KG 400 building services: structure and allocation

Unlike cost group 300, the ordering here does not follow the construction sequence but the trades of building services engineering. That eases collaboration with the specialist designers, whose remits align with the same groups.

The standard designates the group as Bauwerk Technische Anlagen. In practice it is almost universally referred to as technische Gebäudeausrüstung, abbreviated TGA.

The difference is not merely linguistic. Since the 2018 edition cost group 400 applies uniformly to building construction, civil engineering and infrastructure works, for which "building services" does not fit. In a cost determination the designation of the standard is therefore the one to use.

Cost group 470, use-specific and process installations, differs fundamentally from the others. It captures installations serving not the operation of the building but the activity carried on within it: catering equipment, medical installations, workshop and production plant, laboratory services.

The distinction matters for cost determination because these installations fall away on a change of use while the basic provision remains. In a whole-life appraisal they are therefore treated differently from, say, heat supply.

Cost group 480, building and plant automation, is the fastest growing group. It captures the higher-level control reaching across several installation groups. The allocation question here is regularly whether a control system is part of the installation it controls or part of the overarching automation. A consistent determination within the project matters more than the theoretically correct answer, since otherwise reordering occurs between stages.

This allocation is the most fee-relevant in the whole standard, and the reason lies not in the standard but in the HOAI. The reason lies in the threshold rule of the fee ordinance.

The cost of technical installations is chargeable in full only up to an amount equal to 25 per cent of the other chargeable costs; the portion above that at half. Moving an item from the fabric into the technical installations therefore lowers the threshold and increases the portion chargeable only at half. The fee basis comes out lower without anything having changed in the construction cost.

The system behind that rule is covered in the article on chargeable costs. It also sets out how the threshold is calculated.

As a rule of thumb: cost group 400 covers the technical installations and parts of installations built into the structure, connected to it or permanently joined to it. What serves to house an installation but is itself fabric stays in cost group 300.

The last row is project-dependent and belongs on the record explicitly. For machine foundations structurally separated from the floor slab so as not to transmit vibration into the building, allocation to the installation is defensible. What matters is that the determination is recorded and stays the same across every stage.

The share of cost group 400 within building cost has grown for decades. The drivers are well established and continue to operate: tightened energy requirements, heat generators running on renewable energy, ventilation with heat recovery, cooling in response to rising summer temperatures, charging infrastructure, photovoltaics, security systems and building automation.

Two consequences follow for cost planning. Both concern the level of the fee basis.

Benchmarks from older projects are not transferable, not even after updating with a price index. The index corrects the price level, not the scope of plant. Datasets identify the cost group 400 share separately for exactly this reason.

The shift acts on the fee side, and in two directions: it raises the chargeable costs of the building services designer while causing a growing share of costs to fall under half chargeability.

Cost group 410 covers drainage, water and gas installations, that is the trades whose pipework cuts deepest into the fabric. It deserves particular attention for two reasons.

Utility connections belong here. Connection runs for water, drainage and gas are part of the respective technical installation, not of the preparatory works. Public servicing and the charges for it belong in cost group 200. This dividing line is regularly overlooked in cost determinations, and the error runs both ways: either connection costs are carried twice or they are missing entirely.

Below-slab drainage sits within the foundation zone. The pipe itself belongs to cost group 410, the excavation and backfill to cost group 310 or 320. In refurbishment work this separation matters particularly, because the cost of exposing the runs frequently exceeds the price of the pipework.

The figures for cost group 400 as a rule come not from the lead designer but from the building services designer. In practice their appointment frequently follows completion of work phase 4, that is after the point at which the cost calculation is to be prepared.

This produces the commonest source of error in this group: the cost calculation contains benchmarks rather than designed installations for the technical services, and those benchmarks come from older projects with a smaller scope of plant. The allowance comes out too low, and because it simultaneously governs the threshold of the special rule, the error acts twice over.

Anyone obliged to take that route should state the origin of the figures and the plant standard assumed. The system is covered in the article on the cost calculation.

• The cost groups of DIN 276 at a glance
• KG 300 building fabric: structure and allocation
• Chargeable costs under DIN 276 and the HOAI
• Cost calculation at the third level of the cost structure
• The version problem: DIN 276 of 2008 and of 2018