Last edited 06 Nov 2020


The term ‘units’ can have several different applications in the context of the built environment.

The term can refer to devices that form part of a more complex mechanism and have a specified function. For example; air handling units, chiller units, consumer units, fan coil units and so on.

It can also refer to a unit of measurement, which is used as a standard for measuring similar items. When any other quantity of the same kind is measured it can be expressed in those units. For example, the physical quantities of length or height. Metres, centimetres and millimetres are units of length that represent a definite predetermined length. In other words, 5 metres refers to five times the predetermined length of a metre.

The International System of Units (SI) is the most commonly adopted system of units.

The main units that are used are as shown in table below.

Table of symbols and notation.png

The same unit symbol, i.e. m, mm, kg, should be used for singular and plural values (e.g. 1 kg, 10 kg), and no full stops or any other punctuation marks should be used after the symbol, unless it occurs at the end of a sentence.

For more information, see Notation and units on drawings and documents.

Units can also refer to parts of a buildings or development, such as a ‘housing unit’; that is, a separate and independent dwelling that is intended for habitation by a single household. Since 2001, a dwelling has been defined as a self-contained unit of accommodation. This can include individual houses as well as individual flats within a tower block.

In project management, the term unit might be used to refer to a group of workers responsible for a particular element of the project.

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