Facade insulation or roof insulation, home insulation, specialist consultant?

Hello everyone,

we are a happy married couple currently looking for a suitable house.
We have just started and have many question marks written all over our faces.

A house is under closer consideration and, according to information on the internet, has a final energy demand of 156 kWh/(m²*a).
It is an end terrace house with 118m² of living space with gas central heating from 1973 in the beautiful NRW.

We have received the exposé and now two values appear there.
One is again the final energy demand value of the building shown on the internet presence of 156 kWh/(m²*a).
The other is the primary energy demand value of the building of 180 kWh/(m²*a). What exactly is the difference between the two figures?
According to the agent, the gas costs are 1200€ per year. Is that realistic with the above-mentioned values?

If one now comes up with the idea of insulating anew, what savings can be achieved?
As façade insulation, there are 3 options as I have read, and of course, there is also the possibility of roof insulation.
What I have read is that an elaborate façade insulation is supposed to bring a maximum of 30% savings.
On the other hand, we read values of 20% for roof insulation.
The gas heating can of course also be replaced, but we will leave that calculation aside for now.

The question for us is, is a new insulation worthwhile at all? Companies will tell me that I better insulate anew. But that will not be an objective opinion, as it is not neutral! One lives in a house until one can no longer climb the stairs, until retirement.
That means with 30 years it’s still 35 years of living time. Of course, one also achieves an increase in the value of the house through insulation, which one partly recovers upon later sale.

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Now to the 3 sample calculations that I have made:

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Another question is, how can one insulate later on (house already bought and lived in for 5 or 10 years)? Is that possible without major restrictions if one already lives there? Or should the insulation work be done before moving in in any case?

Thank you in advance for all info & contributions!

ReLaX ;-)

Insulating is also somewhat a question of the "green conscience," not necessarily just about saving a lot of money.

However, with a 40-year-old house, you should consider the house as a whole if you want to renovate energetically:
- Insulation of the facade
- Insulation of the roof
- Insulation of the ceiling below the roof
- Insulation of the basement ceiling
- New windows
- New heating system
- Is hot water preparation included in gas consumption? (If yes, the savings you calculate will be significantly lower, since only part of the gas consumption for heating can be reduced. There are no savings for the hot water portion).

If the house, for example, still has the very old windows, I would (personal opinion) rather focus on the windows.

Facade insulation can always be done, even if you have the windows moved outward, it doesn’t cause much mess for you.

From a purely economic point of view, insulation in existing buildings is often not worthwhile if you assume that energy costs will not change (upwards).

Whether it is comfortable to live in a place from the 70s that drafts, is possibly damp, etc., is another matter. Whether this later results in higher follow-up costs for the repair of moisture/mold damage, etc., is also another question.

Is a new television worth it if the old tube still works without a remote control?

156 vs 180 mag rechnerisch vs. real sein? In new buildings, the energy providers still play a role in the calculation of primary energy (electricity has a higher primary energy factor than e.g. gas... this does not change the fact that the heat demand is the same) - the idea is that some energy sources are less emission-intensive than others. However, this should not be relevant here.
1200 € p.a. can be about right. My parents have a terraced house and pay just under 800 € p.a.
1200 € / 0.7 € * 10 / 180 = 95 sqm... or 108 sqm. How many sqm does the good piece have?
Is the heating from 1973?! Then you should replace it, by the way.
Regarding renovation: I would not do it. 160 kWh/sqm a is not new construction, but also not a settlement house. If the roof needs to be redone anyway at some point, you can do that in the course of that. The house works as it stands (that should not be underestimated). If you notice in year 3 that it is always cold by the window and you feel uncomfortable, you can still replace it - but then to improve living comfort and not because someone has nicely calculated it for you.

We consciously decided against exterior wall insulation. However, we renewed and insulated the rest. So far, we do not regret our decision. But retrofitting facade insulation is usually not economically viable.

Wiki: "The primary energy demand (according to abbreviated: QP) of a system includes, in addition to the actual of an energy carrier, the amount of energy required by upstream process chains outside the system boundary during the extraction, conversion, and distribution of the energy carrier (primary energy)." Wiki: Final energy is the portion of primary energy remaining after energy conversion and transmission losses that has passed through the consumer's house connection."

Calculation: €1,200 gross = €1,008 net / 5.28 Ct7kWh (gas price for Euskirchen area) = 19,098 kWh / 118m2 = 161 kWh/m2. The value on the certificate is therefore correct, which cannot be said of all certificates.

The energetic renovation of a house should not only be considered from the perspective of saving as much of this final energy as possible, but also of living in a house where so-called "comfort" is ensured. The rooms should be designed structurally and with an insulation standard so that one enjoys living in them. Comfort, which should not be confused with the notorious German "Gemütlichkeit," has a physiological/psychological component that should not be underestimated. A key value is, for example, a maximum difference between indoor air temperature and surface temperature of the inner side of the exterior walls of max. 2-3 °C = minimum 18 °C. This value is often significantly undershot in poorly insulated old buildings: the user of these rooms distances themselves from cold walls and feels uncomfortable. In particularly cold spots (thermal bridges), condensation from warm, humid air can occur, followed by mold formation.

Energetic building renovation must necessarily be viewed and planned in the overall context of the building. This includes the insulation of components from the basement ceiling/floor slab to the ceiling above the upper floor/the roof, the windows, the building technology (heating, ventilation). If only individual components are insulated, the non-insulated components increasingly become points of condensation failure. New windows in an uninsulated façade have the same effect.

In your case, a so-called building energy consultation according to BAFA standards, which is also subsidized, is worthwhile. A qualified consultant, preferably an architect/structural engineer with in-depth knowledge of old building renovation, calculates the energetic actual state of the building using approved software after a building survey and prepares variants of insulation and heating, each with the calculated final energy demand and amortization period.

Usually worthwhile is the insulation of the top floor ceiling (= retrofit obligation according to Energieeinsparverordnung within 2 years after purchase), which is also the most cost-effective. All other measures must be examined within a concept that also integrates remodeling wishes, possible construction defects/moisture damage, and structural peculiarities (building waterproofing).

Before purchase, you should have the house inspected by an expert/architect/structural engineer within the framework of a real estate purchase consultation under these aspects to realistically estimate the renovation and modernization effort for your financing planning.