Foundation/Substrate WPC Terrace

But interesting that water drains just as well/poorly with a slope as without - even physics is being explained to you here again

How much water actually drains with a % slope? In the end, there is a film of water left on the terrace, whether with or without slope. With grooves, it even stays at 1% and does not drain at all. Proper draining only happens with a steep slope (terrace canopies at around +/- 10%) and not with terraces.
Of course, decking suppliers recommend a slope, I would do the same to avoid liability issues / complaints.
P.S. Although my background is a bank clerk, I have been dealing with real estate for 20 years and can therefore draw on quite extensive experience in real estate – from small condominiums up to large commercial properties with tens of thousands of square meters.

My experience shows that decking where a film of water remains stands to deteriorate much faster.

That may be the case with simple wood, but as soon as it goes towards the "bad" tropical wood, the problem only exists if the wood lies in water for a really long time. I have experienced that problems occur more often with the substructure, since constructive wood protection is neglected there (e.g. simply placing beams directly on well-prepared gravel and letting them soak through or screwing the decking boards directly onto the substructure).
The film of water dries within a very short time after the rain, just like on all damp areas – whether wood or concrete. The last drop simply won’t drain at such a low slope.
The original poster has even fewer problems since he was steered towards WPC by his boss. Those are even less sensitive – but of course not wood.

Especially with WPC it is not only recommended...

And your real estate experience is to be respected, but why should you be (particularly) competent in something like this?

WPC would not even be an option for me. Problems (as often seen) that I see with it are that the surface crumbles over the years if it is exposed to the sun for too long and intensely (if it ever shines here ). But that is a topic that can be endlessly debated. It is true that the UK is an essential and not to be underestimated component that requires special attention. Most mistakes are probably made here.


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but you still need enough support points there because the wooden beams bend quite quickly.

The wooden beams rest on the appropriate rubber pads. Distances to the support points depend on the thickness of the beams (I have a support point every 50 cm).

And the wooden beams also lie in the water

No, they don’t, that’s what the rubber pads are for.

which wood do you use there

I used Bongossi, which is also used, for example, for boat piers or livestock fences because it withstands constant contact with water extremely well.

I had already considered designing the load-bearing substructure from IPE 80 steel profiles.

Won’t that be expensive? But of course you can do that as well.

And your real estate experience aside, why should you be particularly competent in something like this?

If you work together for many years with project developers, planners, architects, etc. and regularly accompany construction projects with project controllers, appraisers, and other experts (not from the desk, but on the construction site – really with boots and helmet ), you learn an incredible amount about real estate.
There are also plenty of properties that include wooden terraces – whether it’s in the outdoor facilities, terraces for gastronomy businesses, rooftop terraces on office buildings, etc.

Therefore, I take my experience – besides four terraces I have built myself and helping out friends.

Just how to fasten the Garapa decking boards to the steel profiles

Addendum: Not at all, wooden substructure on the steel profiles.