Renovating an Old House? Read This Before You Open a Wall

Table of Contents

1. Why Old Houses Break Renovation Budgets
2. Test Before You Touch: Asbestos, Lead, Mould
3. The Systems Nobody Budgets For
4. Foundations and Structure
5. What Hidden Problems Actually Cost
6. The Right Order of Work
7. Council Approvals, Heritage Overlays, and Compliance
8. When Not to Renovate
9. What to Keep
10. Conclusion

Older homes carry a 15 to 20 percent contingency floor on top of the quoted price, according to Sydney renovation budget data, and ABS-based analysis suggests over 40 percent of Australian renovation projects exceed their initial budget by more than 20 percent.

Those two numbers are connected. The overruns cluster in old houses because the expensive problems live behind fibro sheeting, under floorboards, and inside walls, invisible until demo day.

This article covers five things: what to test before any demolition, which systems drain budgets fastest, what each hidden problem costs in real dollars, the order to do the work, and the honest criteria for walking away. Read it before you sign a contract, not after the first wall comes down.

TL;DR: Test for asbestos, lead paint, and mould first. Price the rewire and the underpinning before the kitchen. Work in this order: stabilise, systems, surfaces. Keep a 15–20% contingency. And know your walk-away number before you start.

1. Why Old Houses Break Renovation Budgets

A new-build renovation is mostly a cosmetic risk. An old-house renovation is systemic risk. Homes built before roughly 1990 predate current wiring rules, current plumbing materials, and the phase-out of lead paint and asbestos cement sheeting, so every opened wall can trigger mandatory, unplanned work.

Sydney renovation budget guides note that the 15–20 per cent contingency should be treated as non-negotiable for older housing stock, and that properties in heritage conservation areas or built before 1970 should lean toward the top of that range.

Bottom line: the standard 10–15 percent contingency quoted for a general renovation is a floor for old houses, not a ceiling. Budget the full 20 percent minimum on anything built before 1970, and treat that money as spent until final inspection.

2. Test Before You Touch: Asbestos, Lead, Mould

Three checks, done before demolition, prevent the most expensive category of mid-project surprise: work stoppages for hazardous materials.

2.1 Asbestos

• Assume it if: the house was built or renovated before 1990. An estimated one in three Australian homes still contains asbestos in some form, and it turns up in fibro sheeting, eaves, wet-area wall linings, old vinyl floor backing, and even fences well into the 1990s.
• The rule: harmless when undisturbed, hazardous the moment a drill, saw, or sander hits it.
• The law: a residential job becomes a workplace once a tradie is on site, so WHS asbestos regulations apply regardless of who owns the property, and removal of friable material must be done by a licensed asbestos removalist.
• The cost: get a NATA-accredited lab test before any wall, ceiling, or floor covering comes up. A test is a fraction of the cost of a stop-work order.

2.2 Lead Paint

• Assume it if: the house was built before 1970, when Australian paint could legally contain up to 50 percent lead. That limit dropped to 1 percent in 1970–1992 and 0.1 percent from 1997.
• Where it hides: windowsills, skirting boards, door frames, and old ceiling dust that settles above cornices.
• Why test anyway: sanding or heat-stripping old paint releases lead dust, which is far more dangerous than the paint itself. Wet methods only, and never dry-sand.

2.3 Mould

• Why old houses have it: old houses leak, and old leaks grow mould inside wall cavities, especially behind fibro and under-insulated bathrooms.
• The payoff of testing: finding it before demo lets you fold remediation into the schedule instead of halting it mid-project.

3. The Systems Nobody Budgets For

Kitchens and bathrooms get the Pinterest boards. Wiring and stumps get the money. Plan for these first, because finishing work built on top of failing systems gets torn out later.

3.1 Electrical

Homes with an old ceramic fuse box rather than circuit breakers and safety switches (RCDs) are common in anything built before 1990, and a switchboard upgrade is usually needed before other electrical work can proceed.

• Switchboard upgrade: $700 to $2,500, depending on board size and circuits.
• Full rewire for a standard three-bedroom home: $8,000 to $20,000+, with older terraces, double-brick homes, and heritage properties running toward $15,000 to $26,000+ in tighter-access markets.
• Original rubber, cloth, or lead-sheathed cabling (common in homes built before roughly 1970) is unsafe and non-compliant and should be treated as a full-rewire candidate, not a patch job.

3.2 Plumbing and Stumps

Older galvanised pipes corrode from the inside, choking water pressure long before they visibly leak. If the house still runs original supply lines, get a plumber’s camera inspection before tiling a single bathroom wall.

Timber-stump homes (common in Queenslanders and older weatherboard houses) also need a stump inspection. Get this before flooring or wall linings go in, since restumping after finishes are done means redoing them.

3.3 Insulation and Ventilation

Many pre-1990 homes have little or no wall insulation and poor subfloor ventilation. Address the building envelope while walls are already open. Insulating an opened wall costs a fraction of opening it again in five years.

4. Foundations and Structure: Deal Makers, Deal Breakers

Before any cosmetic planning, hire a structural inspection separate from a standard building and pest report.

Warning signs to look for:

• Stair-step cracks in brick or masonry
• Doors and windows that no longer square in their frames
• Sloping floors that worsen toward one corner
• Gaps between walls and ceilings, or between skirting and floor

Underpinning in Australia typically runs $3,000 to $25,000, with a national average around $9,000, but extensive reactive-clay movement or multi-room subsidence can push repairs into the $40,000 to $80,000 range. Structural engineer reports needed before quoting run $300 to $1,500.

More important than the dollar figure: unresolved structural movement complicates finance approval and insurance, and reactive clay soils (common across much of NSW, Victoria, and South Australia) mean the problem tends to recur without proper drainage and moisture management, not just a one-off pour.

Sloping floors alone are not a death sentence. Old timber-framed houses settle, and a stable century-old lean differs completely from active seasonal movement. The inspection’s job is to tell you which one you have.

5. What Hidden Problems Actually Cost

Hidden problem	Typical Australian cost	When to suspect it
Asbestos testing and removal	Testing: a few hundred dollars. Removal: varies by area and material, licensed removalist required	Built or renovated before 1990; fibro sheeting, old vinyl flooring, eaves
Lead paint management	Wet-scrape and repaint: a few hundred to low thousands depending on area	Built before 1970; peeling or chalking paint on old trim
Switchboard upgrade	$700–$2,500	Ceramic fuses, frequent tripping, no safety switches
Full electrical rewire	$8,000–$20,000+ (up to $26,000+ for heritage/terrace access)	Rubber, cloth, or lead-sheathed cabling; built before ~1970–1980
Underpinning / structural	$3,000–$25,000 typical, up to $80,000 for major works	Stair-step cracks, sticking doors, sloping floors

How to read this table: figures are aggregated from current Australian trade cost guides and vary heavily by state, access, and soil type. Sydney and Melbourne heritage-zone jobs sit toward the top of every range. Get three local quotes for anything on this table before finalising a budget.

6. The Right Order of Work

Sequence protects money. The rule: stabilise, then systems, then surfaces.

Step 1 — Stabilise the shell. 

Foundations, stumps, roof, structural framing, drainage. Nothing else survives if water gets in or the structure moves. If underpinning or excavation work will bring machinery close to mature trees on the block, protecting root zones during construction is worth planning at this stage too, since compacted soil or severed roots can kill a tree years after the builders leave.

Step 2 — Remediate hazards. 

Asbestos removal, lead-safe prep, and mould remediation while the house is empty and the walls are coming open anyway.

Step 3 — Replace systems. 

Wiring, plumbing, insulation, all while cavities are exposed.

Step 4 — Close and finish. 

Wall linings, floors, kitchens, bathrooms, paint.

Every reversal of this order costs double. A finished kitchen above corroded supply lines or an unrewired switchboard is a demolition invoice with a delay on it. This is also why the dream kitchen goes last on the schedule even though it was first in your head.

7. Council Approvals, Heritage Overlays, and Compliance

Approvals. Structural work, plumbing, and electrical replacement generally require a Development Application (DA) or Complying Development Certificate (CDC) depending on your council and the scope of work, plus a Certificate of Compliance for Electrical Work (CCEW) once the sparky’s finished. Skipping approvals risks fines, forced rework, and disclosure problems at resale.

Heritage overlays. If the property sits within a heritage conservation area or is individually listed, contact your local council’s heritage advisor before design work begins. Exterior changes, window replacement, and even paint colour may need approval, and the review cycle adds weeks to months. Budget the calendar, not just the dollars.

Compliance triggers. Touching a system can legally obligate you to bring related elements up to current standard (AS/NZS 3000 wiring rules, current smoke alarm requirements under AS 3786, waterproofing standards in wet areas). Ask your builder which upgrades each phase of work will trigger, in writing, before you start.

8. When Not to Renovate

An honest article admits this option exists. Run the math before emotional sunk cost takes over.

Walk-away signals (individually survivable, dangerous in combination):

1. Stacked system failures. Active structural movement plus a full rewire plus a full stump or pipe replacement needed at once can exceed $50,000 before a single cosmetic improvement.
2. Underwater math. Post-renovation value below purchase price plus renovation cost plus a 20 per cent contingency means you are buying a loss.
3. Blocked or expensive financing. Structural or wiring issues that complicate a renovation loan force higher-interest borrowing for the riskiest phases.

If two or more apply: get a local agent’s opinion of as-is value and compare selling, or a knockdown-rebuild quote, against renovating on paper. In parts of Melbourne’s middle-ring suburbs in particular, a full rebuild is increasingly competitive against renovating a badly deteriorated older home.

The preference to renovate is often emotional. The decision should not be.

9. What to Keep

The opposite mistake also costs money: gutting the character the market pays for.

Usually worth restoring, not replacing:

• Original hardwood flooring (refinishing costs far less than new flooring)
• Old-growth framing timber (often outperforms modern equivalents)
• Period trim, timber sash windows, tessellated tiling, and cast-iron work (differentiate the house at resale, especially in inner-city terraces and Federation-era homes)

The test for any original element: is it hazardous, failing, or blocking a system upgrade? If not, restoring it is usually cheaper than replacing it and is worth more when finished.

This is also where a general builder is often the wrong hire. Timber floor repair, tessellated tiling, cast-iron restoration, and facade work are trade specialties, not general carpentry. Heritage Restorations & Renovations is one Sydney-based example of a builder that works exclusively in this heritage-restoration niche, which is the kind of specialist worth seeking out before defaulting to a standard renovation crew.

10. Conclusion

Should you renovate your old house? It depends, and here is exactly what it depends on.

If the structure is stable or fixable within budget, and you fund testing first, systems second, and finishes last with a 20 per cent contingency locked in, an old-house renovation is a sound project and often better value than moving. If active structural movement stacks on top of a full rewire and stump or pipe replacement, or the finished value cannot cover the total cost, selling as-is or considering a rebuild is the smarter move, and no amount of Pinterest changes that math.

The core points, restated:

• Test for asbestos, lead paint, and mould before any demolition
• Price the rewire, the underpinning, and the switchboard before pricing the kitchen
• Follow the order: stabilise, systems, surfaces
• Get every council approval, and check for a heritage overlay early
• Keep the character that isn’t hazardous
• Decide with the numbers on paper

Old houses reward planners and punish optimists.