Passive design maximises the use of ‘natural’ sources of heating, cooling and ventilation to create comfortable conditions inside buildings. It harness environmental conditions such as solar radiation, cool night air and air pressure differences to drive the internal environment.

‘Active’ design makes use of active building services systems to create comfortable conditions, such as boilers and chillers, mechanical ventilation, electric lighting, and so on. Buildings will generally include both active and passive measures.

Robert Street Architects design active systems to assist passive measures, for example; heat recovery ventilation, solar thermal systems, ground source heat pumps, and so on. Very broadly, where it is possible to do so, we aim to maximise the potential of passive measures, before introducing active systems. This can reduces capital costs and the energy consumed by a building.

Whilst passive design should create buildings that consume less energy, they do not always produce buildings that might be considered ‘sustainable’ as sustainability is dependent on a range of criteria, only one of which is energy usage.

Passive design can include:

• – Passive cooling.
• – Passive heating.
• – Passive ventilation (or natural ventilation).

Passive design should include consideration of:

• – Location.
• – Landscape.
• – Orientation.
• – Massing.
• – Shading.
• – Material selection.
• – Thermal mass.
• – Insulation.
• – Internal layout.
• – The positioning of openings to allow the penetration of solar radiation, visible light and for ventilation.

In its simplest form, a shallow building orientated perpendicular to the prevailing wind with openings on both sides, will allow sunlight to penetrate into the middle of the building and will enable cross ventilation. This should reduce the need for artificial lighting and that cooling systems and mechanical ventilation are not necessary. In taller buildings, stack ventilation can be used to draw fresh air through a building, and in deeper buildings atriums or courtyards can be introduced to allow light into the centre of the floor plan.

As well as reducing energy consumption, adopting passive design strategies can help building ratings across standards such as PassivHaus, BREEAM, the Code for Sustainable Homes and LEED.