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ckcool198411 Mar 2021 16:36Hello everyone,
we are currently planning an extension and renovation of our small detached house (built in 1938). I need advice regarding a potentially necessary underpinning.
The existing house has one and a half stories and a partial basement. The current (former coal) cellar has a clear height of 1.85 m (6 feet). The house base at the cellar is approximately 2.10 m (7 feet) deep. The part of the building without a basement has a strip foundation at a depth of about 80 cm (2.6 feet).
The extension is planned on the southern gable side of the house, measuring 10 x 5 m (33 x 16 feet), and would be placed partly on the cellar and partly on the non-basement section. Now my questions:
- If the extension is not basemented, is underpinning of the existing building still necessary when the extension is built with a strip foundation or a slab foundation?
- If the extension includes a basement (with a foundation footing about 2.40 m (8 feet) deep), as I understand, underpinning is definitely required. If this is done with masonry or concrete, does it have to be carried out in sections? Are there any current cost indications (per linear meter)? How much would the underpinning extend the construction time? Are there any experiences or estimates?
Thank you very much!
we are currently planning an extension and renovation of our small detached house (built in 1938). I need advice regarding a potentially necessary underpinning.
The existing house has one and a half stories and a partial basement. The current (former coal) cellar has a clear height of 1.85 m (6 feet). The house base at the cellar is approximately 2.10 m (7 feet) deep. The part of the building without a basement has a strip foundation at a depth of about 80 cm (2.6 feet).
The extension is planned on the southern gable side of the house, measuring 10 x 5 m (33 x 16 feet), and would be placed partly on the cellar and partly on the non-basement section. Now my questions:
- If the extension is not basemented, is underpinning of the existing building still necessary when the extension is built with a strip foundation or a slab foundation?
- If the extension includes a basement (with a foundation footing about 2.40 m (8 feet) deep), as I understand, underpinning is definitely required. If this is done with masonry or concrete, does it have to be carried out in sections? Are there any current cost indications (per linear meter)? How much would the underpinning extend the construction time? Are there any experiences or estimates?
Thank you very much!
A specialist (e.g., a structural engineer) should take a look at this. Only they can tell you how to carry out your project safely.
You probably don’t need underpinning, as old basements and houses were often built very solidly and can therefore support the loads from a strip foundation or the slab of the extension.
With the information provided here, the question cannot be answered with certainty.
You probably don’t need underpinning, as old basements and houses were often built very solidly and can therefore support the loads from a strip foundation or the slab of the extension.
With the information provided here, the question cannot be answered with certainty.
We are not familiar with your existing floor plan or the topography of your plot. A house built in 1938 will likely have a basement with brick or concrete walls roughly 38 cm (15 inches) or 40 cm (16 inches) thick, and usually a cast-in-place concrete slab.
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ckcool198411 Mar 2021 19:49Thank you for your quick responses! My main concern is to avoid extending the construction period by several weeks or months due to the installation of underpinning at the existing building. The gable side of the existing house is about 9m (30 feet) long, so in my opinion, the underpinning would need to be done in four phases. Considering the curing times of the concrete, this adds up. We do not necessarily need a basement under the extension because of the existing cellar, but it would be a nice-to-have in case the entire gable side must be underpinned anyway, as the excavation would then already be necessary and constructing a basement would not require much additional effort.
Correct, 38 cm (15 inch) exterior walls (including cellar walls and strip foundation of the existing non-basement building). The site is level (i.e., no slope) and the soil is sandy. Groundwater is at a depth of 6m (20 feet).
How would the connection between the extension’s foundation and the existing foundation be constructed without a basement in the extension? Would the foundations under the corners of the existing house be stepped down and then only the corners be underpinned as an "extension" of the foundation for the addition?
11ant schrieb:
A house built in 1938 will typically have a cellar with 38 cm (15 inch) thick masonry or 40 cm (16 inch) thick concrete walls, and usually a cast-in-place concrete slab.
Correct, 38 cm (15 inch) exterior walls (including cellar walls and strip foundation of the existing non-basement building). The site is level (i.e., no slope) and the soil is sandy. Groundwater is at a depth of 6m (20 feet).
icandoit schrieb:
You probably do not need underpinning since old cellars and houses were often built very solidly and can therefore bear the loads of a strip foundation or slab for the extension.
How would the connection between the extension’s foundation and the existing foundation be constructed without a basement in the extension? Would the foundations under the corners of the existing house be stepped down and then only the corners be underpinned as an "extension" of the foundation for the addition?
ckcool1984 schrieb:
Correct, 38cm (15 inches) exterior walls (including basement walls and strip foundation of the non-basement existing building).Why include the basement? I would have expected only the basement—the reference is to a one-and-a-half-story house. At that time, 25cm (10 inches) walls were still common for the ground floor and upper floor/attic.https://www.instagram.com/11antgmxde/
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ckcool198411 Mar 2021 19:58Our exterior walls on the ground floor as well as in the basement are made of 38cm (15 inches) thick brick walls.
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