Hello everyone!
This is my first post since we started planning to become homeowners.
It’s about the cost estimation—specifically for our earthworks. Here’s what we know about the plot:
- It is 374 sqm (4029 sq ft) in size
- The house has external dimensions of 9.27 m x 11.07 m (30.4 ft x 36.3 ft) and will be built without a basement on a concrete slab
- A garage and a parking space in front of it are planned
- Currently, there is a height difference of 1.30 m (4.3 ft) between the ground level and the underside of the slab, so about 90 cm (35 in) to the bottom edge of the slab
- Our builder will supply 40 cm (16 in) of capillary-breaking material for backfilling (free of charge or included in the house price)
- According to the soil report for the building site (attached, starting on page 33 Baufeld WA 4a*), an average of 40 cm (16 in) of topsoil has to be excavated
- If I understand the above report correctly, no soil replacement is necessary
I wanted to ask for a realistic estimate of the costs involved (excluding utility connections, which I will calculate separately). We are currently estimating around 30,000 euros. Online, I find anywhere between 5,000 and 80,000 euros, which doesn’t really help. The soil conditions are probably not ideal due to the significant amount of fill material.
Looking forward to your advice, and thanks in advance to everyone involved!
This is my first post since we started planning to become homeowners.
It’s about the cost estimation—specifically for our earthworks. Here’s what we know about the plot:
- It is 374 sqm (4029 sq ft) in size
- The house has external dimensions of 9.27 m x 11.07 m (30.4 ft x 36.3 ft) and will be built without a basement on a concrete slab
- A garage and a parking space in front of it are planned
- Currently, there is a height difference of 1.30 m (4.3 ft) between the ground level and the underside of the slab, so about 90 cm (35 in) to the bottom edge of the slab
- Our builder will supply 40 cm (16 in) of capillary-breaking material for backfilling (free of charge or included in the house price)
- According to the soil report for the building site (attached, starting on page 33 Baufeld WA 4a*), an average of 40 cm (16 in) of topsoil has to be excavated
- If I understand the above report correctly, no soil replacement is necessary
I wanted to ask for a realistic estimate of the costs involved (excluding utility connections, which I will calculate separately). We are currently estimating around 30,000 euros. Online, I find anywhere between 5,000 and 80,000 euros, which doesn’t really help. The soil conditions are probably not ideal due to the significant amount of fill material.
Looking forward to your advice, and thanks in advance to everyone involved!
H
Hafenstraße11 Mar 2022 12:19Hello Pinkiponk! Thanks for your detailed response, and sorry for my late reply...
A lot has happened on our end since then. So much, in fact, that I would immediately accept your 15,000 euro estimate. Specifically, we now have a soil report for our building plot. One of the many boreholes was drilled directly next to our property (I know this doesn’t necessarily say much about our exact building ground, but it serves as a reference).
Currently, the difference between the minimum finished floor level (OKFmin) and the existing ground level is 1.30 meters (4.3 feet). The soil consists of 30 cm (12 inches) of topsoil, which needs to be removed. Another 50 cm (20 inches) contains root residues, after which only “medium firm” and “stiff” layers remain, which are suitable for building (?). After consulting with the expert, at least the top 80 cm (32 inches) must be removed and replaced (this is called soil replacement, right?), and the foundation is planned as strip foundations. With the 1.30-meter (4.3 feet) site elevation (minus 40 cm (16 inches) slab thickness, so "only" 90 cm (35 inches)), I would therefore need to fill 1.7 meters (5.6 feet) of Z0 gravel/crushed stone (groundwater protection zone, no RCL). Is that correct, assuming the report applies to our plot?
So I would need 1.7 meters (5.6 feet) × 120 m² (1,292 ft²) = 204 m³ (7,200 ft³) of Z0 fill material? Additionally, for the remaining 255 m² (2,745 ft²) of our lot, a raising of 1.30 meters (4.3 feet), for which parts of the topsoil can be used.
Our architect, who unfortunately turned out to be quite uncommitted early on, just said: “Let it unfold, you can’t really say or calculate all of that at this stage.” Please, dear readers, seriously: We are budgeting around 25,000 euros for the earthworks; 5,000 euros more is annoying, but not a “big” problem. But: Could this become a money pit? What might such soil replacement cost, the “special” Z0 material for the groundwater protection area, and the additional strip foundation? Or am I completely overreacting? Don’t get me wrong—I don’t want a price quoted down to the last euro, just an honest assessment from people who aren’t my architect.
We are building on a concrete slab, without a basement, in the southern part of Duisburg.
Thanks for reading and for your assessment.
A lot has happened on our end since then. So much, in fact, that I would immediately accept your 15,000 euro estimate. Specifically, we now have a soil report for our building plot. One of the many boreholes was drilled directly next to our property (I know this doesn’t necessarily say much about our exact building ground, but it serves as a reference).
Currently, the difference between the minimum finished floor level (OKFmin) and the existing ground level is 1.30 meters (4.3 feet). The soil consists of 30 cm (12 inches) of topsoil, which needs to be removed. Another 50 cm (20 inches) contains root residues, after which only “medium firm” and “stiff” layers remain, which are suitable for building (?). After consulting with the expert, at least the top 80 cm (32 inches) must be removed and replaced (this is called soil replacement, right?), and the foundation is planned as strip foundations. With the 1.30-meter (4.3 feet) site elevation (minus 40 cm (16 inches) slab thickness, so "only" 90 cm (35 inches)), I would therefore need to fill 1.7 meters (5.6 feet) of Z0 gravel/crushed stone (groundwater protection zone, no RCL). Is that correct, assuming the report applies to our plot?
So I would need 1.7 meters (5.6 feet) × 120 m² (1,292 ft²) = 204 m³ (7,200 ft³) of Z0 fill material? Additionally, for the remaining 255 m² (2,745 ft²) of our lot, a raising of 1.30 meters (4.3 feet), for which parts of the topsoil can be used.
Our architect, who unfortunately turned out to be quite uncommitted early on, just said: “Let it unfold, you can’t really say or calculate all of that at this stage.” Please, dear readers, seriously: We are budgeting around 25,000 euros for the earthworks; 5,000 euros more is annoying, but not a “big” problem. But: Could this become a money pit? What might such soil replacement cost, the “special” Z0 material for the groundwater protection area, and the additional strip foundation? Or am I completely overreacting? Don’t get me wrong—I don’t want a price quoted down to the last euro, just an honest assessment from people who aren’t my architect.
We are building on a concrete slab, without a basement, in the southern part of Duisburg.
Thanks for reading and for your assessment.
H
Hafenstraße11 Mar 2022 12:45I would like to add the following: The purchase agreement for the land (seller: City of Duisburg) explicitly states that additional foundation work is to be expected and the buyer is aware of this at the time of signing. In other words, the city disclaims liability, and I am responsible for all necessary work that must be done before I can start building...
K
karl.jonas11 Mar 2022 18:17Are you allowed to build a basement? Maybe just a crawl space? Would you have a maximum limit on the additional costs (far from a money pit)? Is there an obligation to backfill the remaining ground with soil?
P
Pinkiponk11 Mar 2022 18:26Hafenstraße schrieb:
Hello Pinkiponk!
Thank you for your detailed response and sorry for my late reply... No need to apologize, it’s clear that you have a lot going on right now. 🙂
Hafenstraße schrieb:
... Unfortunately, I can’t comment competently on the other figures and questions. Maybe except for what concerns the strip foundation. I don’t know the technical details, but for our current house construction, they initially talked about a strip foundation and then the builder switched to a full slab foundation. I don’t know the reasons for this change; I lack the experience. This did result in a credit of around 5,000 euros from the builder, while the site excavation contractor charged about 15,000 euros more. That would be positive for you. I’m not familiar with all the details, but in the comparison between strip foundation and slab foundation, it seems that with strip foundations you save more on earthworks than the other way around.
Regarding your elevation data, I’m afraid I’m a bit slow to understand; I don’t even get it for our own plot. ;-)
G
gtgeorge7911 Mar 2022 19:38Hafenstraße schrieb:
I would like to add the following: The purchase contract for the plot (seller: City of Duisburg) explicitly states that additional foundation work should be expected and that the buyer is aware of this at the time of signing. So essentially, the city disclaims responsibility, meaning I am liable for any extra work needed before I can start building...Hello Hafenstraße, I have approximately 250 m3 (330 cubic yards) of Z 0 soil available. The plot is very close to yours. You can reach me at gtgeorge79@gmx.de. Unfortunately, I cannot send you a private message.H
Hafenstraße14 Mar 2022 11:19Hello gtgeorge79, hello to everyone else!
Great offer, thank you very much! Unfortunately, I can’t commit right now since we are currently ordering the surveyor. I think our civil engineering work will only start in the summer, even though it’s really frustrating not to be able to accept such an offer immediately...
I have meanwhile received additional information from the geotechnical engineer. Perhaps you could help me understand some of the terms used:
"As already explained during the phone call last week, the foundation risk is already minimized with a load-bearing slab foundation.
1. QUESTION: Is a slab foundation always load-bearing?? Mine is from Weberhaus (Weberith), will be 20 cm (8 inches) thick, has 15 kg (33 lbs) of reinforcement per square meter, 120 mm (5 inches) perimeter insulation, and frost protection strips (80 x 40 cm / 31 x 16 inches).
Due to a build-up of about 90 cm (36 inches) above the current ground level, the need for any further soil replacement is eliminated.
2. QUESTION: Is that really the case? Does silty (= poor) soil not have to be removed if I just add the good gravel I need for raising the ground level on top?
The topsoil must definitely be removed beforehand and can be reused later in green areas or gardens. After removing the topsoil, the ground can be raised on the existing surface.
3. QUESTION: See question 2. Removing the topsoil is clear, but then the ground raise can take place on the silty soil (partly described as stiff, partly as medium dense) without me needing to excavate a proper building pit (except for the topsoil)?
Before placing the fill material, a geotextile should be installed to prevent the fill material from sinking into the cohesive soil.
4. QUESTION: See questions 2 and 3. So the cohesive (= poor) soil will actually stay in place and does not need to be replaced?
5. QUESTION: What costs does a geotextile typically cause?
It is especially important during construction not to unnecessarily disturb the soil structure mechanically, meaning it should be driven over as little as possible. Furthermore, the exposed subgrade, where the fill will be placed, should be protected from moisture or water penetration as much as possible. The lowest layer of the fill should only be statically compacted to avoid activating capillary-bound water.
6. QUESTION: What does “statically compacted” mean?
Overall, this reply sounds very reassuring to me. I would like to remind you of my original concern that probably every builder faces at some point. We are budgeting 30,000 euros for earthworks including the soil investigation. In your opinion, could this still end up being 50,000, 60,000 euros or more? Or can I put this worry aside for now? I understand there is no legally binding advice here. I am not looking for that! But perhaps someone has built on a similar plot and knows how much or how little effort this will mean, especially financially, based on the points mentioned above...
Wishing you all a great start to the week!
Great offer, thank you very much! Unfortunately, I can’t commit right now since we are currently ordering the surveyor. I think our civil engineering work will only start in the summer, even though it’s really frustrating not to be able to accept such an offer immediately...
I have meanwhile received additional information from the geotechnical engineer. Perhaps you could help me understand some of the terms used:
"As already explained during the phone call last week, the foundation risk is already minimized with a load-bearing slab foundation.
1. QUESTION: Is a slab foundation always load-bearing?? Mine is from Weberhaus (Weberith), will be 20 cm (8 inches) thick, has 15 kg (33 lbs) of reinforcement per square meter, 120 mm (5 inches) perimeter insulation, and frost protection strips (80 x 40 cm / 31 x 16 inches).
Due to a build-up of about 90 cm (36 inches) above the current ground level, the need for any further soil replacement is eliminated.
2. QUESTION: Is that really the case? Does silty (= poor) soil not have to be removed if I just add the good gravel I need for raising the ground level on top?
The topsoil must definitely be removed beforehand and can be reused later in green areas or gardens. After removing the topsoil, the ground can be raised on the existing surface.
3. QUESTION: See question 2. Removing the topsoil is clear, but then the ground raise can take place on the silty soil (partly described as stiff, partly as medium dense) without me needing to excavate a proper building pit (except for the topsoil)?
Before placing the fill material, a geotextile should be installed to prevent the fill material from sinking into the cohesive soil.
4. QUESTION: See questions 2 and 3. So the cohesive (= poor) soil will actually stay in place and does not need to be replaced?
5. QUESTION: What costs does a geotextile typically cause?
It is especially important during construction not to unnecessarily disturb the soil structure mechanically, meaning it should be driven over as little as possible. Furthermore, the exposed subgrade, where the fill will be placed, should be protected from moisture or water penetration as much as possible. The lowest layer of the fill should only be statically compacted to avoid activating capillary-bound water.
6. QUESTION: What does “statically compacted” mean?
Overall, this reply sounds very reassuring to me. I would like to remind you of my original concern that probably every builder faces at some point. We are budgeting 30,000 euros for earthworks including the soil investigation. In your opinion, could this still end up being 50,000, 60,000 euros or more? Or can I put this worry aside for now? I understand there is no legally binding advice here. I am not looking for that! But perhaps someone has built on a similar plot and knows how much or how little effort this will mean, especially financially, based on the points mentioned above...
Wishing you all a great start to the week!
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