ᐅ Floor construction for cement screed

Hello everyone,

The screed is scheduled for next month. Now I want to order the insulation for the floor construction.
I need your advice on how to implement this.

Basement construction floor height 20cm (8 inches).
Upper floor construction floor height 16cm (6 inches).
The screed installer (cement screed) requires at least 6.5cm (2.5 inches) of screed.

- Upper floor: 8cm (3 inches) insulation > 6.5cm (2.5 inches) screed > 1.5cm (0.6 inches) floor covering (tiles/laminate)
- Basement: 12cm (5 inches) insulation > 6.5cm (2.5 inches) screed > 1.5cm (0.6 inches) floor covering (tiles/laminate)

Should I install a vapor barrier film beneath the insulation? The concrete slab already has a vapor barrier underneath (no insulated slab).
What is the best way to build up the insulation in basement and upper floor (insulation / impact sound insulation / roll insulation)?

How did you handle this in your build, or what do the professionals recommend as the best construction method?

Thanks in advance for your preliminary advice.
Regards,
Konstantin

In the basement (UG), you need a waterproof membrane suitable against rising damp. Ideally, in your case, it should also be heat-reflective to minimize heat loss, for example, a product like Alujet Floorjet Speed or similar. What is the wall construction of your basement? You need to ensure that your waterproofing connects seamlessly to all other waterproof layers (e.g., cavity barrier membranes). Ideally, this should extend up to the top of the reinforced floor slab (OKRFB), for example by extending a "fillet" of membrane upwards or alternatively using connection strips.

Are you planning to install underfloor heating? If yes, you need to plan "backwards," starting below the screed – here, you will need either studded, staple-fixing, or hook-and-loop panels, depending on the pipe system you intend to lay. Allow about 2 cm (1 inch) here, ideally with panels made of Neopor / WLG032, which also serve as impact sound insulation. With staple or hook-and-loop systems, you could theoretically use just a membrane and extend your main insulation all the way up, but you need to be cautious about impact sound insulation (this depends on the floor below and can be more or less important).

For the main insulation in the basement, I would definitely use rigid PUR insulation boards, at least one-sided aluminum foil-faced. Whether you choose, for example, 10 cm (4 inches) thick boards or a combination such as one layer of 6 cm (2.5 inches) and one layer of 4 cm (1.5 inches) depends on whether you need to run installation lines in your slab (e.g., connections for heating circuits, water pipes, ventilation ducts, electrical cables, etc.). If yes, it makes sense to determine the thickness of the thickest insulation around these lines and select your first layer of boards accordingly—this way, you can neatly incorporate everything flush and then lay the second layer evenly on top.

For the upper floor (OG), the situation is similar, although it is usually not economical to use expensive PUR insulation there. You can use Neopor or even standard EPS.

Harakiri schrieb:

In the basement, you need a waterproof membrane suitable against rising damp. Ideally, in your case, it should also reflect heat to minimize heat loss, for example, Alujet Floorjet Speed or something similar. What is the wall construction of your basement?

The slab is made of waterproof concrete.
In the energy certificate, the build-up is specified as follows: concrete > vapor retarder PE foil > insulation > vapor retarder PE foil > screed > tiles.
I still have two rolls of vapor retarder 😀 which I could theoretically use there.
But if Alujet should rather be installed below that, then of course I would do it that way.

The wall construction is outside 24 cm (9.5 inches) Poroton blocks, 180 mm (7 inches) EPS insulation with a thermal conductivity of 0.034 W/(m·K).
Inside: 17.5 cm (7 inches) calcium silicate blocks.

Harakiri schrieb:

Do you plan to install underfloor heating? If yes, you have to calculate "backwards," starting below the screed – there you need, for example, either studded mats, staple plates, or Velcro mounting plates depending on the pipe system you want to install. You should plan about 2 cm (0.8 inches) for this, ideally with panels made of Neopor / WLG 032 – these also serve as impact sound insulation. With staple or Velcro systems, you could theoretically use just a foil and extend your main insulation all the way up. However, you need to be careful about impact sound insulation here (depending on the floor, this can be more or less relevant).

Exactly. Underfloor heating will be installed. For this, I had planned the Rolljet directly with the raster foil, which also provides some impact sound insulation.

Harakiri schrieb:

I would definitely use rigid PUR insulation boards for the main basement insulation, at least one side aluminum-coated. Whether you take 10 cm (4 inches) thick boards or, alternatively, one layer of 6 cm (2.4 inches) and one layer of 4 cm (1.6 inches) depends on whether you need installation pipes on your slab (e.g. connections to heating circuits, water pipes, ventilation ducts, electrical conduits, etc.). If yes, it makes sense to determine the thickest insulation around the pipes and choose your first insulation layer accordingly – this way you can neatly embed everything flush and then lay the second layer flat on top.

Electrical and heating/plumbing pipes are already installed.
So the question about Alujet again: can it simply be laid over the pipes?

Is your concrete slab currently completely bare? No bitumen membrane applied?

Tolentino schrieb:

Is your concrete slab really completely bare right now? No bitumen waterproofing membrane on it?

Exactly. Heating and water pipes as well as electrical cables/conduits are attached directly to the concrete floor.

Unfortunately, this is not ideal – I strongly assume the doors and windows are already installed. However, the waterproofing should actually extend to the outer edge of the floor slab in the passage area, meaning the floor connection profiles for doors and, if applicable, floor-to-ceiling windows should only be installed afterward. Hopefully, you’re only dealing with concrete moisture, so it might not be too severe, but still...

It’s also not good to lay the membranes over the pipes – it will be quite tricky to cut everything so that the insulation boards can be properly placed. It would have been better to install the waterproofing first, and then separately seal the pipe fasteners (dowels or fix pins) with waterproofing adhesive. But I assume it’s probably too late now – is it at all possible to remove the fasteners in certain areas to slide the membrane underneath?

How is your cavity wall barrier installed?