Construction service descriptions: floor slab insulation

Hello,

Yes; it should generally be found under "Structure above the base slab and/or floor slab" or "Insulation."

Rhenish greetings

May I ask a "stupid" question, what is the advantage of insulating the base slab from above instead of from below?

...because this is exactly the point where, for example, two construction and service specifications from two possible construction companies currently differ.

Thank you very much

Hello,

May I ask a "dumb" question, what is the advantage of insulating the floor slab from above instead of from below?
...because this is exactly the point where, for example, two building and service descriptions from two possible construction companies currently differ.

This is also a kind of "Jehovah" topic, so my answer only reflects "my" subjective opinion

I am not in favor of insulation under the floor slab – even though we are often forced to do so according to KFW 55 – because no one knows what the weight of the single-family house built above will do to the insulation over the years. I dare to assert that, if such a founded single-family house were measured again years later, the measured ridge height would deviate downward from the input plan at the building authority.

Furthermore, I do not really see the necessity to go to this effort if I can keep the heat inside the house, where it – in my humble opinion – is also better placed

Rhenish regards

Also faced the decision and my architect advises me, both cost-wise and for [Epis] reasons, against insulating under the slab. We are doing 10cm insulation under the screed in the basement, that is sufficient. So we are not insulating and are doing something else on the house with the "saved" money.

We have a so-called climate base slab... first layer 10 cm Styrodur insulation, second layer another 10 cm but only in the room area, underfloor heating laid directly on top, reinforcement added, and 10 cm WU concrete which is then smoothed ready for covering. Where the interior walls and exterior walls run, it remains with the first layer of 10 cm insulation, but with 20 cm concrete (including appropriate reinforcement in the exterior wall area). Don’t ask me about insulation values etc. now, I’d have to look that up, but it was definitely better than insulation under the slab plus screed insulation/screed and has the advantage that the base area is also insulated (L-elements), which does not happen with the normal slab, since the underfloor heating is integrated, insulation is of course needed and should (whether that is advertising or fact) have a positive effect as a heat storage in the concrete slab with lower energy demand.

We used this method both in our first build (now 10 years old) and in our last build from 2013. In terms of costs it was about the same as a “normal” slab with screed insulation/screed, but you saved the possible cost of a construction dryer if needed and the time for the screed drying period. I would always do it this way again. You just have to know in advance how you want to divide the rooms; for anyone who wants to do the interior finishing themselves after the shell construction by spontaneous decision this is not suitable (as mentioned, the heating circuit distributor and underfloor heating are cast in, the location for the chimney—if one is to be installed—must be fixed because 20 cm concrete is also poured there). What we didn’t like was that around the outside fiber cement boards (20 cm high) were used as formwork/which were directly glued to the lower layer of insulation; in our second house they were not properly primed so the concrete did not adhere to the boards and the boards loosened from the concrete, dirt then fell into the gap that formed and pushed the boards so far away that we had them removed and then it was plastered.