Background of AS 2870

The first edition of AS 2870 claimed ‘Adherence to this Standard will reduce litigation’. However, there is a growing body of evidence denying this claim. The Queensland Building Services Authority (QBSA) [2] reported in May 1998, ‘A large percentage of damage compensation claims involved subsidence problems’. A subsequent QBSA press release revealed, ‘The cost of subsidence problems was doubling each year’. The Sydney Morning Herald newspaper published an article on 11 February 2007, ‘A survey of 75,000 homes across Australia by Archicenter, the building advisory service of the Royal Australian Institute of Architects, revealed that, in most states, more than 35 per cent of homes had experienced cracking’. The Victorian Building Authority (VBA) [3] reported in May 2014, ‘Research found that 5.3 percent of dwellings built in an area of Melbourne’s western suburbs between 2003 and 2011 showed some form of distress (such as cracks in the floor and walls) attributed to slab heave’. The VBA concluded, ‘The key issues relating to slab heave were associated with deficiencies in the stormwater drainage systems of the dwellings’. The Age newspaper published an article on 08 June 2014, ‘Estimates suggest up to 4,300 homes in Wyndham, Melton and Hume Local Government areas may be suffering from slab heave’.

Many, if not all, reported slab heave problems occurred within a few years after construction, some even within a few months, all well short of the prescribed 50 years design life. AS 2870 acknowledges that buildings constructed on sites subject to ‘Abnormal moisture conditions’ have a higher probability of damage than those on normal sites. AS 2870 stipulates that site classifiers, qualified engineers, designers and builders are responsible for abnormal moisture conditions existing prior to or resulting from building construction, and home-owners are responsible for abnormal moisture conditions developing after construction.

Anecdotal evidence suggests that when AS 2870 has been applied and there is a damage investigation, home-owners are all too often blamed for abnormal moisture conditions developing after construction, and are thereby effectively prevented from proceeding to litigation. This has left many new home-owners with no avenue of recourse after their homes have suffered damage.

Whilst there is no doubt whatsoever that foundation movement due to soil moisture changes is the principal cause of damage, investigators are not in a position to determine the quantum of moisture changes that actually caused the damage. Nevertheless, bearing in mind that site characteristic surface movements are defined and determined in accordance with AS 2870 as occurring between extreme moisture changes that have less than 5% chance of being exceeded in 50 years, it is very surprising that many, if not all, investigators to date have not looked for other explanations of damage. Moreover, the fact that cracking is one of the main symptoms of damage, suggests that insufficient strength is the most likely explanation. However, and with due respect, damage investigators are reasonably entitled to expect that standard deemed-to-comply slab design solutions have sufficient strength to sustain foundation movements at the design levels prescribed in AS 2870. Unfortunately, this is not the case. More …