Why Melbourne Houses Need Reblocking More Than Other Cities

Melbourne restumpers are busier than anywhere else in the country, and it's not close. The combination of reactive clay soils, tens of thousands of houses built on untreated timber stumps, and a climate that swings between drought and downpour makes this city uniquely hard on foundations.

Here's what's actually going on under your house and why it matters more in Melbourne than in Sydney, Brisbane, or anywhere else.

The soil problem: basalt clay in the western suburbs

Melbourne's western suburbs sit on some of the most reactive clay soil in Australia. Footscray, Sunshine, Werribee, Altona, Point Cook - the basalt plains that stretch west of the city are made of volcanic clay that expands dramatically when wet and shrinks just as hard when dry.

This isn't subtle movement. Reactive clay can swell by 50mm or more in the wet season and shrink by the same amount during summer. Your house is sitting on top of ground that's physically changing shape throughout the year.

The eastern suburbs have different soil profiles - more sand and silt in places, sandstone in others - but pockets of reactive clay turn up across the entire metro area. Ringwood, Croydon, and Lilydale all have clay zones. If you're on a slope, the uphill side of your house behaves differently to the downhill side, and that differential movement is what cracks walls and jams doors.

Timber stumps that were never built to last

Before the 1960s, Melbourne houses were almost universally built on red gum timber stumps. Red gum is tough - it resists termites reasonably well and holds up in dry conditions. But it was never treated with modern preservatives, and it was never meant to last 70 or 80 years.

Those stumps are now failing across Melbourne in huge numbers. The timber dries out, cracks, and loses structural integrity. Stumps that were solid in 1955 are now splitting, leaning, or rotting at the base where they meet the soil.

Concrete stumps became standard from the 1970s onward, but there are still hundreds of thousands of houses across the metro area running on original timber. If your house was built before 1965, there's a strong chance you're on red gum stumps unless a previous owner had the place restumped.

Drought cycles and what they do to your footings

Melbourne's drought cycles are particularly destructive to foundations. During extended dry periods, the clay soil shrinks away from the stumps, leaving them unsupported at the base. The stump is still holding the house up, but the ground it's sitting on has physically pulled away.

When the rain returns, the soil swells back. But it doesn't swell evenly. Some areas recover faster than others depending on drainage, shade, and how compacted the ground is. The house moves one way during drought and a slightly different way during recovery.

Over multiple drought-recovery cycles, the cumulative effect is significant. Each cycle leaves the stumps slightly worse off. The soil pressure works the timber, opening cracks and accelerating rot at the base. A stump that survived one drought might not survive the next.

The Millennium Drought (1997 to 2009) did enormous damage to Melbourne foundations. Restumping companies reported a surge in bookings from 2010 onward as the rain returned and houses that had been quietly moving for years suddenly showed visible cracking and floor movement.

Tree roots: the hidden wrecking ball

Eucalyptus trees are the worst offenders. Their root systems spread wide and draw massive amounts of moisture from the soil, accelerating clay shrinkage around your foundations. A mature eucalyptus can extract hundreds of litres of water from the soil daily, and its roots can extend well beyond the canopy line.

Elm trees are nearly as bad. Melbourne's older suburbs are full of mature elms, both on private property and as street trees planted by council. Their roots run shallow and aggressive, pulling moisture from under houses up to 15 metres away.

Other common culprits include liquid ambers, oaks, and willows. If you have a large tree within 10 metres of your house and you're on reactive clay, you're at higher risk of foundation movement on the side of the house nearest the tree.

Removing the tree doesn't always fix it either. When a big tree comes down, the soil it was drying out suddenly rehydrates. The clay swells, and the house can heave upward on that side. It's called "heave recovery" and it can cause just as many cracks as the original shrinkage.

Council drainage changes

Council infrastructure work can quietly change the water flow around your property. New stormwater drains, upgraded kerbs, footpath replacements, and road resurfacing all alter where water goes and how it moves through the soil.

A new drain that redirects water away from your property can dry out the soil on one side. A blocked council drain that pools water near your boundary can oversaturate it. Either way, the moisture balance around your foundations changes, and the clay responds.

This is especially common in the inner suburbs where councils are constantly upgrading Victorian-era infrastructure. Northcote, Brunswick, Fitzroy, and Collingwood are all seeing ongoing works that can affect surrounding properties.

Why the inner suburbs get hit hardest

Northcote, Brunswick, Fitzroy, Carlton, Richmond, Collingwood - these suburbs have the highest concentration of Victorian and Edwardian houses in Australia. Most were built between 1880 and 1920 on timber stumps, with minimal foundations by modern standards.

These houses are now 100 to 140 years old. The original stumps - if they haven't been replaced - are well past any reasonable service life. Many have been restumped at least once, some twice. The soil underneath has been disturbed, compacted, and rehydrated multiple times over a century.

Add in mature trees, shared party walls on terraces, and the constant vibration from tram lines, and you've got foundations under more stress than almost any other housing stock in the country.

How Melbourne compares to other cities

Sydney

Sydney's geology is fundamentally different. Large parts of the metro area sit on Hawkesbury sandstone, which is stable and doesn't react to moisture the way clay does. The northern beaches, eastern suburbs, and much of the inner west have rock or sandy soil relatively close to the surface.

Sydney does have clay pockets - particularly in the western suburbs around Penrith and Liverpool - and those areas do see foundation issues. But the scale is nothing like Melbourne. Fewer houses on timber stumps, less reactive soil overall, and a climate with more consistent rainfall means less dramatic wet-dry cycling.

Brisbane

Queenslanders (the house type, not the people) are built on tall timber stumps, but the construction is much lighter than Melbourne houses. Timber frame, tin roof, lightweight cladding. The house puts less load on each stump, so partial stump failure causes less structural damage.

Brisbane's soil is also less reactive overall. There are clay areas, especially in the southern suburbs and parts of Ipswich, but the typical Queenslander on sandy loam doesn't experience the same soil movement Melbourne houses do.

Brisbane's bigger risk is flooding rather than soil reactivity.

Adelaide and Perth

Adelaide has pockets of reactive clay, particularly in the northern and southern suburbs, and does see reblocking work. But the housing stock is different - more double-brick construction, which sits on strip footings rather than stumps.

Perth sits mostly on sand. Foundation problems there are more about sand washing out than clay moving. Different problem, different solutions.

What this means for your house

If you own a pre-1970 house in Melbourne, especially in the western or inner suburbs, you should assume your foundations need monitoring. That doesn't mean you need to panic or call a restumper today. It means you should know what to look for.

• Check your doors and windows seasonally - are they sticking more than they used to?
• Look for new cracks or cracks that are getting wider
• If you can access the subfloor, look at your stumps once a year
• Keep trees trimmed and manage drainage around the house
• If you're buying an older home, get a specific foundation inspection, not just a standard building report

Melbourne's soil, climate, and building history make reblocking a reality for a huge number of homeowners. The good news is that a properly restumped house on concrete or steel stumps will last decades without drama. It's the houses that haven't been done yet that need watching.

Wondering where your house sits on the risk scale? Try the free reblocking assessment tool for an instant estimate.