Is it possible to construct a studio in a concrete bunker?

[Hellhoff]

Okay. I really can't keep this short. So I will begin with a summary, and the background is below.

Altogether concrete building with potential humidity issues. Concrete floor is not flat so structure on top has to be "shimmed".
Would it be possible to build the shimmed floor with metal studs and glassfibre insulation, then a layer of plastic vapor barrier to avoid potential humidity from reaching the structure above; Chipboard flooring which holds walls/roof with regular wood studs. Walls and roof will have no contact with the rest of the structure. Vapor barrier will wrap around the top of the chipboard flooring and continue up the walls just inside two layers of drywall.

Background:

I have this concrete military bunker where my band has been reharsing forever. The building is approximately 1200 square feet and was previously split in half by a simple wood wall. This is in Sweden, and in my location outside temperature can range from -30C to +30C. The bunker is not heated, so even though it's warmer than outside, it tends to get really, really cold.

To try to improve this, a looong time ago, I built a floor and walls in the rehearsal section - half of the premises. I had no knowledge and basically I put wooden studs and insulation right on top of the concrete floor. The walls were built without any air gap. Direct contact. Yeah I know - most likely there is mold and the entire thing has to be redone. To make matters worse I was recently diagnosed with mold allergy and house dust allergy.


Nonetheless - I now want to start constructing a studio in the other space. The main reason for this is I now keep all my studio gear in the rehearsal place, and conditions are just far too cold. I need to get the gear into a room with less fluctuation of the temperature and figured I'd start with a control room. Once it's finished I can tear down the old constructions in the rehearsal place, and build a live room.

BUT. Will the conditions do? I mean. This military bunker is probably at least 50 years old. The walls are thick, and it sits above ground. But concrete means moisture.

Now, the building is equipped with a dehumidifier system from the same era. There are two metal pipes reaching across the roof on both sides of this structure. One sucks air out, and the other blows it in. Also, the sensor seems to work just fine, because if I physically blow hot air on it, it kicks in and runs for a while. Also it kicks in now and then when we rehearse.
But let's face it - I have no idea how efficient such an old contraption is. Even though the bunker seems dry I will have to assume there is moisture, or at least that moisture can form if I build a warm room inside this structure.

At the moment my budget is 2000 USD. This is ONLY for building the room. Electrics, acoustics and ventilation will have separate budgets, but that is only if I can verify the following;
Is this possible at all, in terms of avoiding humidity/mold? Is a conventional room of 2x4 studs enough so that I can keep it at least acceptably warm at all times?

Thanks for reading all of this. I will include photos so you can better see what I am dealing with.

This is the half where I wish to build:

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For some reason, floor has a metal frame in the middle:

2.jpg

One of the dehumidifier pipes. I was told the white residue is not mold, but natural from concrete?

3.jpg

Building has heavy steel doors.

4.jpg

The rehearsal part of the building.

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Thank you in advance!

[Soundman2020]

Hi there "Hellhoff", and Welcome! Sorry about the long delay in responding, but for some reason I missed your post when you first made it, and only found it again now.

Is it possible to construct a studio in a concrete bunker?

It sure is! Many forum members have done that.

Concrete floor is not flat so structure on top has to be "shimmed".

It would be much better to just pour leveling cement, to get it even and flat. Cheaper too, probably. You do not want to have air cavities under your floor...

Would it be possible to build the shimmed floor with metal studs and glassfibre insulation, then a layer of plastic vapor barrier to avoid potential humidity from reaching the structure above;

Bad idea, for many reasons, but why do you expect to have humidity problems? Of that's the case, then first you need to solve the cause of the humidity, before you can start building anything: You cannot build a sealed structure inside an area that has damp issues.

The walls were built without any air gap. Direct contact. Yeah I know - most likely there is mold and the entire thing has to be redone. To make matters worse I was recently diagnosed with mold allergy and house dust allergy.

Even more reason why you should not have a vapor barrier under your floor! If you trap humidity in there, then it WILL lead to mold growth... First you need to solve the water problem, THEN build the studio. Find out what is causing the damp in the concrete (very strange, for military grade concrete!), fix that, then worry about the studio.

I need to get the gear into a room with less fluctuation of the temperature and figured I'd start with a control room.

That's fine, but a big part of your build is going to be an HVAC system that can control the humidity and the temperature correctly. It needs to keep the humidity at around 40% and the temperature at around 22° all the time, even when you are not there. Even when you are on vacation for two weeks: It must be running all the time.

Once it's finished I can tear down the old constructions in the rehearsal place, and build a live room.

The problem with that plan is that the isolation wall between the two rooms will need to be built as part of the control room. You can't use the existing wall, since you already said that it is badly done...

But concrete means moisture.

No it does not. Concrete means moisture only if there is a problem! Concrete cures for many years, but it is basically dry to the touch within a few days. After that, there should NEVER be any issue with moisture, damp, or humidity caused by the concrete itself. Especially military grade concrete. And especially after 50 years. It should be almost fully cured by now (no more hydration going on, or very, very little). So if the concrete is damp, the cause is NOT the concrete: it is due to something else. Unless it is really, really lousy concrete!

Why do you suspect that your concrete is causing humidity issues?

Here's a test: Pick an area of concrete that looks dry, tape a piece of plastic over it for a few days, then look under it and see if there is any water condensation under the plastic or on the concrete. If there is, then you have a serious problem and will need to call in the experts to fix it. If not, then you don't have a problem with humidity in the concrete: you have a problem with humidity in the air, and you will need an HVAC system that is designed to take care of that,

Even though the bunker seems dry I will have to assume there is moisture,

I don't understand: If it is dry, then when you think it is not dry?

Do yourself a favor, and buy some cheap digital thermometers that also indicate humidity. Put three of four of those in different places around the room, and check what they say on a regular basis.

or at least that moisture can form if I build a warm room inside this structure.

Why would moisture form if you WARM the room? That doesn't make sense. Air can hold MORE moisture at higher temperatures. Moisture only forms when air is cooled, not when it warms. The moisture in the air will condense out on cold surfaces around the room, or will condense out as visible vapor if the air itself is cooled. That's why you see "steam" coming out of your mouth when you breathe out in cold air: the warm air loaded with moisture coming out of your mouth rapidly cools as it hits the cold air outside, and the moisture condenses into visible water vapor. If you warm the air, then the opposite happens: any visible water vapor will evaporate into the air. So I don't understand why you think that heating your room will cause a problem with humidity. That doesn't make sense.

At the moment my budget is 2000 USD.

I think you missed out a zero there? OR perhaps another number? Maybe you intended to write "12000" or "20000"?

Is this possible at all, in terms of avoiding humidity/mold? Is a conventional room of 2x4 studs enough so that I can keep it at least acceptably warm at all times?

I still don't understand why you think that warming the room will cause problems with humidity. Please explain.

But to answer the pother question: Yes, you can indeed get very good thermal insulation with 2x4 framing and a couple of layers of drywall, plus thick mineral wool or fiberglass insulation in the cavity, and a good HVAC system.

I was told the white residue is not mold, but natural from concrete?

Correct. Various types of salts can leach out of conrete as it cures. But it's surprising to see that after 50 years of curing....

- Stuart -