Foundation/Substrate WPC Terrace

Hi,

I chose Bongossi, which is also used, for example, for boat docks or livestock fences because it comes into contact with water continuously and is extremely durable.

Ah, isn't that the stuff also called ironwood? It doesn't even float, does it?!?
That's definitely a strong statement.

What beam thickness did you use?

Bongossi doesn't seem to be cheap either. For 80*80 beams, I find prices around 8-9 €/meter.

That's about the price you pay for an IPE 80 profile. Hence my basic idea to really make the bottom, load-bearing layer out of steel beams. On top of that, you could lay a cross layer of wooden beams, and those in turn would hold the actual terrace decking.

Best regards,

Andreas

Ah, isn't that the stuff also called ironwood? That doesn't even float?!?
That's quite a statement.

Yes, it actually sinks

What beam thickness did you take?
Bongossi also doesn't seem to be that cheap. For 80*80 beams I find prices around 8-9 €/meter.

I took 60x60. It was around 3.5 € per meter. However, I had to pick it up at the wood wholesaler in Bremen. In the Hamburg / Bremen region, there's a lot of wood on offer due to the ports. They also wanted to offer me my Ipe decking – they had thousands of sqm in stock

That's why my basic idea is to really make the lowest load-bearing layer out of steel beams. Then you could lay a cross layer of wooden beams on top, and those would in turn hold the actual terrace boards.

Exactly, you can do it that way. But then you need the steel beams AND the wooden beams again.

You will then need the steel beams AND the wooden beams again.

But you have to decouple the wooden beams from the steel beams, otherwise they will rot away. That would be unnecessary and double work, if I understood correctly. Why not a substructure made of larch or Douglas fir? Properly done, it will last forever.

Back to the topic regardless of the slope. I still have a few questions:
1. Can you see the fleece or the concrete freezer bags through the joints afterwards (mine would be 8mm according to the manufacturer)?
2. How do you design the transition between terrace and lawn? (Should an L-shaped concrete profile be laid at the lawn edge? Basically as a neat finish.)
3. How do I adapt the surrounding lawn area to the slope? What I mean by that: Even if I only make a 1-2% slope and the terrace is e.g. 6 m wide, it would basically "disappear" under the surrounding lawn edge...
I hope it is understandable what I mean and not thought of as too complicated. Thanks in advance and greetings from Canada....

1. Can you see through the joints afterwards (mine would be 8mm according to the manufacturer) the fleece or the concrete freezer bags?

I have narrower joints. Then you don't look at anything or just into the dark.

2. How do you design the transition terrace - lawn? (Should an L-shaped concrete profile be laid at the lawn edge? Basically as a clean finish.)

Depending on mood. However, we have so far decided that the terrace is always higher than the lawn. Finish either by vertically mounted boards or currently edging with anthracite-colored concrete curbs.

3. How do I adapt the surrounding lawn area to the slope?

I don't quite understand the question. Either the terrace is a bit higher than the lawn, then you have no problem at all. However, if you want barrier-free access to the terrace = the same height as the lawn, then you don't have to adjust anything either. It just has to be clear during the earthworks that the lawn area must be somewhat lower than the beginning of the terrace.

Thank you for the help and sorry for the late reply! We now have paving stones in front of the terrace door, and these border the lawn. The new terrace is supposed to be bigger and would cover paving stones and lawn. Unfortunately, it can't simply be placed on top because then the build-up height would exceed the door. So I have to remove the paving stones and dig a "path" into the lawn to achieve the build-up height and a minimal slope. And here is my question about that: The terrace is then basically half recessed compared to the surrounding lawn. Not really flush with the ground and not really raised either. How do I handle the side ventilation? Not so important? Or is it advisable to remove so much from the surroundings that the terrace really rests on the ground and is ventilated on all sides? Is this a bit clearer now? Best regards from Boston