Failure to remedy
The table to the right (click table to zoom) is a fully random sample of outcomes taken from tests carried out over the years shown. The data is not a complete analysis of all projects undertaken and excludes work undertaken within a particular retail framework since this is atypical and would skew the results but it does include stock of all kinds - retail, offices, storage, business and educational.
The "failed and never retested" column is of particular importance since in all probability the building will have passed into use at the failed value. We have no way of tracking the progress of compliance from the point of issue of the failed certificate but it would be unusual for the job to be retendered to a new testing agency. Similarly it is unlikely that additional measures to compensate for the reduced performance would have been approved, installed and carried through to the final EPC since airtightness testing tends to be very late in the construction cycle.
The more compliant figure of 12% in 2008 is thought to be a result of early builder fears of non-compliance which have subsequently evaporated.
From this we can conclude that around 20% of all buildings tested fail the airtightness test and pass into use unmodified.
The "passed first time" column should be read in conjunction with the average targets shown in the last column. Over the period 2007-2010 the average target value has fallen from 9.36 to 7.15 but the number of buildings succeeding first time (a good indication of successful design and construction) has remained largely constant. We consider that this is indicative that builders and designers are coming to terms with the airtightness requirements and that further gains will take place in the future.
As indicated this sample does not include information from a large sample of buildings operated by a single, highly motivated owner. Although the detailed data is privileged it is well known that the target value for both large stores and smaller units is better than 3m³/m²/hr and that contractually this is held to be an important operational parameter. This suggests that there is ample scope for continued downward pressure on allowable leakage values in commercial buildings since the difficulties of maintaining internal air quality are less onerous than in the domestic sector as most commerci8al buildings have designed ventilation solutions
What the data suggest however is that without powerful commercial imperatives to perform further lowering of the target rate (either by statute or design intent) there is a strong likelihood that the 20% present non-compliance rate noted from the data will grow unless greater attention is paid to the process that tracks test results through to Certificates of Practical completion.