Terrace construction: aluminum rails lined with construction protection mats underneath

Hello everyone,

we are currently having our terrace built, and I have a quick question about the construction.

The landscaper prepared the base and finally laid about 8 cm high edge or border stones, which rest on a weed control fabric.

Now the carpenter came, who is supposed to finish the terrace. Today he placed his aluminum substructure directly on the border stones – however, the structure is not lying directly on them, but is supported with building protection mats of varying thicknesses. At almost every spot, compensation was made with more or fewer building protection mats.

This seems a bit adventurous to me. Shouldn't the gardener have already precisely prepared the correct heights and slope during the base construction?

So my question:
Is this usual and acceptable – or rather sloppy work or a makeshift solution that should better be avoided?

Many thanks in advance for your opinions and experiences!

That seems a bit adventurous to me. Shouldn't the gardener actually prepare the correct heights and the slope precisely already during the substructure?

He will never get that exactly right. It went better, but it is functional and perfectly fine (as long as the construction is properly aligned). Wood or WPC? I hope the terrace is level without a slope. That is actually not necessary, unless with WPC the joints are completely closed.

The terrace is to be laid with bamboo planks. As far as I understand, the aluminum rails now have a 2% slope away from the house. They should, right?

As far as I understood, the aluminum rails now have a 2% slope away from the house. Let them have it, right?

What do you need the slope for? So that the rain maybe runs off a few seconds faster through the gap between the decking boards? The water is drained away underneath the terrace anyway. With a construction like this, there are always the "but then water stands on the decking boards" arguments, which is not entirely wrong, but negligible. I have been building my terraces this way without a slope myself for 20 years. So also some experience (about 200 sqm by now). Most recently a few weeks ago.

Bamboo planks are slightly wider, so a 2% slope is justified.

Bamboo looks classy after installation but gets grimy after a short time, in my opinion.

Protective underlay for leveling is okay. You barely notice it later across the surface.

Bamboo planks are somewhat wider, so a 2% slope is justified.

I don't understand... Whether it's 11.5 or 13.7 or 14.5 cm wide makes no difference at all.