ᐅ Increased foundation work due to a 12% sloping site descending from the road
Created on: 15 Dec 2013 21:01
M
MausJHello dear experts,
we are currently planning the construction of a single-family house with about 120m² (1,292 sq ft) of living space and a footprint of approximately 9x9m (29.5x29.5 ft) without a basement, as we do not need the space and want to save costs. The plot currently reserved slopes away from the street with about 12-13% longitudinal gradient and approximately 6% cross slope dropping from left to right. The building area starts 3m (10 ft) from the street edge. Therefore, the left front corner would need to be raised by about 40 cm (16 inches) relative to the current ground level to avoid being below street level. The rear right corner would then be about 150 cm (59 inches) above the ground level there.
The opinions from potential builders vary from: "No problem, just place a few concrete blocks on the strip foundations and build up the walls, then put the slab on top for an additional 3,000-4,000€" to "We’ll add several hundred tons of frost protection material and compact it for an extra 8,000-10,000€" to "Oh, that’s difficult, actually a basement is necessary, which would cost an additional 25,000-35,000€"—all compared to a planned foundation on level ground with a slab.
I would like to trust the provider with the lowest price but suspect there might be a catch, and “unexpected” difficulties could arise during construction.
Therefore, my questions are: Based on your experience, do you have any recommendations on what would be advisable here or what will probably not work? What costs are realistic? What problems could still come up that would cause additional expenses?
Thank you for your advice,
MausJ
we are currently planning the construction of a single-family house with about 120m² (1,292 sq ft) of living space and a footprint of approximately 9x9m (29.5x29.5 ft) without a basement, as we do not need the space and want to save costs. The plot currently reserved slopes away from the street with about 12-13% longitudinal gradient and approximately 6% cross slope dropping from left to right. The building area starts 3m (10 ft) from the street edge. Therefore, the left front corner would need to be raised by about 40 cm (16 inches) relative to the current ground level to avoid being below street level. The rear right corner would then be about 150 cm (59 inches) above the ground level there.
The opinions from potential builders vary from: "No problem, just place a few concrete blocks on the strip foundations and build up the walls, then put the slab on top for an additional 3,000-4,000€" to "We’ll add several hundred tons of frost protection material and compact it for an extra 8,000-10,000€" to "Oh, that’s difficult, actually a basement is necessary, which would cost an additional 25,000-35,000€"—all compared to a planned foundation on level ground with a slab.
I would like to trust the provider with the lowest price but suspect there might be a catch, and “unexpected” difficulties could arise during construction.
Therefore, my questions are: Based on your experience, do you have any recommendations on what would be advisable here or what will probably not work? What costs are realistic? What problems could still come up that would cause additional expenses?
Thank you for your advice,
MausJ
Hi,
we also raised our house by 50cm (20 inches) because otherwise it would have been located in a low spot on the property. The house is built on a concrete slab, and the raising was simply done by adding a layer of (what was it again :confused concrete recycling (??)). In any case, it was relatively straightforward—though not really a hillside location. So, no idea about the structural engineering aspects.
I think the soil composition plays an important role here. Our soil is all clay, which is quite firm and suitable for foundations. It’s probably different in your case. The best thing is to ask the local construction company that has built in your area before. They usually know the soil conditions well and can advise what’s best for you.
we also raised our house by 50cm (20 inches) because otherwise it would have been located in a low spot on the property. The house is built on a concrete slab, and the raising was simply done by adding a layer of (what was it again :confused concrete recycling (??)). In any case, it was relatively straightforward—though not really a hillside location. So, no idea about the structural engineering aspects.
I think the soil composition plays an important role here. Our soil is all clay, which is quite firm and suitable for foundations. It’s probably different in your case. The best thing is to ask the local construction company that has built in your area before. They usually know the soil conditions well and can advise what’s best for you.
B
Bauexperte16 Dec 2013 10:49Hello,
You will hardly want to build the single-family house on foundations that are supported on only one side and suspended in the air; therefore, a significant amount of fill is necessary. Costs in the range of around 15,000€ can easily arise.
If the soil conditions are also challenging and it’s not just a matter of gravel, but a soil replacement is required, then costs of 20,000€ to 25,000€ or more can quickly accumulate. In this respect, the option “it’s worth considering a basement here” is not unrealistic.
This whole issue is called "additional foundation costs"; for this item, an appropriate contingency should always be reserved in the additional construction costs, especially for uneven plots and sloped sites.
Best regards, Bauexperte
MausJ schrieb:This question cannot really be answered for two reasons. First, we don’t know your plot of land, and second, the soil report is probably not yet available.
The front left corner would need to be raised by about 40cm (16 inches) compared to the current ground level to avoid being below the road. The rear right corner would then be roughly 150cm (59 inches) above the local ground level.
The opinions from potential builders range from: "No problem, just place a few concrete blocks on the strip foundations and build up walls, then pour the slab on top for an additional cost of 3000–4000€" to "We’ll put in a few hundred tons of frost protection material and compact it, adding 8000–10000€ in costs" up to "Oh, that’s difficult; a basement would actually be necessary, costing an extra 25000–35000€," all compared to a planned foundation on flat ground with a slab."
You will hardly want to build the single-family house on foundations that are supported on only one side and suspended in the air; therefore, a significant amount of fill is necessary. Costs in the range of around 15,000€ can easily arise.
If the soil conditions are also challenging and it’s not just a matter of gravel, but a soil replacement is required, then costs of 20,000€ to 25,000€ or more can quickly accumulate. In this respect, the option “it’s worth considering a basement here” is not unrealistic.
This whole issue is called "additional foundation costs"; for this item, an appropriate contingency should always be reserved in the additional construction costs, especially for uneven plots and sloped sites.
Best regards, Bauexperte
First of all, thank you for the feedback.
So far, I only have a general geotechnical report for the whole development area and have spoken with neighbors from the adjacent section of the new development. But that doesn’t help me much regarding the specific plot. I’m considering paying for the geotechnical report myself before the final purchase to know what I’m getting into, but I probably have to wait for the land survey first. (newly developed area)
Yes, unfortunately I realized that the initially mentioned 3,000–4,000 EUR (about 3,200–4,300 USD) was probably just a sales pitch to get a contract, listed under a vague item like “earthworks based on effort.” Still, the technical question: Can you simply place a concrete slab on a ring of shuttering blocks sitting on a foundation on undisturbed soil and then later fill in the “empty space” with soil to create, for example, a terrace?
Well, I hope that no serious soil problems will arise.
Thanks, MausJ
Bauexperte schrieb:
Hello,
This question really cannot be answered for two reasons. On the one hand, we don’t know your plot of land, and on the other hand, the geotechnical report is most likely not available yet.
So far, I only have a general geotechnical report for the whole development area and have spoken with neighbors from the adjacent section of the new development. But that doesn’t help me much regarding the specific plot. I’m considering paying for the geotechnical report myself before the final purchase to know what I’m getting into, but I probably have to wait for the land survey first. (newly developed area)
Bauexperte schrieb:
You will hardly want to build the single-family house on foundations that are hanging in the air on just one side; so a significant amount of fill will be necessary. Costs around 15,000 EUR (about 16,000 USD) can easily be expected here.
Yes, unfortunately I realized that the initially mentioned 3,000–4,000 EUR (about 3,200–4,300 USD) was probably just a sales pitch to get a contract, listed under a vague item like “earthworks based on effort.” Still, the technical question: Can you simply place a concrete slab on a ring of shuttering blocks sitting on a foundation on undisturbed soil and then later fill in the “empty space” with soil to create, for example, a terrace?
Bauexperte schrieb:
If the soil conditions are critical and it’s not just a matter of gravel, but a soil replacement is necessary, costs of 20,000 to 25,000 EUR (about 21,500 to 27,000 USD) are common. Therefore, the option “it may be worthwhile to consider a basement here” is not off the mark.
This is called “additional foundation costs”; for this item, a corresponding reserve should always be included in the ancillary building costs, especially for uneven plots and sloped sites.
Regards, Bauexperte
Well, I hope that no serious soil problems will arise.
Thanks, MausJ
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