Twins - How to create living space?

We have been living comfortably with our two children for years in a small 80sqm house - ground floor, basement, no upper floor. Surprise: I am suddenly expecting twins. The joy is great, but it is now definitely too tight for us. How do we gain living space? The plot is very small, an extension will probably be difficult - actually, there is really no way to extend on any side. We don’t find the idea of putting the children in the basement or sleeping there ourselves very appealing... So the idea came up to add a floor. (For a pure attic conversion, the roof is too low.) According to the development plan, it is possible. We have absolutely no idea what awaits us, what is possible (or impossible), or what costs we will face. We have never dealt with anything like this before. What experiences have you had with adding a floor? What costs can we expect for 80sqm? Is a partial conversion of the roof possible? (30 or 40 sqm more would actually be enough for us.) What is the first step and who should we contact first? How do you properly inform yourself? What questions should you ask whom? Or are there other ideas for gaining living space? Questions upon questions ;-) ... Nina

Just throwing some ideas out there, to consider/keep in mind:
- Development of the future upper floor (stairs)
- Supply of utilities (electricity, water, if desired)
- Floor slab (structural integrity, impact sound insulation)

In a partial expansion, dormers can increase the available space.

A contact person would be an architect.

Why don't you reveal more about the house (year built, construction method, design of the floor slab, the roof structure, the stairs to the attic, floor plan) ;-).

First of all, congratulations! Twins are definitely quite a package.

Describe your living situation. How old are the older children? In other words, will one of them possibly move out soon?
Would an extension be possible? Even if it's just a few meters on each side, it can already help to get another room.

You will probably not be able to avoid an architect.
Also keep in mind that with the twins you will soon become very immobile. My husband's cousin is now at the end of the 7th month and looks like I did at the end of the pregnancy.