ᐅ Patio slabs installed on pedestals over a FPO membrane

Hello everyone,

We have several balconies with FPO membranes.

Construction:
200mm (8 inches) concrete slab
120mm (5 inches) PU insulation - WLS 0.23, 120 kPa
EPS sloped insulation boards - WLS 0.35, 150 kPa
Separation layer (polyester fleece)
FPO membrane

I am currently considering which type of flooring to use here. At the moment, I am leaning towards either terrace slabs or WPC decking boards. Both options would be installed with pedestal supports.

My questions regarding the terrace slabs:

1. These often have a thickness of 2cm (0.8 inches) and come in sizes like 60x60 cm (24x24 inches), 80x80 cm (31x31 inches), 60x40 cm (24x16 inches), or 120x60 cm (47x24 inches). Are these thinner slabs prone to breaking when they are supported above pedestals and thus have hollow spaces underneath?

2. Would the flooring feel spongy because of the insulation layer underneath, making terrace tiles feel odd underfoot? Has anyone had experience with this? I think this would be less noticeable with WPC decking boards.

Does anyone have experience with insulated balconies and stilt supports?

It depends on how much build-up height is still available. Vapor barrier + waterproofing + 12cm (5 inches) + at least 2cm (1 inch), or rather 4cm (1.5 inches) to direct water away from the house.

In recent years, no pedestal supports have been seen in new constructions.

Usually, an aluminum rail system is used.

The flooring doesn’t feel spongy when walked on; the protective mat is barely noticeable.

I would prefer 60x60x2cm (24x24x0.8 inches) slabs.

When laid smartly, they won’t slide even at exits.

Joint spacers of 5mm (0.2 inches) are essential (I’m not sure what they are called, but they have a plate underneath) to prevent the slabs from lifting during movement.

Singelküche schrieb:

It depends on how much build-up height is still available.

I would have to measure that. But I could build up the flooring with at least 10cm (4 inches). Maybe even more.

Singelküche schrieb:

Usually an aluminum rail system

I would have to look into it further. There are some rail systems on Google, but it doesn’t seem to be very common.

Singelküche schrieb:

Mostly an aluminum rail system.

I once requested a quote for such a rail system. For a balcony of about 22 m² (240 sq ft), it costs around 2000€ at Obi. At Bauhaus, I was immediately quoted about 4000€.

We tried taking along 4 terrace tiles (porcelain stoneware, 2 cm (0.8 inches) thick) with pedestal supports. It is somewhat springy. Since it gives way more or less in some spots, I think it will be quite difficult to adjust the pedestals properly.

I am considering installing the whole thing in a gravel bed. My roofer (who installed the FPO membrane) said that water drains much better with pedestal supports than with a gravel bed.

1. What kind of gravel is generally used here? Crushed stone is not suitable because of the sharp edges.

2. Would it possibly make sense to lay a full-area protective mat (6 or 8 mm (0.24 or 0.31 inches)) underneath the gravel bed?

netzplan schrieb:

What type of gravel is generally used here? Crushed stone is not suitable because of the sharp edges.

They usually use 16/32 rounded gravel or roofing gravel. Tomorrow, I'll ask the quarry if they specifically carry roofing gravel. (I'm curious whether you can properly lay patio slabs on 16/32 gravel. I'll probably test a small area first.)