In real estate, “due diligence” means the set of checks carried out before buying: establishing what you are actually acquiring, and at what risk. In Switzerland that work is split across five disciplines — and only one of them decides what may be built, converted or extended upwards.
What the term covers in Switzerland
The expression comes from the transaction world: before signing, the buyer exercises “due care” by verifying for themselves what the seller asserts. Applied to a Swiss property, it spans ownership and buildability, building condition and taxation alike.
The difficulty is that these checks do not sit in one place, do not fall under the same authorities, and do not take the same time to obtain. A failed acquisition rarely fails for lack of information: it fails because one strand was handled too late, or assumed to be settled.
The five strands, and who handles them
| Strand | What it establishes | Where it is handled |
|---|---|---|
| Ownership and legal | Title, easements, charges, building lease, annotations | Land register, notary |
| Planning and building law | Zone, indices, building envelope, enforceable restrictions, procedure | RDPPF/ÖREB cadastre, municipal regulations, land-use plan |
| Technical | Structure, systems, asbestos, state of repair | Engineer, building surveyor |
| Environmental | Contaminated sites, soil quality, natural hazards | Cantonal cadastres, specialist consultancy |
| Financial and tax | Yield, transfer duty, property gains tax | Fiduciary, bank |
The strands do not carry equal weight. For an income property held as is, technical and financial dominate. As soon as there is an intention to build, convert or densify, the planning-law strand becomes decisive: it determines whether the project is possible at all, and within what limits.
The planning-law strand, in the order that matters
The order is not cosmetic. Points capable of eliminating a property come before those used to calculate an area: there is no point optimising an index on a plot burdened by a no-build easement.
Identify the plot unambiguously
An address is not enough: a building can straddle two plots, and two neighbouring properties can share an entrance. The federal EGRID identifier removes the ambiguity, and buildings attach to it through their EGID.
Zone and permitted use
The zone sets what is allowed — housing, commercial, mixed — before any question of floor area. A plot outside the building zone falls under a markedly stricter regime: see building outside the building zone.
Public-law restrictions (RDPPF / ÖREB)
Alignments, noise sensitivity levels, contaminated sites, protected perimeters: the extract records what public law enforces against the owner. To decode it: reading an RDPPF extract.
Special plan and municipal regulations
The most common blind spot. A neighbourhood or detailed development plan can cap height below what the zone index allows. Municipal regulations then override the cantonal reading.
Natural hazards
Flooding, landslides, rockfall: depending on the hazard level, building is conditional on mitigation measures, or excluded. The classification binds the project; it is not negotiable.
Heritage and architectural inventory
A single inventory rating is enough to make any conversion subject to prior review, and to sharply reduce the room for manoeuvre on façades and roof. To be checked before the offer, never after.
Indices, envelope and net potential
Only now: the floor area allowed by the land utilisation index, less the existing building, bounded by height and boundary distances. That is the net potential — the only one that counts.
Procedure and timelines
Ordinary or simplified permit, required cantonal reviews, objection periods. A feasible but slow project is not worth the same as a feasible and fast one.
The five most expensive mistakes
- Reading the zone index without the special plan. The neighbourhood plan often caps height or footprint below the stated index. The gap is paid for in the land price.
- Treating the free RDPPF extract as exhaustive. It gives a reading, not a guarantee: some restrictions appear only in municipal plans.
- Confusing theoretical and net potential. Index times area gives a ceiling, not a right: the existing building and setbacks still have to be deducted.
- Discovering the architectural inventory after the offer. No other factor damages a conversion business plan so abruptly.
- Treating a plot outside the building zone as buildable land. The regime differs in kind, not merely in degree.
When to run it
Before the offer, not between the preliminary agreement and the deed. A check carried out upstream serves two purposes: ruling out a property that does not hold up, or negotiating the price on the real potential rather than the assumed one. Run after signing, it can only record.
For the specific case of bare land, the detailed sequence is in checking a plot before buying. For a built property intended for renovation, see buying to renovate.
What the planning-law strand does not tell you
It replaces neither the notary, nor the building survey, nor the financial analysis. Contractual easements, charges and building leases are read at the land register. Asbestos, structure and systems require an on-site inspection. Investigating contaminated soil requires boreholes, which the cadastre does not provide.