Measuring a building

There are different conventions for measuring the floor area of a building. The most common way is to measure 'off plan'. This involves using relevant information provided by floor plans (done to scale) and architectural drawings to calculate the actual size of the building. If plans are not available the building will require measurement of the Gross Internal Area for the production of a DEC.

Plans and Drawings
Accurate floor plans are essential to determine total usable floor area and to determine physical properties of the building. All plans or drawings should be fully dimensioned or provided as scaled drawings. Where no plans or drawings exist a suitably qualified person should be employed to survey the building and produce accurate scaled drawings.

A plan or drawing should provide:
• Overall building dimensions to determine total usable floor area
• Dimensions of each individual area or room
• Details of the primary activities in an area or room
• Dimensions of externally glazed areas
• Construction properties of internal walls / partitions and external walls
• Construction properties of external glazing
• Construction properties of solid and suspended floors (including ceilings)
• Construction properties of the roof(s)

To enable the energy consumption to be calculated the assessor will ‘zone' the building into activity areas, based on use and/or shared HVAC or lighting systems. Provide the assessor with as much information as you can on these to assist him/her in modelling the most appropriate zones.

Total Useful Floor Area (TUFA)
This is the total gross floor area of all enclosed spaces, measured to the internal face of the external walls as measured in accordance with the guidance issued by RICS. Using this convention the area of sloping surfaces are taken at plan and areas that are not enclosed are excluded.

Unconditioned Space
Unconditioned space is included in TUFA and this can make a difference to the operational rating displayed on the DEC, hence the importance during the assessment to identify and register the unconditioned areas in measurements so that the certificate rating is fully understood and can be explained by your assessor.

Further reading
Code of Measuring Practice: A guide for property professionals' available from 
A guide to Display Energy Certificates and Advisory Reports for public buildings' available 
A guide to Energy Performance Certificates for the construction, sale and let of non-dwellings' available