Cost estimation for hillside construction

Dear Home Builders,

we are currently in the early phase of our construction project. A suitable plot has been found and now it must be checked whether we can realize our dream. For this, I hope to receive some valuable tips, ideas, and advice from you.

About the plot: a slope with a relatively steep gradient, assumed to be > 20 degrees. The 20 degrees are based on an initial rather amateurish measurement at the outermost points of the terrain. The slope rises to about 8m in height. “Behind” the slope, another house is built, also on the slope accordingly. According to the soil report, no rocks are to be expected and the soil is easy to work with.

The building window is approximately 22m x 10m. The idea is now to put “half” of the house into the slope (garage and first floor). And to put an extended floor “on top” of the slope.

The total living area should be about 130-150 sqm, plus garage etc.

Now the question arises as to what budget one should at least approach the matter with. We had planned a limit (for the house without plot) of about €650,000. Most costs should be included here (apart from “trivial” DIY tasks like wallpapering etc.). From a bit of reading through other threads and other websites, I have come across figures of about €3,500 per sqm. We are currently at €4,300. Does that cover the “slope surcharge”?

What is your assessment for a construction project on a slope? Too little? Too much? Particularly the slope stabilization worries me. The information I got from googling is hardly usable...

We have already arranged consultation appointments with 2 architects. The question now is with which figures we should go into the race? What should we pay attention to during the discussions?

Best regards Bowow

Hello ,
the figure most often mentioned here is €2500 per m2. In BW as well as BY, you quickly exceed that.
With your budget, the project is absolutely realistic. It will be cheaper if you can dispose of the excavation on your property or if someone takes the soil off your hands (transport at your expense).
Start with €450,000 - €500,000 at the architect. It will get more expensive on its own.
This way you still have a buffer for incidental building costs, garage, outdoor area, upgrades, etc.
During the construction phase, a slope (if possible) will be created. Once the basement is finished, it will be backfilled. Whether and how the slope needs to be secured additionally during the construction phase will be decided only on site in the end.

Yes, the budget looks very good. I think with 550k to 600k you will manage all inclusive without the land very well. Good luck!

We currently have a similar project running in Bavaria, with 160 sqm of living space. The architect's cost estimate, including earthworks (excavated material can mostly be used on the property), is €480,000 - excluding garage and exterior facilities. For these as well as other ancillary building costs and unforeseen expenses, we have approximately €120,000 planned.
If you have a total of €650,000 available, that should also be feasible.

Start with €450,000 - €500,000 with the architect. It will get more expensive on its own.

I see it exactly the same way.

The budget should be sufficient. The BG requires slope stabilization during the construction phase. Among other things, we left the old retaining walls standing for this reason, and friends had a construction stop due to lack of stabilization. Without earthworks and exterior landscaping, the slope has cost us about 40,000 euros more on the house. Exterior landscaping costs. However, I cannot quantify what is excluded at the homeowner's request, such as a double-layered sandstone wall and on the slope (terrace and play area should be level).

Your approach is a good first approximation. On to the discussions with the architects.