A handful of decisions, almost all made in the first few weeks, account for most of the money lost on a renovation. In Canberra those decisions have a shape that exists nowhere else in Australia, because this is the only Australian city built entirely on leasehold land, the only one with mandatory Energy Efficiency Rating disclosure, and the only one with loose-fill asbestos at scale.
Here are the mistakes that cost the most, grouped by when they are made.
Mistakes Made Before You Own the Property
Not commissioning a loose-fill asbestos assessment
The most serious mistake available in Canberra, and the one with the worst consequence.
- Loose-fill amosite asbestos insulation was installed in more than 1,000 Canberra homes in the 1960s and 1970s. A small number contain crocidolite, which is more hazardous.
- A removal program ran from 1988 to 1993, but material remained in wall cavities, subfloor spaces and behind cornices
- The ACT government has run an eradication scheme involving acquisition and demolition, and government officials have acknowledged loose-fill material is probably still present in the community
- A standard building inspection does not cover this. Commission a licensed asbestos assessor specifically, on any pre-1980 house, before any work opens a wall cavity, ceiling or subfloor.
- The ACT Loose Fill Asbestos Coordination team holds information on affected properties; Access Canberra can be reached on 13 22 81
The assessment costs a few hundred to a few thousand dollars. Disturbing loose-fill asbestos contaminates the house and its contents, and the remedy is demolition rather than repair.
Not reading the Crown lease
All ACT land is leasehold. The purpose clause in your Crown lease governs what the land may be used for, including how many dwellings are permitted. If your plan involves a second dwelling and the lease permits one, you need a lease variation — and that triggers the Lease Variation Charge, which can be substantial. Your conveyancer holds a copy from the purchase. Read it before you make an offer, not after.
Not getting a Lease Variation Charge estimate
Where a lease variation is required, the charge is frequently the item that decides whether the project works at all. It is estimable at concept stage. The 50 per cent partial waiver for eligible RZ1 missing middle development until June 2029 changes the arithmetic considerably, and it is worth knowing whether your proposal qualifies before you commit to anything.
Not checking the trees
The ACT has one of Australia’s strictest urban tree protection regimes. Registered trees and trees in the Tree Management Precinct are protected, and protection extends to the root zone — so excavation, footings, trenching, paving and soil compaction within the protection zone can all constitute damage. Trees on a neighbouring block or the verge can constrain your footprint. On a typical treed Canberra block, the arborist report determines where an extension can physically go, and it costs $800 to $2,500.
Not getting a geotechnical investigation
Shallow bedrock is common across much of Canberra. Hitting rock moves footings and service trenching from excavation rates to rock breaking rates — commonly three to eight times higher per cubic metre, and a $15,000 to $50,000 swing on a modest extension. Reactive clay in parts of Tuggeranong, Belconnen and Gungahlin brings its own engineered footing cost. The investigation is $1,000 to $2,500.
Assuming the pre-July-2026 rules still apply
The Missing Middle Housing Reforms commenced on 1 July 2026. RZ1 now permits missing middle housing up to two storeys and RZ2 up to three; the former minimum block size for a second dwelling in RZ1 is gone; the size cap for unit titling a second dwelling is gone; and unit titling is available on a wider range of blocks. Buying or planning on the old assumptions understates what many Canberra blocks can now support.
Mistakes Made Setting Up the Project
Assuming DA-exempt means approval-free
A compliant single-dwelling extension can be exempt from a development application. It still needs building approval and a building commencement notice from a private building certifier before work starts. These are separate things, and unapproved work is a defect at sale, a potential insurance problem and an enforcement risk.
Not verifying the builder’s licence and insurance
- Verify the licence, class and currency on the Access Canberra public register yourself
- Search ASIC for the company, its directors and any related or previously deregistered entities. Repeated company failures under the same directors is the clearest warning available.
- Residential building work insurance is mandatory for houses of three storeys and below, must be obtained before the builder applies for the building commencement notice, and evidence must be given to you. Minimum cover rose to $200,000 on 1 January 2025, with the claim window extended to 180 days.
- A builder slow to produce that evidence has told you something.
Missing an exemption criterion by a small margin
Exceeding a setback, a height, a plot ratio or a canopy cover requirement by a small amount converts a no-DA project into a full development application, adding two to five months. Ask your designer what it would take to stay inside the criteria, and what you would give up.
Setting a budget with no real contingency
Fifteen to twenty per cent for anything pre-1990. Rock, asbestos and the state of the original services are all real possibilities in this stock.
Choosing the cheapest quote
Canberra quotes spread 30 to 50 per cent on the same drawings, and it is about scope, allowances and exclusions rather than margin. Equalise every quote line by line — asbestos, rock excavation, footings to the actual site classification, tree protection measures, the envelope specification, preliminaries and the switchboard.
Mistakes Made During Construction
Building an extension to code minimum and leaving the old house cold
The most common Canberra renovation failure. A well-insulated, double-glazed extension attached to an uninsulated, single-glazed, draughty ex-government house produces a home with one comfortable room. The envelope upgrade to the retained house — ceiling, walls, underfloor, glazing, sealing — costs $30,000 to $90,000 and it is what determines whether you enjoy living there. In the ACT it also shows up in the Energy Efficiency Rating disclosed at sale.
For more detail on this part of the project, see Renovating an Ex-Government House in Canberra: A Practical Guide.
Insulating without sealing, or sealing without ventilating
- Insulation without draught sealing leaves the largest heat loss path open
- Sealing without controlled ventilation produces winter condensation and mould on cold surfaces — window reveals, wardrobes on external walls, behind furniture on south walls
- Do both, and provide ducted exhausts with a make-up air path at minimum
Leaving thermal bridges
Un-broken aluminium window frames, un-insulated slab edges and gaps around downlights undo a disproportionate share of the bulk insulation. In a cold climate the thermal bridge is also where the condensation appears, so it becomes a durability problem rather than just an efficiency one.
Not lagging pipework in unheated spaces
Frozen and burst pipes in an unheated subfloor or an external wall are a real Canberra event. Trades who have worked mainly in warmer cities routinely omit this. Lag everything in an unheated space, and do it while access is open during a replumb.
Blocking subfloor vents while insulating underfloor
Insulate the floor; do not seal the subfloor. A sealed subfloor is where rot begins.
Removing a wall without engineering
Internal walls in a double brick ex-government house are frequently load-bearing. Each opening needs an engineer’s design, a steel beam, propping and adequate footings — $11,000 to $24,000. Done without engineering, the failure develops over years and takes the ceiling with it.
Excavating within a tree protection zone
Footings, trenching, paving and even heavy vehicle traffic compacting the soil can constitute damage to a protected tree. The penalties are substantial and the tree does not recover. Have the protection zones marked on the site plan and fenced before work starts.
Compromising on waterproofing
The cheapest line item to cut and the most expensive to get wrong. Watch for falls corrected with tile adhesive rather than set into the screed, missing bond breakers at wall-floor junctions, membrane coats rushed without curing, and no flood test. In a cold climate, allow longer cure times in winter than the data sheet’s minimum.
Grouting internal corners
Internal corners in a tiled wet area must be silicone, not grout. Grout cannot accommodate movement, it cracks, and water gets past the tiling into the substrate.
Installing gas appliances
The ACT is transitioning away from fossil fuel gas. Installing a new gas cooktop, heater or hot water unit during a renovation is investing in an asset with a limited future and, at resale, an increasingly visible negative.
Making decisions during construction
Every selection made on site is made at build-time prices with no competitive tension, and it breaks the trade sequence. In a small trade market like Canberra’s, a rescheduled trade may not be available again for weeks.
A related guide to consider while planning this work is How to Find and Vet a Renovation Builder in Canberra.
Ignoring winter in the program
Concrete pours are restricted on frosty mornings, external rendering and painting suffer below a few degrees, and roofing slows. A program that assumes uninterrupted winter progress is wrong, and the correction is either float or sequencing the external work outside the coldest months.
Mistakes Made at the End
Not photographing concealed work
Framing, services rough-in, insulation, sealing, pipe lagging, waterproofing coats, the flood test, footing reinforcement before the pour. Date-stamped, wide and close. Once it is covered the evidence is gone, and this documentation is worth more than any contract clause if something fails in year three.
Paying the final invoice without the certificate of occupancy
The certifier’s certificate of occupancy confirms the work is complete and compliant, and it is what a future buyer’s solicitor will ask for. The final payment is the only leverage you have left.
Not collecting the compliance documentation
- Certificate of occupancy from the building certifier
- Electrical certificate of compliance
- Plumbing compliance certification
- Waterproofing certification and the photographic record
- Engineer’s inspection records for footings and structural work
- Asbestos clearance certificates for any removal work
- Evidence of residential building work insurance
- Arborist sign-off where tree protection conditions applied
- Warranties and manuals for every appliance and system
Not getting an updated Energy Efficiency Rating
Unique to the ACT, and consistently overlooked. You will need a rating at sale or lease anyway. Getting it after a proper envelope upgrade converts the work into a documented, disclosed advantage — and if the property is rented, the ceiling insulation compliance evidence is required regardless. Existing tenancies must meet the R5 minimum by 30 November 2026; new tenancy agreements within nine months of signing.
Overcapitalising past the street
Canberra’s suburbs have well-defined ceilings and a buyer pool that knows the market intimately. The street sets the limit, and no specification moves it for one house. A renovation above the street ceiling is a lifestyle decision, which is a fine thing to choose — the mistake is believing it is an investment.
A Pre-Start Checklist
- Commission a loose-fill asbestos assessment on any pre-1980 house, before anything else
- Read the Crown lease and confirm the purpose clause permits what you intend
- Get a Lease Variation Charge estimate if the project adds a dwelling, and check eligibility for the partial waiver
- Get an arborist report and have protection zones mapped before the design is drawn
- Get a geotechnical investigation and find out whether you are on rock or reactive clay
- Check the zone, the development controls and the essential design elements, including canopy cover
- Get an existing Energy Efficiency Rating with modelled improvements, so the envelope budget is evidence-based
- Verify the builder’s licence on the Access Canberra register and search ASIC for the directors
- Insist on evidence of residential building work insurance before the commencement notice is applied for
- Engage the building certifier at concept stage
- Set the contingency at 15 to 20 per cent and treat it as untouchable
- Lock every selection before construction starts
- Use a written contract with variations priced in writing before the work is done
The Pattern
Every expensive Canberra mistake on this list is made in the first three weeks, before anyone picks up a tool, and almost all of them are answered by a small set of investigations: an asbestos assessment, a lease review, an arborist report, a geotechnical investigation and an energy rating. Together they cost around $5,000 and take a fortnight.
Against a project of several hundred thousand dollars on a sixty-year-old house, on leasehold land, possibly on rock, possibly with protected trees and possibly with loose-fill asbestos in the wall cavity, that is comfortably the best money in the budget.
For the detail behind each of these, see the Canberra renovation cost guide, the 2026 approval rules, renovating an ex-government house and how to find and vet a renovation builder in Canberra.