ᐅ Choosing the Insulation Thickness (Cost-Benefit Analysis)

So roughly estimated, a "12cm (5 inch) wall" would have a U-value of about 0.27, while 18cm (7 inch) should reduce it to around 0.19. (I simply assumed plaster, 20cm (8 inch) concrete, external thermal insulation composite system (ETICS), and plaster.)

This should have a significantly greater impact than 20 euros per year.

You’ll only get a better feeling once you have the energy performance calculation in your hands.

But I’m not an expert, so maybe don’t put too much weight on my opinion.

Still, it’s puzzling to me how one could meet the 2016 energy saving regulations with just 12cm (5 inch).

I have the energy saving regulation certificate ready.

It passes easily both with and without controlled residential ventilation. It seems to be due to the geothermal system – it "covers everything."

Therefore, my question remains: 12 or 16 – 18 doesn't seem to make sense price-wise.

Regards
markus

It remains confusing to me, but that doesn’t really matter.

I still believe that increasing the insulation thickness by 50% must have a significantly larger impact on heating demand. See my comparison of U-values further above. Therefore, I think your calculation must be wrong. Off the top of my head, I would say insulation could save you somewhere between 10 and 20% of heating costs. However, I cannot prove this due to lack of knowledge.

Other factors to consider are, of course, the insulation values of the windows.
Ventilation losses are at least eliminated with controlled mechanical ventilation.

What I don’t understand is this:
You use an energy source (geothermal heat) that is relatively expensive, add controlled mechanical ventilation, which is also not cheap, and then want to save a few dozen dollars on insulation? I just don’t get it. I mean, we’re talking about €2,000 [or currency], which is not even close to 1% of the construction costs. Honestly, every kWh of heat that the building doesn’t lose in the first place is better than every newly produced kWh...

I would even go so far as to install as much photovoltaic on the roof as possible (<10kWp) with controlled mechanical ventilation plus ground-source heat pump, but that is a different topic.

I’m also skeptical, so I’m asking. Hopefully, someone can clarify the correct calculation method.

Regarding the other points, I can write a more detailed response in due course.

The fact is, we now have to watch the budget closely – if 18 versus 16 doesn’t make a difference, I don’t necessarily need it.

I have already set 16 for myself – since the available quotes are still unnegotiated, I assume we can manage within the budget with 16.

Regards,
Markus

I have taken a closer look at the energy saving regulation calculation. Your estimates were actually quite accurate.

For the exterior wall, the U-value is 0.268 at 12cm (5 inches) thickness, and about 0.205 at 16cm (6.3 inches). According to the calculation, the affected wall area is just under 200 square meters (2,150 square feet).

Changing only this parameter lowers the final energy demand from 17.27 to 16.71 and the primary energy demand from 31.09 to 30.08.

As mentioned, all other parameters remain the same (roof insulation, heating system, windows, doors, etc.).

On a more detailed review, I noticed there is also a projection provided (a “total balance”). I’m not sure how realistic it is, but it is still quite helpful:

12cm (5 inches) per year
- Primary energy demand 9961 kWh
- Final energy demand 5534 kWh

16cm (6.3 inches) per year
- Primary energy demand 9637 kWh
- Final energy demand 5354 kWh

Difference
- Primary energy demand 324 kWh
- Final energy demand 180 kWh

If I apply the calculation based on primary energy demand mentioned by (I believe) denz. and simply assume an annual performance factor of 4, this would mean:
324 kWh per year / 4 annual performance factor = 81 kWh per year additional electricity demand.

Assuming an electricity price of €0.30, this results in additional costs of €24 per year.

If I now consider the extra cost of €1300, it doesn’t really pay off. 18cm (7 inches) thickness is even less cost-effective.
If the negotiations allow for a good discount, I think we will still go for it.

I hope I haven’t made any mistakes.

Regards,
-Markus-

There isn’t that much heat loss through the facade, so the savings from increasing insulation on the exterior are not very high. This is also the case with renovation projects for existing buildings, where there are 100 other things to address before tackling the facade :-)