Key Interiors · Est. Auckland
Home Extension in Auckland
Designed & Built for Your Home
Key Interiors designs and builds home extensions across Auckland — extra living, a second storey or indoor-outdoor flow, matched seamlessly to your existing home, with a fixed price after design.
Moving house in Auckland is brutal — agents, lawyers, LIM reports, a stressful market and a small fortune in fees, all to leave the location you actually love. An extension lets you stay exactly where you are and finally get the space your family has grown into.
Key Interiors is a true design-and-build studio. We design and build your addition under one roof — feasibility, consent, foundations, structure, services and finishes — and tie it into your existing home so cleanly it looks original. One project manager, one fixed price after design, no gaps between designer and builder.
What's involved
A successful home extension involves much more than adding extra floor space. From initial feasibility and architectural design through to building consent, structural work, services and final finishes, every stage needs to work with your existing home. Our design-and-build approach brings these elements together under one team.
We test what your site and budget allow — sun, outlook, boundaries and how the new space should flow from the old.
Site coverage, recession planes, heritage overlays and building consent — managed for you, from documentation to sign-off.
New footings and framing engineered to carry the addition and tie cleanly into the existing structure.
Matching the roof and cladding and getting the junctions watertight — the make-or-break detail of any extension.
Power, plumbing, heating and lighting run into the new space and balanced across the whole home.
Weatherboards, windows, floors and paint matched so the addition reads as part of the original home, not bolted on.
The cost of a home extension depends on the size and complexity of the project, site conditions, structural requirements, materials and finishes, and whether a building or resource consent is required. Second-storey additions can also cost more because the existing structure may need reinforcement.
Open up and extend out — a bigger kitchen, a family living space and a home that finally breathes.
Add up where you can't add out — new bedrooms, a master suite or a whole upper floor, on your existing footprint.
Decks, alfresco rooms and sleepouts that extend your living straight out into the garden.
Before
After
Structural extension & opening-up, Auckland. Drag the handle to reveal the transformation.
A roofline that lines up. Weatherboards that match. A floor that runs straight through from old to new with no awkward step. Done well, an addition doesn't look added — it looks like the home was always meant to be this size. That seamless join is the hardest part, and it's exactly where we obsess.
Choosing one team to manage your home extension from design through construction can simplify the entire renovation process. Key Interiors coordinates feasibility, design, engineering, consent, construction, and finishing under one roof, giving you a single point of contact throughout the project. Our fixed-price approach after design also provides greater clarity around your final build cost.
Instead of hiring an architect who may design beyond your construction budget, and then tendering to builders who weren't involved in the planning, Key Interiors houses designers, structural engineers, and master builders together. Every design decision is vetted for real-world buildability, Auckland site terrain, and cost efficiency from day one.
You will never have to juggle multiple sub-contractors, chase down electricians, or referee conflicts between trades. Your dedicated project manager is on site every day, provides proactive weekly milestones and photo updates, coordinates all council inspections, and serves as your single accountable voice throughout.
Uncapped budgets and unexpected variation clauses are the biggest source of stress during home extensions. Once your architectural plans, engineering calculations, and interior fixtures are signed off, we provide a binding, transparent fixed-price contract before breaking ground. You know the exact cost before a hammer is lifted.
Navigating the Auckland Unitary Plan, zoning rules (Single House vs Mixed Housing), boundary recession planes, site coverage, stormwater, and geotechnical overlays can cause months of delays. We prepare and submit all Resource Consent and Building Consent documentation directly to Auckland Council and manage every RFI to sign-off.
A well-executed extension should look like it was always meant to be there. Whether extending a classic transitional villa in Ponsonby, a 1930s bungalow in Mount Eden, or a mid-century home in Westmere, our craftspeople match existing rooflines, floor levels, exterior claddings, and interior millwork with surgical accuracy.
From the initial feasibility study and topographical survey through foundation excavation, structural framing, weathertight envelope, bespoke joinery, painting, and the final Auckland Council Code Compliance Certificate (CCC), our team takes complete responsibility for the entire journey. You get total peace of mind from start to finish.
We visit, check what your site and budget allow, and map an honest scope, design direction and budget range.
Free · No obligationConcept, detailed 3D visuals, engineering and consent in our paid design phase — then a clear, fixed-price proposal.
Foundations, structure, roof, services and fit-out — staged to minimise disruption and finished in-house.
The new and old joined seamlessly, every detail checked, and the keys to the extra space you've been needing.
Every extension is different — but here's an honest 2026 starting guide for what Auckland homeowners are actually spending.
A single-room ground-floor extension or enclosing existing covered space — extra room without major upheaval.
A family-sized open-plan living and kitchen extension, tied into the home and opened out to the garden.
A second-storey addition or large extension — new bedrooms, a master suite or a whole upper floor.
As a guide, Auckland extensions run about $3,500–$8,000 per m², with second storeys 10–20% higher once structural reinforcement is factored in. Design and consent add roughly 8–12% of the build. After your design phase, you get a fixed price — so the number you sign off is the number you pay.
Book a free, no-obligation Extension Roadmap. We come to your home, check what your site and budget allow, and give you a design direction, honest scope and budget range — so you know whether to extend, and exactly how, before you commit.
Once you sign off your design, your build price doesn't move — we wear the difference, not you. Every addition is delivered by one accountable team, matched and finished to our master standard, and if a detail isn't right at handover, we make it right. That's the deal.
We deliberately take on only a handful of projects at a time so yours gets our full attention — Auckland calendars book out months ahead.
Book your free Extension Roadmap →No cost. No obligation. Just a clear next step.
"Key Interiors were fantastic to work with — very professional and over-delivered on their service. They made our dream our reality."
"Max has a keen eye for design and is detail orientated. He really listens to your brief and comes back with a beautifully considered design that goes beyond what you asked for. High quality and well priced."
"What a great experience. It felt like the whole team cared about our project and we are so impressed with their exceptional attention to detail."
"Loved the outcome. They helped us add the space we needed while staying in budget. Loved the process — totally recommend."
"Your go-to for kitchen, bathroom and laundry projects. Would highly recommend Max and Suzanne."
"They came up with great suggestions for our project. A great team to work with — really impressed."
Tell us a little about your home and the space you need. We'll be in touch to book your free, no-obligation consult.
Most Auckland home extensions cost between $3,500 and $8,000 per square metre. As a guide, a single-room ground-floor extension typically runs from around $90,000, a mid-range open-plan living extension $135,000 to $280,000, and a second-storey addition from $220,000 up to $450,000 or more. Enclosing existing covered space like a deck is cheaper. After your design phase, we give you a fixed price — so you know exactly what you're investing before the build begins.
Most extensions take around 3 to 5 months on site, depending on size, whether it's single or double storey, and how it ties into the existing home. Design and consent add time before that, so the full journey is usually 9 to 12 months. Your dedicated project manager gives you a clear programme before the build starts.
Almost always, yes. Extensions add floor area and structure, so they need building consent, and in some cases resource consent for things like site coverage, recession planes or heritage overlays. We manage the design, documentation and consent process for you, from application to sign-off.
Often, yes — because an extension is added alongside the existing home, much of the work happens before it's connected, so many families stay put through most of the build. There's usually a shorter disruptive period when the new and old are joined. We'll plan the staging with you in your Extension Roadmap.
That's the whole point. We design the addition to read as part of the original home — matching rooflines, weatherboards, window proportions and finishes — so it looks like it was always there, not bolted on. For villas and bungalows we take particular care to respect the character.
We design and build home extensions right across Auckland — from the central villas of Point Chevalier, Mt Albert, Grey Lynn and Ponsonby to the eastern suburbs, North Shore and the wider region.
Auckland families trust Key Interiors to design and build extensions done right — one team, one fixed price, matched seamlessly to your home. Start with a free Extension Roadmap.
Book your free consultation →
