Most North Shore extensions need either a complying development certificate (CDC) or a development application (DA). Complying development isn't available in heritage conservation areas, on listed heritage items or on bushfire land rated BAL-40 or BAL-FZ, so a DA through your council is the usual path for much of the North Shore.
What kind of extension suits North Shore homes?
On the lower North Shore, narrow Federation and interwar lots in Mosman, Neutral Bay, Naremburn and Willoughby leave little room to build out. Owners often add a rear pavilion, an attic or a first floor set back from the street. On the upper North Shore, big blocks in St Ives, Pymble, Wahroonga and Turramurra leave room to extend at ground level, often with a new family room and kitchen at the back.
Much of the region sits on sandstone ridges, and many blocks fall steeply to creeks and bushland. Excavation, retaining walls and stormwater are common cost drivers.
| Situation | Usual path | What to know |
|---|---|---|
| Ordinary lot, design meets the Housing Code | CDC may be possible | Faster, but the design must meet every standard |
| Heritage conservation area | DA | Council looks closely at anything visible from the street |
| Listed heritage item | DA | A heritage impact statement is usually needed |
| Bush fire prone land up to BAL-29 | CDC may still be possible | Construction must meet the BAL |
| Bush fire prone land, BAL-40 or BAL-FZ | DA | Stricter construction; the Rural Fire Service may be involved |
| Harbour or river foreshore lot | Often a DA | Foreshore building lines and scenic controls can apply |
A simplified guide. Check your Section 10.7 planning certificate and the NSW Planning Portal for your lot.
Which council and controls apply?
Six councils cover the North Shore: North Sydney, Willoughby, Lane Cove, Mosman, Ku-ring-gai and Hornsby Shire. Each has its own LEP and development control plan, so setbacks, height and landscaping rules differ from one side of a boundary to the other.
Heritage is the big one. Large parts of Ku-ring-gai, Mosman, North Sydney and Willoughby are heritage conservation areas, and Ku-ring-gai added more in Pymble, Turramurra and Wahroonga in 2019. In these areas, councils generally want additions at the rear, kept below and behind the main roof, with materials that respect the original house.
Mosman, North Sydney and Lane Cove have harbour and river foreshore controls, and the bushland edges of Ku-ring-gai and Hornsby are mapped as bush fire prone land.
What site issues shape a North Shore extension?
- Trees. Ku-ring-gai and Hornsby are known for their tree canopy, and councils protect many trees. You usually need council approval to remove or prune protected trees, and an arborist report often goes with the DA.
- Sewer and stormwater pipes. On sloping blocks, Sydney Water sewer mains often run through back yards. Building over or near them needs Sydney Water approval, so check early.
- Rock and slope. Excavating sandstone needs the right equipment and a plan for neighbours' footings.
- BASIX. In NSW, alterations and additions worth $50,000 or more need a BASIX certificate for energy and water performance.
Don't remove or prune a large tree to make room for an extension until you've checked your council's tree rules. Ku-ring-gai and Hornsby both have tree controls, and the tree's location can shape the whole design.
What should you tell the crew?
Describe the house, roughly when it was built, and whether it is in a heritage conservation area, a heritage item or on bush fire prone land. Say what you want to add, and whether you have plans, approval or just an idea. Mention slope, big trees, rock, a narrow side passage and street parking, because they affect access and cost.
Costs vary widely, so we don't publish North Shore prices. Our Sydney home extension cost guide explains the cost drivers, our guide to planning a home extension covers the early steps, and the home extensions page covers licences and insurance. See also trades on the North Shore. When you're ready, describe the job to MyTradeCrew and we'll send it to up to three vetted local trades from our crew, who quote you directly.
Common questions
Can I use complying development for an extension in Ku-ring-gai?
Sometimes. A CDC may be possible if your lot isn't in a heritage conservation area or a heritage item, isn't rated BAL-40 or BAL-FZ for bushfire, and the design meets every Housing Code standard. Much of Ku-ring-gai is in conservation areas, though, so many extensions there need a development application. Check your Section 10.7 certificate first.
Do I need a BASIX certificate for my extension?
In NSW, alterations and additions valued at $50,000 or more need a BASIX certificate, which sets energy and water targets for the work. Your designer or a BASIX assessor prepares it online, and it goes in with your CDC or DA. The commitments, such as insulation and glazing, then become part of what the builder must deliver.
Can I remove a tree to fit my extension?
Not without checking first. North Shore councils protect many trees, and removing or pruning one usually needs council approval, either through a tree permit or as part of your DA. Expect an arborist report if trees are near the work. Designing around a significant tree is often quicker than trying to get it removed.
Should I build up or out on the North Shore?
It depends on your block and the controls. Narrow lower North Shore lots often push you up or into the roof, while big upper North Shore blocks suit ground-floor additions. Heritage controls usually favour rear additions that stay below the main roof. A designer can test both options against your council's height, setback and landscaping rules.
More on home extensions
Scope checklists, price drivers and quote comparisons are on the main Home extensions in Sydney page. For costs, read Home Extension Cost Sydney: Ground Floor vs Second Storey.