ᐅ Adding an additional floor to a single-story wooden house elevated on stilts.

Hello,

I would like to add an additional floor to a 40-year-old wooden house with a flat roof and a footprint of 80 sqm (860 sq ft). The zoning plan only allows a setback floor of 40 sqm (430 sq ft). An extension is not possible.

I want to keep the house as it is and avoid interfering with the building’s structural frame as much as possible. My current idea is to build a 40 sqm (430 sq ft) floor on stilts above the house. It might be necessary to install one stilt through the roof of the old house. The first floor would be accessed via an external staircase.

Is this concept fundamentally feasible or completely unrealistic?

I would appreciate any assessment.

Best regards

charly12345

charly12345 schrieb:

I would really appreciate an assessment.

The only way you have is to consult a structural engineer and an architect.
Why the idea of stilts? Wooden houses can generally be extended vertically in a standard way. Anything out of the ordinary usually costs extra money (often a lot more).

nordanney schrieb:

The only chance you have is to consult a structural engineer and an architect.
Why the idea of building on stilts? Wooden houses can generally be extended upward in the usual way. Anything unconventional usually costs extra (often a lot extra).

Thank you very much for the reply.

I forgot to mention that this is a holiday home. My idea was not to touch the old, well-functioning house. It was built in the 1980s. On the roof—not on top of it—there are asbestos cement panels, and the walls contain old fiberglass insulation, etc. If you start working on the old house, you quickly end up needing to demolish it.

I thought it would be easier to start fresh and build a room on stilts. As an amateur, you might think that, after a soil investigation, designing a timber floor slab supported on stilts should not be too difficult from a structural perspective.

But it’s probably a bad idea after all...

Best regards,
Charly

charly12345 schrieb:

The roof features fiber cement boards installed underneath, not on top, and the walls have old fiberglass insulation, among other things. Once you start making changes to an older house, demolition quickly becomes a likely option.

I thought it would be simpler to start fresh and build a room elevated on stilts. As a non-expert, I figured it couldn’t be that difficult to calculate, after a soil investigation, a wooden floor slab on stilts from a structural standpoint.

No, it’s not that simple—and it’s not cheap either. An architect will (unfortunately) bring you back down to earth. Sometimes, even demolition followed by new construction turns out to be more cost-effective.

Is the holiday home intended to become a primary residence later? This is often not possible.

hanghaus2023 schrieb:

Will it then become a primary residence instead of a holiday home? That is often not allowed.

In this case, it would be possible, but it is intended to remain a holiday home.