267suburbs mapped for this jobWe read the planning data for each one, so the match is against the block rather than a postcode.

Service

Home extension and renovation builders

A second storey on footings never designed to carry one is the classic expensive surprise, and where new work meets old is where extensions crack, leak and look wrong. Both are engineering questions, and both are settled before any price means much.

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Insurance sighted
Solvency re-checked

2,361Construction companies entered external administration in 2024–25 — more than any other industry in Australia (ASIC)

267Suburbs where we have read the planning data and this kind of job is what the area is mapped for

65Councils covered across those suburbs, each with its own lodgement process and its own timeline

When this is the right path, and when it is not

Suits you if

The existing house is structurally sound and in the right place, and you want more of it rather than a different one.

Think again if

It is the wrong path where the structure is poor, the floor level is wrong, or the extension would be most of a new house anyway.

How the job actually runs

01
Find out what the existing house is made of
Footings, frame, wiring and plumbing all constrain what can be added and what must be upgraded. An old house is a set of unknowns until someone opens it up.
02
Check the overlays before you design
Heritage, character and vegetation controls bite hardest on extensions, because the assessment is against what is already there.
03
Decide whether you move out
Living through a major extension is possible and it is harder than people expect. It also slows the build and therefore costs money.
04
Expect provisional sums
No builder can price what is behind the walls of a sixty-year-old house without opening them. Insist those allowances are explained rather than buried.

Where these jobs go wrong

What most often costs people money on an extension specifically.

Assuming the existing footings will do
A second storey on footings never designed for one is the classic expensive surprise. It needs engineering assessment before design.
Underestimating the join
Where new meets old is where extensions leak, crack and look wrong. It is detail work and it is not cheap.
Thinking a renovation is cheaper than a rebuild
Sometimes it is. On a poor-condition house it frequently is not, and the comparison should be made honestly before you commit.
Living through it to save money
The saving is smaller than people expect and the cost to your household is larger.

What moves the price

No figures — a number without your site and your specification is a guess. For a extensions job, these are what actually move it.

Condition of the existing structure
Matching or contrasting the existing house
Bringing old services up to current standard
Access for machinery and materials
Whether you stay in the house
Overlay and permit requirements

Where we cover this, and what the planning data says

Mapped constraints is the control that most often decides how a extensions job runs. Read from state planning data.

Suburbs covered for Extensions and their mapped planning controls
Suburb	Council	Mapped constraints
Ainslie	ACT Government	3
Aranda	ACT Government	2
Banks	ACT Government	3
Belconnen	ACT Government	2
Braddon	ACT Government	3
Calwell	ACT Government	2
Campbell	ACT Government	3
Chapman	ACT Government	2
Chifley	ACT Government	2
Conder	ACT Government	2
Cook	ACT Government	2
Curtin	ACT Government	1
Deakin	ACT Government	3
Dickson	ACT Government	3
Downer	ACT Government	1
Duffy	ACT Government	1
Dunlop	ACT Government	3
Florey	ACT Government	1
Forrest	ACT Government	2
Fraser	ACT Government	2
Garran	ACT Government	2
Gordon	ACT Government	3
Kingston	ACT Government	10
Lyneham	ACT Government	3
Watson	ACT Government	4
Yarralumla	ACT Government	4
Alfords Point	Sutherland Shire Council	2
Asquith	Hornsby Shire Council	2
Balgowlah Heights	Northern Beaches Council	2
Balgowlah	Northern Beaches Council	3
Bangor	Sutherland Shire Council	1
Barden Ridge	Sutherland Shire Council	2
Baulkham Hills	The Hills Shire Council	3
Bayview	Northern Beaches Council	2
Beaumont Hills	The Hills Shire Council	1
Beecroft	Hornsby Shire Council	3
Belrose	Northern Beaches Council	1
Berowra Heights	Hornsby Shire Council	3
Berowra	Hornsby Shire Council	3
Beverly Hills	Georges River Council	1
Bexley	Bayside Council	2
Bilgola Plateau	Northern Beaches Council	1
Bondi Beach	Waverley Council	6
Bonnet Bay	Sutherland Shire Council	1
Burraneer	Sutherland Shire Council	2
Carlingford	City of Parramatta Council	1
Carlton	Georges River Council	1
Castle Hill	The Hills Shire Council	4
Chatswood	Willoughby Council	4
Cherrybrook	Hornsby Shire Council	4
Cremorne	North Sydney Council	3
Cronulla	Sutherland Shire Council	2
Dee Why	Northern Beaches Council	3
Double Bay	Woollahra Council	3
Dover Heights	Waverley Council	4
Engadine	Sutherland Shire Council	2
Epping	City of Parramatta Council	3
Figtree	Wollongong City Council	4
Gordon	Ku-ring-gai Council	2
Grays Point	Sutherland Shire Council	1
Heathcote	Sutherland Shire Council	2
Hunters Hill	Hunters Hill Council	3
Hurstville	Georges River Council	2
Illawong	Sutherland Shire Council	2
Jerrabomberra	Queanbeyan-palerang Regional Council	1
Killara	Ku-ring-gai Council	2
Kirrawee	Sutherland Shire Council	2
Kogarah	Georges River Council	2
Lindfield	Ku-ring-gai Council	2
Little Bay	Randwick Council	4
Loftus	Sutherland Shire Council	2
Manly	Northern Beaches Council	4
Marsfield	Ryde Council	1
Menai	Sutherland Shire Council	1
Merewether	City of Newcastle	4
Miranda	Sutherland Shire Council	2
Mona Vale	Northern Beaches Council	2
Monterey	Bayside Council	1
Mosman	Mosman Council	3
Neutral Bay	North Sydney Council	3
Newcastle	City of Newcastle	4
North Bondi	Waverley Council	5
Pennant Hills	Hornsby Shire Council	4
Penshurst	Georges River Council	2
Pymble	Ku-ring-gai Council	2
Randwick	Randwick Council	3
Roseville	Ku-ring-gai Council	2
Sans Souci	Bayside Council	1
Seaforth	Northern Beaches Council	4
St Ives Chase	Ku-ring-gai Council	0
St Ives	Ku-ring-gai Council	2
Sutherland	Sutherland Shire Council	2
Sylvania Waters	Sutherland Shire Council	2
Taren Point	Sutherland Shire Council	2
Turramurra	Ku-ring-gai Council	2
Vaucluse	Woollahra Council	5
Wahroonga	Ku-ring-gai Council	4
West Pennant Hills	The Hills Shire Council	4
Wollongong	Wollongong City Council	4
Woollahra	Woollahra Council	2
Woolwich	Hunters Hill Council	3
Woronora Heights	Sutherland Shire Council	1
Woronora	Sutherland Shire Council	2
Yarrawarrah	Sutherland Shire Council	0
Acacia Ridge	Brisbane City Council	9
Advancetown	City of Gold Coast	5
Albany Creek	City of Moreton Bay	3
Alderley	Brisbane City Council	7
Annerley	Brisbane City Council	8
Anstead	Brisbane City Council	9
Ascot	Brisbane City Council	7
Ashgrove	Brisbane City Council	9
Ashmore	City of Gold Coast	5
Aspley	Brisbane City Council	7
Auchenflower	Brisbane City Council	7
Bald Hills	Brisbane City Council	10
Balmoral	Brisbane City Council	8
Bardon	Brisbane City Council	8
Bellbowrie	Brisbane City Council	9
Belmont	Brisbane City Council	7
Benowa	City of Gold Coast	5
Bethania	Logan City Council	12
Bilinga	City of Gold Coast	6
Bonogin	City of Gold Coast	4
Boronia Heights	Logan City Council	6
Bracken Ridge	Brisbane City Council	9
Bridgeman Downs	Brisbane City Council	8
Broadbeach Waters	City of Gold Coast	5
Broadbeach	City of Gold Coast	5
Brookfield	Brisbane City Council	9
Bulimba	Brisbane City Council	7
Carindale	Brisbane City Council	9
Clayfield	Brisbane City Council	9
Hamilton	Brisbane City Council	10
Hendra	Brisbane City Council	8
Indooroopilly	Brisbane City Council	10
Kenmore	Brisbane City Council	9
Mount Gravatt	Brisbane City Council	6
Nerang	City of Gold Coast	8
Paddington	Brisbane City Council	7
Rangeville	Toowoomba Regional Council	2
Sunnybank	Brisbane City Council	7
The Gap	Brisbane City Council	7
Athelstone	Campbelltown City Council	7
Beaumont	City of Burnside	6
Black Forest	City of Unley	5
Brighton	City of Holdfast Bay	7
Burnside	City of Burnside	6
Clarence Park	City of Unley	5
Colonel Light Gardens	City of Mitcham	4
Dulwich	City of Burnside	3
Erindale	City of Burnside	3
Felixstow	The City of Norwood Payneham and St Peters	5
Findon	City of Charles Sturt	4
Fulham	City of West Torrens	4
Gilberton	The Corporation of the Town of Walkerville	6
Glen Osmond	City of Burnside	6
Glenelg East	City of Holdfast Bay	6
Glenelg North	City of Holdfast Bay	7
Glenelg South	City of Holdfast Bay	7
Glenelg	City of Holdfast Bay	8
Grange	City of Charles Sturt	6
Hazelwood Park	City of Burnside	4
Henley Beach	City of Charles Sturt	6
Hove	City of Holdfast Bay	7
Hyde Park	City of Unley	4
Kensington Gardens	City of Burnside	6
Kensington	The City of Norwood Payneham and St Peters	6
Kingston Park	City of Holdfast Bay	7
Leabrook	City of Burnside	6
Magill	Campbelltown City Council	7
Malvern	City of Unley	4
Marino	City of Marion	5
Medindie	The Corporation of the Town of Walkerville	5
Mile End	City of West Torrens	6
North Adelaide	City of Adelaide	7
North Brighton	City of Holdfast Bay	6
Norwood	The City of Norwood Payneham and St Peters	7
Prospect	City of Prospect	7
Rose Park	City of Burnside	7
Rostrevor	Campbelltown City Council	6
Seacliff	City of Holdfast Bay	7
Semaphore	City of Port Adelaide Enfield	6
Somerton Park	City of Holdfast Bay	7
Tennyson	City of Charles Sturt	4
Toorak Gardens	City of Burnside	6
Unley Park	City of Unley	7
Unley	City of Unley	6
Walkerville	The Corporation of the Town of Walkerville	6
Wattle Park	City of Burnside	6
Invermay	Launceston	11
Lenah Valley	Hobart	8
New Town	Hobart	9
Sandy Bay	Hobart	8
Armadale	Stonnington	9
Ashburton	City of Boroondara	12
Ashwood	Monash	11
Aspendale	Kingston (Vic.)	6
Balwyn North	City of Boroondara	10
Balwyn	City of Boroondara	7
Beaumaris	Bayside City Council	9
Bentleigh East	Glen Eira	7
Bentleigh	Glen Eira	10
Black Rock	Bayside City Council	9
Blackburn North	Whitehorse	9
Blackburn South	Whitehorse	9
Blackburn	Whitehorse	13
Bonbeach	Kingston (Vic.)	8
Box Hill North	Whitehorse	10
Box Hill South	Whitehorse	11
Box Hill	Whitehorse	11
Brighton East	Bayside City Council	9
Brighton	Bayside City Council	10
Camberwell	City of Boroondara	10
Canterbury	City of Boroondara	6
Glen Iris	City of Boroondara	12
Hampton	Bayside City Council	8
Hawthorn	City of Boroondara	10
Kew East	City of Boroondara	11
Kew	City of Boroondara	11
Malvern East	Stonnington	12
Newtown	City of Greater Geelong	9
Sandringham	Bayside City Council	10
South Yarra	Stonnington	11
Surrey Hills	City of Boroondara	9
Alfred Cove	City of Melville	0
Applecross	City of Melville	0
Ardross	City of Melville	0
Attadale	City of Melville	0
Bayswater	City of Bayswater	4
Bentley	City of Canning	1
Bicton	City of Melville	1
Booragoon	City of Melville	0
Brentwood	City of Melville	0
Canning Vale	City of Gosnells	3
Carine	City of Stirling	2
Carlisle	Town of Victoria Park	0
Churchlands	City of Stirling	2
City Beach	Town of Cambridge	3
Claremont	Town of Claremont	2
Dalkeith	City of Nedlands	0
Dianella	City of Stirling	3
Doubleview	City of Stirling	2
East Fremantle	Town of East Fremantle	2
Floreat	Town of Cambridge	3
Fremantle	City of Fremantle	4
Innaloo	City of Stirling	4
Jolimont	City of Subiaco	1
Leederville	City of Vincent	5
Manning	City of South Perth	0
Maylands	City of Bayswater	4
Mosman Park	Town of Mosman Park	2
Mount Hawthorn	City of Vincent	4
Mount Lawley	City of Stirling	9
Mount Tarcoola	City of Greater Geraldton	0
Nedlands	City of Nedlands	5
North Fremantle	City of Fremantle	3
Peppermint Grove	Shire of Peppermint Grove	1
Shenton Park	City of Subiaco	4
South Perth	City of South Perth	1
Subiaco	City of Subiaco	2
Thornlie	City of Gosnells	0
Tuart Hill	City of Stirling	2
Victoria Park	Town of Victoria Park	2
Watermans Bay	City of Stirling	1
Wembley	Town of Cambridge	3
West Leederville	Town of Cambridge	7

Suburb-level, read from state planning data. Not a report on any individual block.

What to ask a builder about an extension

Specific to this kind of job. The general list is in questions to ask a builder.

How will you tie the new structure into the existing footings and roof?
What have you found behind walls on houses of this era?
Can we live here during the works, and what is realistically liveable?
How is the existing house protected and made weathertight during the works?
What is your process when the scope changes after opening up?

Questions people ask

Extend or knock down and rebuild?

It turns on the condition and layout of the existing house, and on whether heritage controls permit demolition at all. Anyone who answers without seeing the building is guessing.

Can I add a second storey to any house?

No. It depends on the footings, the frame and the planning controls. Get a structural assessment before you get attached to the idea.

Why are extension quotes so different from each other?

Usually because they assume different things about the existing structure. Compare the provisional sums, not the headline number.

The mechanism

One recommendation, not six quotes

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