ᐅ Building a Prefabricated House on an Existing Basement/Foundation?
Created on: 7 May 2017 23:02
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BartJSimpson
Good evening,
we have purchased a plot of land in a residential area that includes a 50-year-old prefabricated house with an existing basement. Renovating the house is not worthwhile, but if possible, we would like to keep the basement and then build the new prefabricated single-family house on top of it.
However, the footprint of the existing basement is smaller than that of the prefabricated house we want:
Dimensions of the existing basement (floor plan in the attached file):
10.82 m x 8.58 m (35 ft 6 in x 28 ft 2 in), but with an offset, meaning 4.5 m (15 ft) of the width extends 1.20 m (4 ft) at the front, and the remaining approx. 6.3 m (21 ft) of the width extends 1.20 m (4 ft) at the back.
There is also an additional load-bearing wall in the middle across the entire width of the basement.
Dimensions of the prefabricated house:
12.35 m x 9.10 m (40 ft 6 in x 29 ft 10 in)
+ 4.61 m x 1.20 m (15 ft 1 in x 4 ft) (flat-roofed bay)
A direct connection between the basement and the house is not essential for us, as the basement has an external staircase and is primarily intended to be used as storage space.
Is it possible to fully thermally separate the basement and the prefabricated house and possibly place a slab foundation on top of the basement without structural issues?
What costs should we expect at a minimum, assuming the basement is still very load-bearing and the ground conditions are favorable?
Is this approach worthwhile at all, or would it generally be better to build a new basement from scratch?
Of course, any additional suggestions or advice are very welcome.
Best regards,
Dirk
we have purchased a plot of land in a residential area that includes a 50-year-old prefabricated house with an existing basement. Renovating the house is not worthwhile, but if possible, we would like to keep the basement and then build the new prefabricated single-family house on top of it.
However, the footprint of the existing basement is smaller than that of the prefabricated house we want:
Dimensions of the existing basement (floor plan in the attached file):
10.82 m x 8.58 m (35 ft 6 in x 28 ft 2 in), but with an offset, meaning 4.5 m (15 ft) of the width extends 1.20 m (4 ft) at the front, and the remaining approx. 6.3 m (21 ft) of the width extends 1.20 m (4 ft) at the back.
There is also an additional load-bearing wall in the middle across the entire width of the basement.
Dimensions of the prefabricated house:
12.35 m x 9.10 m (40 ft 6 in x 29 ft 10 in)
+ 4.61 m x 1.20 m (15 ft 1 in x 4 ft) (flat-roofed bay)
A direct connection between the basement and the house is not essential for us, as the basement has an external staircase and is primarily intended to be used as storage space.
Is it possible to fully thermally separate the basement and the prefabricated house and possibly place a slab foundation on top of the basement without structural issues?
What costs should we expect at a minimum, assuming the basement is still very load-bearing and the ground conditions are favorable?
Is this approach worthwhile at all, or would it generally be better to build a new basement from scratch?
Of course, any additional suggestions or advice are very welcome.
Best regards,
Dirk
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BartJSimpson9 May 2017 11:23@11ant:
Thank you very much for your effort and good suggestions.
Unfortunately, the basement is only 8.58 meters (28 feet) deep. Multiplied by the width of the new prefabricated house (12.35 meters (41 feet)), this results in a floor area of 105.96 square meters (1,140 square feet). In comparison, the prefabricated house actually has the following dimensions: 12.35 meters (41 feet) x 9.10 meters (30 feet) plus 4.61 meters (15 feet) x 1.20 meters (4 feet) = 117.92 square meters (1,270 square feet), which is already 12 square meters (130 square feet) more floor area. But I can ask the prefab house supplier if the house can also be wider.
It might also be possible to omit the basement windows on the street side and, by adding additional foundation, gain more square meters.
Has anyone here had experience with how flexible the floor plans of prefabricated houses can be and what kind of additional costs this might involve?
Thank you very much for your effort and good suggestions.
Unfortunately, the basement is only 8.58 meters (28 feet) deep. Multiplied by the width of the new prefabricated house (12.35 meters (41 feet)), this results in a floor area of 105.96 square meters (1,140 square feet). In comparison, the prefabricated house actually has the following dimensions: 12.35 meters (41 feet) x 9.10 meters (30 feet) plus 4.61 meters (15 feet) x 1.20 meters (4 feet) = 117.92 square meters (1,270 square feet), which is already 12 square meters (130 square feet) more floor area. But I can ask the prefab house supplier if the house can also be wider.
It might also be possible to omit the basement windows on the street side and, by adding additional foundation, gain more square meters.
Has anyone here had experience with how flexible the floor plans of prefabricated houses can be and what kind of additional costs this might involve?
Prefabricated houses today are no longer like those from earlier times when the basement had to be adapted to fit under the house, and internal layouts could only be changed in fixed increments (usually five-eighths of a meter). Nowadays, they can be adjusted in centimeters. Custom designs are currently the third most common; in second place are standard plans with minor modifications; and first place goes to standard plans altered in width and depth, roof pitch, room assignments, staircase position, and internal wall layouts. The unchanged standard plan is the least common.
Costs vary depending on the provider. Low-cost suppliers—of which Gussek Haus is not one—often offer tempting base prices with substantial additional fees.
However, to justify the effort of redesigning and compensate for the "free" basement, you would need to change more than four pages.
I see the current state and desired outcome coming together much more easily than you do. It’s just routine.
Expanding in one dimension involves very little effort.
I don’t share your concerns about reducing room size; the floor plan would likely lose no more than minor details, and much can be compensated for even when adjusting in only one dimension.
As mentioned: upload the plot and excerpt of the development plan, then we can take a closer look.
Just for fun: which manufacturer built the existing house? Also, please share some exterior photos.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Costs vary depending on the provider. Low-cost suppliers—of which Gussek Haus is not one—often offer tempting base prices with substantial additional fees.
However, to justify the effort of redesigning and compensate for the "free" basement, you would need to change more than four pages.
I see the current state and desired outcome coming together much more easily than you do. It’s just routine.
Expanding in one dimension involves very little effort.
I don’t share your concerns about reducing room size; the floor plan would likely lose no more than minor details, and much can be compensated for even when adjusting in only one dimension.
As mentioned: upload the plot and excerpt of the development plan, then we can take a closer look.
Just for fun: which manufacturer built the existing house? Also, please share some exterior photos.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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BartJSimpson9 May 2017 23:39I have now also tried a version with new foundations on two sides. Hopefully, a prefab house manufacturer would still accept something like this. However, the roof pitch would probably need to be adjusted significantly, since the section of the house to the left of the bay window is now 9.80 meters (32 feet) deep instead of 9.10 meters (30 feet).
BartJSimpson schrieb:
I’ve now also tried a version with new foundations on two sides.The difference from my proposal is that the notch at the bottom left of the plan is bridged, which affects the laundry cellar and the tank cellar and their light wells.
If you want to do it this way, I would recommend demolishing both of their front walls and extending the foundation continuously here; then only keep the cellar wall on the left side of the plan and butt it on the outside.
The deviation from the original floor plan of "Kiefernallee/V1" is smaller in your version.
BartJSimpson schrieb:
Hopefully, something like this should still be accepted by the prefabricated house supplier.You will be surprised how little trouble these changes will cause the manufacturer. Varying their standard types is their daily routine.
You think you want something complicated, but in reality, they already have that ready to go. After all, this isn’t a rarely requested base model—something like this has already been modified for someone before.
BartJSimpson schrieb:
However, the roof pitch would probably need to be adjusted significantly, since the left part of the house by the bay window now has a depth of 9.80m (32 feet 2 inches) instead of 9.10m (29 feet 10 inches).That may be true (and it wouldn’t be a big problem), but it might also be resolved during the attic remodeling. A major adjustment likely won’t be necessary. This can probably be solved just by altering the knee wall. We’ll see as the redesign progresses.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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BartJSimpson10 May 2017 22:43Here is a new layout option with the bathroom moved to “save” the staircase to the basement. With a proper steel door leading to the basement, a thermal separation should still be possible, right?
The utility room is eliminated in this design, but there is plenty of space in the basement anyway. The washing machine and dryer shown on the ground floor will probably be moved to the basement as well.
There is still plenty of space on the lot to the left and rear sides. So the floor plan could be adjusted in those directions. To the right, however, there is no more space; the required setback from the neighboring property (about 3 m (10 feet); I still need to check this exactly) is just met.
By the way, the old prefabricated house was built by Gebrüder Steger AG. However, this company seems to have been out of business for quite some time; there is nothing to be found online anymore.
The utility room is eliminated in this design, but there is plenty of space in the basement anyway. The washing machine and dryer shown on the ground floor will probably be moved to the basement as well.
There is still plenty of space on the lot to the left and rear sides. So the floor plan could be adjusted in those directions. To the right, however, there is no more space; the required setback from the neighboring property (about 3 m (10 feet); I still need to check this exactly) is just met.
By the way, the old prefabricated house was built by Gebrüder Steger AG. However, this company seems to have been out of business for quite some time; there is nothing to be found online anymore.
Whether the dryer goes in the basement, of course, depends on the internal laundry chute. Carrying laundry around the house won’t be very convenient.
As I said, set up the plot first, including the zoning plan / building permit. Available space on the plot and space within the building envelope are not necessarily the same. Are there any existing outbuildings (garage) on the property (and in the plan)?
Never heard of them before. Where were they supposed to be from? I can’t find them even among the dissolved companies (?) — but that’s not really important.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
BartJSimpson schrieb:
There is still plenty of space to the left and at the back of the plot. So the floor plan could be adjusted in those two directions.
As I said, set up the plot first, including the zoning plan / building permit. Available space on the plot and space within the building envelope are not necessarily the same. Are there any existing outbuildings (garage) on the property (and in the plan)?
BartJSimpson schrieb:
By the way, the old prefabricated house comes from Gebrüder Steger AG.
Never heard of them before. Where were they supposed to be from? I can’t find them even among the dissolved companies (?) — but that’s not really important.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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