ᐅ Cost Estimate for Converting a 70 sqm Shell Structure into a Finished Apartment

Greetings,

Here’s the situation. My father-in-law received a rather devastating diagnosis some time ago and, well, he knows his time is now quite limited. He expressed the wish to spend his remaining years with us.

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

We have very little experience with building work and are not really skilled enough to do much ourselves.

So, the question for us is about the possible costs. Of course, I understand that no one can give a precise estimate without knowing the specifics in person, but we are looking for a rough guideline. Should we be budgeting around 25,000, 50,000, or even 100,000?

Here are the details: converting 70 square meters (750 square feet) of storage/garage into an apartment. Apart from a few electrical cables for lights and electric garage doors or outlets, the space is essentially a shell. Bare 280 millimeters (11 inches) of reinforced concrete, unfinished.

The heating room and laundry room are directly adjacent, so only one wall each would need to be opened to run the necessary pipes.

So, three windows would need to be cut into the concrete, the garage door openings bricked up, about 10 meters (33 feet) of drywall installed, plumbing laid for the bathroom and kitchen, as well as electrical wiring. Everything would also need to be properly insulated and plastered. The existing floor tiles would have to be removed, the floor sanded and leveled, followed by the installation of impact sound insulation and vinyl flooring.

Writing this down now, I realize what we’re facing.

We’d like to have the entire project done by a qualified professional company.

Would you have an estimate of what this might approximately cost, including materials and labor?

Thank you in advance for your help. We’re currently unsure if the project is financially feasible.

Best regards,

Peter

P.S.: Wishing you all a happy New Year!

First of all, it must be checked whether the project is legally permissible under building regulations. You are converting an outbuilding without setback requirements (at least in BY this applies) into a residential building. Completely different rules apply in this case. Considering the necessary modifications to the existing structure (cutting out windows, etc.) and the increased heating capacity and so on, I would expect costs that are not significantly lower than those for constructing about 70 sqm (750 sq ft) of new living space. Maybe reduced by the earthworks and some other expenses, but still around €2,000–2,500 per sqm (€185–230 per sq ft). Essentially, you will need a full interior fit-out, rough installations, interior/exterior plastering, flooring, fixtures, and so forth, including new structural engineering due to the window openings. A good friend built a single-level extension (13 sqm / 140 sq ft) for their third child. The initial budget was €22,000, but it ended up costing €33,000. His final words were, “If I had known exactly how much it would cost, I would have stayed away.” He did most of the work himself, because quotes ranged from €47,000 to €58,000. Such “small-scale projects” usually end up being more expensive per square meter since certain costs are the same regardless of whether it’s a 170 sqm (1,830 sq ft) project or smaller.

Regardless of the cost, is it even allowed to convert the garage into living space?

Hello,

thank you very much for your responses.

It is not really an outbuilding, but the basement of our house. Back then, a solid cellar was built and then a prefabricated house was constructed on top. So nothing extends beyond that; in effect, it is our above-ground cellar. Until the COVID-19 pandemic, the double garage was used as storage space for my company.

At 2,000–2,500 €/sqm (approximately 185–230 USD/sq ft), we will probably have to shelve the project.

Best regards,

Peter

Dendroaspis schrieb:

Now that I’m writing this, I’m starting to realize what we’re actually facing.

Yes, when you write it down, everything suddenly seems quite overwhelming 😉

Dendroaspis schrieb:

So there’s nothing left over or anything like that—in the end, it’s basically our above-ground basement.

At least it’s not edge development, which would have made the project unfeasible.

How about the requirements for habitable rooms? Does the garage meet the standards? Things like natural light, ventilation, ceiling height (these are specified in the building code of your federal state).
Maybe a nice mobile home in the garden would be cheaper and more comfortable to live in? That would at least be accessible.

You can hardly avoid requesting a quote from a construction company. But you should expect something around 50,000 (about 55,000).