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Understood. For that, I will need an expert who can first assess the current situation and then suggest the best measures to achieve the 140%.

I have already registered on the mentioned expert platform. Let’s see if someone responds. Otherwise, we won’t make much progress.

Using an "energy efficiency expert" is usually sensible for existing buildings, especially due to funding options available through the KFW. However, it is also possible to download corresponding software as a trial version and, with a few hours of effort, get a fairly good idea of what is feasible and which factors have what impact.

At least the HT value can be calculated quite easily by multiplying the surface areas of the individual building components by their respective U-values (U-value calculator (ubakus)), summing the results, dividing this total by the overall surface area of all components, and then adding the thermal bridge allowance.

Example (greatly simplified):
For a house with 200m² (2153 sq ft) roof area with a U-value of 0.2 and 300m² (3229 sq ft) wall area with a U-value of 0.4, and a standard thermal bridge allowance for existing buildings of 0.1, the calculation would look like this:

200 * 0.2 = 40
300 * 0.4 = 120
--------
Total surface area: 200 + 300 = 500m² (5382 sq ft)
HT sum: 40 + 120 = 160

HT-building: 160/500 + 0.1 = 0.32 + 0.1 = 0.42

This also clearly shows how much of an effect a detailed thermal bridge calculation can have. If, for example, instead of 0.1 you only need to calculate with 0.07, the HT improves to 0.39.
This improvement has a greater impact than upgrading from basic triple-glazed windows to passive house windows.

By the way, I recommend proactively contacting the experts.

Roof? What roof?
(Just kidding)

I had already started doing my own calculations. The Ubakus is a great tip! Thanks. I hadn’t heard of that before.

We will definitely get in touch with an expert. What’s difficult for me is finding the right one. A chimney sweep won’t be much help to us. We really need a professional, not some wannabe. Maybe we should ask the building authority / planning department?

kaho674 schrieb:
What I find difficult is to find the right one

I would simply try searching for “KFW monument.” Experts who specialize in this area usually have a good understanding of older (preservable) building fabric and can typically suggest appropriate ways to handle it during a renovation.

But yes, in the end, it’s unfortunately always a leap into the unknown – as usual :-(

At the moment, we are getting confused about the regulations. We found the following information online:

Energy Saving Ordinance 2014: Clarification of Component Requirements

A welcome clarification is provided by the Energy Saving Ordinance 2014 in § 9 (Alterations, Extensions, and Renovations of Buildings).

The first paragraph of § 9 (Alterations, Extensions, and Renovations of Buildings) caused the most common misunderstanding under the Energy Saving Ordinance 2009 among both homeowners and professionals: owners of older buildings who wanted to renovate a part of their façade, roof, or some windows mistakenly believed that they were required by the Energy Saving Ordinance 2009 to renovate the entire façade, roof, or all windows.

While the Energy Saving Ordinance 2009 referred in that paragraph to the “affected exterior components” and the requirements for thermal insulation, the Energy Saving Ordinance 2014 formulates the text more clearly in § 9: alterations must, if applicable, be carried out so that “the thermal transmittance (U-values) of the affected areas do not exceed the maximum U-values specified for such exterior components in Appendix 3.”

In short: Only those areas of an exterior component that are actually "touched" or energetically modified need to comply with the Energy Saving Ordinance requirements.

Basically, the question arises as to whether a change of use even requires significant building alterations. Again, from online sources:

... the Energy Saving Ordinance (Energy Saving Ordinance 2014) in § 10 (Retrofits for Systems and Buildings) potentially only requires the following retrofits:

- Replacement of old boilers,
- insulation of uninsulated heating pipes,
- insulation of uninsulated hot water pipes,
- insulation of top floor ceilings.

If this is the case, we would only be strictly obligated to insulate the top floor ceiling; everything else is already new or meets the Energy Saving Ordinance requirements.

The question is about the change of use. If I convert an industrial building into residential space, which regulations apply then? You certainly can’t just declare any old garage a house. On the other hand, this building is not a garage – it has 60cm (24 inches) thick walls with gas, water, plumbing, etc.

I strongly suspect that we could indeed create apartments there without having to carry out extensive Energy Saving Ordinance retrofits. The only question is, where is this stated?

I sent you a link via private message that explains this quite well.

Edit: A brief summary for the interested reader:

1) Change of use without alterations -> No energy saving regulations apply
2) Change of use with structural alterations -> Components (e.g., windows) must comply with energy saving regulations, or the entire building must meet the 140% rule
3) Change of use with extension/expansion -> If new living space is created (e.g., converting a garage into a bedroom), all involved components must comply with energy saving regulations (e.g., windows replacing the garage door).
If the extension exceeds 50m² (540 ft²) and a new heat generator is installed at the same time, the extension as a whole must comply with the energy saving regulations. This includes exterior walls or the garage roof, even if they were not altered.