Just a few more square meters?

From the floor plan, we particularly like one house. It is 124m2 in size. Would it be possible to "simply" make it 130 or 135m2 (of course for an additional charge)?

That is unproblematic. One meter longer (in ridge direction) is almost a standard request, more width is a bit more complicated and where there used to be standard house models, nowadays there are actually only "building proposals".

Thanks to everyone for the answers! It's pretty crazy what that can all lead to... But first of all, it's good to know that it is basically possible.

Yes and no. Prefabricated house providers often work with so-called grids. Expansion possibilities are therefore predetermined by the grid. And the ceiling height is – at least in our experience – limited. Only one of the providers we spoke to could do 3.50 meters.

We have no experience with ceiling heights since we have no special wishes there or do not want very high ceilings, but during our research it did not at all turn out that there are still "grids"! I don’t know if it is still like that with low-budget providers? Or just a prejudice from the past?

We also did not have experience with grids. Regardless of the type of construction, there are flexible and inflexible construction companies.

I’ll throw the opposite into the room, the house downsizing. Of course, that was also not a problem and resulted in a corresponding credit.

It's crazy what all this can entail...

Depending on the direction of the ridge, the extension is, as said, a simple operation, but perpendicular to that, of course, it's different.

but that there are still "grids" was not confirmed at all in our research! I don't know if this is still the case with the low-budget providers? Or just a prejudice from the past?

Yes and no. The grids are still a reality in production, but they no longer mean the usual planning corset of the past. One can imagine this similarly to ceiling beams or rafters, where respective pitches can be "shifted" or replacements can be made. That means economically, planning is still done on a grid and changes in whole grid increments are easier to implement, but on request "made to measure" also works for almost any desired dimensions. The preferred step lengths for enlargement jumps are 62.5 cm for timber frame panel builders and 1.00 meter for bricklayers.

I'll toss the opposite into the ring, downsizing the house. Of course, that was no problem either and led to a corresponding credit.

With houses as with breasts, the enlargement operation is the easier of the two procedures.
The sample building proposals are tested and functionally planned. If you reduce such a floor plan, bottlenecks would occur in some places and the shifting starts, often as a domino effect following the example of