Renovation of an old building from energy class H to efficiency house KfW 55 EE

Hello everyone,

I am new here in the forum and have a question about the following topic:
We (my wife and I) would like to buy a semi-detached house, renovate it, and then rent it out. The property has the following key data:

CURRENT condition:
- Semi-detached house, built in 1956. Classified as Worst Performance Building
- Energy demand according to the energy certificate = 344 kWh/m²*a
- Living area ground floor and upper floor = 110 m². Ground floor and upper floor are two separate residential units.
- Usable area according to energy certificate: 208 m². Plot area 397 m².
- Basement, ground floor, upper floor, attic, all simple equipment
- Basement probably not insulated, but dry
- Ground floor and upper floor are developed. Exterior walls as far as can be seen inside and outside without insulation. Built back then with pumice stones or hollow blocks. The exterior wall is approx. 30 cm thick. Plastered outside.
- Attic is not developed. Inside on the gable side you can see the bare pumice stones. See picture in the attachment.
- Roof is not insulated. You can see the rafters and the tiles. Rafter thickness approx. 13 cm.
- Heating is a floor-level gas heating system. Built in 1980.
- Wooden windows with double glazing. Need to be replaced.
- Basement ceiling is a reinforced ceiling or concrete stone ceiling (see picture in the attachment). The ceiling above the ground floor is probably more of a wooden beam ceiling. Unfortunately, you cannot see inside and the real estate agent did not know either.

So much for the CURRENT condition.

Now the TARGET condition.
The plan is to renovate the house with the KfW loan 261, namely to a KfW 55 EE standard.

The following is to be done:

- Full thermal insulation/external thermal insulation composite system (ETICS) made of styrofoam on the facade. Thickness according to the then available calculation.
- Window replacement to triple glazing. Currently double glazing.
- Roof insulation inside, between rafters (cellulose) and outside (wood fiber). Thicknesses depend on calculation results.
- Insulate basement ceiling from below. Thickness according to calculation. However, not much is possible here because the basement has a clear passage height of only about 1.90 m.
- New heating system (air-water heat pump) with radiators. With underfloor heating, the ceiling height would otherwise probably be too low due to the construction.
- Ground floor and upper floor are separate residential units and shall remain so. In the upper floor only the attic should be added to the upper floor apartment.
- If necessary, a small photovoltaic system to achieve the EE.

That's it for the TARGET condition so far. I hope I haven’t forgotten any important information, otherwise just write.

My question now is whether, with the above conditions, I can achieve the KfW 55 EE standard for the house. I see a problem with the building partition wall to the other semi-detached house because unfortunately I cannot insulate this wall with an ETICS. Has anyone of you maybe already gained experience with renovating a semi-detached house and can give me your assessment on this?

That would be great. Many thanks in advance. If information is missing, just write.

Best regards
Florian

My question now is whether I can get the house at KfW 55 EE with the conditions mentioned above.

Yes, something like that is doable without major problems. The only "small" problem is that it costs a lot of money. Are location, demand, and rent so good and high that renting it out is worthwhile? THAT is the much more important question for me. Because if you have to invest another 350k for the renovation (you will also install new electrical wiring—nicely separated for both apartments, renovate the bathrooms, renew the floors, etc.), the rent should roughly be around 2,000€ net for both apartments together (estimated, because the purchase price is still added, you are in Bavaria, and I do not assume that you are paying only 50k for the semi-detached house).

Thank you for the quick response and the assessment that this is doable. As I said, I was a bit concerned about the non-insulatable building partition wall. But probably the other insulation thicknesses will just have to be increased accordingly.

Yes, regarding the price, you estimated well. Here is a brief overview of my calculation:

- Current purchase price €320,000, without additional costs. With additional costs approximately €348,000.
- My estimate of what we will need to invest is about €300,000.
- New roof and attic conversion
- New electrical and heating system
- Full thermal insulation on the facade
- Insulate basement ceiling from below
- Replace windows
- Renovate bathrooms. They are already very old and the room layout is not optimal. Probably also the floors :/
- Create an additional parking space in front of the house
- Etc. Quite a bit of work :D
- So estimated total production costs of about €650,000.
- If the KfW grant works out, then 20% grant at KfW55EE + 10% due to WPB, so 30% per residential unit. You can borrow €150k per residential unit => grant of €45k x 2 = €90,000 grant.
- Total production costs with grant €650,000 - €90,000 = €560,000.
- If we convert the attic, the living area increases from a total of 110 m² to about 145 m². Ground floor apartment about 55 m², upper floor apartment about 90 m².
- Assumed rent price for fully renovated apartments at the end of 2026: €14/m².
- Living space 145 x €14/m² = €2,030/month cold rent.
- You must not overestimate your own work, but I think I can still contribute something and possibly reduce production costs again (laying flooring, painting, etc.).
- But calculated conservatively, that would be a rental yield of 2030*12=24,360 / 650,000 = 3.7% (without KfW repayment subsidy) and 2030*12=24,360 / 560,000 = 4.35% (with KfW repayment subsidy). The apartments could then almost pay for themselves. Maybe I can also negotiate the purchase price down by another €20k, then it would be around 4.5%.
- The semi-detached house is on the edge of 88161 Lindenberg, quiet location, yet fairly quick to the center.

Link in Maps:

So the location should fit. The cemetery borders to the south/east, but I don’t think that will deter many. They are quiet neighbors ;)
Demand is generally quite high around Lindenberg because the supply is currently just too low. Rent prices for new buildings are today between €14.5-15.5/m². Without a garden. The ground floor apartment would also have a large garden + conservatory, the upper floor apartment a balcony (would be added). I think that by the end of 2026, €14/m² will be more or less realistic and not exaggerated. At least I hope so :D.

What’s important is that the KfW grant works out. Because with BAFA individual measures, the grant is significantly lower and there is no interest advantage with the loan. However, BAFA would be much easier to get. KfW 261 requires everything to fit together as a whole. That is a certain risk. I’ve already contacted an energy consultant, and his first impulse was to recommend BAFA because of the building partition wall and the blower door test required for KfW.

What do you think about my rough calculation? Do you see any major mistake at first glance?

Fits quite well with my assessment.

I had, as I said, some concerns about the non-insulatable building partition wall.

That would worry me the least. As long as the neighbor’s half is occupied and heated, it is a good insulation.

If we finish the attic, the living area will increase from a total of 110 m² to about 145 m².

I would have other concerns. What is the target tenant group supposed to be for the apartment on the ground floor as well as for the apartment in the attic? 55 sqm with garden and about 90 sqm in the attic without a balcony...

That would worry me the least. As long as the neighboring half is occupied and heated, that is good insulation.

That is exactly the point. I also thought at first that the room behind the separating wall of the building should be considered heated. However, the energy consultant said it is not that simple, and he would have to calculate quite a few thermal bridges here, which might make it difficult for KfW 55. But that was just the consultant's initial impulse. He could reconsider if he takes a closer look.

That would worry me the least. As long as the neighboring half is occupied and heated, that is good insulation.

I would have other concerns.
What is supposed to be the tenant target group for the apartment on the ground floor as well as for the apartment in the attic?
55 sqm with garden and about 90 sqm in the attic without balcony...

So for the small apartment on the ground floor with 55 m² the possible target group would be couples with up to one child, singles, or active older tenants.
The apartment has a bathroom, kitchen, living room, and two bedrooms. Small but sufficient. Most likely target group is couples. Thus, probably higher turnover.

The 90 m² apartment with balcony would rather be for small families with up to 2 children or couples who would use the rooms as an office or otherwise.
Older tenants are also a target group, but it is not barrier-free, since there is a staircase to the front door. And for the attic apartment you have to go up another staircase.
The attic apartment has a bathroom, kitchen, living room, master bedroom, small children’s bedroom, and in the attic there would be a large room of about 30-35 m² added.

Do you think the target groups I mentioned are rather not potential tenants?