IVHB: which cantons apply the harmonised building terms

What the IVHB is

The Intercantonal Agreement on the Harmonisation of Building Terms (IVHB) was adopted in 2005 and came into force on 26 November 2010. It harmonises 30 measuring methods and building terms; cantons that join commit to adopting them in their planning and building law. It contains no limits.

Source: BPUK: IVHB (bpuk.ch, in German) · Glossary: plot ratio

Joined: 17 cantons

Aargau, Appenzell Innerrhoden, Bern, Basel-Landschaft, Fribourg, Graubünden, Jura, Lucerne, Neuchâtel, Nidwalden, Obwalden, Schaffhausen, Solothurn, Thurgau, Uri, Valais and Zug. Joining obliges a canton to adapt its law within three years and to set the deadlines for implementing it in land-use plans.

Source: BPUK: accession status (09.11.2022)

Zurich: adopted without joining

Zurich has not joined but adopted 29 of the 30 terms; the law changes came into force at cantonal level on 1 March 2017. The floor space index was not adopted — Zurich keeps the floor-area ratio (Ausnützungsziffer). In a commune the new terms apply only once its building and zoning regulations are harmonised. The deadline ran until 28 February 2025; the cantonal government asked for a three-year extension, which according to the canton was still before the cantonal parliament on the date checked.

Source: zh.ch: Harmonisierung der Baubegriffe (in German)

Schwyz: joined, then withdrew

Schwyz had joined the IVHB and decided on 30 March 2022 to withdraw, effective 22 September 2022. Which definitions Schwyz law has used since is not checked here.

Source: BPUK: accession status (09.11.2022)

Not joined: seven cantons

Appenzell Ausserrhoden, Basel-Stadt, Geneva, Glarus, St. Gallen, Ticino and Vaud have not decided to join. A canton can still adopt individual terms into its own law, as Zurich did; for these seven cantons that is not checked here. What counts is the cantonal building law and the commune's zoning regulations.

Source: BPUK: accession status (09.11.2022)

Reservation: floor-area ratio instead of floor space index

Aargau, Obwalden, Schaffhausen, Uri and Zug joined but, by reservation, keep the floor-area ratio (Ausnützungsziffer) instead of the IVHB's floor space index (Geschossflächenziffer). An "AZ 0.6" in these cantons and a "GFZ 0.6" in another canton are therefore not calculated under the same definition.

Source: BPUK: accession status (09.11.2022) · Guide: calculate buildable floor area

Does the IVHB apply in the canton of Zurich?

Zurich has not joined the IVHB, but adopted 29 of its 30 terms into its planning and building law, in force since 1 March 2017. Zurich did not adopt the floor space index. In a commune the new terms apply only once its building and zoning regulations are harmonised.

What does the "floor-area ratio" reservation mean?

Some member cantons — Aargau, Obwalden, Schaffhausen, Uri and Zug — keep using the floor-area ratio (Ausnützungsziffer) instead of the IVHB's floor space index. The agreement's other terms apply there as in other member cantons.

How do I know which definition applies to a parcel?

From the building and zoning regulations of the commune the parcel is in. Even in a member canton, the IVHB terms often apply in a commune only once its land-use plans are adapted. If in doubt, the commune's building authority can tell you.