How to Extend a Cantilever Balcony: Step-by-Step Guide

apartments with cantilever balconies

Cantilever balconies are among the most common balconies and can help you enjoy a little outdoor area regardless of where your flat or home is located. Second-floor rooms and areas purely rely on these structures for air circulation, natural light, and outdoor space. Extending such balconies can be challenging, but some solutions are easy to implement. 

To extend a cantilevered balcony, you should first consult an engineer. Looking at the structure of the balcony and what is underneath is essential. You can either opt to connect multiple balconies on the same level or add a structure below a single one. The help of an expert is always required.

Below you can find a step-by-step guide to extend your cantilever balcony. But do so only after an engineer has approved the project.

Understand the Structure of a Cantilever Balcony

Firstly, you should have a look at your cantilever balcony. Cantilever balconies are structures that don’t need any support below them to be safe and resistant. Rather, they leverage the property’s walls’ stability to keep the floor and rails in place. 

While they might seem like simple structures, extending them can be complicated. This is because cantilever balconies rely on delicate structures to withstand the weight of objects and people. Usually, cantilevers are used for balconies that are 1500mm to 1800mm (60 to 70 in) in depth. After, other structures are required. 

Additionally, these balconies are often built at a high, meaning that working on these components of your house is impossible or extremely dangerous without the necessary equipment. 

However, if you are only trying to extend a balcony that is a few centimeters off the ground floor, you can just add wooden planks or a concrete extension on the sides. The situation becomes much more challenging if you are operating at height. 

If you wish to find out more about the structure that holds a cantilevered balcony together, you can find more information in the construction video below:

Have a Look at the Specific Structure of Your Property

The most common type of cantilevered balcony is the one you can notice on the sides of taller buildings. These are often located in correspondence of door windows or larger openings. Indeed, balconies are an ideal addition for homeowners to enjoy a little outside area. 

Especially within city centers, these balconies can be located quite high up compared to the ground floor. You should have a look at what the positioning of the balconies is.

  • Side by side – if your flat or apartment is located above other living areas in a building, you might not be able to modify the area below the garden. However, if your residence is lengthy enough for you to enjoy two balconies, you can opt to connect the two openings. For this option, you will need a builder and an engineer – as well as obtaining approved paperwork for the project.
  • Available space below the balcony – if your cantilevered balcony is located above your own grounds, there are other suitable options. One of the most common balcony ideas is to create a wooden or concrete deck under the balcony. 

It is vital to notice that extending a cantilevered balcony on either side without adding supports like columns can make the structure unreliable. Indeed, cantilevered balconies leverage the force of the wall to which they are attached. 

Modifying such a structure would mean that the new components are hung without support. Walking, playing, running, or depositing objects on this extension would not be safe.

Indeed, creating a deck under the balcony can be the safest option. This deck will be approved by an engineer and built by an expert builder. While sustained by metal columns and relying on a sturdy structure, the wooden ceiling at the same level as the balcony allows you to extend the walkable surface of the cantilevered balcony. 

Consult an Expert Engineer

Now you know about the two options available to you. Therefore, it is time to speak to an expert engineer and understand the best way of building this deck extension. 

Unlike other remodeling projects you might undertake in your house, it is crucial to understand that balconies must be extremely safe to be livable. Modifying and manipulating a structure such as the one of a cantilevered balcony without the help of an expert can cause a loss of money and energy. 

READ ALSO: How Much Weight Can a Small Balcony Hold?

Install a Deck Underneath the Balcony

If you have opted for installing a deck underneath your balcony, you can start working on this project. If you are an expert in construction or DIY projects and know your way around the tools for the job, you can start building a deck. 

This deck should be located directly below the balcony and create an addition to the living area below the balcony itself. Depending on what works best for your preferences, you could opt to use window panels or just create a metal structure. 

Below are the four main steps to building this type of structure. Before testing it, it is essential to check with a builder to see if the construction is indeed resistant. 

Add Metal Columns for Support

If the balcony is hanging over a soft surface such as a rocky field, garden, lawn, or patio, you can insert support metal columns without issues. These will become the foundation of your deck extension and the main structure of your balcony. 

Depending on the deck or balcony structure you are building, your contractor will recommend certain columns to be positioned in specific locations. These components are essential to ensure that the structure is reliable. However, they also help to reinforce the structure of the balcony itself, which can now withstand an increased weight. 

Add a Concrete Floor

Now that the foundations of your deck extension are fixed, it is time to create the deck’s base. You can opt for a wooden, metal, or concrete flooring for your patio. 

Concrete will ensure better stability, while wood can be less expensive and ideal if you don’t know how long you will be happy with your patio. In any case, it is essential to ensure that the bottom surface is fixed before building additional components. 

Pick the Right Material for the Project

Now that the base of the project is in its place, you can unleash your creativity! Some homeowners prefer to create a patio that has window-like walls or glass surfaces. This is an excellent choice if your terrace is overlooking nature or a beautiful landscape. 

Alternatively, you could opt to create wooden or concrete walls. While one of the options might withstand temperature changes better than the other, they aim to increase the size of your living space.

Add New Railings

Once all the new deck walls are in place, and the ceiling is built, you will notice an increased area of space around the balcony itself. 

At this point, you might need to remove the current railing of the balcony and replace it with another fence that surrounds the whole ceiling of the deck. 

This construction step is essential, especially if you are planning on using the new space you have created!


Extending a cantilevered balcony is not easy, especially if this is located at a height. The only action you could attempt to take is to merge to balconies encompassed by your same property. 

However, if your balcony is hung over a property that is yours—such as a balcony—you could opt to build a deck underneath the balcony to extend the walkable surface. Therefore, the top part of the deck’s ceiling will become the extension of the balcony’s floor. You should always check with an expert constructor before testing it.

LaShawn Toyoda

I love home decor, DIY, and gardening. During my free time I enjoy looking for new ways to improve my home so that it's more organized, comfortable, and relaxing. My apartment in Japan has a small balcony with a great view. I created this site to share and get ideas for how to decorate and better utilize my balcony space.

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