Help with interior insulation of country house

Hello valued forum members,

I have 3 questions regarding my planned wall assemblies in the existing building (country house built in 1950).

The following initial situations in the existing building:

1)
Wall existing inside → outside → upper floor → north side

11.5 cm inner shell made of pumice stone (pre-war hollow block)
3 cm cavity
11.5 cm solid brick

A supplementary inner shell as a drywall partition is planned.
Constructively: approx. 7 cm air layer → approx. 14 cm mineral wool 035 in a timber stud wall → ProClima Intello vapor retarder → 3 cm installation zone → 1.25 cm gypsum board (see picture 1)

The distance of the cavity between the pumice stone and the drywall partition results from structural reasons and unfortunately cannot be changed or reduced.

2)
Wall existing inside → outside → ground floor → north side or east side

1.5 cm lime-cement plaster
11.5 cm inner shell made of aerated concrete (approx. 600 kg/m³)
3 – 5 cm cavity
11.5 cm shell made of pumice stone (pre-war hollow block)
3 cm cavity
11.5 cm solid brick

An additional interior insulation of approx. 5 cm is planned.
Constructively: 5 cm mineral wool on the plaster → ProClima Intello vapor retarder → 3 cm installation zone → 1.25 cm gypsum board (see picture)

On one hand, the question arises whether these wall assemblies can be executed as planned?
Will too much condensation and consequently mold form in these constructions?

Can an OSB board of 1.25 cm be used instead of the installation zone (3 cm lathing)? Wouldn’t this inhibit the drying back of the vapor retarder, though?

Alternative wall assemblies with insulating stones, etc., should be ruled out because the material is more or less already available, and the existing walls are very uneven. Additional moisture input through plastering work is also not particularly desirable.

Can too much water form in the outer shell with the planned constructions, which then leads to spalling due to frost?

The window reveals are to be finished with silicate boards.

Since I would rather not weaken or damage the existing construction (rafters and masonry, etc.) due to too much condensation, I am turning to you. I have conducted a preliminary calculation with the WUFI program as well as the U-value calculator, but unfortunately I cannot assess the results. (see calculation results)

Thank you very much and best regards

Harald Flessner

Hello,

Internal insulation is never good and actually not recommended. Theoretically, such constructions can always be nicely calculated. But unfortunately, the resulting thermal bridges are not taken into account.

Why no external insulation? Because of the appearance?

Are the air layers really still air layers?

Regards

Hello,

Thank you very much for the reply.

The inner air layer is a still one because it is "sealed" on all sides. The outer one, on the other hand, is connected to the outside air and is therefore not a still air layer. Unfortunately, exterior insulation is not possible as it is very old clinker brickwork that I want to preserve. I personally do not think much of foam-injection methods for hollow spaces, as the walls are not really straight and I could not guarantee that no mistakes were made during the masonry work back then and that there is nothing in the air layer. Thermal bridges can certainly never be completely avoided, but they can also be considered separately in order to almost exclude them. My main concern here is the general construction. Whether it is fundamentally built incorrectly.

Best regards

OK, I understand that about the view :)

But as I said, theoretically you can calculate the construction like that. It can also work. What does not work, however, is the OSB board in front of the humidity-variable vapor barrier, since the OSB board also acts as a vapor barrier and prevents diffusion into the room.

Would interior insulation with mineral insulation board not be an alternative? The company redstone offers some products for that.

In any case, the insulation material should have a certain sorption capacity, meaning it should absorb moisture and of course release it again. Mineral wool actually cannot do that.

Regards

Unfortunately, this is not possible with such boards, as the walls are not plumb, I would have to plaster the wall afterwards. I wanted to avoid that. Hmm, I understand the issue with the hydroscopicity of mineral wool. Isn't the cavity or the variable vapor retarder sufficient to ensure vapor permeability? I will then replace the OSB boards with a 3x5 cm batten as an installation level. That would have the advantage that I wouldn't have to cut the vapor retarder in the area of the sockets anyway. Can you tell from the Wufi evaluation whether the condensate content is high or not? Unfortunately, it's not quite clear to me how to estimate the amount.... :) But thank you very much for the support-- :)

Hello,

according to the calculation, condensation occurs at the 6th layer of your exterior wall 2, which is basically not a problem. However, it must be ensured that the amount of condensation is less than the amount of water that can evaporate during the evaporation period.

Either you calculate it by hand :mad:, or you let a software do the calculation for you :)

According to the U-value calculator (I don’t know the program), the amount of condensation is not too high. Unfortunately, I cannot see anything from the Wufi data.

In any case, I give you the tip to get a professional to plan the measure for you. The construction is not simple and should be well thought out.

Regards