ᐅ Renovating an older building: which insulation measures are mandatory?

Hello everyone, I need your advice because I’m having trouble understanding all the energy requirements for old houses.

We will start renovating a house built in 1930, which has been in the family. The roof will be completely replaced (there was woodworm) and insulated according to current standards. New windows and shutters will also be installed, but with only double glazing, though with a thermal transmittance value of 1.0 W/(m²K) (0.18 BTU/(ft²·h·°F)).

The exterior walls are 60 cm (24 inches) thick slate masonry, and the facade is in good condition. However, we want to avoid insulating the exterior walls for cost reasons.

Therefore, the planned energy efficiency measures are limited to the roof and windows. Is this sufficient to meet legal requirements? Or is it mandatory to insulate the exterior walls when purchasing an old house?

Maybe someone can also tell me the approximate cost of an energy consultant, or is one not necessarily required? There is no energy performance certificate.

Thanks in advance!

For work purposes, we had an energy consultant evaluate a 450 sqm (4,844 sq ft) building, and we paid about 3,000 euros for it. The report was definitely worthwhile because it showed what could be done sensibly. I wrote “sensibly” in extra large letters because with expensive building technologies that they try to sell you, you usually achieve only a limited effect. The result was: remove all intact mahogany windows, extend them with additional frames, install triple glazing, and fit new seals. Blow Perlite insulation into the cavities between the interior walls and the brick cladding. Repair the roof insulation where it was damaged. That’s it. No technical systems, no solar panels, nothing. Costs: 23,000 euros. Result: oil consumption dropped from 9,000 liters (2,378 gallons) to 6,000 liters (1,585 gallons) per year.
Regulations give you complete freedom with older existing houses. Karsten

Unfortunately, the legislature does not allow any flexibility. Usually, little attention is paid to this...

Energy Saving Ordinance Appendix 3 to §8: "If you modify the wall, you must insulate it according to Table 1.
U-value = 0.24, which corresponds to about 12 cm (5 inches) of required insulation.
If you do not modify the wall, you do not have to do anything – but is that really sensible?

Insulating the top-floor ceiling or roof is mandatory within 24 months after purchase. Everything else is optional.
The exterior wall insulation recommended by Lumpi_LE only applies to extensive renovation projects.
So, everything is fine with you—proceed as planned.
Regarding the heating system, something might still come up. If it is older than 30 years and not a condensing or low-temperature boiler, it should also be replaced at some point.

Thank you all!

The entire heating system was converted from electric heating to an oil-fired central heating system in 2000, and it will probably remain that way. I might install a hot water storage tank later and lay the necessary water pipes, since the hot water is still provided by instantaneous heaters. This, of course, depends on whether it works well with the existing Viessmann system.

The exterior wall/facade was repainted about six years ago and still looks quite good, so we won’t be making any changes to the facade or hopefully need to add insulation.

At least, with the completely new roof including insulation and the new windows with matching roller shutter boxes, we expect to achieve a better energy rating. The roof insulation, as is well known, is not cheap and likely accounts for about one-third of the total roof costs.

I’m really curious to see what prices the roofing contractors will quote. Unfortunately, there is hardly any information online about the costs of roofs from people who have renovated older houses.

We have two simple gable roofs (main house and extension) that both need to be completely rebuilt, including the framework. One roof has an area of 144 m² (1,550 sq ft) with a 43-degree pitch, and the extension has 83 m² (893 sq ft) with the same 43-degree pitch. Both roofs will be insulated and each will have two standard-sized Velux windows.

Based on rough calculations from individual figures found online, I came up with a total of around €55,000 (which could be about half of the total renovation costs in our case).

Could that be realistic, or is it overestimated? Unfortunately, the contractors are taking several weeks to provide quotes. This is frustrating, especially since the house transaction is about to take place. Luckily, the purchase price is low.

Best regards

Considering that the old roof still needs to be removed and disposed of, and someone has to spend a few minutes on the planning, in my opinion, the estimate is rather too low.
Roof frame, covering, insulation, and sealing come to around 250 per square meter (gross), demolition and disposal around 10-15 thousand euros.
Altogether, that sums up to roughly 70 thousand euros.