Before you pay a deposit on a plot, open the municipality's Master Plan (PDM). The PDM sets what the council accepts on that lot: the type of use, the building volume, the height and the distance to the boundaries. A developer who skips it risks buying a parcel where the project they imagined does not fit.
Two plans and a regulation
Three parts of the PDM matter for a plot. The zoning plan (planta de ordenamento) shows the class and category of the land the lot sits on. The constraints plan (planta de condicionantes) shows what limits occupation, such as the National Ecological Reserve (REN), the National Agricultural Reserve (RAN) and public-utility easements and restrictions. The regulation writes the rules, article by article, for each land category.
Start with the zoning plan. On rural land, building follows tighter rules than on urban land, and your business plan can change at this step.
The parameters that set the building area
Find your lot's category in the regulation and pull out the parameters that apply. The most common are the land-use index, the impermeabilisation index, the facade height, the number of floors, the setbacks from the boundaries and the front setback (recuo) from the street frontage.
The land-use index is the ratio between the total building area and the land area the index refers to. On a 1,000 m² lot with an index of 0.6, the maximum total building area is 600 m². The impermeabilisation index measures, as a percentage, the area of waterproofed ground. The example is illustrative: the real value is in your municipality's regulation.
The same name can carry different definitions. Regulatory Decree no. 5/2019 of 27 September updated the technical concepts of spatial planning and urban planning and repealed Regulatory Decree no. 9/2009. It applies to plan revisions started after it came into force, so an older PDM may keep its own definitions for building area or facade height. The decree separates the building height, measured to the highest point of the building, from the facade height. Read the definition in the regulation itself before you do the sums.
The constraints the regulation does not show
A lot on urban land can have part of its area in the REN or the RAN, or be crossed by a power line or a watercourse. Each constraint removes buildable area or requires an opinion from a body outside the council. Overlay the lot boundary on the constraints plan and measure the area that remains.
Record the article and the page
When you take a value from the regulation, note the article, the page and the date of the version you consulted. The PDM changes with revisions and amendments, and the version in force is published in the Diário da República and on the municipality's website. When the bank, the architect or the council asks where a number came from, the answer fits on one line.
When reading is not enough
Some plots allow more than one reading of the regulation, or carry constraints whose limits the competent body has to confirm. In those cases, the prior information request (PIP, pedido de informação prévia) asks the council in writing what it accepts for the lot before you invest in the design. The article on the Simplex Urbanístico explains what changed in the PIP.
UrbanCheck does this reading for you: it gives the PDM parameters with the article and page for each value and checks the plot against the REN, the RAN and the easements.
Photo: Georgy Trofimov, Unsplash.