ᐅ Insufficient screed insulation

Hello everyone,

we are facing a small issue on our construction site again.

Here is the situation: The building specification states a floor structure of 19 cm (7.5 inches) and 8 cm (3 inches) perimeter insulation underneath, and 14 cm (5.5 inches) structure above.

Now, there are two things: We have chosen larger underfloor heating pipes and therefore need more screed to maintain the required coverage. Also, a sliding door was installed too low. At the bottom, 5 cm (2 inches) and 3 cm (1.2 inches) of insulation are now being installed, and only 3 cm (1.2 inches) above.

The U-value towards the ground worsens from 0.0166 to 0.0209 W/m²K, which means an additional heat loss of 120 W and about 250 kWh more heating energy (around 15 € per year – geothermal energy).

On the upside, our ceilings are 3 cm (1.2 inches) higher… yay. Honestly, I don’t understand why there are 3 cm (1.2 inches) in the upper floor; I assume it is because of the thickness of the ceiling duct system.

On the ground floor, we do not meet the energy saving regulations in the upper floor – we would actually need 4 cm (1.6 inches). Where does the heat go then? Into the ceiling and partly into the lower floor? That wouldn’t be the worst case, since according to the room heating load calculation, the rooms on the ground floor are the critical ones anyway.

What bothers me a bit is that the water pipes are not 100% covered by insulation – on the other hand, the pipes themselves are embedded within full insulation. It is a reinforced concrete slab about 22 cm (8.7 inches) thick, I believe.

The site manager is not very keen on making corrections so far – if we insist, at least the upper floor might be adjusted (doing it downstairs would mean replacing the door). As a layperson, I don’t really see major disadvantages in the current situation so far (except that it is different from what is specified in the building contract).

Thanks for your comments!

BeHaElJa schrieb:
we decided to use larger underfloor heating pipes

When (and why)?

Due to the higher volume flow – after signing – so the 1 cm (0.4 inches) is on us.

Is impact sound insulation still installed upstairs? Why is there a 19cm (7.5 inches) construction height at the bottom, but only 8cm (3 inches) of insulation?

Then you have 11cm (4.3 inches) of screed – hardly likely, right?

Perimeter insulation under the foundation?

So much for internet advice.

Yes – insulation below the slab is 8 cm (3 inches).
Originally planned were 12 cm (5 inches) insulation, 6 cm (2.5 inches) screed, and 1 cm (0.4 inches) tile. Now it will be 8 cm (3 inches) insulation, 7 cm (2.75 inches) screed, and 1 cm (0.4 inches) tile.
I’m not sure about impact sound insulation – I’m also not quite certain what effect impact sound insulation has... with 22 cm (9 inches) reinforced concrete and 7 cm (2.75 inches) screed, you probably wouldn’t hear anything, right? Or would you?

Of course, impact sound insulation is also an issue in single-family houses – a thick concrete floor alone won’t solve it.

Normally, 4cm (1.5 inches) should be sufficient – but I’m not 100% sure.