A new home extension is a project that has many advantages. But before you start your expansion project, you need to decide on the surface area of your extension, based on your needs and those of your family. An office, a kitchen, a bedroom, will not require the same work or the same dimensions. Maisons SIC, a builder of new homes for over 50 years, helps you find the ideal size for your future new home extension
New house extension: PLU and regulatory framework
The extension of a new house is a project which must comply with a precise regulatory framework, defined in large part by the Local Urban Planning Plan (PLU) of your municipality.
This document sets out the applicable town planning rules, such as: setbacks, maximum building heights, and public utility easementsThese rules must be strictly followed to avoid any sanctions.
For an extension of between 5 and 40 m² in an urban area governed by a PLU, a prior declaration of works is essential. This type of approach applies to L-shaped extensions, whether they are made of wood, bricks or other materials.
On the other hand, if the extension exceeds 40 m², you will have to obtain a building permit. In addition, if the extension brings the total surface area of the house to more than 150 m², using an architect becomes mandatory. This regulation aims to ensure that the extension complies with the safety and aesthetic standards imposed by the PLU.
It is also important to note that If your house is located in a allotment, additional rules may apply, particularly in terms of architectural consistency with other houses in the subdivision.
Before starting your project, it is therefore crucial to consult the internal regulations of the subdivision and to check the additional constraints imposed by it.
Reminder of the regulatory framework for a new house extension depending on the surface area
- To 5 m² of floor space : No formalities required (beware of height limits).
- De 5 m² to 20 m² ground area: Prior declaration required.
- De 20 m² to 40 m² in urban areas (zone U): Prior declaration required.
- De 20 m² to 40 m² in other areas (outside zone U): Building permit required.
- De 20 m² to 40 m² if the total surface area of the house exceeds 150 m²: Building permit required.
- Over 40 m² ground area: Building permit required.
The essential house extension rule: RE 2020
Another essential dimension in a new house extension project is compliance with thermal regulations 2020 (RE 2020)This standard applies to all new construction, including extensions, and imposes strict requirements in terms of energy performance and thermal insulation.
RE 2020 covers many aspects of the building, including the insulation of walls, windows, and roofs, as well as the management of ventilation and heating. If your heating system current is not suitable for the new living space, modifications will have to be considered in accordance with this standard.
For example, installing a pellet boiler, An heat pump (HP) or an very high performance gas boiler may be necessary. The choice of this equipment must be made taking into account the energy requirements defined by RE 2020.
It is strongly advised to get help from a professional, such as Maisons SIC, to ensure that your new home extension project meets all the regulatory and technical requirements of RE 2020.
An expert will not only be able to help you navigate the administrative procedures, but also optimize the energy performance of your extension, by choosing the most appropriate materials and equipment.
Finally, once the work is completed, it is essential not to forget to file a declaration of completion of works (DAACT) with the town planning department of your municipality. This formality must be completed within three months after the end of the work.
It is also recommended to request a certificate of non-contestation, which will protect you in the event of a subsequent dispute. Following these steps will allow you to finalize your project with complete peace of mind.
How to size your new house extension correctly?
When it comes to sizing a new home extension, there are several things to consider.
In the first place, The regulations impose an enlargement limit of 30% of the total surface area of the building before work. or a maximum of 150 m². Exceeding these thresholds may result in additional taxes, which could affect your budget.
Choosing the room to enlarge or add is also crucial. A room of around 12 to 15 m² can be enough for a comfortable space. For an office, 10 m² can be more than enough, especially if you optimize the space with wall storage. A bathroom will require between 5 and 10 m² depending on the layout. A garage, on the other hand, often takes up between 15 and 20 m² for a standard vehicle.
If you are considering a kitchen or a veranda, dimensions can vary considerably. A spacious kitchen might require between 15 and 20 m², while a conservatory can be smaller, around 10 to 15 m², while still providing a pleasant space to relax.
To optimize each square meter, it is recommended to approach a professional like Maisons SIC, which can help you maximize the use of space while respecting current regulations.
- Also read: House extension: the 11 key steps
How to extend your house with an extension without planning permission?
It is entirely possible to extend your house without a building permit under certain specific conditions. For small extensions, you will nevertheless have to file a prior declaration of works. This process is simpler and quicker than the building permit, but it remains mandatory.
If your municipality does not have a Local Urban Planning Plan (PLU) and you are outside an urban area, you can build a house extension without a building permit. as long as the added floor area does not exceed 20 m². The floor area corresponds to the sum of the areas of all constructed, enclosed and covered levels, whose ceiling height is greater than 1,80 m.
If you live in urban areas and your municipality has a PLU, you can expand up to 40 m² without planning permission, but with a prior declaration. However, the total surface area of your house, including an extension, must not exceed 150 m². If this threshold is exceeded, a building permit becomes mandatory.
Whether for a small veranda, an additional bedroom, or an office, these extensions can be carried out without the constraints of a building permit.
However, to avoid any errors and optimize your project, it is advisable to call on a professional like Maisons SIC. Our teams will be able to guide you through the process and help you comply with local regulations.
House extension layouts based on surface area
New 20 m2 house extension: how to optimize it?
A new 20 m² house extension offers many possibilities, provided that the space is optimised.
This type of surface is ideal for adding an extra room such as a room, a desk, or a small bathroom. To maximize space, it is important to think carefully about the interior design.
For example, an office can be optimized with modular or built-in furniture, freeing up floor space while retaining maximum functionality.
For a bedroom, choosing a bed with built-in storage can be an effective solution to avoid cluttering the room. Finally, if you opt for a bathroom, compact and suspended equipment will help you maximize every square inch while creating a feeling of space.
New house extension of 40 m2: how to organize it?
With 40 m², the possibilities expand and allow you to consider more ambitious developments.
For example, you can create a master suite with an adjoining bathroom and a dressing room, or add a new living room such as an open living room or kitchen.
In this case, the organization of space is essential to create distinct areas while maintaining aesthetic coherence. An open kitchen can be delimited by a central island, which serves as both a separation and a storage space.
If you opt for a living room, consider tailored lighting solutions to structure the space without partitioning, such as floor lamps or recessed spotlights. The important thing is to create a layout that allows you to move around freely while making the most of every square meter.
Extension of a new house of more than 150 m2: the use of an architect is mandatory
When the house extension exceeds 150 m², the law requires the use of an architect. This threshold includes the total surface area of the house after extension.
The role of the architect is then essential to design a project that meets both your expectations and current regulations. It ensures that the extension is well integrated into the existing building and that it meets urban planning standards, particularly in terms of height, setback from property boundaries, and compliance with the PLU.
Beyond the regulatory aspect, an architect brings a real added value in terms of design and functionality. He can offer you innovative solutions to optimize space, improve natural light, or even integrate eco-responsible technologies into construction.
For projects of this magnitude, call on a professional like Maisons SIC guarantees you a result that meets your expectations, while respecting legal and technical constraints: Contact us!
