Project modifications during construction: Legal procedures in Portugal

Anyone who has experienced a construction or renovation process knows that changes during the work are almost inevitable. Whether due to unforeseen technical needs, altered requirements, or project optimisation, such modifications are part of construction reality. However, it is crucial to understand that not all changes can be implemented freely.

Making alterations during construction without following the proper legal procedures can lead to serious problems, including halts, fines, and sanctions.

Single-family house under construction in Montijo with approved project modifications

Legal framework for modifications

The Legal Framework for Urbanisation and Building (RJUE) establishes strict rules for project modifications during construction. According to this law, works must be executed in accordance with the project previously approved or communicated to the competent authorities. When adjustments become necessary, specific procedures must be followed to maintain the legality of the project. Non‑compliance can lead to:

• Suspension of construction.

• Mandatory corrective works at the owner’s expense.

• Partial or total demolition in severe cases.

• Financial penalties and legal liability.

Types of modifications and corresponding procedures

Minor changes

Some modifications may be considered minor if they do not substantially affect the original project. They nonetheless require formal communication to the municipal authorities and may still need prior approval.

Substantial changes

Significant changes affecting:

• The building’s volume.

• The space distribution.

• Structural characteristics.

• Number of dwellings.

• Intended use.

These always require a formal request for project modification, following the same procedures as initial licensing.

Procedures for legal modifications

1. Preliminary technical assessment

Before any change, evaluate:

• The nature and scope of the modification.

• Its impact on the overall project.

• The need for municipal approval.

• The costs and timeline involved.

2. Submission of the modification request

The request must include:

• A descriptive report outlining the changes.

• Updated plans and technical drawings.

• A technical justification.

• A signed responsibility statement from the project manager or architect.

3. Municipal analysis

The municipality observes specific deadlines for review. During this period, construction may proceed in unaffected areas if authorised.

4. Decision and implementation

Once approved, the modification may be implemented. All updated documentation must remain on site throughout the works.

Emergencies and urgent alterations

When unforeseen technical issues compromise safety, emergency changes may be introduced, provided that the authorities are:

• Informed immediately.

• Given formal notice and documentation as soon as possible.

Work must be thoroughly documented with technical and photographic records explaining the urgency.

Consequences of non‑compliance

The mayor has authority to suspend construction works not in conformity with the approved design. Consequences include:

• Immediate suspension of work.

• Suspension of the licence.

• Discontinuation of electricity, gas, or water supply.

• Freezing of deadlines.

In severe cases, partial or total demolition may be ordered to restore legal compliance.

Interior view of single-family house under construction in Montijo with approved project modifications

Practical advice for property owners

Preventive planning

• Devote time to design to reduce future changes.

• Consider alternatives early in the process.

• Set aside a financial reserve for unforeseen alterations.

During construction

• Notify the project manager of all intended changes.

• Never approve modifications without prior authorisation.

• Keep detailed records of every adjustment.

Communication with professionals

• Maintain clear communication channels.

• Request written technical justifications.

• Track the progress of municipal procedures.

The role of the project manager

The architect or engineer responsible for the project must:

• Supervise all proposed changes.

• Assess the technical and legal feasibility of each modification.

• Submit alteration requests to the competent authorities.

• Assume technical responsibility for approved changes.

• Keep all documents updated throughout the construction process.

Deadlines and related costs

Administrative deadlines

• Minor changes: review usually within 15–30 days.

• Major changes: up to  60 days depending on complexity.

Costs

In addition to municipal fees, expect:

• Professional fees for technical supervision.

• Possible demolition or reconstruction expenses.

• Delays and financing impacts due to extended timelines.

Modifications and occupancy licence

Unapproved alterations can prevent the issuance of the occupancy permit, a document necessary for:

• Legal habitation.

• Property insurance.

• Property sale or purchase.

• Mortgage or bank financing.

Key takeaway

Managing project modifications is one of the most challenging phases of any construction process. Proceeding with unapproved changes may appear time‑saving, but the legal and financial risks are far too high. Compliance with legal procedures is not only an obligation but a form of protection for all stakeholders, ensuring safety, structural compatibility, and regulatory conformity.

Cooperation between the owner, the project manager, and the municipal authority is essential for efficiency. Transparent communication prevents delays and disputes. Investing in detailed planning helps anticipate potential changes, and when they become unavoidable, experienced professionals and strict adherence to legal procedures guarantee a smooth and lawful process. Construction is complex but benefits greatly from professional, methodical management. Properly handled modifications can significantly enhance the final project’s value.

Do you have a construction project underway and need to manage changes legally and efficiently? At AC‑Arquitetos, we support our clients throughout the entire process, from initial planning to change management during construction. Our experience allows us to anticipate potential modification needs and guide you through the required legal procedures, ensuring your project remains fully compliant at all times. Contact us for a personalised consultation and discover how we can turn your ideas into reality while meeting all legal and technical requirements.