The idea of adding one more floor to an existing building sounds simple: “we have a roof, we have space—why not do it?” In practice, however, a vertical extension is one of the most demanding interventions, because it affects both what is permitted under planning regulations and what is safe from a structural standpoint. It’s not enough to have the intention or the need. You must confirm that the property is legally allowed to “go higher” and that the load-bearing structure can support it—especially in a country with significant seismic activity.
By “vertical extension” we mean the construction of a new floor (or floors) on top of an existing building. This can apply to detached houses, two-storey homes, and apartment buildings, where additional ownership and rights issues often arise. In most cases, a Building Permit is required, and the process is submitted electronically through the e-Permits system.
What “allowed” really means in a vertical extension
When someone asks, “Am I allowed to build a vertical extension?”, they are essentially asking three questions at once. First, whether the area’s planning rules allow additional height or more square meters. Second, whether the existing building is lawful and the documentation is clear, so the permit file can move forward without obstacles. And third, whether the building can technically cope—not only with the weight of a new floor, but also with the impact such a change has on the building’s overall seismic behavior.
The legal framework for general building rules is the New Building Regulation (NOK), together with any special provisions that apply locally. This matters in practice: two properties that look similar can be subject to completely different restrictions, depending on their location and the regulations in force there.
When a vertical extension may be possible
Usually, feasibility starts with a basic question: has the permitted building capacity and height already been exhausted? In many cases—especially with older buildings or plots that were never fully utilized—there may be remaining “allowance” that could enable an additional floor. That doesn’t mean you automatically proceed. It means it’s worth carrying out a serious, structured assessment.
At the same time, you must rule out cases where special restrictions apply. In certain areas or within specific planning frameworks, there may be constraints that directly affect licensing. For example, there are situations where, due to special provisions (such as planned arcades that have not been opened), a building permit is not granted for any kind of extension. That is why the evaluation cannot be based on assumptions or a general impression. It must be grounded in the actual data of the property.
Another point that often comes up is whether an extension can follow the existing building outline. In some cases, it is stated that a vertical extension to a lawfully existing building may extend up to its existing footprint, under specific conditions and provided no special provisions prohibit it. This is an area that requires careful attention: it is not a “rule for everyone.” It is assessed based on the facts and the regulations applicable to each individual case.
What the engineer checks before any design work begins
The right starting point is not to immediately design the new floor. The right starting point is to confirm whether there is a clear path to obtaining a permit and whether the solution can stand safely.
The planning assessment is the first link in the chain. The engineer checks what is permitted for the specific plot: allowable height, allowable floor area, distance requirements, and any special local terms. This clarifies the “can we” and the “up to what limit” before time is spent on drawings that may not be licensable.
Next comes verification of the existing building. Many properties—especially older ones—have discrepancies between plans and reality or missing elements in older permit files. If these issues are not addressed early, the process can slow down or become blocked later. For this reason, a proper survey is carried out, documentation is reviewed, and a clear picture is formed of what is lawful, what is recorded, and what may require correction or regularization.
The most critical evaluation, however, is structural. A vertical extension effectively changes the building: it introduces new loads, alters mass distribution, and in many cases changes the way the structure responds during an earthquake. The structural engineer assesses the load-bearing system and foundations, examines the building’s condition (wear, defects, cracking), and determines whether the building can support the extension as it is or whether strengthening is required. In Greece, assessment of existing structures is linked to the KAN.EPE. framework (Regulation for Interventions).
This is often the point where the entire picture changes. In many cases, the right solution is not simply “build one more floor,” but “build one more floor and strengthen the structure where needed,” so the result is genuinely safe and technically justified.
What permit is required—and why it’s not a “quick” process
For a vertical extension, the process is completed through a Building Permit and includes the required studies (architectural, structural, and any other studies needed depending on the case). Submission and issuance are carried out through the e-Permits system.
If someone is looking for a “quick fix,” they may be disappointed—not because it’s impossible, but because a properly executed vertical extension must rest on two foundations: it must be legal and it must be safe. When the right steps are taken from the beginning, the project moves forward more smoothly and unpleasant surprises are avoided.
Common questions
Is a vertical extension possible on an older building?
It can be, but it requires a serious structural assessment. Age alone does not automatically exclude an extension, but it affects how thoroughly the work must be documented and whether strengthening will be necessary.
If a building “looks solid,” is that enough?
Visual appearance does not replace engineering analysis. Especially for a vertical extension, safety cannot be based on assumptions.
What if there are differences between the drawings and the existing condition?
Typically, the existing condition must be clarified first. It is better to address this early than to have it appear as a major obstacle once the permit file is already underway.
The right first step
If you are considering a vertical extension, the best first step is a preliminary assessment: what is allowed under planning rules, what the legal status of the existing building shows, and what the first structural picture looks like. This gives you a clear answer on whether it is worth proceeding to full design work—and what the safe, realistic plan should be.
If you wish, we can review your property’s information, confirm what is permitted, and outline the steps required, so you can move forward with confidence and without unnecessary delays.
