Research findings on slab heave

It has been 1 year since the Victorian Building Authority (Authority) published research findings about slab heave that caused cracks in floor and walls in Melbourne’s western suburbs. The research was prompted after the Authority was made aware of the cracking trend in this area of Melbourne.

Have you noticed cracking in your home? Read on to find out more and how we can help you.

What the Authority found

5.3% of homes built in Melbourne’s west between 2003 and 2011 displayed cracks in the floor and walls.

Further, due to 95% of homes without cracks, suggested that the long drought was not in fact the main cause, and that the crack affected homes:

  • had followed appropriate engineering design steps
  • had properly performed geotechnical investigations
  • designed their floor slabs according to regulation
  • were spread throughout the western suburbs
  • almost all of the homes in the area were on site with similar soil composition

Regulation of concrete slabs and footings

AS2870 – Residential Slabs and Footings (Standard) is the Australian Standard that regulates the design of concrete floor slabs in homes, guiding the site classification and listing the requirements of the concrete elements. The Standard also nots the potential issues that may be caused by inadequate or incorrect drainage at the dwelling sites that have been classified as “reactive”, and that the key issues causing slab heave were associated with problems with stormwater drainage systems for dwellings.

The Authority believes that these drainage Standards are not well known, understood or complied with by some concrete practitioners, and because of this, makes these recommendations for domestic dwellings:

  • Only carry out geotechnical investigations after sub-division and earthworks are complete (except from those performed by the registered building practitioner)
  • Home owners are to be given a copy of the geotechnical results
  • The Authority is to provide owners with materials about foundations and slab maintenance
  • The Authority is to publish technical notices or guides for registered building practitioners that reinforce the requirements of residential drainage and geotechnical works as required by the Standard
  • Provide adequate falls to site stormwater drainage points of discharge by increasing the legal point of discharge (LPD), and that all sub-divisional designs include this LDP
  • All design information is available for public viewing
  • Building permit approval process include a requirement for slab engineering drawings to include the location of the LPD, plans of the stormwater drains running from LDP to each down-pipe and grate, as well as levels and minimum falls to all stormwater drains
  • The home owner is to be provided with stormwater drainage design documentation as part of the dwelling maintenance info pack
  • As an extension of mandatory inspections, that independent inspection of installed stormwater drainage systems is also carried out upon building structures
  • Independent CCTV inspections be carried out to stormwater drainage as part of the practical completion process to validate the condition of the underground stormwater system, with a copy of the video given to the home owner as part of the maintenance pack

For more information about the research, see the Authority Findings and contact us for quality concrete slabs that meet the Standards and give you peace of mind!