Causes of a shifting house foundation in New South Wales

Homes in many parts of Melbourne may experience ground subsidence that leads to sunken building foundations.

Sinking floors, a visibly widening crack in the wall, an uneven concrete driveway, and doors and windows that won’t close properly can all be warning signs of ground weakness under a structure. If a building becomes un-level due to subsidence, the effects are not just cosmetic. If left unaddressed, these symptoms can result in significant and expensive damage to the home and may also lead to safety issues for the occupants. When cracks and other structural changes present themselves, homeowners may look for solutions, including underpinning services and contractors, to effectively ‘underpin’ their home.

How much does Underpinning Cost?

Get a FREE house assessment in 3 simple steps:

Step 1:

Submit your enquiry using our online form. Include a brief message about the type of underpinning foundation issues you are experiencing.

Step 2:

Our friendly customer service team will be in touch to schedule a site assessment that suits you to discuss cost of underpinning a house.

Step 3:

One of the Mainmark experts will visit your home or property, assess the damage, and ascertain the likely cause. They will establish the approach needed, creating a plan specific to the needs of your building and provide you with a detailed quote.

Sydney is a unique region of Australia with challenging weather conditions, a variety of soil types and other factors that impact coastal and inland ground conditions.

In addition to extreme weather events, particularly torrential rain and storm activity, and extended periods of drought, Sydney homes may be affected by the following causes of foundation problems:

  • Leaking pipes: over time, pipes under a property may deteriorate, become damaged or blocked, causing cracks which allow water to seep into the ground, both around and directly underneath the property. This is very common with clay pipes found in homes older than 20 years.  Leaky gutters and downpipes or dripping outdoor taps are also frequently identified as the source of water collecting near house foundations.
  • Inadequate drainage: moisture management is key for good foundation and footing maintenance. If the soil does not have adequate drainage, water will collect causing the ground to weaken and potentially cause the home to subside or ‘sink’.
  • Poor building work: if there is insufficient ground preparation, including poorly compacted soil, before a house slab is laid, the ground may not be strong enough to support the load above. This is usually when house underpinning is considered, as well as other costly remediation works for fixing cracks in concrete surfaces, such as driveways.
  • Adjacent development: when building or renovation works take place at a neighbouring property, earthmoving and excavation can impact the stability of the soil on your side of the fence. This is even more problematic when coinciding with periods of heavy rain which soften the ground and may lead to soil erosion and voids.  Equally, the clearing of trees associated with development can affect the water table as moisture is no longer drawn out of the soil by the tree’s roots.
  • Tree roots: if pipes start to develop cracks and or have loose joints, tree roots will naturally grow towards these areas in search for water. Eventually, aggressive root systems will infiltrate pipes causing blockages which cause water to spill into the ground, impacting the stability of house foundations.

The Mainmark solution

Mainmark offers some of the most advanced non-invasive resin injection and grout technologies to quickly correct foundation ground issues with minimal mess or disruption, perfected over more than 20 years in business. With a sound knowledge of Sydney’s unique local conditions, Mainmark utilises its Teretek® engineered resin injection solution to effectively raise, re-level, and re-support footings under a home. Teretek is a unique two-in-one solution that provides both ground improvement and re-levels homes, backed by a 50-year product warranty. It increases ground bearing capacity, fills voids, rehabilitates foundation ground which raises sinking floors and reduces wall cracking, all at a fraction of the cost of traditional underpinning, and with no detrimental effects on the environment. Mainmark has successfully raised and re-levelled hundreds of homes and driveways throughout the Sydney region. The process is extremely quick; most house re-levelling and concrete slab lifting takes less than a day, and driveways and slabs can be driven on within hours once the application is complete. As part of Mainmark’s expanded capabilities, we also provide ground improvements solutions specific to coastal areas.

A cost effective alternative

The cost to underpin a house using traditional methods can be high due to the invasive nature of concrete underpinning, which is generally a lengthy and messy process. Teretek is the modern way to re-support the footings in your house. It’s applied like keyhole surgery and most jobs can be done in a day, usually reducing the cost of the works when compared to traditional underpinning. As every home is different, Mainmark finds the best solution to treat the root of the problem. The cost of each job will vary according to:

  • your location
  • the actual cause of the problem – what other things need to be resolved as part of the works eg. drainage
  • the nature and condition of the foundation soil – including an assessment of the soil type
  • the type and profile of the building footings – are the existing footings damaged or in need of replacement?
  • the surroundings e.g. access to the site, adjacent buildings or retaining walls
  • unknown or unforeseeable underground conditions – problem solving on site
  • the volume of material that will be required – an estimate will be provided but may need to be re-assessed following more detailed ground investigation
  • the time that the work will take – based on Mainmark’s extensive experience.

Why choose Mainmark?

Calling in experienced ground engineering consultants for an appraisal can help to quickly diagnose the issue and find a solution tailored to your home. By using Teretek to address building foundation problems, there is minimal intrusion into the property and minimal interruption to the occupants, effectively underpinning by non-invasive expanding resin injection. In most cases, residents are not required to move out or move any furniture during the ‘home lift’ process. In contrast, traditional concrete underpinning involves excavation to make large holes under the home’s footings, pouring in concrete, waiting for it to set and then jacking the house up off the concrete blocks.

The Mainmark solution is:

Cost effective – no hidden fees or extra costs

Non-invasive – our process involves keyhole surgery, hence no major excavations

Resident friendly – work is carried out with minimal disruption, in most cases you won’t even need to move out!

Time efficient – on average we can get your home back to level in little as a day or within 1 – 2 weeks depending on the technologies we utilise

Worry-free – backed by an industry leading 50 year product warranty and a licenced builder that provides Home Warranty Insurance/Builders Warranty Insurance where required

Accurate – using state of the art technology our qualified technicians can re-level extremely accurately

Reputable – our specialised methods have been mastered for over 25 years with thousands of satisfied customers

Sydney by location

Sydney has a variety of soil types including sand and very reactive clay soils which shrink and swell according to moisture levels. While seasonal changes occur, a mixture of high drought and heavy rainfall may cause ground subsidence resulting in shifting slabs. Building movement may also be caused by other underlying or site specific issues which require a professional assessment and working knowledge of the local area.

  • Inner West:

    Older types of houses tend to have shallower brick or stone footings which are generally more susceptible to shrink-swell action – where the ground noticeably contracts and expands depending on moisture levels – which is associated with moderately reactive clay soils. Old brick and stone foundations need special attention because they may become brittle and are therefore considered less suitable for traditional underpinning methods. Areas affected by these conditions include Balmain, Newtown, Marrickville, Strathfield, Cabarita and Five Dock.

  • Eastern suburbs:

    Many homes in Sydney’s east are built on sand, and particular care needs to be taken with foundation treatment in these soils because they are non-cohesive soils, susceptible to settlement caused by leaking pipes, erosion, wash out and excavation near the property. Vibrations from neighbouring properties which are being developed may also cause ground disturbance and aggravate wall cracking.  Sandy soils sometimes need permeation grouting in addition to resin treatment to strengthen the ground before a home is re-levelled.  Areas commonly affected by these conditions include Bronte, Bondi, Bellevue Hill, Point Piper, Paddington, Surry Hills and Darlinghurst.

  • Northern suburbs:

    This region tends to be prone to movement associated with shrinkage and expansion of moderate to high reactive clay soils. Common triggers are broken pipes leaking water into the ground which will impact older houses with usually shallower footings.  In a drought, tree roots infiltrate clay pipes seeking moisture. Areas affected by these conditions include Ryde, Epping, Eastwood, Denistone and Asquith.

  • Western Sydney:

    To the west of Sydney, the ground is often formed of highly reactive clay soils which expand and contract aggressively during periods of heavy rain and drought. When paired with older homes, the foundations of brittle and shallow footings offer almost no ability to span over the soft zone on the ground, causing homes to sink.  Brickwork may also feature older style lime mortar which makes walls more susceptible to visible cracking.  As well as sub soil, surface water management is important across larger backyards where rain may collect and run across a property.  Drain repair and drainage solutions may form part of the ground improvement recommendations in areas including Parramatta, Granville, Lakemba, Wentworthville and Cabramatta.

  • Northern Beaches:

    Clay and sandy soil are experienced along the full stretch of the Northern Beaches, with coastal facing properties most affected by erosion. Alluvial patches are common in low lying suburbs including Warriewood, Manly Vale and Cromer which are known flood zones.  These suburbs have a high concentration of silty, clay and sand combination soils which may require homes to have slab foundation  On sloping blocks heavily affected by rains, it may also be important to treat the ground underneath driveways and paths to prevent cracking and trip hazards.  Mainmark works along the peninsula including Manly, Seaforth and extending to Palm Beach.

  • Hills District:

    While many homes in this area of Sydney have been built more recently, the reactive clay soil may still require resin injection to aid with slab repair and fix cracks in concrete driveways. New housing estates are not immune to sinking, particularly when the ground may not have been prepared properly, resulting in the house settling.   Impacted areas include Castle Hill, Kellyville and Rouse Hill.

  • Upper North Shore:

    This area has many larger blocks with single or double-storey homes which may feature old brick and stone foundations. Reactive clay soils can cause these footings to sink over time, and traditional concrete underpinning would be too invasive a process for remediation.  Larger blocks may also be affected by excessive moisture in the ground as trees are removed, which can have a significant impact on foundations. St Ives, Turramurra, Lindfield and Wahroonga are likely impacted.

  • Lower North Shore:

    Sandy soils and rocky ground can allow water to flow under homes and cause home foundations to shift. Some properties may also experience run off or leaks from neighbouring pools which weaken the ground and impact foundations.  Many older sandstone and brick homes also feature brick and stone footings which require special attention and are less likely to be suitable for concrete underpinning if the home needs to be relevelled.  Mosman, Cremorne, Neutral Bay, Kirribilli and Crows Nest all form part of this area.