Theory of Air Tightness, Air Leakage and Air Sealing Measures

TERMINOLOGY

Air tightness / air permeability / air leakage –

defined as the resistance of the building envelope to inward or outward air permeation. Air leakage is driven by pressure differentials between inside and outside a building caused by the wind, stack effect and mechanical ventilation systems.

Air barrier or air seal line –

the physical components that make up the airtight envelope of the building. The air barrier needs to be continuous around the whole envelope – roof, walls and ground floors – and needs to be durable and maintainable in the long term. The air seal line can be drawn on construction drawings.

Air tightness test or air leakage pressure test –

the building is pressure tested by connecting a fan and measuring the airflow rates required to keep the building at various positive pressures.

Air permeability –

expressed as the amount of air leakage in cubic metres, per hour, per square metre of envelope at a nominal pressure differential of 50 Pascals, between inside and outside the building envelope.

Q50 –

air flow rate required to pressurise the building envelope to 50 Pascals, the measured unit of which is cubic metres per second.

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Air Tightness - Flagship Projects

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Air test result

Tightest building in UK Air test result <0.5 m³/hour/m², HRS involved throughout

Air Tightness Consultancy

IKEA employed the UK's largest fan to check the air tightness of its Glasgow store

Poor Building Envelope Performance - Case Studies

A Complete Solution For Investigating, Analysing Problems and Providing Solutions