The sliding scale
MEP design fees are usually quoted as a percentage of the mechanical, electrical and public health construction value, and that percentage falls as value rises. On a small installation the figure might be around five per cent for full design; on a multi-million pound one it can be closer to two.
Why effort does not scale with value
The number of engineering decisions in a building is a function of its complexity, not its size. Doubling the floor area of a warehouse adds very little to the design effort. Doubling the floor area of a laboratory adds a great deal.
A percentage fee handles this crudely but adequately at the population level: larger projects are, on average, less design-intensive per pound of construction value. It is a proxy, and it is a reasonable one, but it is not a measurement.
What makes fee proposals incomparable
Because the percentage is a proxy, two proposals quoting different percentages may be quoting entirely different work. The variables that matter more than the headline rate:
- RIBA stages included. Stages 1 to 3 are around a third of the total, technical design at Stage 4 over half, with the balance across construction and handover. A proposal covering Stages 2 to 4 is not comparable to one covering 0 to 7.
- Specification level. A performance specification carries considerably less drawing effort than a fully detailed one.
- BIM delivery. Modelling to a defined level of information need is an addition, and a substantial one.
- What is excluded. Utility applications, warrant submissions, site attendance frequency and commissioning witnessing are all commonly excluded and commonly assumed to be included.
The practical advice
Compare deliverables and stages, not percentages. Ask what is excluded before asking what the rate is. A proposal that lists what it does not cover is usually the one that has been thought about.