Functional unit of buildings
The New Rules of Measurement (NRM) are published by the Royal Institute of Chartered Surveyors (RICS). They provide a standard set of measurement rules for estimating, cost planning, procurement and whole-life costing for construction projects.
According to NRM1: Order of cost estimating and cost planning for capital building work, a functional unit is: ‘…a unit of measurement used to represent the prime use of a building or part of a building (e.g. per bed space, per house and per m2 of retail area). It also includes all associated circulation space.'
NRM1 defines the functional unit method as: ‘…a rough budget-setting technique which consists of selecting a suitable standard functional unit of use for the project, and multiplying the projected number of units by an appropriate cost per functional unit.’
BRE's Environmental impact of biomaterials and biomass defines a functional unit as: '...a qualitative description of function specifically defined for the product/service under study and any alternative product/services to which it is compared. The use of a functional unit means that the alternative designs under study are, in theory, compared fairly. For example, a comparison of external walls may be based on every external wall design in the study achieving a U-value of 0.3 W/m²K and compliance with building regulations.'
Embodied Carbon, The Inventory of Carbon and Energy (ICE), By Prof. Geoffrey Hammond and Craig Jones, Ed. Fiona Lowrie and Peter Tse, published by BSRIA in 2011, defines a functional unit as: ‘A reference unit of study normally used for comparative purposes, e.g. “1 m2 of carpet over a lifetime of 10 years”. A fair functional unit is necessary for such assessments.’
PAS 2080:2023 Carbon management in buildings and infrastructure, second edition, published by The British Standards Institution in March 2023, defines the functional unit as the: ‘…quantified performance of a product or system for use as a reference unit. NOTE The functional unit takes into account a function, a quantity, a duration, and a quality of the asset, network or system being assessed. Refer to the Guidance document for PAS 2080 for further explanation and examples of functional units.’
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