Insulate the top floor ceiling without a vapor barrier

Good evening folks,

I have a question here, yes I have already used Google about 1000 times but didn’t find anything useful.

I’ll start.

We bought a house from around 1960.

We want to insulate the top floor ceiling or possibly do it ourselves. But I have a few things I would like to know.

About the structure

In the first section the ceiling structure looks like this:

-Gypsum board ceiling
\/
-Metal substructure for hanging
\/
-Vapor barrier
\/
-Attic (NOT WALKABLE and the roof is NOT INSULATED)
_______________________________________________

In the second section it is like this:

-Gypsum board ceiling
\/
-Wooden substructure
\/
-Sauerkraut boards or Heraklith (plastered)
\/
-Attic (NOT WALKABLE and the roof is NOT INSULATED)

Now come the questions and the problems.

As you have read, there is NO vapor barrier in the second section, and also in the first section it must be assumed that the existing vapor barrier was probably not sealed well enough at the wall connections (but I cannot say this 100%).

Now the question arises for me, which insulation can we use if we insulate ourselves, we would basically need insulation that works without a vapor barrier.

My thought was to insulate with diffusion-open material.

That means for me if I buy diffusion-open insulation and install it, then the water vapor should basically be able to pass through the insulation and escape through the roof tiles (because the entire roof is uninsulated).

I’m not a professional but is that roughly correct?

There is also capillary-active insulation, I’ve heard that this takes up some moisture and then releases it again, do you know if there might be a combination of both (capillary-active and diffusion-open)?

Can you recommend insulation for this project?

Next or the year after that we will get blown-in insulation in the floor ceiling, if I insulate myself it is only to bridge the time or if the self-insulation works it will stay that way.

But even with the blown-in insulation the same questions about diffusion openness arise.

It is unfortunately no longer possible to install a vapor barrier afterwards because the floors are already finished.

So here again the questions summarized.

1 Do I understand the diffusion openness correctly?

2 Do I understand the capillary activity correctly?

3 With which insulation could we insulate the top floor ceiling?

4 To remain diffusion-open, isn’t it sufficient that if the roof is ever redone, only part of the roof slopes is insulated (basically starting from below up to the height of the floor ceiling insulation)?

5 Is the structure of the "second section" okay like this with gypsum board > cavity > sauerkraut boards or can something sweat and damage the gypsum board or the boards?

I hope you can help me a bit here.

Sorry for the long text, I hope the information is sufficient.

We have bought a house built around 1960.

We want to have the top floor ceiling insulated or possibly do it ourselves.

Up to here I can follow.

In the first compartment

... what is the metal construction hanging from, or what is above it? Nothing? Wooden beams? Concrete ceiling?

Not walkable because too shallow? Or because it breaks through since there are only those few metal beams?

If there really are only the metal beams and the drywall panels: Tear everything out, also open everything on the slopes, fully insulate the rafters, if necessary extend with insulation below the rafters, and put drywall with a vapor barrier in front again.

In general: Vapor barrier ALWAYS on the inside, from the insulation, on that mineral wool insulation boards or mineral wool insulation mats, and nothing on top of that.

There are capillary-active insulation materials, but this is the wrong application here and much too expensive, so stay away.

Insulating a bit provisionally to do something different in a year is nonsense. Do it properly once. Both blown-in insulation and laying mats yourself have advantages and disadvantages.

For me, this means that if I buy diffusion-open insulation and install it, then the water vapor should basically crawl through the insulation and flow out through the roof tiles (because everything on the roof is uninsulated).

Addendum: Caution, here Aunt Google has led to dangerous half-knowledge with a tendency towards moisture damage!

The humidity of the indoor air can enter the insulation in gaseous form from the inside without an internal vapor barrier (and it does) and then diffuses further outward. If the temperature in the insulation falls below the respective dew point, which always happens in cold weather, the moisture condenses and the insulation becomes wet. With sufficient ventilation at the back, this moisture can be carried away again. However, depending on the situation, this is not given even in attics! In winter, everything becomes wet on top and starts to mold.

Diffusion openness only helps in that the moisture that enters despite the vapor barrier can again exit outward. Nevertheless, this should be reduced as much as possible.

Hi, thanks already for the answer.

So the construction is attached to the wooden beams at the floor ceiling; there are wire hangers (I hope that’s the right term) screwed directly into the wooden beams, and the metal profiles are basically hanging from these; of course, there are also metal profiles on the wall.

The construction consists of CD profiles and UD profiles.

UD profiles are screwed to the wall, and the CD profiles rest in them and are then held by the wire hangers.

The attic is not accessible because otherwise you would be walking on the drywall or sauerkraut boards, which would not be so good.

Unfortunately, we can no longer tear down the ceilings as the house is already finished except for the insulation.

So we now need a solution without a vapor barrier.

There must be a way to work without a vapor barrier.

I read somewhere that “wood fiber insulation” is supposedly relatively resistant to moisture; does anyone have experience with that?

We can’t be the only house that is finished but cannot be insulated without having to tear everything out.

the construction is attached to the wooden beams at the floor ceiling

Ah, so a wooden beam ceiling that was suspended. And in one part of the ceiling, Heraklith / Sauerkraut boards were additionally placed in between.

I would not recommend insulation without a vapor barrier here, but it is easy to install one. Ideally, the foil should be installed between the drywall and the ceiling beams. But that’s not possible because the boards are already attached. However, you can also lay a vapor barrier foil from above between and over the beams. Then mineral wool/compression felt into the cavities and depending on thickness (in total it should be at LEAST 140, better 200-240 mm) a layer completely on top.

You can also lay OSB boards on the beams, then the vapor barrier foil, and then the insulation.

But insulation in the roof NOT without a vapor barrier.

There are some insulation materials that retain their effectiveness even when damp (sheep wool, for example) – but these are significantly more expensive and can still mold.

If the attic is not used at all, not even for storing rarely used items that could rot, I would say it doesn’t really matter whether you install a vapor barrier there or not.
If the roof itself is completely uninsulated, the ventilation is more than sufficient to remove any vapors, even from a sauna for all I care.
You can also simulate this yourself, for example with the U-value calculator; there are no problems with the dew point in the insulation.