Underfloor heating in an old house, installation above the floor slab. Efficiency and costs?

Hello everyone,
first of all, thank you very much for reading this.

We are in the process of buying a house, built in the mid-70s.
As can be seen from the drawings, the house (end of a terraced house) is apparently built on a strip foundation. It is only partially basemented, about 4m extends into the house, from there half a floor down to the basement, and half a floor up to the living area. (Slight slope)
Currently, there is an approximately 20-year-old oil heating system installed, and corresponding radiators in all rooms.
Unfortunately, I do not know exactly how the construction above the floor slab is, presumably (according to a statement from a future neighbor), a thin layer of Styrofoam and on top of that 6-8cm of screed.
Now the whole thing is supposed to be replaced by a gas condensing boiler ([Tank shall be in the garden]) and underfloor heating.
The quick, still relatively inexpensive way would be to mill the screed with appropriate slots for the pipes and then pour/close it with a thin layer of leveling compound.
I am aware that this will of course waste quite a bit of energy in the floor slab...
On the other hand, I see no point in doing something that will only pay off in 20 or more years, since I will hardly recover the additional costs through savings on heating costs during my lifetime. Or is the difference so huge that it pays off in at most 10 years?

Thank you very much for your opinion

Get an energy consultant who calculates options for you. Everything else is just groping in the dark. Underfloor heating does not save energy per se.

Hello Nightdancer, we have already thought about that as well, also about bringing in a "professional" for the entire renovation. Who would be suitable for that, an architect, a building surveyor? Later it will also be about the facade, e.g. clinker, curtain cladding, insulating the shed roof, etc. Greetings from the Bergisches

Where is the property located? I conduct real estate purchase consultations throughout NRW/RLP, occasionally also further renovation planning/consultations, such as in Radevormwald/Gummersbach 2013/2014. I am happy to send you information about my purchase consultation by email.

Such considerations for energy-efficient renovation must always be planned as a holistic concept including building services/heating technology. Underfloor heating without sufficient and above all Energy Saving Ordinance-compliant floor slab insulation makes little sense. The future insulation standard of the house is also crucial. Underfloor heating as a low-temperature heating system requires a very well-insulated building envelope. The dimensioning and design of the underfloor heating must, for example, be proven in a heat load calculation. Before purchasing, the property should definitely be assessed regarding its condition, any building damage/moisture issues, and the renovation backlog. Additionally, building, planning, and ownership law conditions must be checked so that you as a new owner can acquire a property free of encumbrances.

Of course, the house is still to be further insulated, but with moderation, because I see no point in insulating the house for > 100,000€, as with the latest technology, insulation would probably reach that range, including a ventilation system, etc.

About 100m² of shed roof and 2 side exterior walls (planned insulated brick) are next, along with about 10 windows, which a friendly bricklayer will install, as well as guidance/assistance with bricklaying and tiling. I will do the electrical installation myself (I am trained), and a friendly plumber will handle the water.
All in all, we have 60,000 available for the renovation.
The house is empty and all the walls are covered with old wallpaper/old paint (no latex, nothing hidden behind wood), so I can see relatively well that there is no mold anywhere.

Then I will probably remove the old screed and rebuild it from the floor slab up. Since the budget is tight, it will come down to a dry screed, because I can put in most of the muscle work myself and make sure the material is of good quality.

After all, the house is in a condition that it was lived in without problems until a few weeks ago (the owner is now in a nursing home).
For us, it should last another 15-20 years; our heirs are welcome to energetically renovate it based on the best criteria at that time... in other words, tear it down ;-)


Location is Radevormwald Dahlerau

I would definitely reconsider the underfloor heating... Removing the screed everywhere and rebuilding it and the whole drama. Is the underfloor heating really worth that much to you? I also doubt that you save that much money with it in a well-insulated house, especially when you calculate over 15-20 years. Well, if in the end it's just about having a warm floor, you could simply wear slippers like people used to do or lay down rugs or just accept it as it is. After all, you’re not walking on an ice sheet. Before knocking out the screed, I would have heating and plumbing come by and give a cost estimate.