Introduction
This guide serves to both define and explain the range of material properties that are used within this site and the web applications it provides. The aim is to establish a common reference so that important points and concepts do not need to be continually reiterated in multiple locations, but can be made within the property definition that they pertain most to.
Material properties come in two main types, those that describe the behaviour of a material or element when things impact upon or pass through it, and those describing any emissions from a material or element out into surrounding spaces. This guide considers both.
-ivity vs -ance
Before starting, it is important to clear up any confusion over the difference in meaning between property terms ending in -ivity and those ending in -ance. Whilst not entirely universal, the convention is that terms such as resistivity, transmissivity, conductivity, reflectivity and absorptivity all refer to properties of a particular type of material and are given as values per unit of thickness or size.
On the other hand, terms such as resistance, transmittance, conductance, reflectance and absorptance all refer to actual measured or calculated values from a specific instance or sample of a material which has a known thickness or size. Thus, if you know either value and the thickness/size of your test material, then you can easily derive the other value.
Property Types
In this guide only object or material instance properties are listed – basically those ending in -ance. Where appropriate, the material type version of those properties which end in -ivity are discussed within the corresponding -ance topic.
Behavioural Properties
The behaviour of a material or building element describes what happens when things like air, heat, light, moisture vapour or sound impact upon its surfaces or pass over, through or around it.
Air Flow
Properties affecting the flow of air over, through or around a material or aperture.
Heat Flow
Properties affecting the flow of heat through a material or aperture.
Light Properties
Properties affecting how light reflects, is absorbed or passes through a material or aperture.
Moisture Vapour
Properties affecting the flow of moisture vapour through a material or aperture.
Solar Radiation
Properties affecting how solar radiation reflects, is absorbed or passes through a material or aperture.
Sound Propagation
Properties affecting how sound reflects, is absorbed or passes through a material or aperture.
Visual Properties
Properties affecting the visual presentation of a material.
Emission Properties
Emissions refer to any heat, light, sound or off-gassing that occurs from a material or building element. These properties are usually applied to elements such as appliances, mechanical equipment, lights, speakers and even people who occupy the building.
Gaseous Emissions
Metrics for quantifying off-gassing from materials, appliances or equipment.
Heat Emissions
The different types of heat output by appliances or equipment.
Light and Radiation
Metrics for the amount of light output or radiant emissions by lamps, luminaires, appliances or equipment.
Sound Emissions
Metrics for the amount of sound emitted by appliances, equipment or speakers.
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