Expand the house or a crazy idea

I shared a room with my brother until I was 10. That was never a problem, but rather the opposite, since we played a lot together (age difference also 2 years). Therefore, I also like the suggestion to simply wait until the older child moves out. Of course, one has to approach this carefully, so that the child doesn’t feel thrown out because the siblings need their own rooms.

So if the two are only 2 years apart, I would honestly not change anything, except maybe the distribution of the rooms, so that the two sharing a room then get the largest room.

How much budget would you have? With sufficient budget, I would relocate the bathroom: parent area over the garage/carport with a master bathroom, possibly also a walk-in closet if desired. With the connections, it should work since there is a utility room and a WC on the ground floor. The current bathroom as a passage; a utility room can be realized there, the connections are already there. This could also be a "hallway-utility room," meaning the washing machine and dryer don't have to be hidden behind a wall. Then the current bedroom could become K3. Possibly, the small storage room could be turned into a children's bathroom (though I'm not sure how the drains would work there). But as I said: the current bathroom would have to be torn out – the question is whether the budget allows that. However, it would be a practical solution. (dashed lines in the utility room because I wouldn’t put up a wall here) oops, sorry, forgot the sloping roof, so also the door from the master bathroom into the new bedroom in the middle (then that wouldn’t have worked with the hallway to the front either, right?)

When the older one moves out at 19-20, that would already be a solution... but I don't really want to rely on or "hope" for that either. I moved out at 22 and was one of the early starters. In the village, that's probably different than in the big city.

The budget would be "sufficient." My question is rather how much I would be willing to spend on it... I actually don't want to use more than 50,000 to 60,000 euros for it. That doesn't sound like much... but the prices here are not very high.

Not many windows are included... I probably don't need sanitary facilities either... I would do the roof again on my own.

Actually, only an electrician, structural engineer, planner, and a construction company for the concrete ceiling + walls are needed.

I wouldn’t do anything because of the age spread. For what an expansion/extension costs, you could pay the eldest from 20 their own student apartment for three years if they don’t leave voluntarily... ;)

There was someone here about half a year ago who wanted to do the same. A gable roof house, the only option was to build out the back, basically like with you, but also with an extension downstairs. They used the bedroom as a walk-through closet. Nice built-in cupboards in the slope so that a corridor to the two additional rooms is created. Downstairs they wanted to make their bedroom with a bathroom. But before he showed up here, he informed himself about the floor area ratio, etc.

And now I am at the point where I wonder: if you built yourself in 2015, then you should know that you can’t just do anything. On one hand, the development plan dictates how large you are allowed to build, on the other hand there is the structural engineering. A carport will have a roof load of 150?! That is not enough for the slab, masonry, and roof. Not even the garage.

And I guess it is very likely that you are only allowed to build one story, but you are making the house a two-story. What does the development plan look like? How much is already built, how much is still allowed? Is something still allowed where planned? (There seems to be no boundary construction)

If the building authority or the development plan does not contradict, a drawing must be included in the building application, one from the architect with structural engineering and everything.