Base plate on the top edge or bottom edge? Who has experience?

Hello everyone,

we are planning to buy a plot of land and not to build a basement under our house, but to build on a slab foundation. So far, we are considering a thermal slab foundation.

Yesterday, I saw that the streets are almost finished and they are estimated to be about 1m above the actual plots. Now we are wondering whether this is good or bad. Of course, that also depends on how the slab foundation is constructed. So, bottom edge to top edge of the street or top edge to top edge. We are trying to answer a few questions for ourselves, but are not getting any further and hope that you can help us a little.

1. What are the advantages/disadvantages and costs if you build bottom edge to top edge of the street?
2. What are the advantages/disadvantages and costs if you build top edge to top edge of the street?
3. Which type is recommended if the street is approximately 1m higher than the plot?
4. In this case, would it possibly be worthwhile to build a basement after all?

We could imagine that top edge to top edge would be best. That way you would not have to fill the ground beforehand and would save the costs for stairs to the door. But maybe we are overlooking something?
Then the question also arises whether a basement might actually make sense, since you wouldn't have to dig as deep and could use the excavation for the remaining fill. Whether the basement is worthwhile is always subjective, but could one roughly estimate how much money one saves?

We are aware that everything must be planned precisely, but we would like to have an independent opinion in advance and roughly know where the advantages/disadvantages are and how the costs are.

Thanks for your help

With a slab foundation, I would always want the top of the slab to be above the top of the street; it doesn’t have to be much, but being below street level is unpleasant during heavy rain. When you say the street is 1 m above the property, I assume there is quite a steep slope; there won’t be just a simple step in the terrain, right? How does this slope behave within the building plot? Raising the entire house by 1 m won’t be cheap (the edge of the fill also has to be retained!), depending on the slope, a split level or a "semi-buried" basement is probably more economical. So a floor that is a "normal basement" towards the street and practically at ground level towards the garden side.

Thank you for your assessment. So it will come down to either the top of the foundation slab being above the top of the street, requiring quite a bit of fill, or a "semi-buried" basement as a cheaper alternative. If the basement is the more economical choice, then we will probably tend towards that.

I have sent a photo of the current construction site where the slope can be seen.

What do the sellers say about the heights? It looks to me like a construction road, where additional paving can easily be added and the height increased. However, the height specifications should be known to the seller... it seems as if every property faces this problem.

The finished road is certainly still a bit higher than the construction road. But everything around 1m is nothing special. The base slab with insulation and gravel bed compensates for that easily. You may have additional costs due to backfilling around it, but in the new development area it should not be difficult to find excess material. I wouldn’t start panicking about the costs now.

We only saw this yesterday and have not asked the seller yet. We are still waiting until it is supposed to start next week. So far, we have only had preliminary talks with GUs etc. and are roughly outlining the cost framework. If, for example, a basement is now an option, it would be good to know. Because so far we have excluded the basement and that does change quite a few things.

But if I understand this correctly, the additional costs should be manageable. Only the costs for filling next to the base slab would come up, and here it might be possible to use soil from others who, for example, are digging a basement.

What do you estimate it would otherwise cost? 5k, 10k, 15k?