The freedom of arbitrary exercise of property is not limitless, but is restricted by neighboring law in the interest of living together in a confined space. First and foremost, regulations and house rules are decisive.
Use according to regulations
The new condominium owner has an exclusive right to use the seating area. In the interest of the condominium owners and in order to prevent possible disputes, it is advisable to describe this as precisely and clearly as possible in the regulations. Exclusive use does not mean that this part of the building can be designed and structural changes made at will. The fewer rules the regulations contain, the more limited are the possibilities of use. If the regulations of your community do not explicitly allow a whirlpool, for example, the new condominium owner may only implement the change with the consent of the other condominium owners (qualified majority according to heads and value quotas).
Additional consumption of water and electricity
In the absence of any provision to the contrary in the regulations, all costs - including operating costs - are distributed in proportion to the value shares of the apartments. This also applies to new (cost-driving) facilities that mainly or exclusively serve a single co-owner. Consequently, a supplementary regulation is required if the co-owners not involved are not to be burdened in terms of costs. It is therefore recommended that you propose a supplementary cost regulation in the use and management regulations at the next condominium assembly.
In addition to the legal regulation, there is also the practical question of how the additional consumption of water and electricity (heating energy) should be measured. If a separate measurement and thus billing proves to be technically or structurally impossible, the only remaining option is a correction via the value shares of the apartment or a separate charge of the preferred co-owner.
No excessive noise in case of ordinary bathing fun
In connection with the use of the whirlpool, noises and sounds inevitably arise, which can be perceived by neighbors as noise immissions. Immissions from one condominium to another are permissible as long as they do not lead to an excessive impact on the property of the co-owner (ZGB 684 I). For example, conversations on the garden patio are customary according to general life experience and are to be tolerated by the neighbors. Prohibited are, for example, all impacts that are harmful or not justified according to the location and nature of the property or according to local custom (ZGB 684 II). The surroundings (neighborhood) and the time of day also play a decisive role. A pool party at midnight will probably exceed the tolerable level.
No building permit required
For the installation and normal use of a whirlpool, the co-owner - in contrast to a swimming pool - does not need a building permit under public law. According to a Lucerne court decision of 13.07.2009, bathing in a whirlpool generally does not cause excessive noise emissions, which would have to be reviewed in a building permit procedure.