In case the topic is still relevant for the original poster: We live in a pure moor area (district of Ammerland, Lower Saxony). Our entire village (Friedrichsfehn, 4100 inhabitants) is built on moorland. We are a fairly young community with several large new housing estates. We ourselves have built here for the second time. The average moor layer that has been replaced with fill sand is three meters in our area, but for some builders up to five meters. They usually carried out a pile foundation. I write this in advance to take away your fear of building on moorland. There are just a few important things to consider so that there are no problems later.
1. If no soil replacement has been carried out on the building plot so far, it is still the easiest. The moor must be completely replaced with fill sand up to load-bearing soil in the area to be built on. It is important to make sure that the fill sand introduced is well compacted layer by layer (80cm). The best and safest way to do this is not with a hand compactor but with a vibrating roller. However, if building has already taken place in the immediate neighborhood, this can cause problems. Heavy and powerful vibrating rollers shake the ground so much that the cups in the neighbor’s kitchen cabinet rattle. Then he immediately comes running out because he is afraid of cracks in his house. Then only compaction with the hand-held compactor remains after all.
2. A rule of thumb for us is that as much moor must be removed beyond all built-up areas as must be removed in depth. If, for example, three meters of moor need to be replaced, this should also be done three meters beyond the building. This also applies to terraces, driveways, etc. Anyone who wants to save money can take one meter less there, though.
3. Caution with comparatively particularly cheap offers: To avoid empty runs of the sand trucks and to save costs, the excavated soil is often replaced directly with fill sand. The truck that brings fill sand takes the excavated moor soil back with it. With thick moor layers like ours (three meters), however, there is a tendency in the lower part for moor and fill sand to mix due to shifts. A clean excavation of the moor can hardly be guaranteed. Therefore, I advocate first having the moor completely excavated in the required area and only then filling the clean pit with fill sand. This is a bit more expensive, but you can sleep more peacefully afterwards.
4. Problem boundary construction/garage: If the neighboring property has not yet been built on, an agreement with the owner regarding soil replacement should not be a big problem. In any case, permission must be obtained! If, however, the neighboring property has already been built on and the garden is laid out and, for example, a garage is to be built on the boundary, it becomes difficult. For moor layers over one meter, soil replacement up to the property boundary is by no means sufficient. Then only a pile foundation remains for the garage (alternatively no concrete slab or a carport).
5. An important consideration: If you don’t have to count every last cent, you should consider excavating the entire property. Reason: Surface drainage of a development leads to a lowering of surface water in the upper soil layers, which causes the moor to subside. In our first construction project, we had to add topsoil twice over 15 years and completely redesign the garden each time! The fatal thing: the subsidence never stops! The new topsoil applies additional pressure to the moor, which then subsides again. Incidentally, the new owner of our first house has already had to redesign his garden again. It is also annoying when driveways and terraces subside because the soil replacement was done too sparingly.
6. Regarding the possible scope of earthworks and costs: If building has already taken place in the neighborhood or builders are currently working there, be sure to ask. They have already gained their experience and may be able to say something about the thickness of the moor layer and affordable sand transport companies.
7. It can be problematic if soil replacement has already taken place on the property but I do not know how the civil engineering company worked. It must also be checked whether enough soil has been replaced in terms of area. In this case, I would definitely consult an expert.
Have fun building!