tonttialue

Tonttialue refers to the area of a plot of land that is designated for building and ownership in Finland. It is the two‑dimensional surface defined in cadastral records and the land register, usually expressed in square meters (m2) and sometimes in hectares (ha). The tonttialue serves as a basic measure of property size and is a key factor in real estate transactions, taxation, and valuation.

The tonttialue is determined and documented by public authorities, notably the National Land Survey of Finland (Maanmittauslaitos) and the local cadastral authority. Changes to the tonttialue occur through parcel division (lohkominen), merging of parcels, or other cadastral procedures, and the resulting boundaries are recorded in the land register and cadastral map. The planning system also interacts with tonttialue: the size and shape of a plot influence, and are influenced by, zoning plans (asemakaava) and building regulations.

It is important to distinguish tonttialue from building rights or allowable built space. Building rights—such as maximum floor area, setbacks, and building height—are governed by zoning and building regulations, and may be constrained by the tonttialue, easements, or public rights of way that lie within or across the plot. Tonttialue may also include areas reserved for public use or restricted due to easements, which can limit development.

In practice, buyers and sellers refer to the tonttialue as the plot’s size, while construction and land-use decisions are guided by the interplay between the tonttialue, zoning, and permitting processes.