160m2 detached house in timber frame construction on the north slope with basement

Max. 3 is the air exchange rate for houses according to the Energy Saving Ordinance without mechanical ventilation.

Does your provider only build according to the Energy Saving Ordinance?
For KFW it counts as 1.5. The house manufacturers only have one wall type. Among acquaintances, all have been between 0.6 and 0.9 in recent years except one who had 1.3 and we had 0.32 (Passive house).
Even if they omit seals, how close do they get to 3?

By the way, soil class 5/6 may require a pneumatic hammer. You dispose of all the excavation and have to bring in new soil for the garden area. You are rolling in money with the excavation. Is the excavation including transport and disposal included?

Try to avoid every shovel of excavation. Possibly split level.

The basement is included. We are considering downsizing the whole thing once again.

My quote was probably taken out of context, it should have said:

Is the basement included in the scope of the house manufacturer's offer here? [...]
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How does that fit with a admittedly tight budget – wouldn't it be more effective to choose another route to Rome?

The question was not how the basement fits with the budget, but why the manufacturer is not chosen more effectively from the price segment suitable for the budget level.

The house manufacturers only have one wall type.

What do you mean by that? – there are often two or more wall constructions (aside from plaster or clinker also with other insulation materials for bio freaks or the like).

The airtightness for KFW 55 and KFW 40 is equally high or the same for all houses with ventilation systems, except for passive houses.

The wall construction from the painter's fleece to the fine plaster was identical in the companies with timber frame construction that we looked at, regardless of whether KFW 55 or KFW 40. It also makes sense, as this greatly simplifies production.

Insulations minimally affect airtightness. That is why the first measurement was carried out with us before the installation of screed, interior plaster, insulation, etc.

Every timber frame builder who can do KFW 55 can also handle the Energy Saving Ordinance.
I only have concerns that it is sufficient if the sealing of the joints (wall to wall, wall to ceiling and floor) is missing, that this alone can cause the value to go from below 1.5 to nearly 3.
I know from the person who carried out the first blower door test that many prefab house companies have the same test results regardless of whether it is the Energy Saving Ordinance, KFW 55, or KFW 40, since the walls are identical.

This is also the reason why many can do KFW 40 or KFW 40 Plus, but no certified passive house (or only at a crazy extra cost).

Therefore, the TE should take a look at Stein auf Stein general contractors. I think they are simply more flexible since each house is built stone by stone on site and not wall by wall in the factory.
Perhaps Stein auf Stein GUs don’t treat the basement so carelessly either.

They are happy to install everything we want, they just think it’s not necessary. Our salesperson says despite "airtightness" there are 3 air changes per hour and moisture is not a problem with timber frame construction.

(Nitpicking): he probably meant (or said?) an air change rate of 3 times the room volume per hour with windows and doors closed.

If that’s the case, I would quickly look for another manufacturer, it would be drafty as hell in that house.

In the blower door test for new buildings, an air change rate of 3/h at a PRESSURE DIFFERENCE OF 50 mbar! must not be exceeded. But normally you don’t have a fan in your front door, at least I don’t. And if you don’t have a black hole or a permanently open compressed air bottle in your utility room, you don’t have 50 mbar pressure difference either.
For the natural air exchange through infiltration/leakage, a value (wind protection coefficient) of 0.07 times the n50 value from the blower door test is assumed when creating the ventilation concept according to the Energy Saving Ordinance – which corresponds quite well to reality.

If there are no interior rooms (except hallways), controlled residential ventilation is only necessary if natural air exchange is insufficient to transport away accumulated moisture. For 200m² of space, about 60 m³/h are needed. At an n50 value of e.g. 2.0/h multiplied by 0.07 = 0.14/h. With 500m³ that corresponds to 70 m³/h -> sufficient but far from 3 times per hour!
Often, controlled residential ventilation is not necessary to achieve the minimum air exchange.

Timber frame construction is neither airier nor less airy than solid construction. If it is drafty, it is because of sloppy work with cable and pipe penetrations or the connection of the internal vapor barrier to other components or at transitions.

Controlled residential ventilation serves, besides heat recovery and thus fulfilling the 2016 Energy Saving Ordinance, in 90% of cases only comfort, not the preservation of a mold-free building fabric. If something gets wet / molds somewhere, etc., it’s not because controlled ventilation is missing, but because someone botched the job.

Thank you for the information about the LWR, that wasn’t entirely clear to me. I think our salesperson was orienting themselves on the Energy Saving Ordinance. The wall construction we would get corresponds to Kfw55. I do believe the provider when they say that in prefabricated houses of this construction type it usually doesn’t mold even without a ventilation system. However, I don’t like the idea of having no air supply at all either. On the other hand, I don’t like the idea of being supplied with air through some pipes for decades. No one can convince me that those things can be seriously cleaned. An architect we spoke with recommended window slot vents as intake plus decentralized exhaust through the bathrooms/kitchen. Personally, that solution appeals to me the most. @ haydee Excavation/earthworks are extra Regarding GUs: How do I find good ones?

Regarding GUs: How do I find good ones?

Ask around among acquaintances who are building/have built. Drive through new development areas, look at the construction site signs (and talk to the associated builders). Talk to construction companies and trust your gut feeling (a good place for this: building fairs). Read construction blogs etc. on the internet (but beware: sometimes it’s not the builder who is good but only their legal department, and some surely now also pay people for fake blogging…).