Choosing planting

Garden greenhouse: what does the law say?

Small regulatory point: necessary permits and potential taxes

Contents

Modified the 14 December 2025 by Marion 5 min. Difficulty: Beginner

The arguments in favour of a garden greenhouse are plentiful: it allows for longer growing seasons for plants and young plants, protects tender vegetation during winter, limits the development of certain diseases, and more. Ingrid details all the advantages in the article “A greenhouse in the vegetable garden, what for?“.

However, the installation of a greenhouse is subject to regulations, as it is considered an external annex generally classified as a structure. It is therefore subject to the Planning Code. So what regulations must be followed before fully enjoying your greenhouse in the garden? Let’s take stock.

What does the law say about greenhouses?

Difficulty

Installing a greenhouse without prior permission

According to the article R*421-2 of the Urban Planning Code, there are two cases in which it is possible to install a garden greenhouse without any prior application being necessary.

Small Greenhouse

Small installations are not subject to prior declaration before installation. You can therefore install tunnel greenhouses, forcing tunnels, or frames without any additional steps. For this, your garden greenhouse must comply with the following maximum dimensions:

5m² of total surface area (including floor area and footprint);
height not exceeding 1.8 metres.

Note: the footprint is “the vertical projection of the volume of the construction, including all overhangs and projections.” It refers to the interior surface, plus the shadows cast by external elements (except for ornaments and unsupported roof overhangs).

However, there is an exception to this tolerance: it concerns dwellings located in protected areas, that is to say “in the vicinity of a heritage site or historical monument, in a classified site or in the process of classification.” If you have any doubts, do not hesitate to contact your local council to ensure that your residence is or is not within a protected perimeter. In this case, you will necessarily need to request a planning permission from the local council of your residence to install your greenhouse, even if it is small.

Temporary Greenhouse

If your garden greenhouse is not intended to be installed permanently, but only temporarily for a season, for example, there is no need to request prior authorisation. This greenhouse must not remain in place for more than 3 months in the year. There are no rules regarding the maximum dimensions to be respected for this type of temporary greenhouse.

It should be noted that here again, dwellings located in protected areas do not benefit from the same measures as in the general framework. In this case, you can only install your temporary greenhouse for a maximum of 15 days without having to request prior authorisation.

Small installations are not subject to prior declaration before installation

In which cases is it mandatory to declare your garden greenhouse?

If your garden greenhouse exceeds the dimensions previously mentioned, or if it is intended to be installed permanently, it is considered an external annex installation. It is therefore subject to the same regulations as garden sheds, pergolas, kiosks, or play area structures.

The dimensions of your future greenhouse will determine whether you need to submit a prior declaration of works or if you need to apply for a building permit. There is a general regulation, but this may vary according to the Local Urban Plan (PLU) of your municipality. Therefore, do not hesitate to contact your local council, which will confirm the steps to be taken.

The prior declaration of works

A prior declaration of works is required when your works are not subject to a building permit. It is obligatory under the article R421-9 of the Urban Planning Code if your greenhouse:

has a total area between 5 m² and 2,000 m² (including floor area and footprint);
has a ceiling height (enclosed and covered) between 1.8 metres and 4 metres.

For the installation of most garden greenhouses for personal use, this is generally the case.

You have two options to make this declaration for the installation of your greenhouse:

visit your local council to obtain the form to complete;
complete the prior declaration of works form directly online.

Once your application is submitted, the processing time is 1 month from the date of submission (2 months in a protected area). If you have not received any response by the end of this period, you benefit from a “decision of non-opposition,” which therefore authorises you to install your greenhouse.

The declaration is valid for 3 years, during which you must have at least started the development works without interruption of more than one year.

The building permit

As you will have understood, if your garden greenhouse exceeds the dimensions previously mentioned, that is to say, a ceiling height greater than 4 metres and a total area greater than 2,000 m², you must apply for a building permit. This situation mainly concerns professionals.

Again, you have two options to make this application:

visit your local council to confirm the procedures to follow and obtain the form to complete;
complete the building permit application online.

Once your application is submitted, the processing time is 2 months from the date of submission (3 months in a protected area). Without a response from the administration after this period, you benefit from a tacit permit.

The development tax for garden greenhouses

Garden greenhouses are subject to the same regulations as other outdoor structures, including the well-known development tax. This tax, payable only once, is based on the area declared to the local council and varies depending on the number of m² involved. It also varies according to local authorities. On average, expect to pay between €750 and €850 per m².

But good news: an amendment has been passed as part of the 2022 finance law to exempt garden greenhouses from the development tax for individuals. However, this is an optional exemption, which can be voted on by local authorities wishing to implement it, to take effect in January 2023. So, make sure to check in advance whether you can benefit from it or not!