Skip to main content.

Renovations differ to new builds

Last updated: 15 March 2016

If you are planning a building project, you need to think about the difference between a new build and a renovation or extension.

In any building project there are unknown factors, particularly if the project is large or complex. In a new build, many of these can be resolved before construction begins, during the scope and design stage.

In a renovation or alteration, your existing building's construction may not be understood until part way through the building process. You will also need to make compromises to work with what already exists.

If you're doing the work yourself, plan well so that you are prepared for changes and delays. They can lengthen the process and add costs. If you're using professionals, check that they are familiar with the challenges of renovating.

Talk to your council in the early stages of your project so you know what you need to take into account.

Renovation complications to plan around

In a renovation or alteration you are working with an existing building. You should factor in that you might:

  • not have the original plans
  • not have plans that reflect what was actually built or any other renovations
  • not be able to understand parts of the existing structure until your build starts (for example, inside walls)
  • want or need to keep existing features
  • need to retrofit items (for example, insulation or windows)
  • need to meet additional requirements for the whole building, even if you are only altering part of a building (for example, smoke alarms)
  • need to meet additional requirements if you are changing the use of the building, such as:
    • means of escape from fire
    • access and facilities (for example, residential to retirement home or restaurant).

A council will not grant a building consent for an alteration to an existing building unless they are satisfied that the means of escape from fire, and access and facilities for people with disabilities (where applicable) have been considered. Where appropriate, they will also want to know of any proposed upgrades.

A renovation might require more compromise

Unlike a new build, when you renovate or extend a building you may have to compromise your design to work around what already exists.

Matching existing materials, finishes and tolerances (how much the work varies from stated measurement) may be difficult or even impossible in renovations or extensions.

It is important to be conscious of common issues that can arise when matching old and new materials. For example, older existing building materials will likely be machined or manufactured in imperial sizing where new materials often have a smaller finished size as they are manufactured to metric dimensions. This is typically an issue with materials such as weatherboards, skirting and scotia.

This can take longer and may cost more than building new.

Make sure to get an amendment for changes to your consented plans

You may also have to undo parts of the building before construction can begin, to learn more about the building or as part of the renovation. This can reveal the need for different requirements, and potentially the need to amend your building consent (this must be granted before you start any work and amended with council if anything changes).

Your council can advise you about how your building consent will need to be updated, whether your project will be delayed and whether they require any additional fees or inspections. You may also need to pay more in design and building costs to accommodate the changes.

You also need to consider whether your renovation will change the use of your building. If so, you may need to comply with other parts of the Building Code. For example, changing offices to residential use or vice versa.

Change of use, alterations and extension of life

You need to tell the council about a change of use, even if it doesn't involve building work.

Learn more about Change of use and alterations

Seeking satisfaction at renovation sign-off

There may also be differences at the completion stage of your renovation. As mentioned earlier, tolerances for existing buildings are likely to be below those achievable within new buildings (for example, floor levels and walls out of plumb). There are a number of reasons for this, including the nature of the materials used in existing buildings, and the effects of both time and natural events.

Where an exact match is impractical or cannot be guaranteed, a rational approach needs to be taken to determine the options and agreement reached on acceptable levels of workmanship. It is important the agreed acceptable levels are recorded in writing, preferably by noting it within the contract early in the process. This is particularly the case where a building has been subject to significant damage such as from earthquake, wind, fire or land subsidence.

Repairing and rebuilding houses affected by the Canterbury earthquakes

This comprehensive guidance will help the repair and rebuild of residential Canterbury.

View the guidance

Renovate – the BRANZ website

This Building Research Authority New Zealand website provides technical renovation information for building professionals.

Visit the website

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: