ᐅ Street approximately 50 cm higher than the plot – options: raise the ground level or build a basement

Created on: 17 Oct 2020 20:33
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ValeolKB
V
ValeolKB
17 Oct 2020 20:33
Hello dear house building community,
I have been actively reading here for a few months now, and our project is finally starting.

This week we bought a plot of land from the municipality in a new development area (Northern BW).
We chose this particular plot because, unlike the others, it is "flat." (Most of the other plots are on slopes—either south or north facing; we chose the saddle point.)
Details about the plot are below.
Because of the limited ceiling height of 4.1m (13 ft 5 in), we will have knee walls about 1 to 1.2m (3 ft 3 in to 3 ft 11 in) high. Since we opted for a flat plot, we decided to build without a basement, aiming to make the house as large as possible so that the upper floor simply works (160-170 sqm (1722-1830 sq ft) building footprint = 140-150 sqm (1507-1615 sq ft) living space depending on knee wall height), plus a garage or carport with boundary construction.
That was the plan... However, I noticed something while measuring the plot myself with a ruler on the digital survey plan: The planned street is at an elevation of 303.49, which is at least 50cm (20 inches) higher than the plot level.
We have now asked three potential builders (one of whom will hopefully be selected in about four weeks) for their opinions:

Prefab timber frame house: The foundation slab works perfectly; the house will be elevated anyway due to the gravel foundation.
Prefab solid house: Please build with a basement so you can use the excavation material as fill. Otherwise, you will have to fill the plot for 15,000 with no added value. Also, below street level is always problematic because of rain.
Architect of a general contractor (solid construction, masonry): Avoid the basement due to possible rock and disposal fees. I can even raise your knee wall to 1.5m (4 ft 11 in), and filling won’t really be necessary. I also don’t see a problem if you end up slightly below street level.

Three answers, but I’m no wiser. (The only thing was that my wife was thrilled when she heard about a 1.5-meter (4 ft 11 in) knee wall.)

We plan to position the house as far to the north as possible and put the garage/carport toward the east next to the neighbor.
I’ve attached a section of the plot (including stipulated and planned contour lines).
Right now, I am hoping for advice from @11ant or @Escroda, as we are at a loss.

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Development Plan / Restrictions
Plot size: 451 sqm (4850 sq ft)
Slope: 60cm (24 inches) over 20m (66 ft)—or even less
Plot ratio: 0.35
Floor area ratio: none specified in the development plan
Building envelope, building line, and boundary: see attached building envelope, otherwise 3m (10 ft) to neighbors
Boundary construction: no
Parking spaces: minimum 2 required
Number of floors: 2
Roof shape: gable roof, half-hipped roof (30-40 degrees)
Style: classic
Orientation: either parallel to the boundary or ridge direction per development plan
Maximum heights/limits:
Ceiling height: 4.1m (13 ft 5 in)
Ridge height: 8.9m (29 ft 2 in)
Other requirements:
Miscellaneous (tree planting types, etc.), but nothing relevant for the house
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Cadastral map showing plots, road edge, colored boundary and infrastructure markings
B
Bookstar
17 Oct 2020 20:58
The architect is right. If you don’t want a basement, just leave it out. You’ll save $80,000. With this plot, it’s no problem; 50cm (20 inches) is not much.
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ypg
17 Oct 2020 22:38
ValeolKB schrieb:

Number of floors: 2
Roof type: gable roof, steep gable roof (30-40 degrees)
ValeolKB schrieb:

TH: 4.1

A fixed two-story requirement based on these specifications: there isn’t much room for flexibility, especially considering the plot size. I’m curious to see what the house will have to look like (rather than could look like).

You can definitely skip a basement here when it comes to a flat site.
K
knalltüte
17 Oct 2020 23:20
Where the construction starts depends on the existing soil. So, possibly remove about 15cm (6 inches) of topsoil and store it aside. Then add 30-50cm (12-20 inches) of gravel, insulation around 10cm (4 inches), and a 25-30cm (10-12 inches) concrete slab. This already raises the level by 40-80cm (16-31 inches), but only in the building area. It doesn't make much sense to add topsoil excessively, but spreading some of it over the rest of the site would be possible.

It could also be different if you need to excavate a meter or more to reach load-bearing soil. So, have a soil report conducted.

My feeling is I wouldn’t want to be below street level. I like water, but preferably in combination with lots of sun and palm trees, or alternatively in a pool, but not otherwise in and around the house when it rains.
Nida35a17 Oct 2020 23:47
The other houses are located on the hillside, while yours is in the valley. When it rains heavily, similar to Mediterranean downpours, who is responsible for managing the water coming from several properties and the street?
Extreme weather events and their frequency are increasing.
Y
ypg
18 Oct 2020 00:11
Nida35a schrieb:

you in the hollow,
No, not a hollow, but the saddle, that is, the highest point.