ᐅ Solid Construction or Prefabricated House? Semi-Detached Home, Approx. 160 sqm, Pros and Cons

https://www.hausbau-forum.de/threads/fiananzierung-realisation-doppelhaushaelfte-rhein-main-einschaetzung.44652/ – it would be a great New Year’s resolution if the original poster brought up such points more often themselves ;-)

GDWE2023 schrieb:

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 a variety of opportunities for advice on improvements (if necessary, it’s perfectly fine to be criticized a bit for being resistant to advice, so what). I professionally look for the builder, but you both (including your semi-detached neighbor!) should realize how important it is that a semi-detached house is only designed by someone who is also willing to reduce sums where possible (for this, see “A semi-detached house has TWO halves” in bauen-jetzt or here in the forum’s Goalkeeper thread).

GDWE2023 schrieb:

With prefabricated house providers, I have to cut something out of models, which again speaks in favor of solid construction by a small local builder.

Nonsense. The flexibility of standard house models / proven building proposals is basically the same between timber frame panel construction and "brick-on-brick" solid construction. Only very rarely is the range of variations as limited as in the Dennert Icon series (which, by the way, is “prefab” but still solid).

WilderSueden schrieb:

I think it’s a myth that you only get floor plans from a catalog with a prefab builder. Most happily accept your money and will build your design, as long as it’s physically feasible.

It is actually the case nowadays that a majority of “prefab” house providers offer made-to-measure adjustments “to the centimeter” for every complication, something that was cleanly avoided in the “good old days” of strict modular planning.

WilderSueden schrieb:

After over two years in this forum, I would put a big question mark on whether it’s a good idea for the builder to come with their own design and only want it realized. Floor plans are a complex matter, but you can find help in the relevant subforum.

This question mark actually looks like a warning sign (traffic sign 101) – an exclamation mark inside a red-bordered triangle. A general contractor’s (GC) compliance servant’s job is to copy the client’s wishes without criticism, meaning that apart from permission requirements, no foolishness is corrected. This leads the layperson unrestrained into trouble, while most independent architects earn their fees properly (provided you don’t stop after phase 4 of services).

WilderSueden schrieb:

For special requests regarding the type of construction or certain self-performed work, it might also be sensible to consider building with an architect and individual contracting instead of a general contractor (GC), whether solid or prefab. Removing multiple trades from a GC contract is not necessarily the most cost-effective way to build. And if you plan, for example, to do the electrical work yourself, a prefab house usually only makes sense with an installation shell.

Exactly. You hire the GC consistently either for the shell or “turnkey.” The “premium minus” option ends up being the most expensive. Even with “prefab” providers, explicit shell houses are better than stripped-down full solutions. Kit houses also still exist.

GDWE2023 schrieb:

Initially, my neighbor planned solid construction without a basement but then switched to prefab because it was supposedly cheaper (which I cannot confirm so far). Both are without basements.

In any case, plan together (which has nothing to do with having identical or mirrored halves). This applies even if you prefer different building methods for implementation! The most critical point is the basement question, especially in the worst case scenario (“uneven” halves, one with and one without a basement), because timing coordination becomes decisively important. The second most critical point is the alignment of the house profiles at the joint. Keeping these two biggest complication factors in mind lays the foundation for avoiding a construction fiasco. Now, if you want, you can indulge in individualism for its own sake and use different contractors or even different construction methods. However, the ideal is to use the same contractor at the shell stage and only afterward try the challenge of whether “Villacracker” or “Villaquerer” is better at cutting channels and installing tiles. You don’t have to treat every semi-detached project like a “battle at the barbecue” 🙂 On the other hand, I fully agree with this assessment:

GDWE2023 schrieb:

I also asked about synergy and cost-saving aspects, but everywhere I was told there’s not much; maybe savings on a portable toilet and electricity, at most the crane, otherwise everything doubles.

This matches practical experience. The often-expressed dream that “bundling the purchasing power” of two small clients leads to spectacular volume discounts is in fact a 100% myth.

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From my experience so far—we are currently building and have compared solid (massive) construction versus wood frame construction. We ultimately chose solid construction with monolithic poroton blocks. Here are some thoughts that come to mind.

Advantages of monolithic solid construction:
- More forgiving of small errors in waterproofing compared to a wooden house.
- Issues noticed during the shell construction phase (e.g., socket positions) can still be easily adjusted. However, proper planning is essential here as well.
- More flexible house dimensions compared to prefabricated houses. Prefabricated homes often have standard exterior dimensions, likely due to the grid system of the wood studs. Our lot was relatively narrow, and with solid construction, we were able to build with centimeter (inch) precision.
- Easier connection between the house and garage when both are built using solid masonry.
- No concerns about pests in the facade or structure.
- The house is built entirely on-site, meaning the owner can monitor the entire construction process. In a prefab house, the walls are already pre-assembled, so you cannot see how the construction was carried out.
- In 2021, solid construction was also more cost-effective than wood construction in our case.

Advantages of wood (wood frame or solid wood):
- Generally the more ecological building method.
- Much of the construction is pre-assembled in the factory, which makes it easier to ensure good quality (e.g., window joint sealing).
- The house is usually erected and weather-tight within a few days, a particular advantage in autumn and winter.
- With double-layer sheathing (OSB + drywall), no dowels are necessary.

Conclusion: Especially given the current situation with high raw material prices driven by energy costs, I find wood construction increasingly attractive. The price of construction lumber has been steadily decreasing for some time. As a new builder, you might have a strong negotiating position, as companies are starting to compete again. For me personally, a solid wood house would be more appealing than wood frame construction (a matter of taste; both work well!). Alternatively, the classic solid house, but only using monolithic construction. For wooden houses, it is absolutely critical that measures for structural wood protection and all sealing works (window sills, building base, window connections, vapor barriers, or airtight layers, etc.) are executed very carefully to prevent damage to the structure and insulation. Local reputable carpenters or long-established prefab house providers are aware of this, but it is still important to be vigilant.

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

Crixton schrieb:

Pros of wood (wood frame or solid wood):
- usually the more environmentally friendly construction method

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

Crixton schrieb:

Pros of solid monolithic construction:
- tends to forgive minor errors in waterproofing better than a wooden house.
- more flexible house dimensions compared to prefabricated houses. Prefab homes often have standard external dimensions, probably due to the grid of the wood frame. Our plot was relatively narrow, and with solid construction it can be built precisely to the centimeter.
- easier connection of house and garage when both are built together using solid construction.

Emphasis on "minor" errors. Practical construction grids* exist in both masonry and wood framing ("-ständer" is a popular incorrect term). The grid increments differ in size but not in strictness or flexibility, nor in how mistakes are treated (tolerance and negligence are often confused in plans by laypersons and draftsmen). The typical construction grids for wood panel systems are usually 625 or 833 millimeters (2.5 meters divided by four or three), and for masonry with external insulation systems 25 centimeters (10 inches) per "brick," or monolithic masonry 12.5 centimeters (5 inches) per "header." The spacing of wood frame panels has no systematic subdivision but is more flexible to adjust. Designing exact dimensions to the centimeter in masonry regularly leads to violations of the overlap dimension and patchwork fixes. Incidentally, the external insulation system of wood frame construction, with its generally thinner walls, proves advantageous especially in tight building gaps. Regarding integrated or attached garages, the consequences of the critical question about thermal separation are very often overlooked.

*) I recommend that self-planners think in large increments of 75 centimeters (30 inches) for masonry and 80 centimeters (31.5 inches) for wood construction.

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But is the wall thickness still actually thinner with prefabricated builders? We are now building with 42.5cm (17 inches) Ytong at KfW40 standard, plus plaster. Weberhaus only offers KfW40 walls with 39.5cm (15.5 inches), which I understand is also without plaster. Schwörerhaus was also in the same class for KfW40 walls, but including plaster, if I remember correctly. For a KfW55 house, 36.5cm (14.5 inches) Ytong is sufficient, and the Schwörer wall was around 33–34cm (13–13.5 inches).

It may be that there are row houses where every bit of thickness matters. But for 99% of houses, that shouldn’t be the case. I see greater potential for savings by using drywall for interior walls instead of 11.5cm (4.5 inches) blocks plus plaster.

WilderSueden schrieb:

But is the wall thickness really that much thinner with prefab builders? [...] I see the bigger saving potential more in using drywall for interior walls instead of 11.5 cm (4.5 inch) bricks plus plaster.

For example, 29 cm (11.4 inches) versus 36.5 cm (14.4 inches) is obviously not a huge difference. Whether it’s a 10 cm (4 inch) gypsum board, 12.5 cm (5 inch) lightweight construction, or 11.5 cm (4.5 inch) sand-lime brick, it’s also not that significant. Drywall or gypsum board doesn’t save floor space in walls, but it does save time.

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WilderSueden schrieb:

But is the wall thickness really significantly thinner with prefabricated builders? We are currently building with 42.5cm (17 inches) Ytong blocks for KfW40, plus plaster. Weberhaus only has KfW40 walls with 39.5cm (15.5 inches). As far as I understand, also without plaster. Schwörerhaus was in the KfW40 category as well, but including plaster, if I remember correctly. For a KfW55 house, 36.5cm (14.5 inches) Ytong blocks are sufficient, and the Schwörer wall was in the range of 33-34cm (13-13.5 inches).
It may be that for some row houses every inch counts. But for 99% of houses, that shouldn’t apply. I see more potential savings by using drywall for interior walls instead of 11.5 cm (4.5 inches) masonry blocks plus plaster.

- For solid masonry houses, about 1.5 cm (0.6 inches) of plaster is applied both inside and outside. For single-family houses, only a few millimeters (around 0.1 inch) on the outside, and usually no plaster inside.
- Weberhaus builds more ecologically, meaning they use wood fiber insulation instead of polystyrene, but have a lower insulation value for this reason. Danwood achieves a KfW40 wall with just under 35 cm (14 inches) wall thickness, including plaster.