Jargon Buster

Performance Terms

As – Solar Absorbance

The fraction of solar energy absorbed by the fabric. A low value means that the material absorbs little solar energy.

Direct Energy Transmission – DET

The percentage of solar energy transmitted directly through the glass with spectral distribution between 300nm and 2150nm.

Fc – Shading Factor

The ratio of solar factor of the combined glazing and solar shade (gtot) to that of the glazing alone (g).


The measure of the total energy passing through the glazing when exposed to solar radiation.


The measure of the total energy transmittance of the glazing in combination with the blind or other shading when exposed to solar radiation. Also known as the Solar Factor.

Lx – Lux

The measure of illuminance on a surface (1 lux = 1 lumen/m2).

Openness Coefficient Co

The ratio between the area of openings in the fabric/material and its total area.

Secondary Heat Transfer Factor – Qi

This results from heat transfer by convection and longwave infra-red radiation of that part of the incident solar radiation which has been absorbed by the glazing. It is the absorbed heat that will not go back through the glass.

Shading Coefficient – SC

Ratio of solar gain passing through a window unit (gtot) to the solar energy which passes 3mm float glass (0.87). Expressed as a value between 0 and 1. The lower the value the more efficient the fabric is at reducing heat flow.

Solar Heat Gain Coefficient – SHGC

This is the North American term for g-value.

Solar Reflectance – Rs

The measure of the fraction of solar energy reflected by the fabric. A high value means that the fabric performs well at reflecting solar energy.

Solar Transmittance – Ts

The measure of the fraction of the solar energy transmitted through the fabric. A low value means that the fabric performs well at reducing solar energy transmission.


A measure of thermal conductance which is the ability of a material to transfer heat. The lower the value the better the material is as an insulator.

Visible Light Transmittance – Tv

The proportion of visible light transmitted through the shading material. Also shown as Tvis

Shading Terms

Air permeability

The unintended leakage of air through gaps and cracks in the external envelope of a building.


The horizontal angular distance between the vertical plane containing the sun and the vertical plane containing true south.

Biophilic Design

A sustainable design strategy that incorporates reconnecting people with the natural environment through elements such as views to the outside, natural ventilation and use of plants.


The transfer of heat between substances that are in direct contact with each other.


The transfer of the heat in fluid or air, caused by the movement of the heated air or fluid itself. In a building warm air rises and cold air settles to create a convection loop and is termed free convection.

Colour Rendering Index – CRI

This describes how closely a light source renders colours compared to “standard” sunlight observed by a “standard” human eye. Expressed as a value between 0-100, with the higher the figure the truer the colour rendition. Poor colour rendition has been linked to sick building syndrome.

Day Light Factor

The ratio of illumination on a horizontal work plane indoors to the horizontal illumination outdoors, expressed as a percentage. Direct solar beam is excluded.

Diffuse Light

Light that does not come from a particular direction.

Discomfort/disability glare

Condition caused when illuminance causes unacceptable contrasts by exceeding the comfort level of the human eye, under the aperture setting of the eye which has been adjusted according to other illuminance levels in the area.

Energy Balance

The balance between solar energy that enters a building and the heat loss that escapes through the fabric of the building.


The condition of vision in which there is discomfort or a reduction in the ability to see significant objects, due to an unsuitable distribution of or range of luminance.

Indoor Air Quality

The air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants.

Internal Gain

Heat produced in the interior of a building from the operation of lights, appliances etc.


The amount of light energy reaching a given point on a defined surface area, namely the luminous flux (i.e. lumens) per square metre.

Light Shelf

A horizontal shelf (overhang) positioned above head height to reflect daylight onto the ceiling and to shield direct flare from the sky.


The intensity of light emitted from a surface per unit area in a given direction.

Moiré effect

Moiré effect is a visual perception that occurs when viewing a set of lines or dots that is superimposed on another set of lines or dots, where the sets differ in relative size, angle, or spacing. The moiré effect can be seen when looking through ordinary window screens at another screen or background.

Nanometers (nm)

A unit of one billionth of a metre, which is used to measure the wavelength of the light emitted by the sun.

Natural Ventilation

The supply of adequate fresh air to space within a building through windows, trickle vents etc. Removal of air may take place by natural or mechanical means.


The emission or transfer of energy in the form of electromagnetic waves or particles transferring energy from a warm body to a cold body without heating the air in between.

Standard Assessment Procedure (SAP)

A software that calculates the energy performance of dwellings. It has been developed by the Building Research Establishment (BRE) for the Department of Energy and Climate Chance (DECC). SAP assess the cost per year to provide a home with heating, lighting and hot water and presents the cost per square metre of floor area.

Simplified Building Energy Model (SBEM)

A software that calculates the energy performance of buildings that are not dwellings. It was developed by the Building Research Establishment (BRE) for the Department of Communities and Local Government (DCLG). SBEM estimates the amount of CO2 emissions produced by the building per square metre of floor rather than the cost.

Passive Solar Gain

The solar radiation that enters the building through glazing hits objects and is converted to heat. This reduces the need to artificially heat the space.

Post Occupancy Evaluation (POE)

The process of evaluating whether a building has met the intended performance criteria when the building has been occupied. This is usually achieved by qualitative and quantitative feedback.

Soft Landings

A strategy to ensure the transition from deign through to build and then occupation of a building is smooth and the operational performance of the building is optimised.

Solar Shading

Also referred to as ‘solar control’ or ‘solar protection’ is the term used to identify a number of systems to control the amount of heat and light from the sun admitted to a building.

Sun Angle

The angle of incidence of direct solar beam in relation to the building or glazing.

Temperature – Air

Air temperature is a measure of how hot or cold the air is. It is the most commonly measured weather parameter.

Temperature – Mean Radiant

The mean radiant temperature (MRT) is defined as the uniform temperature of an imaginary enclosure in which the radiant heat transfer from the human body is equal to the radiant heat transfer in the actual non-uniform enclosure.

Temperature – Operative Temperature

A simplified measure of human thermal comfort derived from air temperature, mean radiant temperature and air speed.

Temperature – Radiant

Radiant temperature is a measure of hot or cold air radiated from humans, objects or appliances.

Temperature – Surface

Surface temperature is a measure of how hot or cold the surface of any given object is. Surface temperatures can vary from the air temperatures around them.

Ventilative Cooling

The use of natural or mechanical ventilation strategies to cool indoor spaces. This effective use of outside air reduces the energy consumption of cooling systems while maintaining thermal comfort. The most common technique is the use of increased ventilation airflow rates and night ventilation.



Association for the Conservation of Energy



British Blind and Shutter Association



British Council for Offices



British Energy Efficiency Federation


British Institute of Facilities Management



Building Information Modelling


Department for Business Energy & Industrial Strategy



Building Management System


Building Research Establishment



Building Research Establishment Environmental Assessment Method



Building Services Engineering Association



Chartered Institute of Architectural Technologists



Chartered Institution of Building Services Engineers



Colour Rendering Index


Department for Communities and Local Government



Double Skin Façade


Energy Performance of Buildings Directive


Energy Performance Indicator


Early Stage Building Optimisation


European Solar Shading Database



European Solar Shading Organisation



Glass and Glazing Federation



Greenhouse Gas Emissions


Heating Ventilation and Air Conditioning


Industrieverband Technische Textilien-Rollladen-Sonnenschutz



Leadership in Energy and Environmental Design



Local Operating Network


National Building Specification



National Energy Foundation



National House Building Council



Nearly Zero Energy Buildings


Federation of European Heating, Ventilation and Air-conditioning Associations



Royal Institute of British Architects



Standard Assessment Procedure



Simplified Building Energy Model