ᐅ KfW 55 – Insulation Below the Concrete Slab

Thermal bridges are logically relevant, also according to the 2013 Energy Saving Ordinance, and they must be individually documented for KfW houses as well, even if generally optimized thermal bridges are assumed.

Where should the problem be if you want to have a heated basement?
You can also work with external and internal insulation.

Why guess here when there are experts on site,...

When you mention the heated basement, it is not common to heat the basement if the slab-on-grade is insulated. It doesn’t have to be 21°C (70°F).

Is your basement cold? Our basement is not meant to be a living space, only for technical equipment, a utility room, and a workshop.

Dopamin schrieb:

U-values:
Roof 0.15
Exterior wall 0.20 (42.5cm (17 inches) T9)
Basement wall 0.24
Ground slab 0.25
Thermal bridge allowance ???

Brine-water heat pump (horizontal ground loop collector) with controlled ventilation with heat recovery.

We don’t have a basement, but that would actually improve things even more. As mentioned, it really depends on the details; your basement walls will be insulated from the outside, right?
For comparison:
We also have 42.5cm (17 inches) T9
Roof is 0.13 and ground slab 0.19.
Brine-water heat pump and controlled ventilation with heat recovery.

By the way, we simply used a thermal bridge allowance since it didn’t matter (no KfW subsidy applied).
What heating load are you calculating? Have you run the numbers?
KfW 55 shouldn’t be a problem with these specifications. Windows probably around 0.8 as well?

pffreestyler schrieb:

It is the Iko Enertherm PIR Aluminum insulation WLS 023.

Where did you buy the insulation? I need 10cm (4 inches) insulation -> 60 and 40mm (2.4 and 1.6 inches) and am currently looking for the most affordable place to get the insulation.

I bought 2 pieces of 5 cm (2 inches) each at the local hardware store for €9.71 including VAT. It was even slightly cheaper than online, but more importantly, I could return the leftover material on site. If you do the work yourself and order online, don’t expect a 10% waste rate. You hardly have to throw anything away. You can always find ways to use up leftovers. We had maybe a 1% waste rate... we cut both sides with a utility knife and then simply snapped the material as usual.

pffreestyler schrieb:

I bought 2 pieces of 5 cm (2 inches) thickness insulation at the local hardware store for €9.71 including VAT. It was even slightly cheaper than online, but more importantly, it was available on site, so I could return the leftover material. If you’re doing it yourself and ordering online, don’t expect a 10% waste factor. You hardly have to throw anything away. Leftovers can almost always be fitted in somewhere. We probably had about 1% waste... we cut both sides with a utility knife and then snapped it normally.

Was that perhaps a chain hardware store? I can’t seem to get the insulation for less than €12 anywhere. Your price is really great. We already installed the insulation and screed ourselves in the utility room. Although here it’s only 9 cm (3.5 inches) of rigid polyurethane foam, but in that room it doesn’t really matter.