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Sinking Extension Underpinned in a Day

Case Study

Sinking Extension Underpinned in a Day

HomeownerBlacktown, NSW

  • 100mm+How far the extension had sunk
  • 10,000 LThe rainwater tank whose overflow was never connected
  • 20 yearsOf water spilling under the extension
  • 1 dayUnderpinned and relevelled

Twenty years of watching the extension sink

The original structure of this double-storey Western Sydney home was in good shape for its age and showed few problems.

During the early 2000s, the owners constructed a single-storey extension at the rear of the house to accommodate their growing family.

Naturally, after construction, the extension developed some minor cracks, and the owners first put them down to the regular settlement. However, over the following years the cracks became larger and it became obvious the extension was sinking. After twenty years, the homeowners grew tired of watching their extension sinking deeper into the ground - so they called us to investigate and fix it.

Front of the double-storey brick home in Western Sydney with the single-storey extension at the rear

A 10,000-litre tank with its overflow never connected

Like most suburban houses, a sizeable 10,000-litre water tank sat at the side of the house next to the extension. During our investigations, we discovered overflow drainage was not connected, and water had been spilling underneath the extension for twenty years.

The overflow from the rainwater tank allowed the extension to sink more than 100mm.

Eroding soil under the extension was causing it to subside.

The 10,000-litre rainwater tank beside the brick extension, with the overflow pipe that was never connected

Fill the voids, strengthen the ground, lift the extension

Our number one priority was to fill the voids formed from the soil erosion and underpin the extension. To do so, we injected our own ground stabilising solution, GeoPoly™, under the house extension, directly into the voids. This instantly strengthened the soil under the house and gave it a firm foundation to sit upon.

From there we could continue to lift the structure.

The open crack between the house and the extension running up the brickwork beside the downpipe before the lift

The gap closed as if nothing had happened

Within a couple of hours, the extension was re-levelled. The large gap in the wall closed up as if nothing had happened. Inside, the floor was level once again after twenty years of sagging. The water tank was slid back into place and reconnected by the homeowner's plumber.

The owner was so happy with our work that we could save the sinking extension of his house and relevel it in just one day.

An extension pulling away from the house, or a crack that keeps widening where the two meet? A free assessment measures the drop and finds where the water has been going — usually a tank, a downpipe or a drain nobody has looked at in years.

The same brick joint between the house and the extension closed up after GeoPoly™ lifted the extension back to level

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