ᐅ Scope of Work Descriptions: Insulation of the Foundation Slab

Hello everyone,

I am currently comparing several construction specifications from different building companies. I noticed that one of them apparently does not insulate the ground floor slab. The slab is built on a continuous frost protection border and is placed on a 10cm (4 inch) thick layer of gravel. A PE (polyethylene) sheet is used for waterproofing.

The other builders also include insulation beneath the slab.

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

Thank you very much

No idea what is common practice. For our house built to the 2009 Energy Saving Ordinance standards (not any KFW program!), we are installing 28 cm (11 inches) of insulation under the slab, 36 cm (14 inches) in the roof, and the walls are 36.5 cm (14.5 inches) thick. Triple-glazed windows. We need this to comply with the so-called "15% rule," since we are only heating with gas and are not installing solar panels or heat pumps.

Hello,

Salomea schrieb:

Is it common not to insulate the slab on grade with KfW100?

What is "required" depends on the soil report in combination with the structural engineering and the desired energy standard.

The topic of slab on grade insulation has become somewhat of a dogma these days with the internet: everyone thinks they know best. Personally, I am generally against insulating beneath the slab on grade and have been considering sending our surveyor to single-family houses from existing clients built to KFW 55 or better (here, unfortunately, the energy saving regulations often require this measure) to recheck the levels.

Basically, you have to read the construction contract like a certificate; anything not included there is not considered agreed upon. In other words, additional costs arise if you deviate from the contract documents.

Best regards,
Bauexperte

Bauexperte schrieb:



Personally, I’m not in favor of insulating below the foundation slab at all...

Regards, Bauexperte

Would you insulate above the foundation slab then? That would fall under the category of screed, wouldn’t it?

Bauexperte schrieb:


Basically, you have to read a construction specification (building brief) like a report card; anything not included in it is considered not purchased. In other words, if you deviate from the specification, additional costs will arise.

Regards, Bauexperte

I agree with you there. However, as a layperson like me, there are certainly many important points that might be overlooked.

Hello,

Salomea schrieb:

Would insulation be applied above the concrete slab? That would then fall under the screed category, right?

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

Regards, Bauexperte

Good evening,

Manu1976 schrieb:

By the way, insulation will still be installed on the foundation slab in our case. But that is quite common with underfloor heating anyway.

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

Regards, Bauexperte