Bungalow - 2 floors with large layout / 3 floors with small layout?

Good day everyone,

I would like to inquire in the forum whether anyone has already gained experience in my current situation or has any ideas or suggestions.

We are currently facing the following situation: We live in a single-family house (bungalow style) and want to build an extension for our parents on the adjacent property (which already belongs to us and is designated as building land). In order to maintain a consistent appearance for the entire property, only the bungalow style is really an option here – with a pitched roof it would look very strange, since otherwise a large building would have two different roof types.

We are located on a hillside, so our current house has "only" a ground floor and a basement, with the ground being at street and hill side (so no windows - cellar rooms) while on the other side there are normal living rooms in the basement.

The extension is supposed to be built more or less parallel to this, and we are now in a very early planning phase, i.e. we are currently "brainstorming" what could theoretically be done in order to later check the feasibility of the ideas.

We are currently thinking about the following:

We could give the extension a floor plan of 10x13 meters (which would result in about 130 m² of living space on the upper floor regardless of walls, etc.) and in the basement we would have some cellar rooms as well as living space on the hillside side – one would probably end up with about 180 to 190 m² of living space.

The floor plan is thus relatively large, meaning I assume that the flat roof would be very expensive at this size, and the cellar will also be very large. Therefore, the following alternative occurred to me:

One builds with a smaller floor plan, e.g. 10x8 meters, but adds an upper floor on top. Then the upper and ground floors would offer about 160 m² of living space (again simplified without walls, etc.) and the basement would probably provide about 40 m² – so roughly speaking one would also end up with just under 200 m² in total. However, the cellar would be smaller and the flat roof much smaller as well (80 m² roof instead of 130 m²!!).

Of course, we will discuss all our ideas with an architect in the next few months, but I would already be interested in a gut feeling about the cost implications, because a smaller story is added, but I believe one can save quite a lot on the cellar and the roof.

In this sense, my question: What are your thoughts on this? I would greatly appreciate an exchange of experiences!

PS: Building costs are hard to estimate, but we currently plan (only for construction, excluding land) about 275,000 based on 1,400 to 1,500 euros per square meter for a normal, non-luxurious finish. We might be able to do small things ourselves as own contribution. A comment would also be nice here if someone thinks I am way off with this figure.

We live in a single-family house (bungalow style) and want to build [...] an extension.

So far so good, the further text makes me assume that you do not want to build an extension but a detached single-family house with a flat roof. Your question is whether
A) two floors, or
B) three floors,
make sense (considering construction costs and the resulting basement area), with the first floor each time being about half below ground level, i.e. a basement.

What are your thoughts on this?

In my opinion, your question is related to whether a bungalow is cheaper than a two-story house with the same living area. Short answer: it doesn’t matter and depends on completely different things. This has been discussed many times on the internet.

I would first clarify what I (here: your parents) want: which rooms, how much spaciousness, and how much basement space? If that makes sense on one level (plus "basement"), I would build that way.

Thank you very much! So it is actually supposed to be an extension, both buildings should be connected by a common corridor. However, the extension will have its own heating etc. and is independently "livable". We do not really need much basement space - however, the argument for "everything on one floor" is that we want to design the building to be age- and care-appropriate from the start. Stair lifts will be installed anyway, but the more that is on one floor, the easier it is, of course.

Why should the houses necessarily be combined and not designed as separate semi-detached houses? As separate semi-detached houses, it is much easier to sell or rent the other house if the parents are no longer around. Besides, you can also close the door sometimes without the "young ones" constantly dropping in on the "old ones" or the "old ones" on the "young ones." The first thing I did when we renovated the apartment in [Schwiegermutter Haus] was to install a proper door with a knob on the outside.

Moreover, in my opinion, it contradicts building 180-190m² of living space for two people and at the same time having to watch the money.

8*10 meters with 2 floors (basement + ground floor) should be more than enough for 2 people, right? As already mentioned above: Which rooms / areas are needed? A larger extension with 1 more floor will look pretty strange. Better to have the larger floor area.

: That is indeed the point where I’m stuck, because with 3 floors such an "attached tower" looks a bit odd. This strongly argues in favor of the 2-story model.

: If one day our parents are no longer here, there is no interest in selling or renting the extension. We are located at the edge of the forest and have only one neighboring house. We want to preserve this freedom and in this distant future do not want to have neighbors, which would mean being enclosed on our property in a single plot. Instead, the building should be flexible enough to be used by our entire family (e.g. as an apartment for the children, office space, etc.). Therefore, the entire building should be usable either as one large building or as two semi-detached houses.

The reuse will be an issue in about 40 to 50 years, when we ourselves are no longer alive and our children will likely want to sell the property.