The majority of Wagga Wagga homes built before the 1980s use a pier and beam foundation system, what locals often simply call “stumps.” These foundations have supported Riverina homes through decades of extreme heat, dry summers, wet winters, and flood events. When well maintained, they perform admirably. When neglected, they are responsible for most of the sloping floors, sticking doors, and cracked walls that bring homeowners to us. Understanding how pier and beam foundations work, and why they fail, is the foundation of good maintenance decisions. For detail on how stump homes compare with slab construction, see our guide on stump vs concrete slab foundations in the Riverina.
Quick answer (BLUF)
Pier and beam foundations consist of individual stumps or piers set into the ground, carrying a grid of timber bearers that support floor joists and the floor sheeting above. They fail when stumps deteriorate, sink, heave, or tilt, most often due to reactive clay movement, timber decay, termite damage, or flood exposure. Repair is by restumping and relevelling, which is practical and cost-effective.
How pier and beam foundations work
A pier and beam system distributes the load of the structure above through a series of discrete support points (the piers or stumps) into the ground. Each element of the system has a specific role:
Stumps or piers. The vertical compression members. In traditional Wagga homes, these are red gum (Eucalyptus camaldulensis) or treated pine timber, approximately 100 × 100 mm in section. Modern restumping uses pre-cast concrete stumps (typically 125 × 125 mm or 150 × 150 mm) or adjustable steel stumps. The stump transfers the load from the bearer above into the soil below.
Sole plates or footings. At the base of the stump sits a concrete footing pad or timber sole plate, distributing the point load across a larger soil area. In very old Wagga homes, stumps were sometimes set directly into the soil without any footing, relying on skin friction. These perform poorly in reactive clay.
Bearers. Horizontal timber members (typically 100 × 50 mm, 150 × 50 mm, or larger in LVL for modern work) that span between stumps, collecting their loads. The bearer sits on or is notched into the top of the stump.
Floor joists. Lighter horizontal members spanning between bearers, supporting the floor sheeting. In timber floor construction, joists are typically 100 × 38 mm or 75 × 38 mm at 450 mm or 600 mm spacing.
Floor sheeting. The surface the occupants walk on, in older homes typically 19 mm tongue-and-groove hardwood boards, in post-war homes often particleboard or plywood.
The whole system is elevated above the ground, typically 300 to 600 mm in Wagga’s residential stock, creating a subfloor crawl space that allows air circulation, provides access to services, and separates the timber structure from ground moisture.
How pier and beam foundations fail in Wagga Wagga
Timber stump decay
Red gum stumps have impressive natural durability, but they are not immortal. In Wagga’s reactive clay soil, stumps cycle between very dry and very moist conditions. The base of the stump, buried in soil that alternately saturates and desiccates, is under the greatest stress. Decay typically begins at the soil line and progresses upward. A stump that looks sound externally may be severely compromised at its base.
Pine stumps (both CCA-treated and untreated) are generally less durable than red gum in reactive clay environments and commonly begin to fail after 30-50 years.
Termite attack
Termites are active throughout Wagga Wagga and the Riverina. Timber stumps that are partially decayed are an entry point for termites, which can then travel through the stump and bearer system into the main timber frame. A severely termite-damaged stump provides little structural support.
Reactive clay movement
The stumps themselves are embedded in reactive clay. As the clay shrinks and swells, it can push stumps sideways (heave-induced tilt), drop stumps as the soil beneath them dries and consolidates, or lift stumps as the soil expands. When stumps at different locations move by different amounts or in different directions, the floor above becomes uneven and the structure cracks.
Inadequate original design
Many older Wagga homes were built at a time when stump spacing was generous and footings were minimal. On Class H2 or E reactive clay, these original designs have simply been overtaken by the soil conditions they were never designed for. As the clay progressively moves, inadequate stumps struggle to maintain the floor level.
Flood and water damage
Prolonged inundation, from the Murrumbidgee or from poor local drainage, saturates the subfloor space, accelerating stump decay and softening the soil beneath footings. Post-flood inspections regularly reveal stumps that have been compromised by saturation even if they appeared sound beforehand.
Identifying pier and beam failure
Common signs that your pier and beam foundation is failing include:
- Floors that slope noticeably, feel the gradient when walking barefoot across a room
- Doors and windows that jam, drop on one side, or develop visible gaps in their frames
- Gaps between skirting boards and the floor surface
- Cracking at wall-floor or wall-ceiling junctions
- Creaking or bouncing floors (may indicate joist failure rather than stump failure)
- Visible tilt or lean when inspecting stumps from the subfloor access hatch
Our guide on signs your house needs restumping covers these warning signs in more detail.
Repair options
Restumping (reblocking). Replacing deteriorated timber stumps with new concrete or steel stumps. This is the core intervention for pier and beam failure. Restumping and reblocking involves temporary jacking to lift the bearer, removing the old stump, placing a new footing, setting the new stump, and lowering the bearer back to the correct height.
Relevelling. Where stumps are structurally sound but have moved, they can be adjusted (packing up sunken stumps, trimming raised stumps) to restore floor level. House relevelling is appropriate when the stumps themselves are serviceable.
Underpinning. Where the subsoil conditions are inadequate to support new stumps at shallow depth, deeper underpinning is required, typically bored concrete piers that extend into stable material below the reactive zone.
FAQs
How long do concrete stumps last compared to timber?
Pre-cast concrete stumps used in modern restumping projects have a design life exceeding 50 years and are not subject to termite attack or fungal decay. They are the standard choice for restumping in Wagga Wagga. Adjustable steel stumps have similar durability advantages and additionally allow post-installation height adjustment.
Can I see from above whether my stumps need replacing?
Not reliably. Stump condition assessment requires subfloor access and physical inspection, visually and by probing with a pointed instrument to test for softness. If you cannot access your subfloor or are uncertain about what you are seeing, a foundation inspection by a professional is the appropriate next step.
How many stumps does a typical Wagga home have?
It varies with the house size and era of construction. A typical post-war Wagga home of 100-150 m² might have 30 to 60 stumps. Older homes sometimes have more due to closer stump spacing used in the 1930s and 1940s. Your contractor can count them during the inspection.