What § 4 HOAI lays down
The wording governs four points that bind directly in practice. They concern the fee basis and its limits.
Paragraph 1 sentence 1 defines chargeable costs as part of the costs of constructing, converting, modernising, maintaining or repairing an object, together with the associated expenditure.
Paragraph 1 sentence 2 requires determination according to generally recognised rules of technology or to administrative regulations, on the basis of locally customary prices.
Paragraph 1 sentence 3 provides that where the ordinance refers to DIN 276 in connection with cost determination, the December 2008 edition is to be applied for determining chargeable costs.
Paragraph 1 sentence 4 states that value added tax on the cost of objects is not part of chargeable costs. They are therefore determined net throughout.
The third sentence carries the most consequence. The edition governing cost planning dates from December 2018; the edition governing fee determination from December 2008. Both apply side by side, each for its own purpose. The article on the version problem covers this situation and its practical effects.
Which cost groups count
The following system applies to the service profile for buildings and interiors. Note that the HOAI does not itself use the cost group designations but speaks of building fabric and technical installations. Mapping to cost groups serves illustration.
| Cost group | Chargeability |
|---|---|
| KG 100 Site | not chargeable |
| KG 200 Site preparation | only where the designer provides services for it |
| KG 300 Building fabric | fully chargeable |
| KG 400 Building services | chargeable under the special rule below |
| KG 500 External works | only for landscape design commissions or where designed alongside |
| KG 600 Furnishings and artworks | only where the designer provides design services for them |
| KG 700 Ancillary construction costs | not chargeable |
| KG 800 Financing | not chargeable |
The underlying logic is consistent: what is chargeable is what the designer designs. They do not design the site, nor their own fees, and financing lies outside their remit.
For the conditionally chargeable groups the contract decides. Whether the building designer also designs the external works, whether they design the furnishings, whether they provide services for site preparation: these are questions of agreed scope and therefore belong in the contract rather than in the cost determination.
The special rule for building services
The cost of technical installations does not enter chargeable costs in full without limit. The rule works with a threshold: Above the threshold they enter at half.
- Up to an amount equal to 25 per cent of the other chargeable costs, they are chargeable in full.
- The portion above that is chargeable at half.
The other chargeable costs are here essentially the building fabric plus the existing fabric being incorporated. Allowing for that fabric therefore also raises the threshold.
This rule acts on every project with a high services content, and it acts more strongly now that the share of technical installations within building cost has risen over the years. In practice it means a technically demanding building carries a fee basis that grows less than proportionately.
Existing fabric being incorporated
Paragraph 3 of § 4 provides that existing building fabric to be incorporated into the works must be appropriately taken into account within chargeable costs. In refurbishment work this is the economically most significant provision of the whole section, and simultaneously the one most frequently passed over.
The reason lies in its indeterminacy: the standard of appropriateness is not quantified. How the extent is established, valued and recorded is covered in the article on existing fabric in chargeable costs.
Which cost determination governs
Chargeable costs are determined on the basis of the Kostenberechnung, the cost calculation prepared during developed design. Not on the basis of the earlier cost estimate, and not on the basis of the costs finally invoiced.
The fee basis therefore hangs on a determination made at a point when a substantial part of the project is already fixed but nothing has yet been procured. The system of stages and their depth of detail is covered in the branch on the stages of cost determination.
Not every stage is a basic service. Which count as additional services to be remunerated separately is covered in basic services versus additional services.
The framework changed in 2021
Since the 2021 revision, the HOAI fee tables are no longer binding minimum and maximum rates but values for orientation, following the 2019 judgment of the Court of Justice of the European Union. The calculation quantities, by contrast, apply unchanged.
Chargeable costs are unaffected by this. They remain the central reference quantity for determining fees, even though the rate derived from them is now freely negotiable. Determining chargeable costs poorly therefore leaves no sound basis even for a freely agreed fee.
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This article reflects the position at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.