Semi-detached house without a basement next to a semi-detached house with a basement

My husband and I were completely unexpectedly offered a plot for a semi-detached house under the local resident model in the Munich surrounding area. The second half of the mentioned semi-detached house had already been allocated some time ago; we have already met our potential neighbor: his development plan has already been approved and he is only waiting for the groundbreaking.

A development plan is something different, namely a legal framework from the municipality that regulates and coordinates the development of an entire area. What you mean is a building application – so is he not building under the simplified procedure?

Now, in our case, it is such that we want to do without a basement (not only) for financial reasons, but he will definitely build one. In addition, he is building solidly, while we are planning to have a turnkey prefabricated wooden house built.

Renouncing a basement is rarely a matter of taste alone, since the plot or its evenness can significantly influence whether this can also be economically reasonable. The "11ant basement rule" roughly summarized states that from a height difference of two meters in the area of the house’s footprint, avoiding a basement costs as much as building one, and roughly proportionally this applies as well, so for example, with a 60 cm height difference, the basement avoidance costs correspond to about 30% of the basement construction costs.

What are the motives for your preference for a "prefabricated wooden house"? Do you mean one in the widespread and often mistakenly called "timber frame construction" wood frame panel construction, and how much expertise is behind this preference?
I always recommend to my advisees to leave the decision about the construction method open at least until the “dough rest” phase of the house-building schedule. In my experience, there is no fundamentally right construction method between the wooden and the masonry spectrum (and the other one then being "wrong"), rather it is always worth considering individually.

Where on these 300 pages would I now find the information relevant to us?

The thread is definitely worth reading, even though unfortunately many posts necessarily also involve a bit of the stupidity contest between the mayor and the neighbor ex-middle-class houses (and later new middle-class houses). The most relevant statement for you is that the biggest bomb has already been defused: namely that the one building with a basement builds first. On this front, you as a no-basement builder can therefore be relaxed. Another sore point in uncoordinated semi-detached house construction is, as far as I remember, not elaborated in the Goalkeeper thread but addressed by me in all relevant threads: namely the fitting of the halves at the seam "house profile(s) on the common wall side". Ask the neighbor regardless of possibly different construction methods about his architect.

You can find my collected advice on the topic here mainly via the forum search function using the keyword "Doppelhaus" and the search option "written by: 11ant" as well as the keywords "Ohnekellerer" or "Mitkellerer", and externally (to be googled in quotes) in "Ein Doppelhaus hat ZWEI Hälften". You can also find several posts on sound insulation in terraced houses here via the search function.

: Many thanks for your numerous tips and hints! I am still not quite proficient with the technical vocabulary, that's true. ;-) I didn't mean the development plan, but actually the building application, sorry. He has probably already submitted it and it was approved by the municipality, so we now have to adapt to it (due to the profile uniformity prescribed in the development plan). The plot is "brettleben," as they say here, or also: "Oh, nice, a beginner's plot!" (quote from my brother-in-law). A soil survey report is already available and the house provider also knows the building area (he is apparently building about 10 more houses there in parallel) and described it as uncomplicated. I therefore suspect that—following your rule—a basement is not actually financially sensible for us. That we are building with ... wait a moment ... timber frame panel construction ;-) is only because we like the offer from this house builder and we want / have to build a KfW 40+ house (due to KfW funding). Regarding this, we were told by a competitor that this would not be possible with bricks for him. Unfortunately, the neighbor's architect is "a family friend who is already retired," otherwise we would have of course tried to get him on board as well. The alignment of the house sides also gives me some concern, but I suppose I have to rely at least partly on our house building company...? What else could I do?

and the house provider already knows the development area (he is apparently building about 10 more houses there in parallel) and called it uncomplicated. [...] The fitting of the house sides also gives me headaches, but I guess I have to rely at least partly on our house building company...?

The fitting of the house profiles worries me the most here, especially when a mixed-gender twin house is to be built. The provider’s routine from ten other houses nearby – which presumably do not have to fit together in this constellation – is more dangerous than reassuring. Unlike the municipality, I am not concerned with rough visual similarity (where a difference of three or even five centimeters does not stand out), but with the tightness of the component connections. Especially water gets in at places where even a cat would give up. In site-built masonry, you can adjust very differently than with prefabrication. Aiming millimeter-exact at a target can nonetheless lead to glaring gaps in reality.

Therefore, following your rule, I suspect that a basement is not actually financially more reasonable for us.

Yes, that is exactly correct. Especially since terraced houses typically offer plenty of "basement replacement room" potential in the attic.

That we are building with ... wait ... timber frame panel construction ;-) is only because we like the offer from this house builder and want / have to build a KfW 40+ house (because of KfW funding). In this regard, a competitor told us this was not possible for him with bricks. [...] What else could I do?

You could do without the priority reversal between tail and dog. Efficiency house 40 is in the masonry construction methods actually more expensive to achieve than with the timber frame panels and their quasi-genetic thermal insulation integral system. But even here this Building Energy Act “fat stage” is economically negligible; the KfW discounts only roughly compensate the additional costs. Moreover, with the profile-identical end terraced house (because that is nothing other than a semi-detached house; the middle house that is omitted can be excluded here) you have “full man coverage” at the largest radiation surface. The payback period in consumption will easily exceed the holding period of such a property. Therefore, you can gladly drop this Building Energy Act overfulfillment and thereby gain the advantage of the construction method that is easier to adapt to the neighboring half. According to my recommendation, it is virtually “set” here to take the same roofer.

We had EXACTLY your case in our circle of acquaintances. From the reports, I can tell you the following: Build together.

It’s not just the basement but also all the transition points that are affected. First, it looks visually like ***, if the halves don’t harmonize (eaves, window sizes, house color), but the purely technical process is a disaster.

- Scaffolding of one disturbs the other
- The insulation of one half must be in place when the other connects, but the insulation doesn’t last forever against wind and weather and weathers away. The insulation thicknesses must absolutely be discussed beforehand.
- The connection points on the roof are not simple.

The end of the story is that the semi-detached house now has an offset of 10 cm. Of course, looks premium. Not to mention the style.

But basically, the side with the basement must ALWAYS be built first. Supporting it otherwise would cost a five-digit amount.

I can only say, in response to the contribution from fullest agreement (from four decades of residential construction planning). In theory, this has always been my approach as well. Unfortunately, in practice, there are restrictions that prevent implementing the pure doctrine straightforwardly (in cases like this usually because the neighbor does not have the patience to wait for their counterpart, mainly for financial reasons). Nevertheless, I would aim to get close to the ideal that one aligns the timing of one's own foundation slab with the basement ceiling of the neighbor, and ideally use the same shell construction company and, as already mentioned, also the same roofer (using the same carpenter would be even better). It is also highly recommended to coordinate the elevation levels of the structural ceilings. If the neighbor's architect is really retired, he usually has also deregistered his professional liability insurance and thus practically hung up his planning authorization, then there is a corresponding stamping official. If he himself is an architect, he would be the ideal coordinator for the whole matter. Otherwise, I am also happy to offer my own involvement. In all finishing trades, you would have full freedom to award contracts and select materials differently than the neighbor.