Last edited 21 Jan 2021

Principles of enclosure

‘Enclosure’ is the term given to any part of a building that physically separates the external from the interior environment. It is often referred to as the ‘building envelope’, although ‘enclosure’ is considered the more precise term.

Human physiology is capable of tolerating only a narrow range of environmental conditions. Beyond this range, health and wellbeing are compromised. Through the materialisation of volumes, architecture is able to create enclosed spaces in the form of structures. A building consists of a collection of spaces bounded by separators of the interior environment, and separators of the exterior environment (the enclosure).

Where exactly the enclosure begins and the exterior environment stops can sometimes be unclear, such as in the case of ‘buffer spaces’ such as garages, screened porches, attics or vented crawlspaces.

The physical components of the building enclosure include:

The roof system.
The above-grade wall system (including windows and doors).
The below-grade wall system.
The base floor system.

The principles of building enclosure were defined by the building scientist Neil Hucheon in 1963:

Strength and rigidity.
Control of heat flow.
Control of air flow.
Control of water vapour flow.
Control of liquid water movement.
Stability and durability of materials.
Fire.
Aesthetic considerations.
Cost.

In addition to Hutcheon’s principles, there are also considerations relating to the natural phenomena occurring in the external world, and the functions required. Some of the environmental phenomena, or ‘loadings’, that can impact on enclosure include:

Gravity (i.e. structural loads).
Climate and weather.
Seismic forces.
Noise and vibration.
Soil type.
Topography.
Organic agents (i.e. aerobic life forms such as insects and mould).
Inorganic agents (i.e. natural and artificial substances such as radon and methane).

The general functions of the building enclosure may be divided into four areas:

Support: To support, resist and transfer all structural forms of loading imposed by the interior and exterior environments.
Control: To control, air transfer, heat, sound, access and security, privacy, the provision of views and daylight, and so on.
Finish: To finish the enclosure surfaces in terms of visual, aesthetic, durability, and so on.
Distribute: To distribute services or utilities such as electricity, communications, water, and so on.

Generally, enclosures are either monolithic or composite assemblies. Monolithic enclosures involve a single material acting as the structure, the cladding and interior finish, such as load-bearing masonry. In composite assemblies, separate materials or combinations are assigned critical control functions, such as control of heat transfer or air leakage.

In general terms, enclosure types include can be categorised as the following:

Compact or distributed.
High rise or low rise.
Permeable or impermeable.
Transparent or opaque.
Passive or active.
Massive or lightweight.
Temporary or permanent.
Single or multiple units.
Hybrids: Combinations of the above.

NB Urban Design Guidelines for Victoria, published by the State of Victoria (Australia) in 2016, defines enclosure (or 'sense of enclosure') as: ‘Where the building frontage height, street width and street tree canopy creates a feeling of a contained space within the street.’