Air Tightness Testing

On 6th April 2006 the ODPM published the Approved Document L 'Work in new dwellings' (2006 edition) in line with the Government's Energy White Paper and Action Plan for Energy Efficiency published in February 2003 and April 2004 respectively.  The main directive is to seek significant improvements in the energy efficiency of new buildings.  Air Tightness was highlighted as a major contributing factor.

Air tightness testing, long in used in other countries, is used to discover unplanned sources of draughts created by sloppy building techniques where windows and doors are not well-fitted, or gaping holes left where services (such as pipes) enter the building.  The unplanned sources of draught were traditionally hidden behind cosmetic finishes, and as such, were rarely dealt with.

The main reason for Air Tightness Testing is not to produce a hermetically sealed building, but to produce a home in which the airflow can be controlled, and expensively achieved heat is not wasted.  This means air should not be able to escape or enter via unplanned routes.   ‘What you can’t see doesn’t matter’ is no longer the builder’s maxim, and the quality of the ‘hidden’ building work around window frames, skirting boards, and service exits is now of prime importance if the finished building is to pass the Air Tightness test.
                                                   
As part of compliance with the new building regulation Part L1A 2006, Air Leakage Testing must be carried out on new individual dwellings.  On housing developments the testing of each generic dwelling type is a minimum requirement, but the ATTMA standards recommend testing for each type (Mid, End Detached) where the floor area is greater than 15% different, and where there is a difference of more than one opening (window/door).  The ATTMA testing standard is likely to become the norm.  When the SAP is calculated, a Target C02 Emission Rate (TER) is generated, which has to be met or bettered by the actual Dwelling Emission Rate (DER).

The actual air tightness figure produced in the SAP software is set at a default value of 10m3/hr/m2, (metres cubed per hour per square metre of surface area at 50 pascals) but this sometimes needs to be dropped to achieve a pass, particularly  if the thermal element of the building fabric does not quite achieve at the desired level.  This figure is then used within the final SAP calculation to produce a Dwelling Carbon Emission Rate (DER). Should the actual tested DER not meet the TER, remedial work would be required prior to a re-test.  The most recent Building Regulations state that it is mandatory for the dwelling to pass this test. As such, it is important for developers to be aware of the standards required for their particular specifications in order to avoid the potentially high remedial costs.

As a sister company to AES Southern Ltd, Daltec Ltd deals specifically with both air pressure testing and sound testing.  The test can only be carried out when the building is in a virtually completed stage. 

Prior to the test the house has to be prepared as:

• all external doors and windows are closed and secured to avoid them being blown open.
• Internal doors are wedged open to avoid them slamming shut. The fan unit will create draughts in the building. Lightweight objects and paper near the fan unit should be removed or covered to avoid them being blown about. Fixtures and furniture will not be affected.
• Mechanical ventilation systems are switched off.
• Ventilation grilles and openings to the outside temporarily sealed with plywood or plastic sheeting and strong adhesive tape.  
• Smoke vents are closed but not sealed.
• Dainage traps closed according to expected usage (ie, with water). 

A fan, or a number of fans, are then fitted to a suitable aperture in the building envelope, usually the front door, and the house is pressurised to a predetermined range of values. The fan speed is increased in steps up to a maximum and then decreased in steps.  A strong draught is produced during the procedure. Air volume flow rate through the fan (equal to the air leaking through the building envelope) and the pressure difference across the building envelope are recorded at each fan speed. In calculating air permeability, corrections are made for temperature and barometric pressure. Local wind speed should preferably be below 3m s-1.

Access in and out of the building during the test is not possible (unless there is an emergency and a need to evacuate the building).  Site workers can choose to remain in the building during the test. There are no health risks, however there may be some discomfort due to cold draughts and some noise from the fan.  The test takes approximately 30 minutes.