Solid house or prefabricated house? Semi-detached house, approx. 160 sqm, pros and cons

- it would be a nice New Year's resolution if the original posters brought up such hints more often themselves ;-)

Let's continue with the floor plan: basically, we already have our house on paper and just need someone to build it.

Show us this house and gain diverse opportunities for advice on improvements (if necessary, one lets oneself be reproached for a bit of advice resistance here and there, so what). I professionally search for who builds it, but you (both, so also the neighbor of your half!) should first very seriously realize that only someone who is also willing to cut sums plans half a semi-detached house (see "A semi-detached house has TWO halves," see bauen-jetzt or the Goalkeeper thread here in the forum).

With prefabricated house providers, I have to cut from models, which again would speak for solid construction at the small local contractor.

Nonsense bingo. The variability of model houses / proven construction proposals is basically identical between timber frame panel and "brick on brick." Only extremely rarely is the variety frame as narrow as with the Dennert Icon series (by the way "prefab," but "solid").

I consider it a myth that you only get floor plans from the catalog from a prefab builder. Most gladly take your money and build your design if it is physically possible.

It's even such that nowadays, unfortunately, most "prefab" house providers are ready to do Made2Measure "to the centimeter" for every complication, which one cleanly circumvented in the "good old" times of grid fidelity.

After more than 2 years in this forum, I would put a big question mark behind whether it's a good idea for the builder to show up with their design and only want it implemented. Floor plans are a complex topic, but you can find help in the corresponding subforum.

This question mark takes the form of an exclamation mark in the German traffic regulations (sign 101) and stands in a red-bordered triangle. A general contractor’s lackey has the task of copying the customer's wishes without criticism, i.e., apart from approval obstacles, not to erase any stupidity therein. This way, the layman runs headlong into a trap, while most freelance architects earn their fees (if you don’t only take them up to service phase 4).

With special requests regarding the type of construction execution or certain own work, it might also make sense to consider building with an architect and individual awarding instead of a general contractor (regardless of whether solid or prefab). Removing trades one after another from a GC is not necessarily the cheapest way to build. And if, for example, you do the electrical work yourself, a prefab house usually only makes sense with an installation level.

That’s right. One consistently takes the GC either for the shell construction or "turnkey"; "premium minus" is the ultimately most expensive variant. Even with prefabers, explicit shell houses are better than slimmed-down complete solutions. And kit houses still exist as well.

The other half initially tended to solid construction without a basement, then switched to prefab because it supposedly is cheaper (which I can’t confirm so far). Both without a basement.

In any case, plan jointly (which has nothing to do with identical or mirror-identical halves). This even applies if you prefer different construction methods for implementation! The most critical point is the basement question, especially in the worst case ("crooked" halves, one with and one without basement); the temporal coordination also gains decisive importance. The second most critical point is the fitting of the house profiles at the seam. If you keep these two largest complication dimensions in focus, the foundation to avoid a construction ruin is laid at least. Now one can — if one considers it a panacea — indulge in individualism for its own sake, using different construction companies or even construction methods. Ideally, however, you take the same contractor at the shell level, and afterwards you can then "if you like" try the challenge of whether Villabajo or Villariba better cuts slots and lays tiles. But you do not have to necessarily approach every semi-detached project as a "war at the grill" :)
On the other hand, I can only confirm from practice the assessment

I also asked about synergy & cost-saving aspects, but everywhere I was told it’s not much, the porta-potty and electricity, at most the crane would be saved; otherwise everything x2.

The often-expressed dream idea that the "bundling of purchasing power" of two small clients leads to spectacular quantity discounts is indeed a 100% myth.

From my previous experience, we are currently building and have extensively compared solid construction vs. timber (post-and-beam) construction methods. In the end, we chose solid construction with poroton monolithic blocks. That’s what just came to mind.
Pros of monolithic solid construction:
- It is more forgiving of minor sealing errors than a wooden house.
- Issues that appear during the shell construction phase (e.g. socket positions) can still be easily implemented. However, proper planning is also fundamental here.
- More flexible house dimensions than prefab houses. Prefab houses often have standard external dimensions, probably due to the timber post-and-beam grid. Our plot was relatively narrow, and with solid construction, it can be built down to the centimeter.
- Easier connection between house and garage if both are built in solid construction.
- No issues with pests in the facade/construction.
- The house is built from scratch on site, meaning as the client you have insight into the entire construction progress. (In a prefab house, the walls come pre-assembled, so you can’t see how it was built.)
- For us, in 2021 it was more cost-effective than timber construction.

Pros of timber (post-and-beam or solid wood):
- Usually the more ecological construction method.
- Much is pre-assembled in the factory, which makes it easier to ensure good quality (e.g. window connection joints).
- The house is usually erected and weather-tight very quickly within a few days, especially an advantage in autumn/winter.
- With double-layer cladding (OSB + drywall), no plugs/dowels are necessary.

Conclusion: Especially in the current situation with high producer prices driven by energy costs, I also see timber construction as attractive. The price of construction timber has been steadily decreasing for some time. As a new builder, you could have a good negotiating position because companies are slowly having to compete again. For me personally, however, a solid wood house would be more of an option than post-and-beam construction. (A matter of taste, both work!) Or the classic solid house, but for me only in monolithic construction. With a wooden house, it is fundamentally important that measures for structural wood protection and all seals (window sills, house base, window connections, vapor barrier or airtight layer, etc.) are executed very cleanly so that the construction and insulation do not suffer damage. Locally renowned carpenters or long-established prefab house providers know this, but you should still be careful here.

Thank you for your template on the topic "Myths in Bags":

Pro wood (wood frame or solid wood):
- usually the more ecological construction method

But there is also a lot of romantic green dreaming in that ;-)

Pro solid monolithic construction:
- more forgiving of smaller errors in sealing than a wooden house.
- more flexible house dimensions than prefabricated houses. Prefabricated houses often have standard external dimensions, probably due to the grid of the wood studs. Our plot was relatively narrow, and with solid construction it can be built to the exact centimeter.
- easier connection of house and garage if both are built together in solid construction.

With an emphasis on "smaller" errors. Effective real construction grids* exist in stone as well as in wood frame ("-ständer" is a popular incorrect term). The grid spacings differ in size but neither in strictness or flexibility nor in the consequence of ignorance (tolerance and ignorance are often mixed up in layman and CAD drafter planning). The effective construction grids for wood frame panels are usually 625 or 833 mm (two and a half meters divided by four or three) and in stone with ETICS 25 (= one "stone") or monolithic 12.5 (= one "header") cm. The rafter axis spacing of the wood frame panels has no systematic subdivision, but is more flexible to "replace". Centimeter-flexible target dimensions regularly lead to violations of the overlapping dimension and to botched spots in masonry. Incidentally, the ETICS of wood frame construction with its usually lower wall thicknesses proves useful especially in infill sites. Regarding integrated or attached garages, the consequences of the crucial question of thermal separation are very often not considered.

*) I recommend the self-planner to "think" in large steps of 75 cm in stone construction or 80 cm in wood construction.

But is the wall thickness really still thinner with prefabricated builders? We are now building with 42.5cm Ytong for KfW40, plus plaster. Weberhaus only has KfW40 wall with 39.5cm. To my understanding, also without plaster. Schwörerhaus was also in the class for the KfW40 wall, but including plaster, if I remember correctly. For a KfW55 house, 36.5cm Ytong is sufficient and the Schwörer wall was in the range of 33-34cm. It may be that there are terraced houses where a hand's breadth matters. But for 99% of houses, that should not apply. I now see the greater saving potential rather in using drywall for interior walls instead of 11.5cm stones plus plaster.

But is the wall thickness really still that much thinner with prefab builders? [...] I now see the greater saving potential rather in using drywall for interior walls instead of 11.5 cm bricks plus plaster

For example, 29 to 36.5 cm is obviously not a huge difference. Whether 10 cm gypsum board or 12.5 cm lightweight construction or 11.5 cm sand-lime brick is also not. Drywall or gypsum board does not save wall floor area, but time.

But is the wall thickness really still thinner with prefab builders? We are now building with 42.5 cm Ytong for KfW40, plus plaster. Weberhaus only has KfW40 walls with 39.5 cm. As far as I understand, also without plaster. Schwörerhaus was also in the KfW40 wall class, but including plaster, if I remember correctly. For a KfW55 house, 36.5 cm Ytong is sufficient, and the Schwörer wall was in the range of 33-34 cm. It may be that there are row houses where a hand's breadth matters. But this should not apply to 99% of houses. I see the greater potential for savings now rather in using drywall for interior walls instead of 11.5 cm bricks plus plaster

- For solid houses, about 1.5 cm of plaster is applied inside and outside respectively. For prefab houses, only a few millimeters outside, normally no plaster inside at all. - Weberhaus builds more ecologically, i.e. wood fiber instead of Styrofoam insulation, but has a worse insulation value for that. Danwood achieves a KfW 40 wall with just under 35 cm wall thickness. (Plaster already included)