Building physics made simple: Glossary

This collection of terms covers the physics of heat, moisture, sound, and energy within buildings. It is also an accompaniment to our e-learning course ‘Building physics essentials’, which delves into the fundamental principles of building physics and how they can provide a transferable skillset in the ever-evolving construction industry, as although our building methods may change, the physics behind buildings remains constant.

Heat

Convection: The movement of air caused by warm air rising and cool air sinking, creating a continuous circulation of heat.
Conduction: The transfer of heat through a solid material or between solids in direct contact, like heat moving from a hot roof into an attic.
Low thermal conductivity: A property of materials that slows down the transfer of heat, like insulation, which help keep heat in or out of a building.
Radiation: The transfer of heat through infrared waves that can move energy across empty space without needing air or solid materials.
Thermal transmittance: is the rate at which heat passes through a building element, accounting for both conduction and convection.
U-value: is the numerical measure of thermal transmittance, indicating how well a material resists heat flow – the lower the value, the better the insulation.
Thermal bridge: A part of a building where heat escapes more easily due to high conductivity materials or construction that bypass insulation.

Moisture

Interstitial condensation: Moisture that forms and becomes trapped inside walls, roofs, or other hidden layers of a building, often going unnoticed until it causes visible damage like mould or structural decay.
Vapour diffusion: The slow movement of water vapour through materials from areas of high moisture concentration to low concentration.
Capillary action: The movement of liquid moisture through tiny pores or gaps in materials, often against gravity.
Dew point: The temperature at which air becomes fully saturated with moisture, causing water vapour to condense into liquid.
Permeability: A measure of how easily a material allows water vapour to pass through it.
Mu-value (μ-value): A number that shows how resistant a material is to vapour diffusion compared to air; higher values mean greater resistance.

Sound

Airborne transmission: The movement of sound through the air, such as voices or music, which travels from one space to another and passes through walls, floors, or ceilings.
Impact transmission: Sound that is created by physical contact or vibration with a surface – like footsteps or moving furniture – and travels through the structure of a building.
Flanking transmission: The indirect movement of sound through connected building elements (like floors, ceilings, or walls), bypassing the main barrier designed to block noise.
Reflection (of sound): When sound waves bounce off hard, smooth surfaces – like walls or ceilings – causing the sound to remain in a space and potentially make it louder or less clear.
Absorption (of sound): When sound is taken in by soft or porous materials – like carpets or acoustic panels – reducing the amount of sound that bounces around a room and making it quieter.
Sound reduction index (R): A measure of how well a building element (like a wall, floor, or door) can block sound from passing through it – higher values mean better sound insulation.
Noise reduction coefficient (NRC): A rating that shows how much sound a material can absorb (rather than reflect) – higher numbers indicate better sound absorption and quieter spaces.

Energy

Energy efficiency: A measure of how effectively a building uses energy, comparing the amount of energy consumed to the services delivered – such as heating, cooling, or lighting.
MVHR (mechanical ventilation with heat recovery): A whole-house ventilation system that supplies fresh air and removes stale air while recovering heat from the outgoing air to improve energy efficiency.
Operational energy: The energy a building uses during its day-to-day operation – for heating, cooling, lighting, hot water, and appliances.
Embodied energy: The total energy used to extract, process, transport, and install building materials, as well as to repair and maintain them over the building’s life.