Increased founding effort on a slope descending from the street by 12%

Hello dear experts,

we are currently planning the construction of a single-family house with about 120m² of living space and a footprint of approximately 9x9m without a basement, as we do not need the space and want to save costs. The plot currently reserved has a slope falling away from the street with about 12-13% longitudinal inclination and about 6% transverse inclination sloping down from left to right. The building window begins 3m from the edge of the street. The left front corner would therefore need to be raised by about 40 cm relative to the current ground level in order not to end up below the street. The rear right corner would then already be about 150cm above the ground level there.

The opinions of the potential construction companies range from: "No problem, just set a few shuttering blocks on the ring foundations and build up the walls and then the slab on top for an additional 3000-4000€" to "we dump a few hundred tons of frost protection and compact it for an additional 8000-10000€" up to "Oh difficult, actually a basement is necessary, additional 25000-35000€" each compared to a planned foundation on flat terrain with a slab.

I would like to believe the provider with the lowest price, but I suspect that there may be a catch and that "unexpected" difficulties may arise during implementation.

Therefore my questions: Based on your experience, do you have a recommendation what would be suitable here or what probably won’t work? What costs are realistic here? What other problems might arise that could produce additional costs?

Thanks for your tips,
MausJ

Hi, we also raised our house by 50cm because otherwise it would have stood in a dip on the property. The house is on a slab foundation and the raising was simply done by adding a layer of (what was it again :confused concrete recycling (??)). In any case, it was relatively undramatic - but also not a real slope location. So no idea about the structural engineering. I think the soil structure plays an important role in this. For us, everything is clay and it is quite firm and good for foundation. It is surely different for you. The best thing is to ask the local construction company that has already built there. They usually know the soil conditions and know what is best for you.

Hello,

The front left corner would have to be raised by about 40 cm in relation to the current ground level in order not to end up below the street. The rear right corner would then be about 150 cm above the local ground level.

The opinions of potential construction companies range from: "No problem, just put a few shuttering blocks on the ring foundations and build up the walls, and put the slab on top for an additional cost of €3000-4000" to "we’ll throw in a few hundred tons of frost protection and compact it for an additional cost of €8000-10000" to "Oh difficult, a basement is actually necessary, additional costs of €25000-35000," each compared to a planned foundation on flat ground with a slab.

This question cannot really be answered for two reasons. On one hand, we don’t know your property; on the other hand, the soil report most likely has not yet been issued.

You will hardly want to found the single-family house on foundations hanging in the air on one side; so substantial fill has to be applied. Costs in the range of €15,000 are easily possible here.

If the soil conditions are also critical and gravel alone is not enough but soil replacement is necessary, the €15,000 can quickly become €20,000 or €25,000. In this respect, the option "it’s worth considering a basement here" is not unfounded.

This whole thing is called "additional foundation costs"; for this item, a corresponding reserve should always be set aside in the ancillary construction costs, especially for uneven plots and slopes.

Rhenish greetings

First of all, many thanks for the feedback.

Hello,


This question cannot really be answered for two reasons. On the one hand, we do not know your property, on the other hand, the soil survey report most likely is not yet available.

So far, I only have a general soil survey report of the entire construction area and have spoken with neighbors from the adjacent development section. But that does me no good regarding the specific plot. I am considering paying for the soil survey out of my own pocket before the final purchase to know what to expect, but I probably still have to wait for the survey. (newly developed area)

You will hardly want to build the single-family house on foundations hanging on one side in the air; so a considerable amount of fill is necessary. Costs of around EUR 15,000 can easily arise here.

Yes, unfortunately I realized that the initially mentioned 3000-4000€ were probably just bait to get a contract with an item: "earthworks as incurred". Still the technical question: Can a slab foundation simply be placed on a ring of shuttering blocks standing on a foundation in the natural soil and then fill this "empty space" later with earth to, for example, create a terrace?

If the soil conditions are now critical and it’s not just a matter of gravel but a soil replacement is necessary, the EUR 15,000 can easily become EUR 20,000 or 25,000. Therefore, the option “it is worth considering a basement here” is not far-fetched.

This is called "foundation additional costs"; an appropriate reserve should always be set aside in the ancillary construction costs for this item, especially for uneven plots and hillside locations.

Rhenish regards

Well then, I hope that no worse soil conditions will come to light.

Thank you, MausJ