Underpinning strengthens or deepens a building's foundations when the existing footings can no longer support it properly. In Sydney it is most common on older homes on reactive clay, fill, or sloping sites. It is a significant structural job, so it pays to understand when it is really needed.
Signs a house may need underpinning
- Large or growing diagonal cracks in walls.
- Uneven or sloping floors.
- Doors and windows that stick or no longer close.
- Gaps between walls and floors or ceilings.
- Cracks in slabs with one side higher than the other.
Many of these signs can also come from leaking pipes, poor drainage or trees, which can sometimes be fixed without underpinning. An engineer's assessment confirms what is needed. See do I need underpinning?
Common underpinning methods
Mass concrete underpinning
Excavating in short sections under the existing footing and filling with concrete down to stronger ground. A traditional, well-proven method, done in a careful sequence so the building stays supported.
Piers and beams
Concrete piers taken down to stable ground, with beams transferring the building load to them. Suits deeper problem soils.
Screw piles
Steel piles screwed into the ground to a set capacity, often used where access is tight or loads are lighter.
Resin injection
Expanding resin injected under footings to fill voids and lift slightly. Suitable for some situations, not all.
What drives the cost of underpinning
- How much of the house needs underpinning, and how deep stable ground is.
- The method the engineer specifies.
- Access for excavation and spoil removal, especially in terraces and tight sites.
- Engineering, geotechnical investigation and approvals.
- Repairs to cracks, plaster and finishes afterwards.
- Drainage and plumbing repairs that contributed to the movement.
Approvals
Underpinning is structural work and generally needs engineering and an approval pathway such as a complying development certificate or development application. Work near boundaries may need dilapidation reports for neighbouring properties.
Underpinning in Sydney
See our underpinning service or book a site assessment.
Frequently asked questions
How do I know if my house needs underpinning?
Large or growing cracks, uneven floors and sticking doors are common signs, but an engineer should confirm, because drainage and leak repairs sometimes solve the problem instead.
What is the most common underpinning method?
Mass concrete underpinning is a common and well-proven method. Piers and beams or screw piles may suit deeper problem soils or tight access.
Does underpinning need council approval?
Underpinning is structural work and generally needs engineering and an approval such as a CDC or DA. We confirm the pathway for your property.
