Apartment renovation: what requires a permit, what doesn't, and how to legalize what's already done

Apartment renovation is one of the most common real estate interventions — whether you want to modernize the space, increase functionality, or boost market value.

However, before you start, it is crucial to understand what you can do without a permit, when you need a project, and in which cases you will enter a more serious administrative procedure.
To help you navigate this, we offer a practical guide through three levels of intervention: works without a permit, works requiring a project, and interventions for which a building permit is necessary.

No Permit Zone: What You Can Do Immediately

The good news is that a large portion of renovations do not require a building permit. According to current regulations, certain works are classified as simple interventions.
However, it is important to emphasize — the fact that a permit is not required does not mean there are no obligations.
In some cases, owner or building manager consent may be required, especially when dealing with common areas.

This category most commonly includes:

• painting walls and ceilings, and decorative work
• replacing floor coverings (parquet, laminate, tiles) without structural intervention
• replacing interior doors
• replacing sanitary ware (toilet, sink, shower, bathtub) without changing the installation system
• minor repairs to electrical and plumbing installations
• replacing radiators of the same type and power

Special attention should be paid to:

Replacing windows and exterior carpentry — although permitted if opening dimensions are not changed, in multi-apartment buildings, the facade appearance must be respected, and manager or owner consent is often required.

Key rule: you can change elements, but you must not interfere with the structure or change the system.

Works Without a Permit, but With a Mandatory Project

There is a common misconception that works not requiring a building permit do not require any professional documentation. In practice, this is not true.

Certain interventions require the preparation of a main project by an authorized architect or engineer.

This category includes:

• Demolition of non-load-bearing walls
• Removal of partition walls to create open-space areas generally does not require a building permit.
• However, it is very important to first determine if it is indeed a non-load-bearing wall — which often requires expert assessment or a project.
• Complete replacement of installations

If:

• you are changing the layout of electrical installations
• you are moving plumbing or drainage connections
• you are creating a new kitchen or bathroom in a different location

— then we are no longer talking about "minor repairs," but an intervention that requires project documentation.

Structural Interventions (With Project)

Creating openings in load-bearing walls or any intervention that could affect the building's stability requires the involvement of an authorized professional.

In practice:

• a main project is required
• owner consent is often needed
• in certain cases, a building permit may also be required

This is where mistakes are most often made — and where the consequences are most costly.

Works Requiring a Building Permit

For certain interventions, there is no room for interpretation — a building permit is mandatory.

This includes:

Interventions on the load-bearing structure (demolition of load-bearing walls)

• interventions on columns, beams, or floor structures
• Change of use of space (conversion of commercial space into an apartment or apartment into commercial space) ; Such changes require harmonization with the spatial plan and new documentation.
• Subdivision and division of an apartment

Dividing one property into multiple separate units includes:

• project
• owner consent
• registration in the land registry

Increasing the area

• enclosing a loggia
• adding a balcony
• expanding living space

Any increase in gross area requires a building permit.

What if the works have already been done without a permit?

This is a common situation — especially with older renovations.

It is important to know that the classic legalization that once existed in Croatia is no longer open for new applications.

Today, irregularities are resolved through:

• creating a survey of the existing condition
• preparing project documentation
• attempting to harmonize with current regulations

In some cases:

• it is possible to obtain the necessary permits retrospectively
• in others — the intervention cannot be legalized

This directly affects:

• selling the property
• valuation
• possibility of obtaining a loan

How to Avoid Problems: Practical Advice

To ensure a smooth renovation, it is important to think ahead:

• Consult a professional before starting work — even when you think it's not necessary
• Inform the manager and neighbors — especially in apartment buildings
• Check if owner consent is required
• Choose contractors who understand the legal framework
• Document installations before covering walls

The biggest mistake owners make is not the renovation itself — but the assumption that everything is allowed as long as it is done "within the apartment."

A good renovation starts with good information

Apartment renovation can significantly increase quality of life and property value — but only if it is carried out in accordance with the law.

The line between what is permitted and what is problematic is often thin, and wrong decisions can result in additional costs, legal problems, or difficulties in selling.

If you are planning a renovation or are unsure about the condition of your property, a timely professional assessment can save you time, money, and stress.