Building an extension: the 6 rules to know


Building an extension: the 6 rules to know

Nicolas Masurel Architect

The house we love or the one we are about to buy sometimes needs a little more space. Make an extension is the best solution. Additional room on one level, extension on several levels or elevation of roof ... The possible configurations are almost infinite. However, build an extension is a very restrictive exercise, first by land and then by town planning rules. Two architects with resolutely contemporary signatures recall the rules to follow for enlarge the house.

A extension, those are square meters more. But not only. By opening the space, we will rework the volumes, rethink the circulation in the house, expand and facilitate access to the outside, the terrace or the garden. Thanks to the openings, the light will flow, greatly improving comfort and quality of life. Here are the tips for Gilles Bertrand (AAGB Architecture in Tours) and Nicolas Masurel (Koutok Architecture, in Nantes) to build an extension without a bad surprise.

Read also> Wooden extensions: the rules to know

1. Use of the architect: think about it even when the law does not require it

You will need to call an architect for your extension project if the total project area (after works) exceeds 150 m2. However, even if your project is below these limits, the contribution of the architect is very valuable. Moreover, the smaller the extension, the more it must be optimized

"The architect will listen to the family, understand how it is constituted, will it grow up, will we receive a lot at home, then it will consider all the constraints and propose a or several projects ", explains Gilles Bertrand. "In general, I present the progression of my reflections with the help of a succession of drawings, as different tracks on which the customer can react or rebound", chains Nicolas Masurel.

See also> Extension of a town house of 45 m2

The architect will work the shape of the extension, its volume and make the connection between the buildings. If this is necessary and consistent, he will propose to review the insulation, joinery, or facade of the existing building. An architect never proposes the same project twice. Your extension is unique.

Also read> 60 m2 for a wooden extension

Invisible from the street, this contemporary extension (wood frame and zinc cladding) adds 70m2, on two levels, to a beautiful house in Touraine. The ground floor is occupied by a large kitchen, upstairs by an office and a bedroom. The large bay window is angled to maximize solar gain. Creation Gilles Bertrand.

Sebastien Andrei

2. Identify constraints, make them strong!

Building an extension is like juggling a set of constraints, among which: planning rules and respect for property boundaries, the orientation of the parcel and its environment, the available footprint, the nature of the land or the elevations. The lights are rarely all green!

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"The constraints require to turn and return the project in all directions, until finding the solutions that will incorporate all the criteria," confirms Nicolas Masurel who sees these constraints as a creative challenge. "An extension project is built by successive exchanges with the client, nothing is fixed at the beginning, it must remain open.For example, the rediscovery of a beautiful stone wall on an old house can prompt, in response, to use a wood / zinc wedding on the extension. "

Same analysis for Gilles Bertrand: "a very limited footprint, manage the parking of several vehicles, a slope, access to the pool, vis-à-vis and, of course, the limits imposed by the Local Plan Urban Planning (PLU) ... this is part of the project data. "

Read also> Before / after: enlarge a house in its own juice

Extension wood (ground floor) and wood elevation of the floor (plaster). We guess, above the extension, the roof of origin. Wood cladding (red cedar) and aluminum joinery.

Nicolas Masurel Architect

3. Dare contemporary forms

"Today's contemporary is the traditional of tomorrow, likes to remind Gilles Bertrand.Every period has its own architectural language and one can be good in his time while respecting an old building or a regional character. Zinc is both traditional and adapted to contemporary lines. "

Do not hesitate to bet on codes of today, like flat roofs or clean lines but beware, contemporary does not necessarily mean cubic !

Because they allow a great freedom of creation, Nicolas Masurel favors wood frame extensions. "On a recent project, located on a very small plot, we created several levels of terrace. In the end and despite the extension, the surface of the outdoor spaces is greater than it was before the project. "

Also read> 12 verandas to take as a model

Extension of 103 m2 contiguous to a house in a small hamlet. The volume, entirely covered with dark zinc, unfolds to gently connect the two levels. Zinc offers a contemporary reading, like a carapace voluntarily separating itself from the existing architecture. Director Gilles Bertrand

Philippe Hervouet

4. Go get the light

When the orientation is favorable (full south), the light naturally bathes the house. "It's ideal because you can take advantage of the maximum amount of winter solar gain," says Masurel, "just make sure you protect yourself from the summer sun, with, for example, outside sunshade.

But often, you have to deal with a less obvious orientation. "There are always solutions," continues Gilles Bertrand. create a bay angled to get a little south or a patio in an angle always to capture this southern light. "

We will also think about double height joinery (or glazed walls) and skylights. The windows are also interesting for their ability to fade to erase the limit in / out. Think of folding bays, large sunshades, or spectacular post-free corner slides.

See also> Bay windows and windows: our tips for choosing well

5. Know the basics of thermal regulation

The buildings' RT considers the case of extensions ("new part of an existing building").

For small extensions (less than 150 m2 and less than 30% of SHONRT surface created) a "light" thermal regulation applies, much less restrictive than for new buildings and exempt from thermal study.

Recall that the SHONRT is the sum of the floor surfaces of each level, after deduction of unheated surfaces (such as garage, basement or undeveloped attic, unheated porch).

For the large extensions (≥150 m2 or ≥30% of SHONRT created), it will be necessary to comply with the requirements of the RT 2012, that is to say to reach a level of performance fixed by the texts, in terms of insulation and energy production .

Admittedly, this is a serious constraint, especially because it will have to go through a phase of thermal study. But you will win an ultra-efficient house, with low energy consumption and low greenhouse gas emissions (GHG).

Read also> What heating for a home extension?

On a small plot, a wood extension (with wood cladding) enlarges the old house in street corner. The garage has been reworked (we hardly guess the door). The extension incorporates terraces on 3 levels, to preserve a beautiful exterior surface. The opening on the gable of the old house was created during the works.

Nicolas Masurel Architect

6. Understand urban planning rules

The Local Urban Plan (PLU) of your municipality defines rules to follow. It can limit the footprint, the height of the extension, its volume, the implantation compared to the separative limits or even prohibit some colors.

Read also> Eco-renovation: what helps?

In addition, if you live in a protected or protected sector, your project will be subject to the approval of theArchitect of Buildings of France, whose mission is to ensure the architectural quality of the territory. Submit your project very early.

In municipalities not covered by an urban planning document, the law of soils is governed by default by the National Urban Planning Regulation. Outside the urban areas of these municipalities, the constructibility is limited (the extensions must absolutely be adjacent). Inquire with your municipality.

Contemporary extension on old building, the coherence is ensured by the subtle marriage of materials (stones / wood / zinc). Originally, the house was covered with a cement coating. The discovery of beautiful stones gave a new dimension to the project.

Nicolas Masurel Architect

Good to know :

Building permit or declaration of work?

If you live in a urban area with a local urban plan (PLU), you will need to application for a building permit if :

- the works add floor area (also referred to as ground clearance) greater than 40 m2

- or if the works, adding a floor area between 20 and 40 m2, have the effect of bringing the total surface of the construction (house + extension) to 150 m2 since March 1, 2017.

Note that if you create a floor area between 5 and 40 m2, you will need to submit a prior declaration of work. Below 5 m2 and if you do not change the appearance of the house (for example, attic without creating an opening) you have no obligation.

Where can I get help to set up your project?

  • to the urban planning department of your municipality
  • or the Council of Architecture, Urbanism and Environment (CAUE) of your department

thanks to

Gilles Bertrand, AAGB Architecture (in Tours) - and Nicolas Masurel, Koutok Architects (in Nantes) -