The price of a plot reflects an assumed development potential. Before making an offer, the real issue is not "how much it costs" but "how much it actually allows". A buildability check, done up front, is the most profitable due diligence of an acquisition: it stops you paying for a potential that does not exist.
Why check before making an offer
A plot classified as "buildable" is not a blank cheque. The zone sets a use, the index caps the floor area, the building envelope and the boundary setbacks erode the envelope, and the RDPPF can encumber an entire strip. Two plots of the same area and the same price can offer very different potentials.
Discovering this after signing means paying dearly for it. Doing it before means negotiating — or walking away — with full knowledge of the facts.
The checklist, in order
The order matters: the points that can rule out a plot come before the floor-area calculation.
Zone and permitted use
Is the plot in the building zone, and for the intended use? The plot is uniquely identified by its EGRID. See the land-use plan.
Servicing and access
Often a deal-breaker: an unserviced plot (access, connections) may not be buildable until servicing is secured (art. 19 SPA / LAT) — a hold-up of several years, not a mere extra cost.
Easements, charges and notes (land register)
A no-build easement cancels every calculation — to be checked before the index. Some statutory or apparent easements (necessary right of way, drainage of water) apply even without an entry.
Index and building envelope → net potential
Permitted floor area via the index, bounded by height and boundary setbacks.
Enforceable restrictions (RDPPF)
Building lines, hazard zones, noise (noise abatement ordinance / OPB), contaminated sites: see reading an RDPPF extract. The free extract is neither exhaustive nor enforceable as it stands.
Net potential, not theoretical potential
This is the calculation that decides a purchase. An example: an 800 m² plot with an index of 0.5 shows 400 m² of floor area "on paper". Subtract 120 m² of existing built fabric to be kept and a portion encumbered by a building line, and there may be only around 230 m² genuinely available.
And it is not a simple subtraction: the net potential is the more constraining of two ceilings — the index ceiling (floor area) and the envelope allowed by the building envelope and setbacks (ground coverage × height). On a low-density plot, it is often the index that limits; on a dense plot, it is the building envelope.
What makes you lose weeks
This information is public but scattered: land-use plan and regulations at the municipality, RDPPF extract at the cadastre, easements at the land register, built fabric at the RegBL. Gathering and cross-referencing them correctly takes days — a timeframe rarely compatible with the tempo of an offer.
This is exactly what Parcellis compresses: from an address, the report identifies the plot, reads these official sources at their origin, and distinguishes what is confirmed from what remains to be verified. You arrive at the negotiating table with a sourced reading, not a hunch.
Several plots in the running?
When you are torn between several properties, compare their net potential, not their price per square metre: that is often what reshuffles the ranking. Analysing each option before choosing prevents you from committing to the one that looked best and that, once the constraints are deducted, was not.