The basis of every architect fee
The HOAI fee depends directly on the eligible costs (anrechenbare Kosten). The higher they are, the higher the table value, though not proportionally: the fee table is degressive, so the fee as a percentage falls as costs rise. That makes it all the more important to determine eligible costs correctly. In the HOAI fee calculator they are the first and most important input.
What the law says
Under § 4(1) HOAI, eligible costs are the part of the costs of constructing, converting, modernising, maintaining or repairing buildings that is determined according to recognised engineering practice on the basis of local prices. For cost planning the HOAI refers to DIN 276 in the December 2008 version. VAT is expressly not part of the eligible costs.
Which cost groups count for buildings?
§ 33 HOAI sets out the details for buildings and interiors:
1. Cost group 300 (building structure): eligible in full.
2. Cost group 400 (technical systems): eligible in full up to 25% of the other eligible costs and by half above that, if the architect does not design or supervise these systems.
3. Not eligible are, in particular, costs for site preparation, private site development, furnishings and artworks, unless the architect designs them, helps procure them or supervises their installation.
Land costs, ancillary costs such as notary fees, surveys and the architect's fee itself, and financing costs are not included either.
Example: the 25 per cent rule for building services
A single-family house has €360,000 of structural costs and €120,000 for technical systems (heating, plumbing, electrics). The systems are designed by a specialist engineer. 25% of €360,000 is €90,000, which counts in full. The remaining €30,000 counts by half, i.e. €15,000. Eligible costs are therefore €360,000 + €90,000 + €15,000 = €465,000, not €480,000.
In zone III at the base rate with all work stages, the difference is about €1,700 of net fee. Separating the cost groups properly therefore gives a more accurate result.
Cost estimate or cost calculation?
Under § 6(1) HOAI, the fee is based on the cost calculation from the final design (work stage 3). If this is not yet available, the cost estimate from the preliminary design is used. Later cost increases from tendering or construction generally do not change the fee. If, however, the client changes the scope, for example by adding rooms, the fee can be adjusted (§ 10 HOAI).
Existing building fabric
In conversions the question is how to value existing components the architect has to integrate into the design, such as load-bearing walls or an existing facade. Under § 4(3) HOAI, this existing fabric must be reasonably taken into account in the eligible costs. Its extent and value must be determined for the specific building at the time of the cost calculation and agreed in text form. More on this in HOAI refurbishment surcharge.
Self-build and discounts
If the client carries out work themselves, receives unusual discounts or has existing materials installed, local prices still apply under § 4(2) HOAI. Self-build therefore does not reduce the eligible costs, because the architect's design work stays the same.
How to get a first figure
For a rough estimate before the actual design, look at the construction costs. For existing buildings, the renovation cost calculator gives a first reference point. Deduct the non-eligible items and VAT and enter the result in the HOAI fee calculator.