Cost of Adding a Second Storey Extension



Building a second story extension is exciting. You have the opportunity to renovate the home you love into a larger one that better suits your family needs.

– Jan Antoni Glinkowski • Director • Style Plus Renovations

Adding on to the available space that you have is often a better option than selling your house and finding a larger one. For a number of homeowners moving is not the best option.

The team at Style Plus Renovations North Shore Auckland take a look at the ins and outs and cost of adding a second storey extension to your home:

cost of adding a second storey extension


A commonly asked question by our clients is will one bedroom and ensuite bathroom cost less than three bedrooms and two bathrooms? The answer is yes it will. 

However, the additional cost to add those two extra bedrooms and one bathroom whilst you are building will be less than tackling them at a later date. This is the point where more thought is required at the planning stage.

Adding a second storey is going to be more costly than extending outwards at ground level. Whether you are adding one ensuite or three bedrooms and two bathrooms, there is still the same associated costs. For example:

  • Structural
  • Roofing
  • Plumbing
  • Electrical
  • A new staircase

Tip: Planning your renovation is essential. This is when rough ideas become detailed plans with scaled drawings to guide your renovation. It can take a few attempts to get the plans absolutely right.

How Much Will it Cost?

When considering extending upwards and adding a second-storey, there are a number of factors that you will need to consider when setting your budget. You will also need to think about what you want to achieve. For example, do you want to change the style/modernise the look of the house or keep to sympathetic renovation?

For example the cost of adding a second storey extension – medium to large second storey addition – plan around $250,000 to $550,000+. The quality and price of construction materials and inclusions will make a difference and if the ground floor needs reinforcing to carry the load of the extension, it can add a substantial amount to the cost.

Have a contingency for those unexpected costs and time delays due to current materials availability. For example you may have to undertake additional electrical work such as updating the mains power board or undertake additional plumbing. Your roof system may also have to be reconfigured.

The cost of adding a second storey extension – going up – will always be higher than going out. This is mainly because the existing house will need to be strengthened and the work is being carried out at height that will require scaffolding and shrink wrap.


Finding an architect and chartered engineer is one of the most important steps in your renovation process.

Typical questions from the architect are:

  • Design features you want to be included.
  • The degree of changes do you want to undertake? For example, basic, middle or extensive.
  • How much do you want to add on to your existing home in terms of floor space?
  • Your budget allocation includes a contingency.

Creating a second storey does mean adding extra weight to the existing house structure. You need to ensure that the building is able to handle the pressure as some older style homes are not structurally built to handle the extra weight. Therefore, an engineer’s assessment may be required to establish feasibility.

The first step in the process is to have concept plans developed by an architect along with the engineer’s and project managers’ input.

Concept plans will help you understand what is realistic. For example, creating the second level will require a staircase. At Style Plus Renovations, we provide a free service to estimate the cost of creating the concept plans.

As a rule of thumb, you will probably need to sacrifice a room on the ground floor to create enough space for the stairwell. Alternatively, build an external staircase that will not reduce the internal space.


  • Can I make changes during the renovation?
    Yes you can make changes during the renovation . We would discuss the changes with you to. If the requests incur additional labour time and/or material costs, this request will be treated as a variation to the contract. All variations will be cost evaluated and presented to you for approval and sign-off using our cloud based construction system. No variation work would be undertaken until variation is approved/signed-off.
  • What unitary plan zone is my house in?
    You can find out which zone your house is in by using Auckland Councils Geomap. Just enter you address in Geomap (
  • Can Style Plus Renovations help with my interior design and finishing options?
    With so many options to select from and many decisions to make, Style Plus Renovations offers an interior design service that can assist you for all of the design choices.
  • How Long To Build A Second Storey Extension?
    The time period of the completion of the second storey build varies depending on the size and scope of the project. Style Plus Renovations North Shore Auckland have project management processes in place to ensure high levels of efficiency in completing each stage of a job and strive to meet deadlines as best as possible.
  • Do I need to move out whilst construction takes place?
    Generally it is recommended that you do need to move out during renovations, as it can mean extended delays as the Style Plus Renovations team work around you. Also there is the Health & Safety requirements. However, it does depend on the extent of the renovations. This is something that can be discussed at the initial consultation.
  • Will my second storey extension fit with my existing home?
    At Style Plus Renovations we pride ourselves on our design skills and our ability to produce high quality renovations which are sympathetic with your existing home.
  • Is building consent required?
    You will need a building consent, and possibly a resource consent, for additions and alterations, depending on the rules in your area. Check out our article on Building & Resource Consent.

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As an Auckland North Shore family-owned and run business, Style Plus Renovations cares about what we do and we take the time to fully understand your renovation needs. We are also proud to receive some exceptional compliments from our Auckland clients.

Get started with a Free
Architects Renovation Feasibility Report



Tel us about your renovation project and we’ll call you back for a no-obligation chat about your ideas.

Alternatively, if you prefer, we can initially set up a meeting using Microsoft Teams or Zoom (and other meeting apps) for a no-obligation chat about your ideas.

We look forward to hearing from you to discuss your project and get you started on your renovation journey.

If you would like to know more about our renovation process, check it out here.

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