Purchase decision small semi-detached house 100 sqm from 1930

Unfortunately, I have not yet received any offers from the companies that offer this here in the region - the selection is unfortunately very limited and they are correspondingly busy. But: I have made the inquiries and yes, it should fit within the budget. I actually expect no more than €10k here? I wouldn't have thought that 6cm could make such a huge difference.

Do you know ubakus? With it, you can calculate the U-value of your walls. If you do that, you will find that there is a world of difference between your walls without blown-in insulation and with blown-in insulation. The first centimeters of insulation are always the most effective. So do it - if the budget allows.

Regarding blown-in insulation, several people advised us against it, for example. You can’t get it in evenly, and then you get thermal bridges. Friends of ours just stripped one of their walls because of an extension. It showed that it’s not a “clean” cavity, and there was a lot of debris and crumbs in the lower part of the wall.

I could imagine that this is already blown in with a lot of pressure - the individual particles must also be quite densely packed. Maybe someone here is familiar with this.

Regarding blown-in insulation, several people, for example, have advised us against it. You can't get it evenly distributed in there, and then you end up with thermal bridges.

1. If done by a professional, then you have—provided the cavity is accessible everywhere—insulation without gaps. Blown-in insulation is no longer exotic today but a very common technique. However, mistakes and mishaps can always happen, regardless of the trade.
2. And even if one spot is missed (unlikely), you still have 98% of the wall insulated, which is 98% more than without insulation. Energetically still simply good.
3. Who exactly are the "several"?

Friends of ours recently stripped one of their walls for an extension. It was visible that it’s not a "clean" cavity, and there was a lot of debris and crumbs in the lower part of the wall.

Then so be it. To forego affordable insulation because of a little debris and crumbs in the lower area of a wall (which, by the way, you can see beforehand if you look into the wall)? Because what is the alternative? Exactly, no insulation at all. And that is simply stupid.

How should the pressure be built up?

There were people who came from construction or had already renovated old buildings.

There were people who came from construction or who have already renovated old buildings.

Then I generally claim that they have no idea about blow-in insulation.

How is the pressure supposed to be built up?

The insulation is "blown in" with increased pressure into the cavities according to a previously determined scheme. There are special blowing machines for this purpose.
Professionals first inspect the cavity through these approximately 2cm holes and can even remove a brick to clear debris at the base.
Good contractors are even certified specifically for these tasks. This has been established for about +/- 40 years. So it’s well established.