Foundation/Substrate WPC Terrace

Hello dear forum community, I was instructed by the boss to create a WPC terrace. Currently, there is still grass growing there. The area is 4x5 m and starts from the terrace door. I am only concerned about the foundation. I have planned it as follows: 1. Excavate to spade depth (approx. 30cm). 2. Lay fleece. 3. Gravel layer approx. 20 cm, compacted with a tamper and 4% slope. 4. Bedding layer approx. 10 cm, compacted again and 2% slope. Then individual rows of concrete edge stones on which I can place the substructure. I also wanted to edge the whole thing to prevent lateral slipping. So far so good. That also corresponds to the specifications of the hearth plate. Now a gentleman from a gardening company came to make me an offer and he said he would definitely not do it without concrete and reinforcement mesh and would not be able to give a guarantee if it were done the way I intend. As I said, I wanted to do it myself anyway but now I am a bit uncertain. Please share your opinion/knowledge on the subject. Many thanks in advance and have a nice weekend

Forget all the fuss.

1. Excavate pointwise at the spots where the substructure should rest
2. Fill and compact gravel there
3. Fill freezer bags with lean concrete, place them on the respective spots, and lay the substructure on top

Cover the remaining lawn with fleece.

That’s it. I have built four terraces like this myself and know it partly from wooden terrace builders as well.

This is what it looks like in real life, what I described. However, with us, the compacted gravel was still in place and I had to reach the appropriate heights through remnants of the pavement. You have it a bit easier there.

That does indeed sound easier. How deep did you excavate pointwise and fill with gravel? In your picture, there are still "little concrete hills" and paving stones visible on the fleece. Is that the mentioned height adjustment? Thanks in advance! That would save a tremendous amount of cost and work.

I have not excavated anything. The substrate on which the fleece lies is the compacted gravel (from the civil engineer). The fleece was placed directly on that. I slapped a little concrete on the fleece so that the paving stones (which provide the height adjustment) can lie properly. Then came the bags of concrete on which my wooden substructure rests.

Since it is wood (Bongossi) and should not lie in water, the wood rests on small pads and thus remains dry. You don't have that problem with WPC.

Addendum/Alternative: I will also build a terrace around our pool. However, somewhat modified, since there is currently a lawn area there and I am not keen on digging. 1. Rent an earth drill 2. Drill holes (about 35-40 cm for me, as I then reach the fill soil), into which 100mm KG pipes will be inserted 3. Adjust the height of the KG pipes 4. Fill the KG pipes with gravel or alternatively concrete You then have the points on which the substructure can rest.

I am also interested in this topic, but I am rather a lazy person and had considered buying these height-adjustable terrace pedestals to make it as easy as possible to create the height and slope. Is that really unnecessary, or how do you ensure that there is still a reasonably even surface when compacting?? Because a solution with concrete slabs is of course much cheaper in terms of price. Basically, I need to build up about 30cm including frost protection. I hope it's okay that I just join in here.