Builder of individual houses for 50 years

throughout the south-west of France

House extension: the 11 key steps

Table of contents

Un house extension is an ambitious project which may have been planned and thought out from the construction or purchase of the house. More advantageous than moving to a new house, it allows you toincrease the surface area of their accommodation without moving. Extension, attic conversion, etc., what are the key steps to follow to successfully complete such a project?

Step 1- Define your expansion needs

For a house extension at the best quality/cost, you must first take stock of your needs. Do you want a larger and brighter living room? A new kitchen? Do you want to add a bedroom to accommodate a child, parents or friends? Would you like a desk isolated to telework in the best conditions? Are you considering investing in a independent studio ? Many opportunities are available to you depending on your budget and the existing potential. L'house extension can be an opportunity to redefine interior spaces and circulation. Gain fluidity, brightness but also comfort.

Step 2 – Consult the PLU

PLU: what house extension am I entitled to?

Even if you have the space, you are not allowed to do everything you want on your own land. It is indeed necessary to respect the PLU (local town planning plan) whose objective is to balance urban development and preservation of natural spaces.
Available for free consultation in the town planning department of your town hall or on your municipality's website, it describes, for each zone, the maximum height of the building, its architectural characteristics, its surface area, its footprint, its location and even its exterior appearance.

Check the footprint and maximum height

No question of building an extension therefore, in an area which only accommodates single-storey houses. Likewise, if the maximum footprint of your existing house is reached, it will be impossible to build a side extension. Other elements may limit enlargement, such as installation rules in relation to roads, to dividing limits or the parking area of ​​your house.

Step 3 – Which professional for the extension of the house?

When expanding a house, should an architect be hired?

If your house measures more than 150 m2 after expansion, you are required to work with an architect. He will draw up the plans for the extension and create a perfect connection with your original house. He will also be able to provide good advice for carrying out the most interesting work according to your budget and your needs. It will then be necessary to sign a project management contract with the architect.

Can we go through a builder for a house extension?

With their knowledge and ability to organize the different trades, mason, plumber, carpenter, electrician, carpenter, etc., the individual home builders are the interlocutors of choice for a house extension project. You also benefit from CCMI (detached house construction contract), individual house construction contract, a very protective contract which requires compliance with deadlines, agreement on the price, a guarantee of perfect completion and all ten-year and other insurances.


To find out more, read our article: “ Building in the South-West: the CCMI protects you »

the extension of the house can be done from above or laterally.
The house extension builder is looking for the best way to extend the house at a low cost.

Step 4: Make a plan for your expansion and your future home

do it plan of its expansion is a wonderful stage, where the project takes shape.
This includes determining the shape and architectural style of the extension: roof terrace, architectural continuity, or different style…. Furthermore, aesthetic and structural compatibility with the existing house is a crucial aspect not to be neglected to ensure harmonious integration of the extension. It highlights the multiple technical issues that the builder will be happy to resolve while respecting the budget (plumbing, electricity, load-bearing walls, etc.).
In the case of an elevation, it is imperative to determine the location of the staircase. The integration of the latter may require rethinking the initial space and circulation of the house.
Whatever the project, it offers you the opportunity to also create new cupboards and reinvent the space. The new living rooms will be tailor-made according to your needs. Kitchen, office, bathroom… design the space of your dreams down to the smallest detail.

Step 5: Wooden extension or masonry house enlargement?

Built in a workshop, thewooden extension is often quicker to install on site, which creates less nuisance on site. Lighter, it also makes it possible to create elevations without necessarily reinforcing the foundations. The aesthetics are also there with a material that offers great flexibility in terms of design and can create a warm and contemporary aesthetic.
On the other hand, the masonry extensions have their own advantages. Brick can provide better protection from summer heat and will blend in well with the existing structure of the home, especially if it is already masonry. Additionally, they may require less maintenance in the long term compared to wood.
The choice will often be made based on cost, personal preferences and local constraints.

To go further, read the article: Brick or wooden house in the South-West? 13 points of comparison »

Step 6: Take thermal regulations into account

House extensions are subject to the environmental regulations 2020 say RE2020. This means that these extensions are very well insulated and designed to limit the energy consumption of the House. This work is therefore an opportunity to also rethink the entire house from an energy point of view and to carry out a thermal renovation overall of the house which entitles itself to state aid. Insulation, heating method, gain in solar gain..., what if these additional square meters allowed you to reduce your future energy bills?

To better understand the issues of environmental regulations, consult the article: “ New house RE 2020 in the South-West: what consequences for my project? »

Step 7: submission of the building permit or prior declaration of work?

Any work carried out on your land must be declared to the town hall. On the other hand, you will not make the same request depending on the number of m2 of the constructed area.
– New constructed area less than or equal to 20 m2 of footprint: A simple prior declaration of works is enough to achieve this enlargement.
– New surface area greater than 20 m2, you must submit a building permit.
The chosen professional will help you or take care of the deposit of permission.

Step 8: respect the administrative deadlines for a house extension

Time limit for building permit processing or prior declaration for an extension

Once the building permit or the prior declaration has been filed with the town hall, you must wait for the latter's decision before starting the work. Deadlines vary depending on the project concerned:
– 1 month for a prior declaration
– 2 months for a building permit
The absence of a response from the administration constitutes tacit acceptance (articles R. 423-1 et seq. of the town planning code).

Display of planning permission

Once received, you must display this authorization in the field in order to inform the neighborhood. The latter are in fact entitled to file an appeal against the planning authorization.

Deadline for contesting planning permission

For 2 months from the first day of posting on the ground, your neighbors can make a free return to the town hall.
The absence of display of the planning authorization on the land extends the time limit for third parties to appeal. The authorization can then be contested for 6 months from the completion of the work.


Wooden frame, a method well suited to house extensions.
A wooden extension is installed very quickly on site.

Step 9: carrying out the structural work

The big difficulty with an expansion is that the work takes place on a generally occupied site.
For a lateral extension, it will first be necessary to create the foundations. The steps to follow will be the same as those for a classic single-family house.
For a elevation, we generally prefer a wood construction. The walls of the latter are lighter and designed in the workshop for assembly on site in a few hours! The extension will be quickly out of water/out of air, which avoids nuisance for the occupants of the house.

To go further, consult our article “ Building your detached house in the South West: the steps ».

Step 10: completion of the second work

Insulation, plumbing, plastering, electricity, insulation, heating, installation of floor and wall coverings, painting... many professionals follow one another on the site to ensure that the integration of the new structure takes place harmoniously.
The builder coordinates all the trades so that the construction site takes place as quickly as possible, until the work is received.

Step 11: declaration of completion of house extension work

When you have completed your work, you must send the town hall a declaration attesting to the completion and conformity of your work.
Declare your new living space to Property Tax Center within 90 days of completion of the work. These additional square meters also increase the property tax.


Continue reading

Other recent articles