The Fee Structure for Architects and Engineers (HOAI) is a legal ordinance of the Federal Government regulating the fees for architectural and engineering services. The service profiles regulated in the HOAI are fee elements for the calculation of the fee in terms of amount. The HOAI is therefore a "tax" within the meaning of Section 632 (2) of the German Civil Code (BGB).
What an architect/engineer owes, however, results solely from the concluded architect/engineer contract, the content of which is to be determined or interpreted according to the general principles of civil contract law.
"The HOAI does not affect the freedom of contract. Whether the architect can claim fees at all is determined by the general provisions of civil law. Only when his claim is established on the merits are the provisions of the regulation applicable to the calculations of his fee (§ 1 HOAI)."
- BGH, judgement of 28 March 1985 - Ref. VII ZR 180/84.
The scope of application of the HOAI is in principle opened, provided that an architect or engineer has undertaken to perform tasks described in the HOAI (cf. BGH, judgement of 23 February 2006 - ref. VII ZR 168/04).
Section 6 (1) of the HOAI stipulates that the fee for the basic services is generally based on
- according to the chargeable costs,
- according to the respective scope of services,
- the fee zone to which the object or service belongs,
- according to the relevant fee schedule
- and, in the case of existing services, additionally according to the conversion and modernisation surcharge on the fee.