The pre-purchase foundation inspection: buy the house, not the problem

Foundation problems are the most expensive common surprise in older Australian homes — and the most avoidable one, because every symptom is on display before auction day to anyone who knows where to look. Here's the buyer's foundation playbook, from first open to final offer.

First: know what the house stands on

Everything downstream depends on this. A timber-floored home with a crawl space stands on stumps — its foundation risk is stump condition, and the fix is restumping ($9,000–$22,000 for most full jobs). A brick home on a concrete slab or strip footings has no stumps — its risk is footing movement, and the fix is underpinning ($10,000–$40,000+). Brick-veneer on stumps (common regionally) behaves like a stump house. Ten seconds at the subfloor vents or a look at the floor construction tells you which inspection you're actually doing.

What you can check yourself at the open

• Bring a marble. Set it down in each room. A consistent roll direction across rooms is settlement, not "character".
• Work the doors and windows, especially south and west sides. Sticking, planed top edges, moved latch plates — a maintenance history of movement written in the joinery.
• Read the walls. Diagonal cracks from door/window corners inside; stepped cracks in brickwork outside; fresh paint or render over crack-shaped lines (very common pre-sale). Note width and pattern — our crack severity checker works just as well on a house you're buying as one you own.
• Look through the subfloor vents with your phone torch: leaning or patched stumps, damp ground, rusted ant caps are all visible from outside.
• Check the water story: downpipes ending at the wall base, big trees hard against the house, paving graded inward — the causes of tomorrow's movement are visible today.
• Date the house. Pre-1970 on original timber stumps means the stumps are at or past service life regardless of how the floors feel.

Why the standard building report isn't enough

A generic pre-purchase building inspection is worth having, but on foundations it often stops at "evidence of movement noted; further investigation recommended" — language that could mean $3,000 or $40,000. For an older stump home, add a specialist subfloor inspection: someone who crawls the full subfloor, counts and condition-maps every stump, and checks bearers and joists. For a cracked slab home, that means a structural engineer's assessment, sometimes with a geotech report. A few hundred dollars here prices the biggest unknown in the purchase.

Questions to ask the vendor or agent

1. "Has the house ever been restumped or underpinned?" — and if yes, when, by whom, and where's the paperwork?
2. "Can I see the permit and certification?" A documented, certified restump or underpin is a selling feature; an undocumented one is a question mark you price accordingly.
3. "Any history of plumbing leaks, drainage work or tree removal?" All three are subsidence backstory.
4. "Why is this wall/ceiling freshly painted?" Sometimes the answer is honest. Ask anyway.

Turning findings into negotiation

Foundation findings are the strongest renegotiation lever in property because they're specific, quotable and structural. "The subfloor report shows 23 failed stumps; restumping quotes run $14,000–$18,000" is not an opinion the vendor can wave away — it's a bill they'll face with any buyer. Sharp buyers routinely recover the full repair cost (and an uncertainty margin) at settlement, effectively getting the restump paid for. The full negotiation walkthrough is in our buying a house with stump problems guide.

What the inspections cost — and return

Order-of-magnitude numbers so nothing here feels like a leap: a standard pre-purchase building and pest inspection typically runs $400–$800 regionally; a specialist subfloor/stump inspection a few hundred more; a structural engineer's crack assessment on a slab home commonly $500–$1,500. Set against a purchase where the downside is a five-figure repair — and where a documented finding routinely moves the price by more than the repair itself — foundation due diligence is the best-returning few hundred dollars in the whole transaction. On auction purchases, do it before auction day: there's no cooling-off to hide behind once the hammer falls.

The honest bottom line

A house with tired foundations is not a house to walk away from — it's a house to buy with your eyes open and the price adjusted. Foundations are among the most fixable "serious" defects a house can have: known methods, fixed quotes, certified outcomes. The only genuinely expensive mistake is not looking.