Anyone who calculates fees for planning services cannot avoid a term that sounds technical at first glance but is crucial to revenue and project success: the HOAI service group. It determines which fee framework applies to technical equipment, how complex a system is assessed, and which services are even billable. Anyone who understands the HOAI system group understands the foundation of the fee schedule for engineers and architects in Germany.
- What the HOAI plant group is and how it fits into the fee schedule
- Which facility groups the HOAI distinguishes and what they encompass
- How facility groups influence fee calculation for technical equipment
- What role fee zones and billable costs play in conjunction with the HOAI plant groups
- How planners can correctly assign facility groups and avoid common mistakes
- The significance of the system groups for landscape architects and open-space planners
- How the legal situation following the ECJ ruling on the HOAI affects its binding nature
- What practical consequences the assignment of facility groups has for contract drafting and fee negotiations
What the HOAI installation group means: Definition and classification
The Fee Schedule for Architects and Engineers (HOAI) is the central fee schedule for planning services in Germany. It sets forth the principles according to which fees for architects, engineers, and related planning professions are calculated. Within this system, the HOAI plant group serves a structuring function: It categorizes the various types of technical systems in buildings and outdoor facilities, thereby forming the basis for fee calculation in the area of technical equipment, which is regulated as a separate service category in the HOAI.
Technical equipment encompasses all building services and building systems necessary for the operation of a structure: from heating and ventilation to electrical installations and material handling systems. The HOAI groups these systems into categories, each of which shares similar technical characteristics and comparable design requirements. Each HOAI system group thus corresponds to a defined scope of services for which specific fee parameters apply. Assigning a specific system to the correct group is therefore not a mere formality, but a technically justified decision with direct economic consequences.
In its current version, the HOAI distinguishes between eight systems groups, ranging from Group 1 (sewage, water, and gas systems) to Group 8 (building automation). Each group is assigned to a specific technical discipline and is considered separately when determining fees. This means that if a project encompasses multiple systems groups—which is typically the case with complex construction projects—the fees for each group are calculated individually and then combined. This principle of separate consideration is intended to ensure that the compensation appropriately reflects the actual planning effort for each trade.
An Overview of the Eight System Groups: Contents and Delimitations
The HOAI divides technical equipment into eight system groups, each of which comprises clearly defined trades and system types. System Group 1 covers wastewater, water, and gas systems—that is, the entire plumbing and utility infrastructure within a building. System Group 2 encompasses heat supply systems, including boilers, heat pumps, district heating connections, and the associated distribution systems. System Group 3 covers air-handling systems, i.e., ventilation, air conditioning, and cooling. These three groups form the classic core of building services engineering, which is relevant to nearly every building construction project.
System Group 4 pertains to high-voltage electrical systems, i.e., the entire electrical supply system, including switchgear, transformers, and emergency power supply. System Group 5 encompasses telecommunications and information technology systems, which include telephone, data, alarm, and security systems. System Group 6 covers transportation systems such as elevators, escalators, and conveyor belts. Finally, System Group 7 encompasses usage-specific systems—that is, all technical systems that do not fall under the standard building trades but are specifically required for a particular building use, such as medical technology in hospitals, kitchen technology in commercial kitchens, or stage technology in theaters. System Group 8 pertains to building automation—that is, the overarching control and regulation technology that networks and coordinates the various building systems.
In practice, the distinction between the groups is not always clear-cut. Where does the ventilation technology of Group 3 end and where does the building automation of Group 8 begin when a ventilation system is fully integrated into a higher-level building management system? Such overlaps require a technically sound classification based on the primary function of the respective system. In cases of doubt, it is advisable to include a clear contractual provision specifying which services are assigned to which group in order to avoid future fee disputes.
Fee Calculation for Technical Equipment: System Groups, Fee Zones, and Billable Costs
The calculation of fees for technical equipment according to the HOAI follows a multi-stage system in which the HOAI equipment group is one of several determining variables. The starting point is the determination of the billable costs—that is, the portion of the construction costs on which the fee calculation is based. For technical equipment, these are the costs of the respective systems themselves, not the total construction costs of the project. The billable costs are determined separately for each system group.
Based on the billable costs and the fee zone, the fee is determined using the HOAI fee schedules. The fee zone describes the level of difficulty of the design task and ranges from Zone I (low requirements) to Zone III (high requirements). Classification into a fee zone is based on evaluation criteria defined in the HOAI for technical equipment. These include, among other things, the number of functional areas, the degree of integration among the systems, special requirements for energy efficiency or operational safety, and unusual usage requirements.
The combination of chargeable costs and the fee zone results in a fee range with minimum and maximum rates. Within this framework, the client and the contractor can agree on the specific fee. However, since the 2019 ruling by the European Court of Justice, which declared the HOAI’s mandatory minimum and maximum rates incompatible with European law, the legal situation has become more complex. Since then, the HOAI fee schedules have served as a guideline but are no longer legally binding if the parties reach a different agreement. Nevertheless, the system of facility groups remains the authoritative reference model for calculating and structuring fee proposals.
One aspect that is often underestimated is how to handle projects that encompass multiple facility groups. The HOAI stipulates that fees for each group are calculated separately and then added together. Synergy effects can arise when a planner handles multiple groups from a single source, which is common in practice. Such situations require a careful delineation of services in the contract to ensure clarity regarding which services are compensated with which portion of the fee.
System Groups in Landscape Architecture and Open Space: What Planners Need to Know
For landscape architects and open-space planners, the HOAI’s “technical systems” category may at first glance seem to be a topic that primarily concerns building construction. In fact, however, technical systems also affect many outdoor projects: irrigation systems in public parks and sports facilities, lighting infrastructure in city squares and promenades, pumping stations and drainage systems in open-space projects, fountains and water features in city parks, as well as control systems for complex green spaces. As soon as such systems are part of a planning contract, the question arises regarding the correct calculation of fees and, consequently, their assignment to an HOAI systems group.
Irrigation systems for open spaces can generally be assigned to System Group 1, as they are classified as water systems. Outdoor electrical lighting falls under System Group 4 (high-voltage systems). Control systems for automated irrigation or lighting may, depending on their complexity, be assigned to System Group 8 (building automation), even if they are installed in open spaces rather than inside buildings. These classifications are not always clearly defined and require a professional assessment on a case-by-case basis.
The issue of system groups takes on particular relevance in integrated projects where building construction and outdoor spaces are closely intertwined: for example, in new school buildings with outdoor facilities, sports facilities with technical infrastructure, or urban development projects with complex outdoor and building systems. In such scenarios, landscape architects and building services engineers must coordinate their scope of services and fee calculations to avoid double counting or gaps in compensation. Early coordination of the scope of services is not merely a bureaucratic requirement here, but an economic necessity.
Common Mistakes in Assigning System Groups and How to Avoid Them
In planning practice, fee disputes often arise at the interface between system groups. A classic mistake is grouping multiple trades under a single system group to reduce administrative overhead. For example, if heating, ventilation, and plumbing are lumped together into a single group—even though they correspond to three different groups under the HOAI—this leads to a systematic distortion in fee calculation. The billable costs are allocated incorrectly, and the fee zone cannot be properly determined.
Another common error concerns the distinction between system group 7 (use-specific systems) and the other groups. Use-specific systems are those that are required solely by the specific purpose of a building and are not part of the general standard of equipment. If such systems are incorrectly assigned to a standard group, this can lead to an underestimation of the planning effort and, consequently, to a fee that is too low. Conversely, some planners tend to prematurely classify systems as use-specific in order to qualify for a higher fee bracket, which can lead to corrections during a fee review.
The classification of building automation systems (Group 8) is particularly delicate. This group encompasses the overarching control and regulation systems, but not the control technology that is directly assigned to an individual system and enables its operation. The control system for a ventilation system that operates exclusively for that system is part of ventilation design (Group 3). Group 8 applies only when a higher-level system integration of multiple disciplines is planned. In practice, this distinction is often the subject of discussion between planners and clients.
To avoid such errors, the following approach is recommended:
- Structure the scope of work and cost estimate by system group from the outset, rather than by trade or contract unit
- Justify the assignment of each system to a group in writing and document it in the contract
- In borderline cases, use the system’s primary function as the classification criterion
- Identify and document changes made during the planning process that affect new equipment groups as grounds for a contract amendment
- For complex projects, consult a fee consultant or the relevant architectural association early on
Legal Framework: HOAI Reform, ECJ Ruling, and Current Applicability
The HOAI has undergone several amendments throughout its history, most recently a fundamental reform in 2021, which should be understood as a direct response to the 2019 ECJ ruling. The Court had ruled that the HOAI’s mandatory minimum and maximum rates violated the European Services Directive because they restricted free competition in the single market. Although the fee schedules are still included in the reformed version, they are no longer considered mandatory law. Contracting parties may agree on different fee arrangements without these automatically being invalid.
In practice, this means that the HOAI system of service categories and the associated fee schedules remain the most important reference model for determining fees in Germany, even though their legal binding force is limited. Anyone who prepares a fee proposal based on the HOAI system is operating on familiar and recognized ground. Anyone who deviates from it must justify the deviation and ensure it is contractually secured. In fee disputes, courts continue to rely on the HOAI system as a benchmark, even if no explicit agreement regarding the HOAI has been reached.
Special regulations apply to public contracting authorities: In the area of public procurement, the HOAI is frequently used as the basis for fee proposals and evaluation thresholds. Even though the minimum and maximum rates are no longer mandatory, many contracting authorities use the HOAI values as a guide to ensure that bids are comparable and that appropriate compensation is provided. Planners working for public clients should therefore have a thorough understanding of the HOAI classification system, including the annex groups, even if they enter into different fee agreements in individual cases.
HOAI Service Groups as a Planning Tool: Conclusion and Practical Application
The HOAI facility group is not a bureaucratic relic, but rather a structuring tool that breaks down complex technical planning services into comparable units. Those who understand the logic of the eight groups, who know which facilities belong to which group, and how this classification affects the fee zone and billable costs, possess a set of tools that goes far beyond mere fee calculation. It helps structure scope of work, formulate contracts precisely, and justify contract amendments appropriately.
For landscape architects and open-space planners who are increasingly working on integrated projects involving technical infrastructure, knowledge of the HOAI system of facility groups is not an optional additional qualification. Anyone who plans or coordinates irrigation systems, outdoor lighting, or control technology must know within which fee framework these services are to be billed. This protects against underfunding and strengthens the negotiating position vis-à-vis clients who wish to commission planning services on a flat-rate and undifferentiated basis.
The debate over the binding nature of the HOAI following the European Court of Justice ruling has not rendered the system of installation groups obsolete; rather, it has actually reinforced its importance as a framework for guidance. In a market where fees are negotiated more intensely than in the past, a thorough understanding of the HOAI system is the best foundation for fair and transparent fee agreements. The HOAI service group thus remains what it has been from the very beginning: a tool for the proper valuation of planning services, one that only fully realizes its value when it is understood and consistently applied by all parties involved.
