Floor construction for cement screed

Hello everyone,

The screed is planned for next month. Now I want to order the insulation for the floor construction.
I need your advice on the implementation here.

Basement construction FF 20cm.
Upper floor construction FF 16cm.
The screed layer (cement screed) requires at least 6.5cm screed.

- Upper floor: 8cm insulation > 6.5cm screed > 1.5cm covering (tiles/laminate)
- Basement: 12cm insulation > 6.5cm screed > 1.5cm covering (tiles/laminate)

Should I lay a foil under the insulation? The floor slab has a foil underneath. (No insulated slab)
What is the best way to realize the insulation setup in the basement/upper floor (insulation / impact sound insulation / Rolljet)?

How did you do it in your construction, or what do the specialists say about the best way to do the setup?

Thanks in advance for the preliminary advice
Regards
Konstantin

In the basement, you need a sealing membrane suitable against rising damp. Ideally, in your case, also heat-reflective to minimize heat loss. For example, Alujet Floorjet Speed or similar. What is the construction of the basement walls? You need to ensure that your sealing membrane connects seamlessly to all other sealings (e.g., [Mauersperrbahn]). Ideally, this should be extended up to [OKRFB] (e.g., lifting a "fillet" made of foil, or alternatively using connection strips).

Are you planning to install underfloor heating? If yes, you have to calculate "backwards," starting below the screed – there you need, for example, either studded, stapler, or also hook-and-loop plates – depending on the type of pipe systems to be laid. You should plan about 2 cm here, ideally with boards made of Neopor / WLG032 – they also serve as impact sound insulation. With stapler or hook-and-loop systems, you could theoretically also use only a foil and extend your main insulation all the way to the top. However, you have to be careful about impact sound insulation here (depending on the floor, this may be more or less relevant).

I would definitely use PUR insulation boards for the main basement insulation, at least one-sided aluminum laminated. Whether you take 10 cm thick boards, or alternatively something like one layer of 6 cm and one layer of 4 cm, depends on whether you need installation lines on your floor slab (e.g., connections for [HKV], water pipes, ventilation ducts, electrical lines, etc.). If yes, it makes sense to determine the thickest insulation of the pipes and select your first board layer accordingly – this way you can nicely embed everything flush and then lay the second layer evenly on top.

The upper floor is similar, although it is rather pointless to use expensive PUR insulation there. You can use Neopor, or even regular EPS.

In the basement, you need a sealing membrane suitable against rising moisture. Ideally, in your case, also heat-reflective to minimize heat loss. For example, Alujet Floorjet Speed or similar. What is the wall structure of your basement?

The slab is made of waterproof concrete.
In the energy certificate, the structure is given as follows: concrete > vapor barrier PE film > insulation > vapor barrier PE film > screed > tiles.
I still have 2 rolls of vapor barrier :D which I could theoretically use there.
But if Alujet is supposed to go underneath, then of course I would do it that way.

The wall structure is exterior: 24 cm Poroton, 180 mm EPS insulation 034
Interior: 17.5 cm sand-lime brick.

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, stapler, or Velcro plates – depending on which pipe systems are to be installed. Here you need to plan about 2 cm, ideally with panels made of Neopor / WLG032 – they also serve as impact sound insulation. With stapler or Velcro systems, you could theoretically also use only one foil and extend your main insulation all the way to the top. But you have to be careful about impact sound here (depending on the floor, this can be more or less relevant).

Exactly. Underfloor heating will be installed. For that, I was thinking of the Rolljet directly with raster foil, which also provides a bit of impact sound insulation.

I would definitely make the main insulation in the basement out of PUR insulation boards, at least one-sided aluminum-coated. Whether you take, for example, 10 cm thick boards, or alternatively something like one layer 6 cm and one layer 4 cm, depends on whether you need installation lines on your slab (e.g. connections for heating circuits, water pipes, ventilation ducts, electrical cables, etc.). If yes, it is advisable to determine the thickest insulation of the lines and select your first board layer accordingly – this allows you to nicely embed everything flush and then lay the second layer evenly on top.

Electrical and heating/plumbing lines are already installed.
That brings up the question regarding the Alujet: can it simply be laid over the lines (pipes)?

Is your foundation slab currently completely bare? No bitumen waterproofing membrane on it?

Your base slab is currently really bare? No bitumen waterproofing membrane on it?

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

Unfortunately, this is not so optimal – I strongly assume that the doors & windows are already installed as well. However, the sealing actually needs to be extended to the outer edge of the floor slab in the passage area, i.e., the recessed floor profiles for doors and possibly floor-to-ceiling windows should only be installed afterwards. Hopefully you are only dealing with concrete moisture, so it may not be so serious, but still...

It is also not good to lay the membranes over the pipes – it will be tedious to cut everything in such a way that the insulation boards can be properly placed. It would have been better to lay the sealing first, and then seal the pipe fasteners (plugs or fix pins) separately with sealing adhesive. But I assume it is probably too late now – is it possibly conceivable to remove the fasteners in sections to slide the foil underneath?

How is your wall barrier membrane installed?