How Much Does a Second Storey Addition Cost in Sydney?

A second storey price on its own tells you about as much as a car price that doesn’t say whether the wheels are included. This guide is for families who’ve outgrown the house but want to stay on the street. It covers what a package price includes, what gets priced separately and why, where the $30,000 of preliminaries goes, and how going up compares with moving. I started on the tools as a carpenter, so the structural parts get the most attention.

Second storey addition prices in Sydney at a glance

Package prices are “from” prices, GST inclusive, and cover the new upper floor. Work on the ground floor, like a new kitchen or a reshuffled layout, is priced on top. Early projects also get acoustic insulation in the new floor at no charge, which matters more than people expect the first time someone walks across the room above the TV.

If you’ve seen cheaper figures online, check the date. NSW house construction costs rose 4.8% in the year to June 2026, according to the ABS Producer Price Index. A price from a 2023 article is about as current as a 2023 bus timetable.

What a second storey package includes

Every package covers the full shell and fit-out of the new level:

• Acoustic insulation between the new floor joists, under yellow tongue flooring
• Structural timber framing to the engineer’s details, plus wall and roof framing
• Roofing, external cladding, aluminium windows, insulation and plasterboard
• Internal doors, hardware, skirting, architraves and a standard staircase allowance
• Electrical allowance, LED downlights and smoke alarms
• The bathroom allowance where the package has one, and painting of the new areas
• Builder supervision and construction management

How we build that shell is on our How We Build page, including the acoustic insulation between floors and the tensioned X bracing on every wall.

What the price leaves out, and why we say so upfront

These are quoted separately because nobody can price them properly until an engineer has looked at your house:

• Structural steel (unless listed), footing, pier or foundation upgrades, and extra bracing to the existing house
• Ground floor renovations, layout changes, new downstairs kitchens, bathrooms or laundries
• Repairs to existing termite damage, rot, water damage or defects
• Electrical mains, switchboard, stormwater and air conditioning upgrades
• Design, engineering, BASIX and council approvals, plus site set-up (the preliminaries below)
• Rock excavation or unforeseen ground conditions
• Premium windows, cladding or staircases

We’d rather have this conversation at your kitchen table than in week nine, in your driveway, holding a piece of rotten bearer.

Preliminaries: the $30,000 before the first nail

Preliminaries usually land around $30,000 on a second storey. They pay for two things: the design and approvals that have to happen before a builder can legally start, and setting up the site.

• Architectural or design drawings
• A structural engineer’s assessment and design
• A site survey, and a geotechnical report if the engineer wants one
• The BASIX certificate for energy and water
• Council DA and Construction Certificate fees, or a private certifier’s CDC fees
• Government levies on the building work
• Site set-up: fencing, temporary services, waste removal, insurances and supervision

A straightforward CDC sits at the lower end. A heritage area, a contested DA or a design that goes through three rounds of changes sits higher. Which pathway you’re on makes the biggest difference.

Why going up costs more per square metre than going out

Building up costs $3,500 to $5,500 per m². Extending out at ground level costs $2,500 to $4,500 per m². The gap comes from work a ground floor extension doesn’t need:

• The roof comes off. Your existing roof is stripped, and a new one goes on top of the new level.
• Scaffolding stays up for weeks. Every frame, sheet and tile goes up by hand or by crane.
• The house underneath has to carry it. A second floor roughly doubles the load on the existing structure, so footings and walls get checked and sometimes strengthened.
• The stairs take room downstairs. A staircase needs floor space on the ground floor, usually from a bedroom, hallway or living area.
• The house stays weatherproof during the build. Temporary protection while the roof is open is part of the job.

In short, gravity charges by the kilo. If your yard has the room, a ground floor extension is often cheaper per m². Our older post on whether to extend out or go up covers the trade-offs beyond price.

Seven things that move your second storey price

1. What’s underneath. The engineer checks your footings, walls and timber before we fix a price. Roughly one house in six can’t take a second storey without significant extra spending.
2. The shape of the house and roof. A simple rectangle with a gable roof is the cheapest box to build on. An L-shaped house with a hipped roof and three different ceiling heights is not.
3. Bathrooms. Every wet area upstairs adds plumbing, waterproofing and tiling. Two bathrooms is the main reason Complete costs more than Family.
4. Where the stairs land. A stair that drops into an existing hallway is cheap. One that means moving a downstairs bedroom is a ground floor renovation as well.
5. Site access. Narrow side access, a steep block or power lines over the front yard all add time, labour or a crane.
6. Council controls. Height limits, setbacks and your neighbours’ winter sunlight shape ceiling heights and roof form. Heritage streets add design work. A Strathfield heritage street and a Baulkham Hills cul-de-sac will not get the same drawings.
7. Finishes and upgrades. Double glazed or thermally broken windows, a Hebel or Nexcore floor where the structure can take the weight, plywood bracing or a third bathroom all move the number up.

What cheap second storey quotes leave out

The cheapest quote you get is usually the one where nobody has looked under your house yet. With roughly one home in six needing significant extra work before it can carry a second level, a price given before the engineer’s visit is a guess with a letterhead.

When you compare quotes, check each one for:

• Preliminaries: are design, engineering, approvals and site set-up in or out?
• Structural work: is footing or wall strengthening priced, allowed for, or ignored?
• Provisional sums: are the allowances for unknowns realistic, or set low to make the total look good?
• The staircase and ground floor works: who’s paying for the hole in your ceiling?
• The contract: ours is a fixed price (lump sum) building contract. Ask what yours is, and what could still change the price.

The NSW Government’s guide to preparing to build or renovate, covering quotes, contracts, insurance and licence checks, is worth ten minutes before you sign anything.

What goes into every second storey we build

Our line is Built Once. Built Right. On a second storey, that shows up in the parts you never see once the plasterboard goes on:

• Tensioned X bracing through the floor, walls and ceilings, so the whole house is braced as one
• Hand-cut roofs rather than trusses, which also leave open roof space for services
• Double headers over openings, and floors glued and screwed down
• Four-coat waterproofing in every upstairs bathroom
• Breathable wall wrap, and frames left to dry before they’re sheeted
• A structural engineer inspecting the frame, on top of the certifier
• A photo record of everything before it’s covered, handed over at the end

A good plasterer can hide a lot. A sagging header over a bedroom door is not one of those things, at least not for long.

Some upgrades are worth paying for when the budget allows. Our top pick is piers taken down to shale or rock under any new footings. It costs more in digging, concrete and steel, and it’s the one part of the house you can never get back to once it’s built on. The full list, with what’s standard and what’s an upgrade, is on our How We Build page.

That’s why our price can sit above the cheapest quote on the table. You pay once for a second storey that is still flat, quiet and dry in year ten.

Second storey or move house?

For a family that needs two more bedrooms, moving often costs more than building, before you pay a cent extra for the bigger house. Here’s the maths on selling a $1.5 million house and buying a $2 million one, against adding a Family package second storey.

The selling and buying costs alone come to roughly $118,000 to $133,000. None of that buys a bedroom, and you still have to pack the garage.

Stamp duty is from the Revenue NSW general rates for 2026/27, with no concessions applied. Commission ranges are published Sydney averages, so ask your local agent for theirs.

The one thing to check first is your street. Sydney house values fell 8.2% in the year to September 2026, to a median of $1,466,060 (Cotality Home Value Index). If you’d be spending $350,000 to build the biggest house on a street of small ones, talk to a local agent about what the street will bear before you talk to us.

What NSW rules say about paying for a second storey

These apply to every licensed builder in NSW, and they’re worth knowing before you sign:

• Deposit: the most a builder can ask for is 10% of the contract price.
• Home Building Compensation cover: required for any job over $20,000. The builder must take it out, and give you the certificate, before asking for a deposit.
• Progress payments: must match work done, not time on the job.
• Cooling-off: five clear business days for contracts over $20,000.

The NSW Government’s page on home building contracts sets out the full rules. All our prices include GST, which plenty of online cost guides don’t mention.

How to get an accurate price for your house

1. Tell us about the house. Fill in the consultation questionnaire. It asks a lot, on purpose, so the first call is useful.
2. We call and walk the house. A builder calls within 24 to 48 business hours and comes out to look.
3. You get a written estimate. If you already have plans, we can usually quote within a few days. If you don’t, we start with a preliminary design and an engineer’s look at the structure, so the estimate is based on your house and not a brochure.
4. The price locks in the contract. Anything that can’t be priced until walls open is listed as a provisional sum with a stated allowance.

Where you live moves the price too. On wider, deeper blocks like those in Carlingford, driveways and side access make crane and scaffold work simpler, and that flows straight through to cost. On narrow inner west lots like Ashfield, many houses were built for one floor and need more structural work first. Packages, process and service areas are all on our second storey additions Sydney page.

When a second storey is the wrong move

We’d rather tell you now than halfway through:

• Your all-in budget is under about $300,000. Package plus preliminaries starts there. Below it, a ground floor extension or a renovation will give you more house for the money.
• You’re selling in the next couple of years. You carry the build cost and the disruption, and the next owner gets the view.
• The engineer finds big structural work and you have a backyard. Going out may cost less than strengthening the house to go up.
• You need it finished by Christmas and it’s already August. Design and approval come before construction, and 12 to 24 weeks on site comes after that.

Before your second storey consultation: checklist

• A rough idea of what you want upstairs: bedrooms, bathrooms, living
• Any existing plans or a survey of the house
• Whether the house is in a heritage conservation area (your council or the NSW Planning Portal will tell you)
• Known issues: cracks, termite history, past additions
• Access notes: driveway width, overhead power lines, slope
• Whether you want ground floor changes at the same time, so you pay preliminaries once
• Your budget range, including preliminaries
• Your questions about what’s quoted separately for your house

Second storey cost FAQs

Want a real number for your house? Request a consultation or call Stav on 0450 605 080, Monday to Friday, 7am to 5pm.

Sources and references

• Revenue NSW: Calculate transfer duty
• Australian Bureau of Statistics: Producer Price Indexes, Australia
• Cotality: Home Value Index, October 2026
• NSW Government: Home building contracts
• Strava Group: How we build a second storey and acoustic insulation between floors