What is BINDT?
The British Institute of Non-Destructive Testing is the professional institute for all those engaged in non-destructive testing and condition monitoring. It is concerned with the education and training of its members, and the advancement of the science and practice of the subject.

What is the Design Air Permeability?
The Design Air Permeability for each dwelling type within a development will be determined by designers as part of the overall DER (Dwelling CO2 Emissions Rate) calculation.  The maximum design air permeability allowable (is 10m³/(m².hr) @50Pa.

What do I need to get tested?
Where approved construction details have been adopted, one test should be carried out on each dwelling type on each development. Separate blocks of flats are treated as separate developments. Each of the following constitutes a change of dwelling type:

• Change in method of construction e.g. timber frame and brick and block
  
• Ground floor, mid floor & top floor flats
  
• End of terrace & mid terrace
  
• Semi-detached & detached
  
• Significant changes in building floor area

Where approved construction details have NOT been adopted, then each dwelling type is to be tested as above but with an increased sampling regime as can be seen below:

Number of instances of the dwelling type	Number of tests to be carried out on the dwelling type
4 or less	One test of each dwelling type
Greater than 4, but equal or less than 40	Two tests of each dwelling type
More than 40	At least 5% of the dwelling type*

(* If the first 5 dwellings tested all pass, then the sampling frequency can be subsequent reduced from 5% to 2%)

click to go to Government page with document download

For developments where no more than two dwellings are to be built, one unit must be tested (or two if they are different dwelling types).
The only exceptions are if:

• A dwelling of the same dwelling type has been built by the same builder within the last 12 months and successfully passed the air tightness test
• A default poor value of 15m3/h/m2 has been used in the SAP 2005 calculations.

The effect of using this cautious value would then have to be compensated for by improved standards elsewhere in the dwelling design

Who selects what dwellings will be tested?
The Building Control Officer will choose which units are to be tested in accordance with the sampling regime explained above.

What happens if a dwelling fails a test?
In the unfortunate event that the initial test result is unsatisfactory then Home Integrity Testing is there to help make sure that you pass on the second attempt. Three actions are required:

1. Remedial work will need to be undertaken on that unit.
2. A retest will need to be booked to test the same unit (after remedial work has finished).
3. Also an additional test on the same dwelling type will be required.

What is Air Leakage?
Air Leakage is the uncontrolled flow of air through gaps and cracks in the fabric of a building (sometimes referred to as infiltration and draughts).
This is not to be confused with ventilation, which is the controlled flow of air into and out of the building through purpose built ventilators that are required for the comfort and safety of the occupants.
Too much air leakage leads to unnecessary heat loss and discomfort to the occupants from cold draughts.

Why is air leakage important?

• Air leakage in dwellings through cracks around doors, window frames, electrical and plumbing connections etc. accounts for a significant proportion of heat loss.
• With recent improvements in the insulation of walls and glazing, this proportion has become more significant.
• Heating homes involves burning fossil fuels and producing CO2 emissions.
• CO2 is a greenhouse gas – it contributes to climate change.
• Reduced air permeability results in reduced heating energy use.
• The purpose of reducing air permeability is to reduce CO2 emissions.
• A detached house built in England and Wales, consumes nearly 20% more energy than an equivalent home in Denmark.

How is air tightness measured?
In brief:

• Increase the air pressure in the building
• See how much air leaks out Airtightness is measured in m3/(h.m2)@50Pa.
  This is the leakage of air (m3/hour) in or out of the building, per square metre of building internal envelope at a reference pressure of 50 Pascals between the inside and outside of the building.

What is the UK government doing about it?

• The 2002 Energy White Paper gave a national target of a 20% reduction in CO2 emissions below the 1990 levels by 2010.
• Also in 2002, the EU issued the Energy Performance of Buildings Directive.
• As a result, revised Building Regulations and supporting guidance were issued in April 2006.
• These revisions included CO2 emissions targets and air tightness testing of all new buildings.