Air movement through a typical industrial doorway.
This figure illustrates the principal paths through which uncontrolled airflow can influence heat loss and environmental conditions.
H-035
UNDERSTANDING AIR PERMEABILITY
ENGINEERING
KNOWLEDGE
CENTRE
EKC
What Is Air Permeability?
OBSERVATION
Every industrial building allows some air to pass through its external envelope. This movement occurs through small gaps, joints and imperfections that are often invisible during normal operation. Air permeability is the engineering measure used to quantify the rate at which air passes through the building envelope under standard test conditions. It provides a consistent basis for comparing the airtightness of different industrial buildings.
ENGINEERING PRINCIPLE
EP04 – Industrial buildings continually respond to operational activity
Air movement occurs whenever pressure differences exist across the building envelope. Engineers measure air permeability to understand how readily uncontrolled air leakage occurs and how it influences whole-building performance.
Air permeability expresses the amount of air that passes through one square metre of the building envelope when subjected to a specified pressure difference. The test provides a standardised method of comparing buildings regardless of their size or construction. Lower air permeability values indicate a tighter building envelope with fewer unintended leakage pathways, helping engineers evaluate overall building performance and identify opportunities for improvement.
P-001 This plate introduces the engineering concept of air permeability and explains how engineers quantify uncontrolled air leakage through the building envelope. It illustrates typical air leakage pathways, defines air permeability under standard test conditions and introduces the principle of pressure testing used to compare the airtightness of industrial buildings.
ENGINEERING REFLECTION
Unlike insulation, which is visible within the building fabric, uncontrolled air leakage is largely invisible. Measuring air permeability allows engineers to quantify something that would otherwise be difficult to assess objectively. By replacing assumption with measurement, engineers can make informed decisions that improve energy efficiency and environmental control.
Why Air Permeability Matters
OBSERVATION
Uncontrolled air leakage increases heating demand by allowing warm conditioned air to escape while drawing cooler external air into the building. Measuring air permeability enables engineers to understand the scale of this energy loss and assess how effectively the building envelope controls unwanted air movement.
ENGINEERING PRINCIPLE
EP04 – Industrial buildings continually respond to operational activity.
Pressure differences caused by weather conditions, ventilation systems and everyday operations continually influence air movement through industrial buildings. Engineers measure air permeability to understand how these changing conditions affect energy performance.
High air permeability indicates that the building envelope allows relatively large volumes of uncontrolled air movement. This increases heating demand, reduces temperature stability and places additional load on heating and ventilation systems. Engineers use air permeability measurements to identify where improvements to sealing, detailing and construction quality can reduce energy loss while maintaining appropriate ventilation.
P-002 This plate demonstrates why air permeability is important to overall industrial building performance. It illustrates how uncontrolled air leakage increases heating demand, reduces temperature stability and places additional load on building services, while showing how improved airtightness contributes to lower operating costs and improved environmental control.
ENGINEERING REFLECTION
Many industrial buildings appear well constructed yet still experience significant air leakage. Without measurement, these hidden losses often remain unnoticed. Air permeability testing enables engineers to identify buildings where improving airtightness may deliver substantial long-term energy savings.
How Engineers Measure Air Permeability
OBSERVATION
Air permeability is measured using specialised testing equipment that creates a controlled pressure difference between the inside and outside of the building. By monitoring the volume of air required to maintain this pressure difference, engineers can calculate the building's air permeability under standard conditions.
ENGINEERING PRINCIPLE
EP04 – Industrial buildings continually respond to operational activity.
Standardised testing allows engineers to compare the airtightness of different buildings objectively, providing consistent information for design, assessment and refurbishment.
Air permeability testing is typically carried out using calibrated fan equipment installed temporarily within an external doorway. The equipment creates a controlled pressure difference across the building envelope while measuring the airflow required to maintain that pressure. Engineers use these measurements to calculate the building's air permeability, providing a repeatable method of assessing overall airtightness and comparing different buildings.
P-003 This plate explains how engineers measure air permeability using calibrated pressure testing equipment. It illustrates the installation of a blower door test, the creation of a controlled pressure difference and the calculation of air permeability values that allow engineers to compare the airtightness of industrial buildings under
standard conditions.
ENGINEERING REFLECTION
Engineering relies upon measurement rather than assumption. Air permeability testing transforms invisible air leakage into quantifiable engineering data, allowing building owners to understand how effectively their building envelope controls unwanted air movement.
Improving Air Permeability
OBSERVATION
Reducing air permeability involves limiting unintended leakage pathways while maintaining appropriate planned ventilation. Engineers improve air permeability through careful design, quality construction, effective sealing systems and ongoing maintenance of the building envelope.
ENGINEERING PRINCIPLE
EP04 – Industrial buildings continually respond to operational activity.
Managing air movement requires engineers to distinguish between uncontrolled air leakage and intentional ventilation. Effective building performance depends upon controlling where air enters and leaves the building.
Improvements to air permeability may include sealing construction joints, improving service penetrations, upgrading weather seals, maintaining industrial door assemblies and ensuring insulation and airtightness layers remain continuous. Engineers evaluate these measures collectively to improve building performance while preserving operational functionality and indoor environmental quality.
P-004 This plate illustrates the engineering strategies used to improve air permeability throughout the building envelope. It highlights continuous air barriers, effective sealing systems, industrial door performance, service penetrations and quality construction detailing, demonstrating how numerous small improvements combine to reduce uncontrolled air leakage.
ENGINEERING REFLECTION
A building should never be completely sealed from its environment. Instead, engineers seek to control air movement so that ventilation occurs where it is intended, while unnecessary leakage is minimised. This balance supports both energy efficiency and occupant wellbeing.
Air Permeability Within the Whole Building
OBSERVATION
Air permeability provides valuable information about uncontrolled air leakage, but it represents only one aspect of overall building performance. Engineers consider air permeability alongside insulation, thermal bridges, ventilation systems and operational activity to develop a complete understanding of industrial building behaviour.
ENGINEERING PRINCIPLE
EP04 – Industrial buildings continually respond to operational activity.
Air permeability reflects the interaction between building construction, environmental conditions and operational activity. Engineers assess these factors together to optimise the performance of the complete industrial building.
Professional engineers use air permeability measurements to evaluate the effectiveness of the building envelope, but they also recognise that overall performance depends upon how air leakage interacts with insulation, thermal bridging, pressure differences and operational practices. By combining these engineering disciplines, they develop practical strategies that reduce energy demand, improve occupant comfort and enhance the long-term performance of industrial buildings.
P-005 This plate places air permeability within the wider context of whole-building engineering performance. It demonstrates how air permeability interacts with insulation, ventilation, industrial door systems and operational control to influence energy efficiency, occupant comfort and long-term building performance. The illustration reinforces the systems-based engineering approach promoted throughout the Engineering Knowledge Centre.
ENGINEERING REFLECTION
Air permeability demonstrates that successful engineering is about understanding the building as a complete system. Improving one aspect of performance often influences many others, reinforcing the importance of integrated building assessment rather than isolated improvements.
The previous article explained that uncontrolled air leakage can significantly increase heat loss by allowing conditioned air to escape while drawing colder external air into the building.
To understand and compare the performance of different buildings, engineers require a consistent method of measuring this air movement. Air permeability provides that measure by quantifying how much air passes through the building envelope under standard test conditions.
Although every building experiences some air leakage, understanding air permeability enables engineers to distinguish between acceptable background leakage and excessive uncontrolled infiltration that wastes energy and reduces environmental control.
Every industrial building allows some air to pass through its external envelope. The rate at which this occurs is known as air permeability and provides engineers with a standard method of measuring uncontrolled air leakage. By understanding air permeability, engineers can assess the effectiveness of the building envelope and identify opportunities to improve energy efficiency, occupant comfort and environmental control.
AT A GLANCE
Discipline
Heat Loss
Category
Building Physics
Reading time
8
mins
Last reviewed
July
IN THIS ARTICLE
Understanding Air Leakage
The Key Measurements
Engineering Principles
Practical Example
Engineering Relfection
Summary
KEY TAKEAWAY
Air permeability measures how much air leaks through the building envelope. Lower air permeability generally indicates better control of heat loss and improved building performance.
CONTINUE READING
→ Building Pressure
→ Stack Effect
→ Buildings Breath
→ Air Cnanges Per Hour
→
What Measurements Matter Most?
→
Understanding Air Leakage
CONTINUE READING
Engineering Summary
Air permeability provides a standard engineering measure of uncontrolled air leakage through the building envelope. Engineers use it to assess airtightness, identify opportunities for improvement and compare the performance of industrial buildings.
Understanding Air Permeability in Industrial Buildings
Every industrial building allows some air to pass through its external envelope. The rate at which this occurs is known as air permeability and provides engineers with a standard method of measuring uncontrolled air leakage. By understanding air permeability, engineers can assess the effectiveness of the building envelope and identify opportunities to improve energy efficiency, occupant comfort and environmental control.