Convert rooftop terrace into living space

Hello everyone,

In a very small Swedish house (timber frame construction), there is a space problem and now it is being considered how to cost-effectively gain a few square meters.
From our layman’s perspective, the obvious solution would be to convert the unused roof terrace into living space.
The roof terrace is about 14 sqm and is basically the flat roof of an extension on the gable side of the house.
Theoretically (for us laymen everything is always so simple ), it would only need three walls and a roof. The door opening, previously a terrace door, can remain as it is and be converted into a normal room door. Of course, it should be adapted in terms of material and appearance to the rest of the house, so also built in timber frame construction. A window would of course also be nice.
Before moving forward with this idea towards an architect/carpenter, it would be very helpful to hear if this project is even feasible? Can a roof terrace simply be "sealed off"? Is this idea sensible and practicable or just a fixed idea that would cause immense costs?
Speaking of costs... I know costs are very individual, but can someone give me a ballpark figure for such a project (we will do the interior work ourselves, it’s only about walls and roof)? Is it more up to 10,000 EUR? Up to 25,000? We really have not the slightest clue which way it might go and would be grateful for a rough estimate!

Thanks and best regards!

1. Check or have checked whether an extension of the living space is permitted according to the [B-Planes]. -> Floor area ratio/floor space index. Also: would the house then possibly be considered a two-story building in the calculation? It could be that this is not allowed in your area. Then the boundary distances to the neighbor must be observed. Increasing a boundary building is usually not allowed. So: most of this can be checked by yourself, then ask the building authority, they have open consultation hours. If this extension is permitted, the question of structural engineering arises: for this, you need an architect/structural engineer. The architect can also provide information about prices.

Thank you very much for your reply! There should be no problems with the building authority. Previously, there was a semi-detached house (courtyard building) here, which burned down and two single-family houses standing side by side were rebuilt. According to the plan and information from the building authority, we can definitely build up to the boundary again. But we wouldn't have to do that anyway, since we only want to build upwards. The current extension only has a ground floor; we would simply want to add the first floor, and that would not be higher than the rest of our house. We just don't know if something like this is financially within our means at all. Let's put it this way: we don't want to spend more than 20,000 euros on this project! The question is whether we should even call an architect with this financial idea or if he will burst out laughing.

Since you have to pay specialists such as structural engineers, electricians, heating installers, and electricians, it can get tight. But I don't know.

Greetings

With such an extension, my first thought would be to ask a prefabricated house manufacturer. I haven't dealt with Swedish houses for ages, so apart from Västkust Stugan, no company name is currently running through my mind that I could offer. Are there any clues about the original manufacturer / builder of this house?