Installing air conditioning in a flat is often possible. The risk comes above all from the order in which the project is prepared. Before buying the equipment, the position of the outdoor unit, the route of the pipes, the condensate drainage and the drilling required all have to be surveyed. Only then can you check what touches the co-ownership and prepare the right authorisation.
Start with the route, not with the model of air conditioner
The indoor unit is only one part of the installation.
You need to know where the outdoor unit goes, how the pipes reach it, where the condensate drains away and what has to be drilled.
A good first meeting with the installer should therefore produce a simple diagram of the technical route.
Why are the facade and the slab sensitive?
Where the deeds are silent, the structural shell is presumed common. The facade also belongs to the common envelope of the building. (loi du 16 mai 1975, art. 3.2)
So avoid starting from the reasoning "the air conditioner is mine, therefore the hole is too".
Depending on the building, a slab or a wall may also serve a structural, acoustic or fire-protection function. The applicable technical requirements are then to be checked in the building documents, its permit and local prescriptions, not in a national rule invented for every building.
Can an existing drain be used?
Sometimes, but its nature has to be checked.
The law recalls that a pipe attached to a common installation may remain a common part even where it runs through a private unit. (art. 3.2)
Connecting the condensate is therefore not a detail to be improvised on site.
What file should be prepared for the co-ownership?
The reader does not need an engineering report. They need a project that can be understood.
At a minimum, you must be able to show the position of the outdoor unit, the route of the pipes, the drilling, the water drainage and how the whole thing will look.
Where the works fall under the authorisation provided for in article 16 b), a written draft resolution must be notified with the agenda. (RGD du 13 juin 1975, art. 5, 5°, tel que modifié par le RGD du 28 novembre 2024)
The detail of the majorities and of the possible remedy is set out in “Works in a flat: when do you need the co-ownership's consent?”.
Why also plan for maintenance and reinstatement?
Because an outdoor unit will probably outlast the memory of the meeting that authorised it.
The resolution can state who maintains the equipment, who answers for damage linked to the installation, and what happens when it is removed or replaced.
These conditions must not be assumed. They have to be written down if the co-ownership wants them to frame the authorisation clearly.
And if I am in an office building?
This guide is about a dwelling. In an office building the technical, contractual and operating constraints are not the same: they are dealt with in “Installing air conditioning in a co-owned office building: what to check before the works?”.