ᐅ Terrace Planning – WPC Decking or Paving Slabs?

Hello,

I have been quietly following this interesting forum for a while and have already been able to apply many tips to our new bungalow.
We have now finished the house and are planning our garden and terrace for spring 2016.
I am still looking for some ideas for the terrace and would appreciate your help.

Here is my starting point: The height difference between the finished floor level inside the house, and thus the doors leading to the terrace, and the garden level is about 30cm (12 inches).
Originally, we wanted to build a WPC (wood-plastic composite) terrace, which would compensate for the height difference through an underlying substructure. Around this, two steps down to the garden were planned. During the construction phase, we were advised to pour concrete in this area as a stable base and to prevent weeds from growing underneath.
We followed this advice, so now we have a concrete slab that is 30cm (12 inches) below the desired terrace surface level.

After reading a lot, we are no longer entirely sure if WPC is the best choice for us. Considering costs, terrace slabs (pavers) could be an interesting option. However, I am unsure what to do with the concrete base in that case. Adding a thick layer of gravel on top of the concrete to reach the right height does not seem ideal, especially since water will not drain through the concrete below.

If anyone has a similar situation or tips, or can convince me again that WPC is the better choice, I would be very grateful.

Thank you!

First of all, I have to say that you have served a good purpose with the concrete – filling the construction company's account.
WPC is not exactly cheap. That’s true, especially considering that you are building a plastic deck (I’ll skip the mixed-in wood flour).

The drainage problem arises whether the area is filled with gravel or not – a concrete slab remains a concrete slab, which water can’t pass through.

If anything, I would remove the concrete slab and fill in (this is my personal opinion) and lay paving slabs or, and this is my personal favorite, go for a wooden deck.

An important cost factor is whether you want to build the wooden or WPC deck yourself or if a professional company should do it. What size are we talking about?

Hello.
It is about approximately 40m2 (430 sq ft). The concrete slabs already have a slope toward the lawn. However, this will probably not be sufficient. I would build the terrace myself.

Martens1987 schrieb:
Terrace slabs on pedestals 300mm (12 inches) high are probably just some shaky DIY solution, right?

Using pedestal supports for terrace slabs will probably end up costing you a lot as well.

Okay. As I understand it (though it’s not entirely clear): the terrace area is already concreted with a slope. But this concrete slab is lower than you had envisioned for the exit from the house.

Back in March 2015, I was considering something similar. My sister has two large terraces in southern Germany, nearly 40 years old, with concrete bases and tiled surfaces (the tiles now need replacing after 40 years, which is understandable after that time).

What I liked about it: durability! At the time, I went home and decided to do the same. I was advised against it—not because it’s bad, but because it’s expensive to pour concrete. Okay—now the slab is already there for you, so that cost is sunk.

It’s hard to say anything definite without drawings or photos. There are so many options now… too many to list.
- Build steps or small platforms at the terrace doors, leave the terrace at its current level, and choose a surface covering of your choice. Frost-resistant outdoor tiles would certainly be a good option, but many others are possible too. Personally, I wouldn’t build a wooden deck directly on the slab: they look nice but require maintenance.
- Install a substructure on the slab to level it with the house floor, then cover it with wood (though that raises the question of what to do about the concrete slab underneath; it might feel like a waste).
- ……

You should ask yourselves what exactly you want now:
- Structurally
- Material preferences
- Maintenance requirements
- Necessary drainage measures depending on the design…

I recommend going to a good landscaping contractor (gala contractor / landscaping builder) in your area and getting some proposals… that would be my advice.

Best regards,
Thorsten

The concrete slab already has a slope. It should be at least 1cm per meter (0.4 inches per foot). Good.

You could glue a drainage mat to the concrete, for example from Schlüter. Set a perimeter edge curb 8x25x100 cm (3x10x39 inches) on a 5 cm (2 inches) concrete base around the terrace as a border stone. At the edge where water should drain, provide corresponding gaps in the concrete under the curb. You can insert short pieces of electrical conduit with a diameter of 20 mm (0.8 inches) every 10–15 cm (4–6 inches) for this purpose. Cover this area inside with fleece, as used for drainage.

Then proceed with a standard floor build-up: gravel/crushed stone/terrace slabs or pavers, and the terrace is ready.

I would generally advise against using tiles outdoors. It can work but often does not.

Talk to a knowledgeable building materials supplier about this. They often have solutions for all problems, including DIY projects.