ᐅ Cost Estimate for a Basement in an Almost Shell Stage Building

Vivusorg schrieb:

I am planning a basement and wondering approximately what costs are to be expected.

Probably a lot of avoidable ones, since from what I see in https://www.hausbau-forum.de/threads/grundrissentwurf-einfamilienhaus-ca-230qm-plus-keller.45979/, you seem to be one of those builders who like to "save" on engineering services in the wrong places.

Vivusorg schrieb:

-> Earthworks excluded

That’s a good joke. Foundation and excavation are major individual cost items when building a basement. It won’t help you much to rent an excavator cheaply and operate it yourself. The only thing we know about your ground conditions is that the site is supposed to have an 8% slope.

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11ant schrieb:

Probably a lot of avoidable costs, since you appear to be one of those homeowners from https://www.hausbau-forum.de/threads/grundrissentwurf-einfamilienhaus-ca-230qm-plus-keller.45979/ who like to “save” on engineering services in the wrong places.

The joke is a good one. Foundation and excavation are major cost items for basement construction. Renting an excavator cheaply and operating it yourself won’t save you here. The only thing we know about your soil conditions is that the site has an 8% slope.

I can only confirm that. Site setup, excavation, removal of soil, drainage, waterproofing, and all necessary preliminary work cost around €50,000 gross before the shell builder even started.

Vivusorg schrieb:

Perfect. Thanks for the assessment. Based on your figures, I arrive at about 87,000 EUR. Could you tell me what additional costs would be involved if the basement was constructed as a waterproof “white tank”? The plot is on a slope (around 10%). To estimate the worst case, I would like to include the white tank option in my calculations.

As long as you don’t want or need to use cast-in-place concrete (which is generally significantly more expensive than precast elements) and you don’t have special structural challenges, the “white tank” method should be feasible. However, as soon as you deal with waterproof or flood-resistant windows, light wells, and possibly sump pumps, additional costs will arise. This depends on how your slope is situated.

In any case, it’s important to budget generously – for example, if you have to do concrete work in winter, expect a 5 to 10% winter surcharge. Or if your street needs to be closed for a crane delivery and unfortunately it’s a district road, that could add another 1,000 to 2,000 EUR. And the costs keep adding up – especially if you don’t want to hire a general contractor with a fixed price, it’s better to calculate more generously.

With a 10% slope, you will likely build a basement with at least one open side. Exterior plastering becomes a factor, and you may need to use standard windows and/or exterior doors there – which will increase costs accordingly.

I forgot to mention:

Vivusorg schrieb:

- approx. 90 sqm (square meters) of usable floor area covered with screed
- of the 90 sqm, about 40 sqm with underfloor heating (directly next to the boiler room) – no floor covering

For a “KfW40” (energy standard), it is rather pointless to leave large areas unheated. It may even be impossible if certain thresholds for subsidies have to be met.

Consider installing concrete core activation (or “Swedish slab”) instead – with appropriate design, planning, and execution, you can save the underfloor heating, additional floor insulation, and screed in the basement, and achieve significant improvements in heating efficiency. This is especially advantageous if cooling is planned as well.