Second Storey Addition in Sydney: Design, Approval and What Affects the Cost

A second storey addition in Sydney is a design and approvals project before it is a building project. The cost is shaped by decisions made on paper: whether the existing house can carry the load, where the stair goes, which approval pathway applies and how complete the drawings are when builders price them. This guide walks through each of those in the order you will meet them.

Is your house suited to a second storey addition?

Three checks come first, and none of them needs a builder yet.

Structure. A structural engineer needs to confirm what the existing footings and walls can carry. Full brick houses on good footings often take an upper level well. Brick veneer and timber-framed cottages can too, usually with new posts or beams threaded through the ground floor.

Planning controls. Your council's local environmental plan sets a maximum building height and, in many areas, a floor space ratio. Those two numbers decide how much upper floor is possible.

The site. Heritage conservation areas, bushfire prone land and neighbours close to the boundary all change what will be approved.

A Section 10.7 planning certificate from council lists most of the constraints that apply to your land.

What a second storey addition involves on the design side

The upper floor is the easy part. The ground floor is where the design is won or lost.

The stair takes real space, commonly the footprint of a small room, and it lands in the middle of the existing plan. Put it in the wrong place and you lose a bedroom downstairs to gain two upstairs. A good design uses the stair to reorganise the ground floor at the same time.

The other design problems are consistent across Sydney:

• overlooking into neighbours' yards and windows
• overshadowing of adjoining properties
• how the new level sits against the street, especially on a single storey streetscape
• matching or deliberately contrasting the existing roof form
• getting services, plumbing stacks and ducting down through the old house

DA or CDC: which approval pathway applies

There are two routes in NSW. A complying development certificate, or CDC, is a fast-track approval issued by council or a registered certifier when the design meets every numeric standard in the State's housing code. A development application, or DA, is assessed by council on merit.

A CDC is quicker, and it is rigid. If the design misses one standard, it is not available. Sites in heritage conservation areas generally cannot use it for this kind of work, and nor can land with the highest bushfire ratings.

A DA takes longer and allows more. Council can approve a design that varies a control if the outcome is reasonable. The NSW Planning Portal explains both pathways, and all applications are lodged through it. Choosing the pathway is one of the first things we settle, because it changes how the DA and CDC documentation is prepared.

What affects the cost of a second storey addition

We do not publish build prices, because a figure without a design is a guess. What moves the cost is predictable:

1. Structural work to the existing house. New footings, steel and posts through the ground floor.
2. Roof removal and weather protection. The house is open to the sky for a period and has to be covered.
3. Size and complexity of the upper floor. Bathrooms cost far more per square metre than bedrooms.
4. Ground floor changes. The stair, plus whatever you renovate while the house is disrupted.
5. Site access. Narrow streets and tight side setbacks slow everything down.
6. Bushfire, heritage or acoustic requirements. Each adds specified materials.
7. Whether you live in. Staging work around an occupied house takes longer.
8. Quality of the drawings. Vague documents produce allowances and variations.

Design and approval fees are separate from the build and far smaller. They are also where the build cost is controlled.

Why going up is not always cheaper than going out

This is the caveat people do not expect from a firm that designs upper floor additions. Building up is often promoted as the economical way to add space. It frequently is not. Strengthening an old structure, removing a roof and working at height can cost more per square metre than a ground floor extension.

Going up makes sense when the block is small, when you want to keep the garden, or when a view or outlook justifies it. If you have yard to spare and no strong reason to keep it, a rear extension is usually simpler. We will tell you which one your site favours.

Who does what: architect, engineer, certifier and builder

A common point of confusion, so to be clear: LCG Architects designs, documents and obtains approvals. We do not build. The team on a typical project looks like this:

• Architect: design, planning advice, approval drawings and construction drawings.
• Surveyor: a detail and level survey of the existing house and site.
• Structural engineer: assessment of the existing structure and design of the new.
• Certifier: issues the CDC or, after a DA, the construction certificate, and inspects during the build.
• Builder: prices from the drawings and constructs.

Keeping those consultants working from one coordinated set of information is part of the additions and alterations service.

How long the design and approval stage takes

Expect months, not weeks. Measured survey, concept design, engineering input and documentation come first. A CDC can then be issued in a matter of weeks once the application is complete. A DA commonly takes several months, depending on the council and whether neighbours object.

The fastest projects are the ones where the brief is settled early. Changing the design after lodgement is what costs time.

What to do before your first meeting

Free, and useful to any designer you speak to:

• order the Section 10.7 certificate from your council
• find any old plans of the house
• write a list of rooms you need, in priority order
• photograph the house from the street and from the rear
• decide whether you can move out during construction

Next step

Send us your address and a short note on what you need through our building design and drafting page. We will check the controls on your site and tell you whether going up is the right answer.