Decision on Insulation Thickness (Economic Calculation)

Hello everyone,

I currently have to decide on a thickness for our WDVS (facade). According to the Energy Saving Ordinance, I need at least 12 cm on my precast concrete parts.

I have now requested quotes for 14 cm, 16 cm, and 18 cm as well.

According to the architect, the energy demand differs as follows
Thickness Final energy demand Primary energy demand
12 cm 17.70 31.87
14 cm 17.66 31.78
16 cm 17.04 30.67
18 cm 17.01 30.62

The unit is KWH/m²A

And now?

The house is fully basemented. Basement insulation / roof insulation are not under consideration here. Geothermal energy as an energy source and controlled residential ventilation will be installed. Windows are triple glazed. About 220 m² of living/usable area are fully heated (attic insulated but not heated).

Do I now have to multiply the difference by the living/usable area, apply my average KWH price, and have the additional costs per year? Or is that way of thinking wrong?

Thanks and regards
Markus

Unfortunately, I cannot contribute anything to your exact question (yet), but why do you have precast concrete elements as walls above ground?

We have coordinated with our architect and selected a company that will construct the shell using precast concrete components including a [WU-Keller]. It will be erected in the next 2 weeks – topping-out ceremony at the end of April.

This was about the construction time and we liked the concept.

Regards
Markus

That is not uncommon now either. However, you have to decide a lot in advance, such as sockets, at least that is how I know it.

Setting a lot in advance: So-so.

Apart from the sensibly placed breakthroughs for my cable escapades, the Kaiser boxes cast into the ground floor ceiling for the spotlights, and the openings necessary for drainage, actually nothing.

Sockets are normally channeled - you just have to watch the thickness here.

Contributions on the topic :)?

Regards
Markus

What is your goal? Optimal cost-effectiveness? Then the extra cost of the thicker insulation is missing.

But the calculation is not that simple. Better insulation = lower heating load = fewer drilling meters and possibly even a smaller heat pump. It can be worthwhile, but there are some "ifs" involved.
Then there are factors like "comfort." Does the wall feel cold in winter? So cold that you don’t like sitting against it with your back and neck? I find that quite important, especially for cellars that might someday be used as living spaces. Far from the discussion about cost-effectiveness.
You also never get to the insulation underground again or only at a high cost. Maybe it’s better to add a bit more there?

In the end, it’s a fundamental decision. If you want the minimum, then stick with 12cm. It will also be comfortable to live in. If you believe in rising energy costs or have another motivator, then do more.
A centimeter of insulation thickness probably costs about €1.50 net per square meter, roughly speaking.