{"id":5067,"date":"2026-01-10T15:45:08","date_gmt":"2026-01-10T13:45:08","guid":{"rendered":"https:\/\/katsourisengineering.com\/vertical-extension-when-its-allowed-and-what-an-engineer-checks\/"},"modified":"2026-01-10T16:04:11","modified_gmt":"2026-01-10T14:04:11","slug":"vertical-extension-when-its-allowed-and-what-an-engineer-checks","status":"publish","type":"post","link":"https:\/\/katsourisengineering.com\/en\/vertical-extension-when-its-allowed-and-what-an-engineer-checks\/","title":{"rendered":"Vertical Extension: When It\u2019s Allowed and What an Engineer Checks"},"content":{"rendered":"\n

The idea of adding one more floor to an existing building sounds simple: \u201cwe have a roof, we have space\u2014why not do it?\u201d In practice, however, a vertical extension<\/strong> 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\u2019s not enough to have the intention or the need. You must confirm that the property is legally allowed to \u201cgo higher\u201d and that the load-bearing structure can support it\u2014especially in a country with significant seismic activity.<\/p>\n\n

By \u201cvertical extension\u201d 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<\/strong><\/a> is required, and the process is submitted electronically through the e-Permits system<\/strong><\/a>.<\/p>\n\n

What \u201callowed\u201d really means in a vertical extension<\/h2>\n\n

When someone asks, \u201cAm I allowed to build a vertical extension?\u201d, they are essentially asking three questions at once. First, whether the area\u2019s 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\u2014not only with the weight of a new floor, but also with the impact such a change has on the building\u2019s overall seismic behavior.<\/p>\n\n

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.<\/p>\n\n

\"Flat<\/figure>\n\n

When a vertical extension may be possible<\/h2>\n\n

Usually, feasibility starts with a basic question: has the permitted building capacity and height already been exhausted? In many cases\u2014especially with older buildings or plots that were never fully utilized\u2014there may be remaining \u201callowance\u201d that could enable an additional floor. That doesn\u2019t mean you automatically proceed. It means it\u2019s worth carrying out a serious, structured assessment<\/strong><\/a>.<\/p>\n\n

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.<\/p>\n\n

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 \u201crule for everyone.\u201d It is assessed based on the facts and the regulations applicable to each individual case.<\/p>\n\n

What the engineer checks before any design work begins<\/h2>\n\n

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.<\/p>\n\n

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 \u201ccan we\u201d and the \u201cup to what limit\u201d before time is spent on drawings that may not be licensable.<\/p>\n\n

Next comes verification of the existing building. Many properties\u2014especially older ones\u2014have 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.<\/p>\n\n

The most critical evaluation, however, is structural<\/strong><\/a>. 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\u2019s 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).<\/p>\n\n

This is often the point where the entire picture changes. In many cases, the right solution is not simply \u201cbuild one more floor,\u201d but \u201cbuild one more floor and strengthen the structure where needed,\u201d so the result is genuinely safe and technically justified.<\/p>\n\n

\"Construction<\/figure>\n\n

What permit is required\u2014and why it\u2019s not a \u201cquick\u201d process<\/h2>\n\n

For a vertical extension, the process is completed through a Building Permit and includes the required studies (architectural<\/a>, structural, and any other studies needed depending on the case). Submission and issuance are carried out through the e-Permits system.<\/p>\n\n

If someone is looking for a \u201cquick fix,\u201d they may be disappointed\u2014not because it\u2019s 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.<\/p>\n\n

Common questions<\/h2>\n
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Is a vertical extension possible on an older building?<\/strong><\/h3>\n
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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.<\/p>\n\n<\/div>\n<\/div>\n

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If a building \u201clooks solid,\u201d is that enough?<\/strong><\/h3>\n
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Visual appearance does not replace engineering analysis. Especially for a vertical extension, safety cannot be based on assumptions.<\/p>\n\n<\/div>\n<\/div>\n

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What if there are differences between the drawings and the existing condition?<\/strong><\/h3>\n
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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.<\/p>\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

The right first step<\/h2>\n\n

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\u2014and what the safe, realistic plan should be.<\/p>\n\n

If you wish, we can review your property\u2019s information, confirm what is permitted, and outline the steps required, so you can move forward with confidence and without unnecessary delays.<\/p>\n\n

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Request an offer<\/a><\/div>\n<\/div>\n<\/div>\n\n\n\n
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Contact us<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

The idea of adding one more floor to an existing building sounds simple: \u201cwe have a roof, we have space\u2014why not do it?\u201d 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\u2019s […]<\/p>\n","protected":false},"author":5,"featured_media":5066,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[43],"tags":[],"class_list":["post-5067","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-permits-regulations"],"_links":{"self":[{"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/posts\/5067","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/comments?post=5067"}],"version-history":[{"count":3,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/posts\/5067\/revisions"}],"predecessor-version":[{"id":5070,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/posts\/5067\/revisions\/5070"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/media\/5066"}],"wp:attachment":[{"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/media?parent=5067"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/categories?post=5067"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/katsourisengineering.com\/en\/wp-json\/wp\/v2\/tags?post=5067"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}