Building Performance Factors

To understand the performance of a building and to identify opportunities for mitigation and adaptation interventions, it is important to view it holistically as an interactive system which has at its centre health, energy, and heritage.

There are four factors that affect the performance of buildings and, therefore, the success of any interventions: external environment, building fabric, building services, and people (occupants and use).

1. External environment
   The performance of a building will be affected by its form, location, exposure and vulnerability to climatic factors, such as sun, wind and rain.
2. Building fabric
   The age and type of construction materials, their condition, detailing and hygrothermal behaviour all affect the performance of and energy use in a building.
3. Building services
   The age, type, condition and efficiency of building services and equipment, the type of energy supply and controls used all affect the performance of and energy use in a building.
4. People (occupants and use)
   Occupants use buildings in different ways which can vary the amount of energy used, even in otherwise similar buildings. Occupant engagement levels, the number of people in a building, occupant needs and the level of comfort expected or required for a particular use all have a significant effect on how much energy is consumed.

External environment directly impacts the three other factors, yet changes made to the building fabric, services or use will not have influence on the external environment. In most cases the external environment cannot be modified. In others, some level of modification might be feasible to reduce vulnerability to climatic conditions, such as introducing planting to reduce exposure to high winds, wind-driven rain, solar radiation or risk of flooding.

These three remaining factors are more versatile and are interdependent - a change to one affects all three. This relationship of three interdependent factors sitting within the context of external environment, as an overarching factor that has a bearing on all three, is illustrated by the 'building performance triangle':

It is common for projects to focus on one of these elements, but this inevitably fails to achieve the best outcome. For example, projects to improve energy efficiency too often focus on heat loss alone without considering their impact on occupant health and risks associated with increasing rainfall and higher temperatures and humidity levels. They often do not consider whether:

• a building defect associated with water ingress may be increasing heat loss through the building envelope and causing or exacerbating discomfort. In some cases, repair alone could increase thermal performance to an acceptable level and prevent moisture ingress (condition, thermal transmission)
• the external environment influences which energy efficiency measures may be appropriate. Some interventions could result in moisture accumulation and/or mould growth. This could adversely impact internal air quality and occupant health (location, form, exposure)
• the type of building fabric has inherent heat and moisture buffering properties that may be beneficial if not undermined by energy efficiency interventions (hygrothermal performance, thermal mass, airtightness)
• the type of heating system and controls are best suited to the energy supply and demand, building occupancy and use. Whether they are understandable, easily used by occupants and maintained for maximum efficiency (building services, energy supply, occupants, use)