Most Perth renovation disasters are not caused by bad luck or dishonest builders. They are caused by a small number of decisions made early, usually by well-intentioned owners doing what seemed reasonable at the time.
Several of these are specific to this city — to its double brick, its sand, its salt and its sun. They are the ones that catch out buyers arriving from the eastern states with a renovation budget that made sense somewhere else.
Mistakes made before you own the property
1. Budgeting for a Timber-Framed Renovation and Buying Double Brick
Typical cost: $40,000 to $80,000
The defining Perth mistake. An owner from Melbourne or Brisbane prices a renovation on the assumption that internal walls are partitions and services run through cavities. Then they discover that the inside skin of most internal walls is load-bearing, that removing one costs $8,000 to $18,000, and that every power point means chasing into solid brick.
Removing a load-bearing brick wall costs 20 to 30 per cent more than modifying a timber-stud wall. A plan involving three openings plus relocated plumbing can add $50,000 to $80,000 over the equivalent eastern-states project.
The fix: Before you bid, have a builder or engineer walk through and tell you which walls carry load and what your intended openings would cost. See our guide to renovating a Perth double-brick home.
2. Not Checking the R-Code Coding and Setbacks
Typical cost: two to three months, or a design that cannot be built
Owners design an extension, then discover it breaches the deemed-to-comply setback, site coverage or open space provisions for their R-Code density coding — which converts a 10-business-day certified building permit into a 60-to-90-day planning approval, with neighbour consultation.
The fix: Establish your R-Code density coding and the applicable setbacks with the local government before designing anything, and ask your designer to demonstrate deemed-to-comply compliance clause by clause. See our guide to Perth approvals.
3. Missing Salt Damp and Wall Tie Corrosion
Typical cost: $20,000 to $70,000
Two masonry conditions that a cosmetic inspection can miss and that are expensive to remedy.
- Salt damp presents as blown render, salt crystallisation and deteriorating brickwork at the base of walls. Common where ground levels have risen, where reticulation runs against the building, or near the coast.
- Corroded wall ties in older cavity construction, indicated by horizontal cracking at regular intervals up the wall. Replacement is expensive and disruptive.
The fix: Have both specifically assessed before purchase. Renovating over either means the new work deteriorates from behind.
Mistakes made setting up the project
4. Paying a Deposit Before Receiving the Insurance Certificate
Typical cost: your entire protection if the builder fails
In WA, Home Indemnity Insurance is mandatory for residential building work valued over $20,000, and the builder must provide you with the certificate before commencing work or taking a deposit. That is a legal obligation, not a courtesy.
A builder who takes your deposit without producing it has broken the law, and you may be unprotected if they subsequently die, disappear or become insolvent.
The fix: Verify the builder’s registration through the state regulator, and demand the certificate before any money changes hands. It covers up to $200,000 for completion and defect rectification and $40,000 for deposits, running six years from practical completion. See our guide to vetting a Perth builder.
5. Using the Uncertified Permit Route to Save a Fee
Typical cost: three weeks of programme
An uncertified building permit (BA2) is processed in up to 25 business days. A certified permit (BA1), where a private building surveyor issues a certificate of design compliance, is processed in up to 10 business days.
Owners choose the uncertified route to avoid the surveyor’s fee and lose three weeks — and on structural work the uncertified route is not available anyway.
The fix: Use the certified route on anything with a construction programme attached. The fee buys speed and predictability.
6. Removing a Wall Without Engineering
Typical cost: $30,000 to $150,000, and a genuine safety risk
In a timber-framed house, an unengineered wall removal is a compliance problem. In double brick it is a structural one. Masonry above an inadequately supported opening will crack, sag and in extreme cases fail.
It also surfaces at sale. A double-brick wall visibly removed without an approved beam is a red flag that a buyer’s inspector will find.
The fix: Structural engineering and a building permit for every load-bearing opening, without exception. In Perth, assume a wall is load-bearing until an engineer says otherwise.
For more detail on this part of the project, see How to Check Whether a Wall Is Load-Bearing.
7. Setting a Budget With No Contingency
Typical cost: the difference between finishing and not finishing
Hidden costs add 10 to 25 per cent to most renovation budgets. In Perth the recurring drivers:
- Walls that prove to be load-bearing when the plan assumed otherwise
- Asbestos in eaves, wet area sheeting and fencing
- Corroded galvanised supply plumbing
- Under-slab plumbing at end of life, discovered when the slab is cut
- Salt damp behind render
- Electrical upgrades once walls are chased
- Making good after chasing, which is consistently underestimated
- Limestone retaining where site levels require it
The fix: A 15 per cent contingency is the Perth standard, and 20 per cent on a pre-1980 home or where significant structural change is planned.
8. Choosing the Cheapest Quote
Typical cost: 20 to 60 per cent above the accepted quote
Three quotes at $240,000, $255,000 and $175,000 do not represent a bargain. The low quote has misread the structural scope or intends to recover through variations.
The fix: Tender on identical documentation including the structural engineering. Without it, each builder assumes different beam sizes and bearing arrangements and the quotes are not comparable. Check specifically whether structural steel, slab cutting, making good after chasing and asbestos removal are included or excluded.
Mistakes made during construction
9. Installing a Dark Roof
Typical cost: comfort and running costs for the life of the building
The most consequential free decision available in Perth, and it is routinely made on aesthetic grounds alone. A dark roof absorbs solar radiation and drives roof cavity temperatures far higher than a light one, in a climate where roof heat gain is already the dominant thermal load.
The fix: Choose a light roof colour when re-roofing, and include reflective sarking while the roof is off. Both are free or near-free at that moment and expensive to change later.
10. Skipping the Western Shading
Typical cost: comfort, and unnecessary air conditioning spend
Perth’s afternoon sun from the west is the dominant comfort problem in this city, and external shading is the cheapest effective answer. Owners spend $30,000 on double glazing and leave a west elevation unshaded, which is the wrong order of operations.
The fix: External roller shutters, adjustable louvres or awnings on west and north-west glazing, before any glazing upgrade. Shading stops heat before it reaches the glass; glazing merely slows heat that has already arrived.
11. Injecting Cavity Insulation Into a Damp Wall
Typical cost: $20,000 to $60,000
Cavity insulation is one of the best-value interventions available in a Perth double-brick home — but only where the walls are dry and the cavity is clear. Injecting insulation into a wall with salt damp or a moisture issue traps the moisture and makes the problem substantially worse.
The fix: Have the cavity inspected with a borescope, confirm the wall ties are sound and the cavity is clear of mortar debris, and resolve any damp problem first.
12. Blocking the Weep Holes
Typical cost: $15,000 to $50,000
A Perth classic committed with good intentions. Rendering over weep holes, raising garden beds against the wall, laying new paving up to the brickwork, or building a patio slab against the house — each blocks the weep holes that let the cavity drain.
The result is moisture trapped in the wall, which produces the salt damp this city knows well.
The fix: Keep weep holes clear and visible, maintain ground and paving levels below the damp course, and where a new paved area abuts the house, design a drainage detail rather than butting hard against the brickwork.
13. Running Reticulation Against the Building
Typical cost: $15,000 to $50,000
Perth’s near-universal garden reticulation creates persistent moisture against footings and walls in an otherwise dry climate. It is a leading contributor to both salt damp and termite activity here, and it is entirely avoidable.
The fix: Keep sprinklers and drippers away from the building perimeter. Check the spray pattern rather than assuming — a sprinkler that appears to be watering the garden may be wetting the wall on every cycle.
14. Using Standard Fixings Near the Coast
Typical cost: $10,000 to $40,000 in premature replacement
Perth’s population is concentrated along the coast, and airborne salt extends well inland. Standard galvanised fixings on a deck, pergola or balustrade in Scarborough, Cottesloe or Hillarys will corrode and bleed rust down the structure within two years.
The fix: Grade 316 stainless steel fixings, marine-grade Colorbond and marine-grade window finishes anywhere in the coastal zone. The cost premium is modest; the difference in life is enormous.
15. Compromising on Waterproofing
Typical cost: $22,000 to $50,000 per bathroom
The membrane is four per cent of a bathroom budget and causes most serious residential defect claims. Perth’s failure mode is distinctive: water tracks sideways into adjoining masonry, mobilises salts, and shows up as damp skirtings and blown paint in the next room.
A Perth-specific risk: the dry summer heat makes a membrane skin over quickly while it has not cured through, and an inexperienced applicator applies the second coat too early.
The fix: Insist on the manufacturer’s stated cure times rather than a visual assessment. Photograph the membrane before tiling, and coordinate all fixing positions so nothing is drilled through it afterwards. See our guide to waterproofing and wet area compliance in Perth.
16. Moving the Plumbing Without Pricing the Slab Cutting
Typical cost: $4,000 to $9,000 per relocation
In a slab-on-ground Perth home, moving a sink, shower or toilet means core drilling or saw-cutting the slab, establishing new falls and reinstating. Owners design a new layout on paper without pricing this, and discover it after committing.
The fix: Ask the builder for a slab-cutting rate before finalising the layout, and design around the existing service positions wherever the plan allows. In Perth the saving is substantial and entirely invisible in the finished room.
17. Making Decisions During Construction
Typical cost: $10,000 to $50,000, plus weeks of programme
Owner indecision is among the largest causes of delay, and in masonry construction it is worse — changing your mind about an opening after the steel is in is genuinely expensive.
The fix: Complete every selection before construction begins, and resolve the structural design completely before demolition. Order anything not held locally before the work starts; Perth’s freight timelines add weeks. See our guide to Perth renovation timelines.
18. Overcapitalising for the Street
Typical cost: 30 to 60 per cent of the renovation spend, unrecovered
Every Perth street has a ceiling no renovation can break.
The fix: Check recent renovated sales in your street, not your suburb, before setting the budget. See our guide to Perth suburbs to renovate for profit.
Mistakes made at the end of the job
19. Missing the Building Surveyor’s Inspections
Typical cost: exposing completed work
Where a building permit applies, inspections occur at defined stages. If a stage is covered before it is inspected, the surveyor may require it opened up — and in masonry construction, opening up completed work is expensive.
The fix: Get the inspection schedule at permit stage and track it against the builder’s programme. Never allow tiling before the wet area inspection.
20. Not Obtaining the Completion Documentation
Typical cost: problems at every future sale
The work finishes, everyone moves back in, and nobody completes the paperwork. Years later a buyer’s settlement agent requests building approval records and they are incomplete.
The fix: Make the final progress payment conditional on the notice of completion and all compliance certificates — plumbing, electrical, structural, energy, and the Home Indemnity Insurance certificate. Store them with your property documents.
21. Not Photographing Concealed Work
Typical cost: the value of any future claim
Waterproofing, structural steel and bearing points, chased service runs, cavity insulation and termite management are all covered within days. When a problem appears in year four, the homeowner with dated photographs has a claim under the six-year Home Indemnity cover. The homeowner without them has an argument.
The fix: Photograph every stage before it is covered. In Perth the structural photographs matter most — they record how the beam was supported and packed.
A Pre-Start Checklist That Catches Most of These
Almost every mistake on this list is cheap to avoid and expensive to fix, and nearly all of them are caught by the same short set of checks done before any money changes hands. Run through this list before you sign a contract, not after the frame is up.
- Confirm the construction type. Tap the internal walls and check the wall thickness at a window reveal. Double brick internal walls are structural; every opening needs an engineer and a lintel, and that changes the budget by five figures per opening.
- Pull the property’s R-Code, setbacks and any overlays from the local government’s online mapping before you make an offer. Character, heritage, bushfire, flood and airport noise overlays all change what you can build and how long approval takes.
- Get a building inspection that specifically looks for salt damp, wall tie corrosion and asbestos rather than a generic pre-purchase report. Ask for the inspector’s brief in writing so those items are on it.
- Confirm the builder’s registration number on the Building and Energy register and check it is current and in the right class for your job’s value.
- Insist on the Home Indemnity Insurance certificate before you pay a deposit on any residential job over $20,000. The certificate is a legal precondition to taking a deposit or starting work, and asking for it costs you nothing.
- Set the contingency at 15 to 20 per cent of the contract value for anything involving an older home, and treat it as untouchable rather than as extra scope budget.
- Lock every selection before construction starts. Tiles, tapware, cabinetry finishes, appliances, flooring and lighting all chosen and documented. Variations signed during construction are the single largest source of budget overrun.
- Agree the inspection schedule in writing so you know which stages your building surveyor attends and when concealed work will be covered.
None of this requires expertise. It requires doing the checks in the right order, before the leverage shifts from you to the person holding the tools.
What These Mistakes Cost, Ranked
It helps to see the failures ranked by what they actually cost to remedy, because the ones that feel most alarming during a build are rarely the expensive ones. A late tile delivery is annoying. A structural wall removed without engineering is a different category of problem entirely.
Five-figure and above
- Removing a load-bearing double brick wall without engineering, then having to retrofit propping and a compliant lintel into a wall that has already moved.
- Buying on the assumption of a granny flat, subdivision or second storey that the property’s coding does not support.
- Injecting cavity insulation into walls with an active damp problem, which can mean stripping and replacing internal finishes across whole rooms.
- Waterproofing failure discovered after tiling, which means the full wet area comes out and goes back in.
- Overcapitalising past the street’s ceiling, where the cost is invisible until you sell.
Four figures, and avoidable
- Slab cutting for relocated plumbing that was never priced into the original quote.
- Standard fixings and hardware in a coastal location, replaced within a few years.
- Blocked weep holes and reticulation spraying the wall, which drive damp problems that then need remediation.
- Variations made during construction at build-time rates rather than tender rates.
The pattern is consistent. The expensive mistakes are made in the first three weeks of a project, usually before anyone has picked up a tool, and they are made because the check that would have caught them felt like an unnecessary delay at the time.
The Pattern
Nearly every item here is a decision made before construction, and nearly every one costs a few hundred to a few thousand dollars to avoid. An R-Code check, a structural walk-through, a salt damp and wall tie assessment, a borescope inspection of the cavity, a registration search, an insurance certificate, complete engineering documentation, and a contingency held in reserve.
Together those precautions cost perhaps $7,000 on a substantial Perth project. The mistakes they prevent routinely cost ten times that. It is the cheapest money in the entire renovation, and it is the money most often skipped — because at the moment you spend it, nothing has gone wrong yet.