Hello,
there are countless discussions online about whether to insulate above or below the slab. However, I haven’t found any in connection with a basement built from a 42.5cm (17 inch) thermal block.
We are building a basement with blocks (Bisotherm 42.5cm / 17 inch) instead of concrete because it saves us about €25,000 and only part of the building is in contact with the ground. Unfortunately, the question of whether to insulate above or below the slab has come up again.
Some companies and acquaintances say that insulating below the slab is essential to avoid possible thermal bridges. Others are convinced that insulating on the slab is better because it’s cheaper and the thermal envelope is already created by the insulation on the slab and the thermal block. Actually, the energy certificate wouldn’t change in either case.
It’s true that insulating on the slab is cheaper, but I’m not sure about the rest since everyone seems to have a different opinion.
So, should we save those few thousand euros or not?
Best regards
there are countless discussions online about whether to insulate above or below the slab. However, I haven’t found any in connection with a basement built from a 42.5cm (17 inch) thermal block.
We are building a basement with blocks (Bisotherm 42.5cm / 17 inch) instead of concrete because it saves us about €25,000 and only part of the building is in contact with the ground. Unfortunately, the question of whether to insulate above or below the slab has come up again.
Some companies and acquaintances say that insulating below the slab is essential to avoid possible thermal bridges. Others are convinced that insulating on the slab is better because it’s cheaper and the thermal envelope is already created by the insulation on the slab and the thermal block. Actually, the energy certificate wouldn’t change in either case.
It’s true that insulating on the slab is cheaper, but I’m not sure about the rest since everyone seems to have a different opinion.
So, should we save those few thousand euros or not?
Best regards
0
009_frank29 Apr 2025 19:59nordanney schrieb:
It's just as standard as with the foundation slab. It's like saying today that electric cars are standard. Or gasoline. Or diesel.I honestly thought it was "outdated." Thanks a lot for the clarification.
11ant schrieb:
By the way, a residential basement is nowadays usually included in a controlled mechanical ventilation system – this also helps prevent mold issues.Yes, controlled mechanical ventilation is installed as well. Your explanation really makes sense. That’s exactly why I wanted to get advice again in an independent forum.