ᐅ Designing a Sloped Building Site – Earthworks and Retaining Wall Cost Options
Created on: 28 Apr 2022 09:27
K
Kamikatzekeepe
Hello everyone,
after reading here in the forum for a long time, I would now like to share my concerns.
We have purchased a 600m2 (about 6500 sq ft) sloping plot in a new development area and are currently in final negotiations with a prefab house provider. However, I realize that the plot is not easy to design, so ideally the plot and garden planning should be considered from the very beginning.
I would be interested to hear your thoughts on our concept and how you would proceed.
I have attached two pictures of the plot (one from the bottom, one from above) and one visualization with rough height details for the plot planning.
1. The plot is 600m2 (about 6500 sq ft) and roughly square with 25x25m (82x82 ft). It slopes about 4m (13 ft) from west (street side) to east and about 1.5m (5 ft) from north to south.
2. The gable roof house will be 9x10m (2 floors) with 140m2 (1500 sq ft) plus a full basement. The basement is half exposed on the west side (street side), and those rooms will be used as living spaces.
3. The house should be positioned towards the northeast side to maximize garden space on the south and west sides.
4. The main entrance will also be on the north side, as we do not want to enter the house through the basement. Therefore, the north side will have a driveway with a carport in front of the entrance.
5. The single-family house is defined according to the development plan. If the lowest point of the plot is set to 0m (northwest), the house will be at about 3m (10 ft) in height.
6. If I subtract 50cm (20 inches) for the ceiling thickness, 30cm (12 inches) for the gap between ceiling and the top edge of the window, 90cm (35 inches) for window height, and another 30cm (12 inches) between the floor and bottom edge of the window, this results in about 2m (6.5 ft) of basement exposure relative to the house.
7. This means there is a height difference of 2m (6.5 ft) in our garden between the west side (in front of the basement) and the south side (our terrace).
8. I am now wondering whether it makes sense to introduce three levels (as shown in the picture), or to extend the 3m (10 ft) height from the south side to the street, leaving a relatively large 2m (6.5 ft) difference to the rest of the garden. The latter would likely be much cheaper, as we would pay significantly less in disposal fees/earthworks due to less soil filling. However, this would require a higher retaining wall toward the street.
9. According to the development plan, the retaining wall can be a maximum of 80cm (31 inches) high, with a maximum of two walls in a row, spaced 80cm (31 inches) apart. The slope in between can be graded at a ratio of 1:1.5.
10. For a height difference of about 2m (6.5 ft), approximately 1.6m (5 ft) depth with two retaining walls will be needed.
11. The retaining wall on the east side will probably be the most complex, as almost 2m (6.5 ft) height must be retained along its entire length.
Questions:
1. How would you approach this? Does my very rough visualization make sense, or is it not practical?
2. What costs would you expect for the retaining walls (especially on the east side; for the street side it would also be around 1.5m (5 ft) if the height from the south garden to the street is extended)?
3. Would you discuss these issues with the architect of the prefab house company (with whom we have not yet had contact and are still before signing the contract) or directly with a garden and landscaping specialist? I want to avoid addressing the planning too late and then running into problems due to incorrect house positioning.
Thank you!
Best regards,
Florian
after reading here in the forum for a long time, I would now like to share my concerns.
We have purchased a 600m2 (about 6500 sq ft) sloping plot in a new development area and are currently in final negotiations with a prefab house provider. However, I realize that the plot is not easy to design, so ideally the plot and garden planning should be considered from the very beginning.
I would be interested to hear your thoughts on our concept and how you would proceed.
I have attached two pictures of the plot (one from the bottom, one from above) and one visualization with rough height details for the plot planning.
1. The plot is 600m2 (about 6500 sq ft) and roughly square with 25x25m (82x82 ft). It slopes about 4m (13 ft) from west (street side) to east and about 1.5m (5 ft) from north to south.
2. The gable roof house will be 9x10m (2 floors) with 140m2 (1500 sq ft) plus a full basement. The basement is half exposed on the west side (street side), and those rooms will be used as living spaces.
3. The house should be positioned towards the northeast side to maximize garden space on the south and west sides.
4. The main entrance will also be on the north side, as we do not want to enter the house through the basement. Therefore, the north side will have a driveway with a carport in front of the entrance.
5. The single-family house is defined according to the development plan. If the lowest point of the plot is set to 0m (northwest), the house will be at about 3m (10 ft) in height.
6. If I subtract 50cm (20 inches) for the ceiling thickness, 30cm (12 inches) for the gap between ceiling and the top edge of the window, 90cm (35 inches) for window height, and another 30cm (12 inches) between the floor and bottom edge of the window, this results in about 2m (6.5 ft) of basement exposure relative to the house.
7. This means there is a height difference of 2m (6.5 ft) in our garden between the west side (in front of the basement) and the south side (our terrace).
8. I am now wondering whether it makes sense to introduce three levels (as shown in the picture), or to extend the 3m (10 ft) height from the south side to the street, leaving a relatively large 2m (6.5 ft) difference to the rest of the garden. The latter would likely be much cheaper, as we would pay significantly less in disposal fees/earthworks due to less soil filling. However, this would require a higher retaining wall toward the street.
9. According to the development plan, the retaining wall can be a maximum of 80cm (31 inches) high, with a maximum of two walls in a row, spaced 80cm (31 inches) apart. The slope in between can be graded at a ratio of 1:1.5.
10. For a height difference of about 2m (6.5 ft), approximately 1.6m (5 ft) depth with two retaining walls will be needed.
11. The retaining wall on the east side will probably be the most complex, as almost 2m (6.5 ft) height must be retained along its entire length.
Questions:
1. How would you approach this? Does my very rough visualization make sense, or is it not practical?
2. What costs would you expect for the retaining walls (especially on the east side; for the street side it would also be around 1.5m (5 ft) if the height from the south garden to the street is extended)?
3. Would you discuss these issues with the architect of the prefab house company (with whom we have not yet had contact and are still before signing the contract) or directly with a garden and landscaping specialist? I want to avoid addressing the planning too late and then running into problems due to incorrect house positioning.
Thank you!
Best regards,
Florian
W
WilderSueden28 Apr 2022 13:53If I understood the first post correctly, there is no building permit / planning permission yet and no final positioning. So, go ahead with the floor plan ideas 😉
To me, the whole story sounds like "I’m just digging up my old school math memories again to avoid hiring an architect" :-(
It would be best if you could provide the relevant development plan (WITHOUT a link! – for example, in the format "Posemuckel No. 258 in the slanted field") so that experienced readers can review the textual provisions for themselves. Your (naive?) calculation is largely based on the (unverified and possibly incorrect) assumption that the actual finished ground floor height can be treated as identical with zero tolerance to the theoretical standard floor level used for height calculations. Perhaps clarifying this point alone could immediately dispel all concerns.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Kamikatzekeepe schrieb:
5. The single-family house is defined according to the development plan. If the lowest point of the property is standardized to 0m (north/west), the single-family house will be at about 3m (10 feet).
It would be best if you could provide the relevant development plan (WITHOUT a link! – for example, in the format "Posemuckel No. 258 in the slanted field") so that experienced readers can review the textual provisions for themselves. Your (naive?) calculation is largely based on the (unverified and possibly incorrect) assumption that the actual finished ground floor height can be treated as identical with zero tolerance to the theoretical standard floor level used for height calculations. Perhaps clarifying this point alone could immediately dispel all concerns.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
K
Kamikatzekeepe28 Apr 2022 14:36Sorry for any confusion. Did I post in the wrong subforum?
I wasn’t referring to floor plan discussions of the house itself, but rather to the layout of the outdoor areas (which might influence the position of the house) – so I want to consider everything as a whole from the very beginning.
As for the process: We have the plot of land. We don’t have a house yet, nor a building permit/planning permission (naturally).
We have an offer from a prefab house manufacturer, including a basement.
Right now, the main focus is on determining the maximum budget. I’ve already heard a few horror stories from colleagues about the costs of slope stabilization (sometimes well over 100,000).
That’s why I’m already thinking about how the house could be positioned on the plot and how the elevation differences could be managed accordingly (including rough cost estimates for different scenarios).
We will, of course, also have a meeting with an architect. But that will only take place after signing the contract with the house provider for the house itself (a brief preliminary discussion will happen beforehand, but no detailed planning yet).
I’ve already posted the drawing with the building envelope and the single-family house.
Thanks!!
I wasn’t referring to floor plan discussions of the house itself, but rather to the layout of the outdoor areas (which might influence the position of the house) – so I want to consider everything as a whole from the very beginning.
As for the process: We have the plot of land. We don’t have a house yet, nor a building permit/planning permission (naturally).
We have an offer from a prefab house manufacturer, including a basement.
Right now, the main focus is on determining the maximum budget. I’ve already heard a few horror stories from colleagues about the costs of slope stabilization (sometimes well over 100,000).
That’s why I’m already thinking about how the house could be positioned on the plot and how the elevation differences could be managed accordingly (including rough cost estimates for different scenarios).
We will, of course, also have a meeting with an architect. But that will only take place after signing the contract with the house provider for the house itself (a brief preliminary discussion will happen beforehand, but no detailed planning yet).
I’ve already posted the drawing with the building envelope and the single-family house.
Thanks!!
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