Construction service descriptions: floor slab insulation

Hello everyone,

I am currently comparing several construction service descriptions from different construction companies. I noticed with one that apparently the floor slab is not insulated here. The floor slab is constructed on continuous frost skirts and laid on a 10cm thick gravel layer. A PE foil is used for sealing.

The other construction companies also have a sub-slab insulation.

Is it common for KfW100 not to insulate the floor slab?

Thank you very much

No idea what is usual. For our energy saving ordinance 2009 place (no KFW anything!) we put 28 cm insulation on the floor slab, 36 cm in the roof, and the walls are 36.5 cm thick. Triple-glazed windows. We need that to comply with the so-called "15% rule," since we only heat with gas and don't install any solar or heat pump stuff.

Hello,

Is it common with KfW100 not to insulate the floor slab?

What is "required" becomes apparent from the soil survey in conjunction with the structural analysis and the desired energy standard.

The topic of the floor slab is - in times of the Internet - increasingly becoming a Jehovah's Witness topic: everyone thinks they know better. Personally, I am not in favor at all of insulating beneath the floor slab and have been toying for years with the idea of sending our surveyor to single-family houses of existing customers who have built KFW 55 and lower (here the Energy Saving Ordinance unfortunately often forces this measure) to check the heights.

Basically, the rule is: you have to read a BB like a report card; what is not in it is considered not purchased. This means, in reverse, nothing more than that additional costs arise if you deviate from the BB.

Rhineland regards

I personally think it’s not a good idea at all to insulate below the floor slab...

Rhenish regards

Would you insulate above the floor slab then? That would count under the item screed, right?

Basically, you have to read a BB like a report card; what is not stated there is considered not purchased. This means, conversely, that additional costs will arise if you deviate from the BB.

Rhenish regards

I agree with you. However, as laypersons like me, some important points surely don’t even come to mind.

Hello,

Would one insulate above the floor slab? That would then count under the item screed, right?

Yes; it should be found under "Construction above floor slab and/or ceiling" or "Insulation" in general.

Rhenish regards

Good evening,

By the way, we still put insulation on the base slab. But that is usual with underfloor heating anyway.

The construction would not be different if conventional radiators were installed instead of underfloor heating

Rhenish greetings