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Pressurisation Testing Equipment ranges from high-pressure duct testing units, through single and multiple medium fan units, to large-scale trailer-mounted fan systems. The range of equipment available allows testing to be undertaken throughout the UK on practically any enclosure.

Air pressurisation/depressurisation testing must be undertaken in accordance with relevant national and international standards (CIBSE TM23Testing Buildings for Air Leakage and BS EN 13829:2001
Thermal performance of buildings – Determination of air permeability of buildings – Fan pressurization method.). Testing organisations should have UKAS accreditation in accordance with BS EN 17025: General requirements for the competence of testing and calibration laboratories and be members of the Air Tightness Testing and Measurement Assossiation (ATTMA)

Tests can be undertaken to establish leakage rates in: -


Whole-building pressurisation tests can establish envelope leakage rates for comparison with client specification or Building Regulation Part L Standards. Testing is undertaken in strict accordance with ATTMA’s Technical Standard 1 (TS1). Residual leakage within the building can be identified so that remedial sealing can be undertaken if needed.


Components include doors, windows, blockwork, cladding systems, etc. Samples can be tested in specialist sample chambers on- or off-site to establish overall leakage rates / leakage per m2 / leakage per linear meter of junction, etc.


Enclosures include computer rooms, switch rooms, floor voids, clean rooms etc. Specialist enclosures which need low levels or residual air leakage because of processes occurring within the enclosure or within their environmental / protection systems can be tested. Areas of residual leakage can be identified to enable remedial sealing to be undertaken if necessary.

There are a number of different tests that can be conducted to detect and evaluate the presence of air leakage within a building. For more information about the specialist Testing Services offered by Building Sciences please visit our website.



TM23 and ATTMA’s new standard, TS1 (applicable to planning applications submitted post 6th April 2006), lay down the testing methodology for Fan Pressurisation Testing of buildings to show compliance with Part L of the Building Regulations. In addition to the testing methodology, these documents lay down recommended air leakage specifications for different building types. The following table is an extract from TS1: -

Air Leakage Index (m3/hr/ m2 @ 50Pa)
Building Type Best Practice Normal
Offices (naturally ventilated) 3.0 7.0
Offices (mixed mode) 2.5 5.0
Offices (air conditioned/low energy) 2.0 5.0
Factories/Warehouses 2.0 6.0
Superstores 1.0 5.0
Schools 3.0 9.0
Hospitals 5.0 9.0
Museums and Archival Stores 1.0 1.5
Cold Stores 0.2 0.35
Dwellings (naturally ventilated) 3.0 9.0
Dwellings (mechanically ventilated) 3.0 5.0

Although these specifications are being achieved on a number of new buildings, many others built to comply with these specifications are failing by significant margins, due to a combination of inadequate design and poor site construction.



Whole-building leakage rates can be established by using single/multiple fan units to produce artificial positive or negative pressures within a building. Air is supplied to the building through the fan(s) for a range of measured airflow rates, and the resulting pressure differential between the inside and outside of the building is measured for each different rate.

The measured air flow rates and resultant pressure differentials are then related by the equation Q = C(Δ)n

= the air flow rates applied to the building in m3/sec-1
= the pressure differential across the building in Pascals
= the air leakage coefficient in the m3/sec-1 Pa-n
= an exponent normally between 0.5 and 1.0

Internal and external temperatures, and the external barometric pressure, are measured during the test so that corrections can be made to allow for any changes in the airflow rate. To calculate the values of C and n, a Regression Analysis is carried out on the pressure differentials through the building envelope and on the corrected airflow rates.

The airflow rate needed to pressurise the building to 50 Pascals can then determined. This is converted from m3/sec to m3/hr, and is divided by the total calculated envelope area of the building to give a leakage rate in m3/hr/m2 at 50 Pa.

A detailed methodology for fan pressurisation tests is included within TM23 - Testing Buildings for Air Leakage, which is referenced within the amendments to Part L2 of the Building Regulations 2000.

  • All mechanical ventilation openings must be sealed during the test, with all external doors and windows closed but not temporarily sealed to provide a realistic measurement of the actual envelope leakage. Natural ventilation openings should be closed but not sealed.
  • Smoke vents should be closed but not sealed and lift shaft vents should be left open.
  • All internal doors should be wedged open to allow rapid pressure equalisation within the building during the test.
  • Pressurisation tests are generally only undertaken under moderate external wind speeds of less than 6m/sec. Wind speeds above this level can have a significant influence on the measured envelope leakage rates and should not generally be accepted.



Smoke can be used in combination either with the natural driving forces acting on the building envelope, or artificially-induced internal pressurisation/depressurisation, to identify air leakage paths. Two methods are primarily used in the UK at present.


Hand-held generators can be used to pinpoint leakage through the external envelope. They can be used to identify areas of leakage that may need remedial sealing either before a pressure test, or after an unsuccessful test. The benefit of hand-held smoke generators is that they can accurately identify those areas that need sealing, allowing carefully-targeted remedial works to be undertaken.


Large-scale smoke generators are generally used to smoke log buildings. The buildings are then typically pressurised with a fan pressurisation unit to blow the smoke out through any discontinuities in the external envelope. Smoke leaking from the building can be seen outside, and photographed or videoed to provide a record of apparent leakage paths.

Smoke logging tests are ideal for identifying generic areas of leakage but will not necessarily pinpoint areas that need remedial sealing. If the external envelope assemblies are multi-component with integral cavities, the smoke can travel for significant distances before it finds a point of egress to the outside. For example, while smoke may appear to be leaking from the eaves of the building, it may in fact be travelling up through a wall cavity from an internal discontinuity at the base of the wall, rather than leaking out at the wall roof junction.



Infrared Thermography produces a visual representation of the surface temperatures of an object or assembly that is being surveyed. Large areas can be surveyed in a relatively short time and a visual record of the results produced as the survey proceeds.

The technique is based on the scientific principle that all objects of absolute zero (minus 273°C) emit invisible infrared radiation from the surface areas. Generally, the warmer the object the greater level of energy that is emitted. Thermography harnesses these physical characteristics and translates the infrared signature into a corresponding two-dimensional image that depicts accurate surface temperatures.

Thermography can be used to identify air leakage paths in the external envelope in conjunction either with the natural driving forces acting on that envelope, or with artificially-induced pressures. Surveying an envelope from within the building allows identification of the generally colder, external, infiltrating air.

This is particularly successful if the survey can be undertaken with an artificially-induced negative pressure within the building. This negative pressure encourages leakage, and as the cooler external air comes in to the building it cools the surfaces adjacent to the ingress point, allowing rapid identification. In the same way, it is possible to identify the ingress of warm external air in temperature-controlled buildings.

External surveys of building envelopes can also be undertaken to identify air exfiltration paths. Such surveys are particularly successfully with artificially-induced positive internal pressures, which will lead to increased external infiltration. As with the smoke logging test, the point of exfiltration will not necessarily correspond to the areas which may need remedial sealing works.