U-values not comprehensible from the energy consultant

Hello everyone,

As part of a detailed heating load calculation for my fully renovated house, there were questions about the U-values from the energy consultant, as these are not comprehensible. Unfortunately, the documentation does not provide any indication of how the wall construction was assumed.
Here are the values:


Let's take the example of the exterior wall on the upper floor: a U-value of 0.18 W/m2K was calculated here.
According to the construction drawings, the wall structure consists of 24 cm Ytong W PP2 and the 16 cm WLS 032 insulation suggested by the energy consultant, applied using EPS.
When I recalculate this in, for example, Ubakus, and deliberately do not include the interior and exterior plaster in order to cover the worst case, I get a U-value of 0.132.
I can't find it at the moment in the many documents, but somewhere a thermal bridge allowance of 0.05 W/m2K was specified.

Can someone who is more knowledgeable in this matter explain where this large difference from 0.18 to 0.132 comes from?

Thank you

I believe I remember: if no explicit individual calculation of the thermal bridges is carried out, this flat-rate surcharge applies (must be added)

I seem to remember: if no explicit individual calculation of the thermal bridges is carried out, this flat-rate surcharge is applied (must be applied)

yes, that would also fit quite well with the 0.05. However, I originally did not think that this surcharge would then be calculated on every value. Especially since the upper floor was newly added and has no extensions at all. I could still understand it for the ground floor due to the entrance and basement stairs.

An energy consultant is also there to ADVISE ;-)

Maybe it makes some kind of sense for you to calculate the cold bridges individually? For example, I had a very good BD test result (about 0.43?) and because of that I could use cheaper insulation in the floor structure (since the overall system has to reach a certain value to achieve the goal (Passive House for me)...

yes, the 0.05 would also fit quite precisely. But originally, I didn't think that this surcharge would be calculated on every value. Especially since the upper floor was newly extended and has no additional attachments.
I would have understood it for the ground floor because of the entrance and basement stairs.

The thermal bridge surcharge is applied to the entire heat-transferring envelope area, excluding opaque components like windows.
The surcharge is 0.1 W/m²K if thermal bridges are not examined more closely and 0.05 W/m²K if they are considered separately. Alternatively, an individual calculation of the thermal bridges can be performed. However, this only makes sense in borderline cases, for example, if it results in achieving a higher funding level. This is not the case in your situation.
This value captures all inhomogeneities in the wall structure that do not consist exactly of 24 cm YTong WPP 2, e.g., window lintels and ring beams as well as geometrically induced thermal bridges like external corners, which have a higher heat transfer than a straight wall.
And always keep in mind:
You can demonstrate whatever you want theoretically, but it has no impact on the actual heating demand.

You are great, thank you for the explanations. Then it is really the thermal bridge surcharge that is the reason for the difference in the U-values.