Cost question: Conversion of 70 sqm shell construction into an apartment

Greetings,

and this is about the following. My father-in-law received a rather devastating diagnosis some time ago and well, knows that his time is now very limited. He therefore expressed the wish to spend his last remaining years with us.

Since I still have a large storage room or a spacious double garage available, which is currently used as a storage closet, we quickly came up with the idea to convert it into an apartment.

Now we are very inexperienced when it comes to building and not really skilled enough to do much ourselves.

Therefore, the question for us is about the potentially arising costs. Of course, I know that no one can give a concrete estimate without knowing the circumstances personally, but it is about a rough guideline. Should we calculate with 25k, 50k or even 100k.

It is about the following. Converting 70sqm of storage/garage into an apartment. Except for a few electrical lines for lighting and electric garage doors or sockets, the whole thing is in shell condition. So bare 28cm reinforced concrete, unplastered.

Heating room and laundry room are directly adjacent, so only one wall each would have to be broken through to lay the corresponding lines.

So 3 windows would have to be cut into the concrete, the garage door openings bricked up, about 10 meters of drywall partition installed, lines laid for bathroom and kitchen, as well as electricity installed. Of course, everything properly insulated and plastered. The floor tiles would have to be removed, the floor sanded and leveled, then impact sound insulation and vinyl flooring laid.

Now that I write this, I first realize what lies ahead of us.

We would of course like to have the whole thing done by a suitable professional company.

Would you have an estimate of what the whole thing could (more or less) cost, including materials and labor?

I thank you in advance for your help. We are currently not sure whether the project is financially manageable at all.

With best regards,

Peter

P.S.: Wishing you all a happy new year!

First of all, it must be checked from a building law perspective whether the project is even permissible. You are turning an outbuilding without setback relevance (at least in BY) into a residential building. Completely different rules apply for this. Considering the necessary adjustments to the existing building structure (cutting out windows, etc.) and the increase in heating capacity & co., I would now assume costs that are not significantly lower than those for the new construction of these 70 sqm of living space. Maybe reduced by the earthworks and a few other costs, but still around 2,000-2,500€/sqm. You basically need the complete interior finishing, rough installations, plaster inside/outside, floor coverings, fittings, etc., including new statics, of course, due to the window cutouts. A good friend built an additional ground-level room (13 sqm) for the third child. The planned budget was 22,000€. In the end, it cost him 33,000€. His words at the end were: “If I had known that precisely beforehand, I would have stayed away from it.” He did most of it himself, as offers ranged from 47,000€ to 58,000€. Such “small construction sites” are usually somewhat more expensive per sqm because certain costs are incurred just like with 170 sqm construction sites.

Regardless of the costs, is the garage allowed to be converted into living space at all?

Hello,

thank you very much for your responses.

It is not a separate building in that sense, but the basement of our house. At that time, a solid cellar was built and then a prefab house was placed on top. So nothing protrudes or anything like that, it is basically our above-ground cellar. Until Corona, the double garage was used as storage space for my company.

So at 2,000-2,500€/sqm we will probably have to shelve the project.

Best regards,

Peter

Now that I’m writing this, I first realize what would be coming our way.

Yes, when writing everything becomes frighteningly clear ;)

So nothing remains above, or similar, but in the end it is our extraterrestrial basement.

At least it’s not a peripheral development where the project would be obsolete.

How does it look regarding the requirements for habitable rooms? Does the garage meet the standard? Lighting, ventilation, room height (check your federal state’s building code). Possibly a nice mobile home in the garden would be a bit cheaper and nicer to live in?! That would at least be barrier-free.

You can hardly avoid a request to a construction company. But I would already expect around 50k.