From what slope is a basement sensible?

I personally would forgo a basement and build a split-level house.

We are not talking about an additional floor here, but about a [OG] which becomes a [UG].

Basically, I would not base the basement question on the topography of the entire property, but rather look at the conditions in the building envelope or even more specifically in the area of the actually desired floor area.

One of my regular readers' already well-known mantras is that about 20 cm height difference translates to approximately 10% basement cost – in the sense that a built basement and a needed but avoided (through terrain modeling, slope support, etc., rather a Pyrrhic victory avoided) basement differ practically nothing in (also cost-related) effort. The mentioned 20 cm = 10% means that with a 2 m height difference (in the relevant area, see above), you practically always pay for a basement – regardless of whether you choose a realized basement or one "avoided" with some kind of substitute terrain manipulation. If the height difference is as high as the clear height of a usable basement, the basement costs the same – six of one, half a dozen of the other. With an 80 cm height difference, the example calculation results in 40% basement costs, which then go into earthworks.

Personally, I would forgo a basement and build a split-level house.

A split-level is – if purely based on the terrain – optimal at about 140 to 150 cm height difference in the relevant area; but personal preferences of course also play a role, as split-level tends to be better compatible with relatively open floor plans. A widespread misconception here is to think "compulsorily" of an offset of half a story height and/or an approximately half division of the floor part areas.

You’re asking the wrong forum. They would advise you here to build a basement even with a slope of 0.5 degrees.

I’ll refrain from dragging this out, which you actually would deserve for this at least provocative to brazen statement, and instead ask: would you be willing to share with us which forum you think applauds slab-on-grade houses more enthusiastically.

Basically, I would not align the basement question with the topography of the entire property, but rather look at the conditions in the building envelope or even more specifically in the area of the actually desired floor area.

One of my regular readers already known mantras is that about 20 cm difference in height translates roughly to 10% of the basement price – meaning that a built basement and a needed but avoided (and then with terrain modeling, slope support etc. tralala rather than a Pyrrhic victory avoided) basement practically do not differ in (also cost-related) effort. The mentioned 20 cm = 10% means that with 2 m height difference (in the relevant area, see above) you practically always pay for a basement – regardless of whether you opt for a realized one or one "avoided" with some kind of substitute terrain juggling. If the height difference is as high as the clear height of a usable basement, then the basement costs – six of one, half a dozen of the other. At 80 cm height difference, you have 40% basement costs in the calculation example, which then flow into earthworks.

That was also roughly the statement of our planner. So that it could certainly get a bit more expensive, but not as drastically as assumed, especially if you put in your own work (floors, painting, perimeter insulation). Also, we can plan the 150 sqm house with two full floors about 15 sqm smaller, since the utility room on the ground floor is omitted and could thus be moved to the basement.

Unfortunately, we completely lack the imagination for the terrain, but that will surely change with an upcoming joint inspection.

According to the development plan, walls are definitely only allowed to be built up to 20 cm above the traffic surface and not at all laterally towards the neighbors (here, embankments with a 1:1.5 slope ratio have to be constructed).

It remains quite exciting whether there will be a basement or not.

I just came up with a really practical idea to use the basement: an integrated double garage. Whether that will be cheaper than a separate garage or even structurally possible... good question. Do you have any experience with that? The driveway would then also be lower than the street, so downhill... one should pursue that idea.

I just had a really useful idea on how to use the basement:

Relatively too expensive due to the Energy Saving Ordinance.