. Now we also ask ourselves: If the walls have probably been covered with wooden cladding for over 30 years, why should it suddenly become a problem with drywall or similar? You can use something like that even in bathrooms. Would it not be possible to at least use that on the interior walls?

2) What options are there to insulate the floor and ceiling and is it worth it? Does it make a noticeable difference? Since the ceiling height is relatively low, quite thin insulation would be needed.
If you can use something like that, can you glue / screw it directly to the ceiling? Currently, there are still many glue residues from the original styrofoam ceiling on the ceiling, which are unfortunately not easy to remove. So we thought maybe just glue thin insulation boards on it and that’s it? Or is that also a potential risk to bring mold into the living space? I was thinking maybe very thin calcium silicate boards or something like that?

Hey KellerMaus,

I just skimmed your first thread - can you tell me more about the basement:
- are there other basement rooms that share walls with the party basement / the study?
- are these other rooms heated?
- above the party basement there is surely heated living space, right?
- does the party basement have windows?

I am currently educating myself on insulation for our renovation, there is a good book about "proper insulation". So my feedback is very theoretical, I prefer to ask practitioners who report from their own experience.

That said, how I would probably proceed:
- if there is a heated room above, I wouldn’t insulate the ceiling (unless required by law).
- I would probably insulate the exterior walls with calcium silicate boards, as they are hydrophilic but mold-resistant. I wouldn’t put anything in front of them, no shelves or so.
- I wouldn’t insulate the floor - soil never gets that cold, and if I only use it as an office, I can live with it.
- I would insulate the walls to the rest of the basement on the side of the unheated basement with insulation wedges, insulate the basement lids there - if I won the lottery, even with vacuum panels.

But that’s just my thought, you should best consult experts further. Maybe another energy consultant or building physicist, until your questions are satisfactorily answered. Although I’m also wondering what answer would satisfy you - you apparently already have a first and second opinion.

By the way, I would measure the thickness of the basement wall at the basement window, to at least have an estimate.

Honestly: No idea. My assessment is that they were cast from concrete; what I can see is that every few meters there's something like a rubber coating or something where the walls were probably joined together. How thick the walls are or whether they are insulated in any way, I don't know myself.

Make some photos of the situation, then we might even be able to imagine something under the "rubber coating."

Thank you very much for the reply.

The party basement adjoins 2 other rooms, both of which are currently not heated. Each room has a basement window and above all the basement rooms there is also heated living space.

Regarding the rubber coating, you can see it here:





And this is how the room originally looked. The exterior wall is on the right in the picture (completely clad with wood).

Regarding the rubber coating, you can see it here:

Looks to me like joint filler, silicone, adhesive.

In our house built in 1986, there is an apartment in the basement. The walls are also made of poured concrete and are not insulated on the outside. The exterior walls have internal insulation, plasterboard with Styrofoam facing. There have been no problems with mold for over 30 years. Just want to say, internal insulation with Styrofoam can also work without problems.