A recent VCAT decision highlights the need for builders to carefully follow engineering drawings when undertaking site excavation and to ensure that proper drainage is installed to stop water reaching the foundation of the slab to prevent the possibility of slab heave.

Background to the Dispute

Ms Watson was the Owner of a house located in West Melton, Victoria. Richwall Pty Ltd (“the Builder”) was engaged by the Owner under a building contract dated 7 July 2007 to construct a house for the Owner for an agreed price of $224,650.00.

The house was constructed on a waffle pod raft slab designed by McFarlane and Partners Pty Ltd (“McFarlane”). McFarlane were initially joined to the proceedings but were removed prior to the commencement of the hearing.

Construction of the house commenced in early August 2007 and possession of the completed house was given to the Owner on 6 December 2007.


The Owner gave evidence that approximately 3 months after moving into the house she noticed cracks in the lounge room and front bedroom. After that time further cracks appeared in the en suite bathroom, the kitchen and along a wall in the family room. The Builder was notified and carried out repairs in April 2009 as well as additional repairs from time to time thereafter.

Despite the repairs the cracking continued to worsen. The Owner also noticed that during periods of high wind a creaking noise could be heard in the roof space. The Builder refused to undertake further rectification work and the Owner commenced proceedings in November 2013.

Slab Heave

The main issue considered by VCAT related to the movement of the slab upon which the House was constructed.

Upon examination it was found that there was a significant amount of subsidence in the slab with a difference of some 66mm between the base point of the slab and the north east corner of the house which was the highest point of the slab.

The difference in slab height was compounded by the fact that the fall between the highest and lowest points of the slab was uneven with a noticeable heave present half way along the back wall of the house resulting from a separated articulation joint. This had left a 30mm rise relative to the base point. An additional rise in the slab was also noted in the garage floor area where a rise of over 40mm was noted.

What Went Wrong and Why?

The primary questions considered by VACT were why had the slab deformed in the way it did and was the slab heave in some way caused by poor workmanship on the part of the Builder? Some additional building defects were also considered although not all defects related to the slab heave problem.

The Onus of Proof

VCAT found that in order for the Owner to be successful it was insufficient for the Owner simply to prove because the onus of proof rested with the Owner to show that the slab heave and movement was caused by the Builder’s faulty workmanship.

Relevant Considerations

The question of whether the geotechnical engineer had correctly assessed the soil classification was considered and a general consensus was reached that the classification of “H” indicating a highly reactive soil was correct.

From a number of photographs taken by the Owner during construction a conclusion was reached that the Builder had not included any spoon drain even though an early draft floor plan prepared by the Builder’s designer indicated the need for such drainage.

Although this document was not a contractual document and had no binding force on the Builder, expert evidence suggested that the direct consequence of failing to put in place proper drainage was that water pooled next to the footprint of the slab. It was suggested that the pooled water then soaked into the soil and caused the slab heave to occur.

Additionally, during the hearing it came to light that the Builder had not installed sealed clay around the edge of the slab footprint with the effect that moisture content was not consistent for the entirety of the slab.

What Caused the Slab Heave?

Photographs taken during construction showed that the slab was left open while the frame was constructed. These photographs also appeared to confirm the lack of a spoon drain or grading of the soil away from the slab during construction.

During the hearing it also became apparent that following construction of the roof and guttering, no temporary downpipes were attached to direct water away from the footprint of the slab. Further photographs taken during construction suggested that even at the time the brickwork for the house was largely completed downpipes had still not been installed.

In the Builder’s favour VCAT found that problems with the alfresco area of the house were not caused by any defective workmanship on the part of the Builder but had been caused by the reactive nature of the soil coupled with a variation requested by the Owner, being the construction of a timber deck rather than the concrete covered area provided for in the drawings as well as the later construction of the Owner of a roof to protect the adjacent area from rainwater.

Taking into account all of the expert and factual evidence it was found that the slab heave problems arose because the Builder failed to prepare the site as directed in the engineering drawings by grading the soil away from the building footprint and then by placing uncompacted fill up to the level of the rebate.

The effect of this was that any water that entered the fill and reached the level of excavation was not directed away from the house but continued to affect the foundation of the slab. As the clay at the level of the base of slab was not sloped away from the footprint, as was required in the design, water was still able to reach the slab though the soil that the Builder had deposited around the edge of the slab.

The Cost of Rectification

The Builder was ordered to pay the Owner the sum of $62,066.67 being the sum calculated for rectification works to the slab as well as the repair of consequential damage caused by the slab heave such as re-tiling in the en suite bathroom.

The rectification costs ordered to be paid by the Builder were equivalent to almost 28% (over a quarter) of the original contract price and would almost certainly have wiped out most if not all of the profit earned by the Builder on this particular job.

The question of costs was reserved. However, given the length of the hearing and the number of expert witnesses called, in our experience costs would have well exceeded the rectification costs which would be a further sting in the tail for the Builder.

If you or someone you know wants more information or needs help or advice, please contact us on 1800 888 783 or email doyles@doylesconstructionlawyers.com.