Roof heightening / extension / annex - cost estimation

Hello everyone,

the following situation:
We want to expand an existing house that is about 20 years old. The ground floor is already fully developed (100 sqm, kitchen, living room, guest WC, bathroom, bedroom, guest room). The attic is to be raised and expanded, possibly with a dormer. On the ground floor, extensions are to be built on both sides. The idea is to build a single-story extension on one side with a separate entrance door (should become a separate apartment). On the other side, a two-story extension is planned. The house is located on private family land, so please only address the cost question.

Now in detail the points:
Raise knee wall + install dormer (approx. 5m long), window installation - costs?
Attic expansion (walls, plumbing, electrical), 2 children’s rooms, 2 bathrooms, 1 bedroom - costs?
1st single-story extension 20 sqm (approx. costs? - without plumbing) - possibly add a roof terrace - costs?
2nd two-story extension 3x8m without plumbing (future office space); costs?
Costs for openings?

Both extensions without basement.

Option, in case of cost overrun:
Conservatory 3x8m (costs?), instead of two-story extension.

We have set a budget of €250,000 and are complete novices in this field, dealing with these topics for the first time. We have a mason in the family (how much could this save us in costs if done by ourselves?).

We thank you in advance for your initial assessment of your expertise.

Best regards Mona & Philipp

The budget should be sufficient. Calculate at least €2,500 per sqm of living space. Heating is missing from the list, bathrooms in the attic floor suitable for the plumbing? It will of course be very expensive in terms of the result, since you always have to intervene in the existing structure and the energy saving ordinance must also be taken into account.

We are also planning a partial extension. Approximately €2,500 per sqm was mentioned. However, I don't know if that includes architect and structural engineering costs. Better to plan a buffer.

Since massive interventions in the roof are planned anyway, and possibly a new roof truss will be constructed, as more than 10% of the component will be affected, we often plan extensions as timber frame. This often results in more living space due to energetically better walls. Incidental costs such as planning are generally not included in the construction costs.

We want to extend an existing house that is about 20 years old. The ground floor is already fully developed (100 sqm, kitchen, living room, guest WC, bathroom, bedroom, guest room). The attic is now to be raised and developed, possibly with a dormer. On the ground floor, extensions are planned on both sides. The idea is to build an extension on one side at ground level with a separate entrance door (this is intended to become a separate apartment). On the other side, a two-story extension is planned. The house is located on the family’s own plot of land, so please only address the cost question.

Without pictures, at most someone could contribute experience in step 2 regarding what comparable measures cost or were offered – but not in step 1 judge how realistic the list of measures is technically and economically in this specific case at all. You have already positively clarified that the floor area ratio and setback distances allow this, right?

The rest of the house is supposed to be renovated as well?

Costs for breakthroughs?

A breakthrough for what? A door, or are you imagining a full width of 8m as a breakthrough? The cost difference is enormously huge.

Actually, only an architect on site who can take a live look will help here. Please report the cost estimate from the architect.

We are also planning a partial extension. Approximately €2,500 per sqm was mentioned.

The ground floor is already fully developed (100 sqm, kitchen, living room, guest WC, bathroom, bedroom, guest room).
[..]
Attic conversion (walls, plumbing, electrical), 2 children's rooms, 2 bathrooms, 1 bedroom – costs?

Am I reading correctly that a complete apartment needs to fit in, everything new? The longer I think about it, the less I believe the budget will be enough for all wishes. According to this estimate from Ysop, the new 100 sqm attic alone swallows the entire budget.