Chapter 4: The Building Envelope

Vocabulary practice covering the components, mechanisms, and impacts of the building envelope on air leakage and heat transfer.

Building Envelope

The term given to designate all parts of the building that separate the interior or conditioned space of the building from the exterior environment, including the roof, exterior walls, foundation, windows, doors, and the basement floor.

Infiltration

Outside air entering the building through unintended openings such as cracks and holes due to differences in internal and external air pressure.

Exfiltration

Inside air escaping from the building to the outdoors.

Heat Load / Cooling Load

The demands placed on the heating and cooling systems by the outdoor air temperature and the energy required to adjust the mass of infiltrated air to the space temperature.

Service Penetrations

Openings through building walls that provide access for electrical conduit, water pipes, and telephone cables, which often serve as sources of air leakage.

Stack Effect

Also known as the "chimney effect," this is air leakage caused by the density difference between cold outdoor air and warm indoor air; warm air rises to upper levels and leaks out while cold air is drawn in at the bottom.

Wind Effect

Infiltration related to wind passing over a building, which creates positive pressure on the up-wind side and lower pressure on the downwind or sheltered side.

Mechanical Effect

Pressure differences between external and internal air caused by air-moving devices such as kitchen and washroom exhaust fans and fresh air intake fans.

Ventilation

The intentional and controlled airflow provided mechanically into and out of a building, distinct from unintended infiltration and exfiltration.

Low-e Coatings

Reflective materials used on windows that are designed to reduce heat transfer by emitted radiation.

Emission

The process by which the surface of a substance emits radiation to other bodies.

Air Barriers

Insulation barriers installed within the building envelope to stop the exfiltration of inside air.

Vapour Barriers

Insulation barriers designed to prevent condensation that could result from heat transfer and destroy the integrity of the building fabric.

$R$-value

A measurement of thermal resistance for specific substances; a higher $R$-value indicates better insulation performance. Wet insulation can reduce this value by over $50\%$.

Fibreglass

An insulation material with very low thermal conductivity that relies on the trapping of thousands of tiny air pockets to reduce heat transfer by conduction.

Green Roof

An emerging trend involving covering a roof with live plants to provide insulation against heat transfer.

ASHRAE

The acronym for the American Society of Heating, Refrigeration and Air Conditioning Engineers.