Amendment of the Horizontal Property after its constitution: When it is possible and how to proceed

Amending the horizontal property regime after it has been created is possible when the works and the proposed use comply with planning rules, the technical suitability of the building and the condominium’s legal requirements; in most cases it requires an appropriate planning title (licence or prior notification), certification of the horizontal property where applicable, and updating of the land registry.

“Amending the horizontal property regime is feasible, provided that the works and the use comply with the RJUE, the constitutive title and the technical suitability of the building.”

Merger of two one‑bedroom units into a two‑bedroom unit in Ribeiro do Porto, after approval of the Horizontal Property and completion of the works

What “amending the horizontal property regime” after its creation means

This refers to interventions that affect a building already established as horizontal property (HP) and its respective constitutive title, namely:

• Reconfiguration of units (merging or splitting dwellings)

• Change in the area or internal layout of units

• Alterations to common parts that affect the units (e.g. infrastructure shafts, stairwells, technical entrances)

• Change of use of units (e.g. from residential to services), where permitted

These changes cumulatively require:

• Planning compliance (plans, regulations, easements, heritage protection)

• Technical suitability of the building for the intended purpose

• Compliance with the legal regime of the condominium (constitutive title and resolutions, where applicable)

• Possible revision/update of the HP constitutive title and land registry, when the change affects the description of the units

Under the RJUE, the key elements lie in prior control of urban operations, in use and in the specific rules for horizontal property buildings and independent units.

Which works may exist and how they are classified

The RJUE defines categories of works with a direct impact on feasibility and procedure:

• Alteration works: change physical characteristics of the building or unit, including load‑bearing structure, number of dwellings, partitions, façade materials, without increasing total floor area, footprint or façade height.

• Extension works: increase footprint, total floor area, façade height or volume.

• Conservation works: maintenance, restoration, repair and cleaning.

The applicable regime (licence, prior notification or exemption) depends on the location, type of works and constraints (heritage status, protection zones, façade heights, among others). Interior works without structural impact, without changes to building height and without affecting the façade may be exempt from prior control, under article 6, no. 1(b). By contrast, changes that increase the number of dwellings, interfere with the structure, alter building heights or affect protected properties require appropriate prior control (licence/notification).

Change of use of units (without prior urban works)

When the change of use is not preceded by works subject to prior control, a prior notification with period must be submitted, with a liability statement that:

• Demonstrates compliance with the rules defining permissible uses

• Declares the suitability of the building/unit for the new purpose, allowing for mixed uses

Use may begin 20 days after submission, unless the Mayor orders an inspection due to incomplete documentation or indications of unsuitability. In HP buildings, the notification of elements relating to use may be made per unit or for the whole building. Objection to the use is possible if the common parts are not in a suitable condition.

Horizontal Property in the RJUE: critical points

The Municipality may certify, on request, that the building meets the requirements for creation of HP; this request may accompany the use notification where certification does not yet exist. In HP, notification (use without works) may relate to individual units; however, if the common parts are not suitable, start of use may be opposed. Works to create/renovate infrastructures in buildings covered by the HP infrastructures regime fall under the construction title, dispensing with specific urbanisation licences.

Usual procedures by type of change

Reconfiguration of units (merging or splitting):

• Check planning framework (plans, uses, indices).

• Determine whether this is alteration works affecting the number of dwellings (prior control).

• Obtain a condominium resolution where required by the constitutive title and the Civil Code (not addressed in the RJUE), especially when dealing with common parts or use allocation.

• Apply for the appropriate planning title (licence/notification) and submit designs (architecture and engineering). After the works, submit as‑built drawings where there have been design changes and a liability statement for use purposes.

• Update the land registry description and HP constitutive title if there are changes in areas/uses of the units.

  
  

Purely internal alteration without structural impact and without façade:

• May be exempt from prior control (art. 6, no. 1(b)), while still having to comply with all technical, safety and health regulations.

• If it entails a change of use without prior works, a prior notification with period and liability statement is required.

Change of use with works:

• Follows the regime for works (licence or notification, as applicable).

• After completion, use begins upon submission of documentation (liability statement and as‑built drawings, where applicable), with no need for a separate use permit.

Works in listed properties/protection zones:

• Subject to licence (art. 4, no. 2(d)).

• Require specific opinions from the heritage authorities and compliance with applicable constraints.

When a licence or notification is required, and when there is no prior control

Subject to licence:

Alteration/extension works outside detailed plans/UE/land subdivision that affect parameters of footprint/height/façades/dwellings/area. Listed or proposed‑for‑listing properties, listed complexes/sites, or protection zones. Reconstruction that increases façade height; demolition outside licensed reconstruction.

Subject to prior notification:

In areas covered by a detailed plan, land subdivision operation or execution unit setting essential parameters, construction/alteration/extension works may be subject to notification. Change of use without prior urban works: prior notification with period and liability statement.

Exempt from prior control:

Conservation and certain internal alterations without structural/facade/height impact, and without removal of façade tiles. Works of minor planning relevance (limits defined in the RJUE and which may be specified in municipal regulations).

NOTE: Exemption from planning control does not remove the obligation to comply fully with applicable regulations, or the need to regularise use and update the land registry when the change affects the description of the units.

Key documents and timelines

Planning title (licence or prior notification), where applicable.

Liability statement by the works director/supervisor for completion and compliance with the design, and as‑built drawings where there are design changes, for use purposes. In change of use without prior works: liability statement by a qualified person, submitted before use begins.

Start of use:

After works subject to prior control: submission of documents is sufficient (immediate use). Without prior works (change of use only): on the 20th day after submission of the notification, unless an inspection is ordered.

Practical examples

• Merging two one‑bedroom units to create a larger two‑bedroom unit: May be alteration works (possible change in number of dwellings, in this case a reduction), with design and prior control depending on area/planning. It requires verification of structural behaviour and installations. After completion, submission of liability statement and as‑built drawings (if there were changes) and updating of registry and HP title.

• Converting a residential unit into an office in a consolidated urban area: If there are no works subject to prior control and the use is permissible, a prior notification with period is submitted, together with a liability statement regarding permissible use and suitability of the space. Use begins on the 20th day, unless an inspection is ordered.

• Opening an opening in a non‑structural wall and refurbishing a kitchen in a unit: If requirements are met (no effect on structure, heights, façades and no removal of façade tiles), this may be exempt from prior control. Technical and safety duties remain. If there is a change of use, the relevant regime applies.

Conversion of a dwelling into an office in a mixed‑use residential and services building in Loures

Advice to speed up and reduce risk

• Check the municipal planning framework and easements/constraints before designing.

• Confirm whether the HP constitutive title allows the intended change, or whether it needs updating and a condominium resolution.

• Design with a “no surprises” approach: clear design report, coordinated engineering, structural verification where applicable.

• For change of use, prepare a technically robust liability statement and attach evidence of suitability (access, ventilation, safety, acoustics, fire safety where applicable).

• Plan land registry updates (property description and HP) from the outset, when the change affects areas/uses.

Common mistakes to avoid

• Assuming interior works are always exempt: structural impact, heights, façade and façade tiles change the applicable regime.

• Starting business activity without prior notification where change of use requires it.

• Ignoring the technical fitness (acoustics, fire safety, health conditions) of the space for the declared new use.

• Failing to anticipate the need to update the constitutive title and land registry after altering units.

In a few words

Amending the horizontal property regime after its creation is both possible and common, but it requires aligning three dimensions: the planning regime (RJUE), the technical suitability of the building/unit for the declared use, and the condominium/constitutive title regime, ensuring the correct procedure (licence/notification/exemption), the use documentation (liability statements and as‑built drawings where applicable) and land‑registry updating whenever necessary.

Points to bear in mind

Each building and each municipality has specific features that influence procedure and timelines. Prior analysis by a qualified technical team reduces costs and time, and prevents refusals or embargoes. In listed properties or protection zones, timelines and requirements increase and designs must anticipate the applicable constraints.

Contact AC‑Arquitetos

AC‑Arquitetos supports owners and condominiums throughout the entire horizontal property amendment cycle: feasibility study, architectural and engineering design, municipal applications and land‑registry regularisation. Contact us to assess your situation and move forward with confidence and efficiency.