Do you need building consent to replace windows or add double glazing?

What we found

Checked against the Building Act 2004 (version as at 8 October 2026) and MBIE guidance

1. Exemption 8 in Schedule 1 of the Building Act 2004 covers building work on a window or exterior doorway in an existing dwelling of up to two storeys, so most window work on a house needs no building consent.
2. Windows must last at least 15 years under the Building Code’s durability clause. MBIE’s guidance: replacing an older window that has rotted or leaks is exempt, but replacing one installed within the last 15 years that has failed needs a consent.
3. It also does not apply if the work modifies or affects a specified system, such as a smoke-control or automatic door system, which are rare in houses but common in apartment buildings.
4. Exempt work still has to comply with the Building Code. A consent exemption is not a licence to fit glass that is not safety glass where the Code requires it, or to leave flashings that let water in.

The two exemptions that cover window work

Exemption 8, windows and exterior doorways. “Building work in connection with a window (including a roof window) or an exterior doorway in an existing dwelling that is not more than 2 storeys or in an existing outbuilding that is not more than 2 storeys”, except where the window or doorway being replaced “has failed to satisfy the provisions of the building code for durability, for example, through a failure to comply with the external moisture requirements of the building code”, or where the work “modifies or affects any specified system”.

Exemption 1, general repair, maintenance and replacement. Replacing a building product with a comparable one in the same position is exempt, except for products that contribute to the building’s structure or fire safety, specified systems, and products that have failed the durability provisions.

For a house, exemption 8 is the one that matters, and it is broad: retrofitting glass units, fitting secondary glazing and replacing whole windows are all “building work in connection with a window”.

When you do need consent

• A window under 15 years old has failed. Windows must last at least 15 years. If one installed within the last 15 years has rotted or let water into the wall, replacing it is not exempt, and the flashings and framing around it may need repair too. Replacing an older window that has failed is exempt.
• Three storeys or more. Apartments and taller houses fall outside exemption 8. Talk to the building’s body corporate and the council.
• Specified systems. If a window is part of a building’s fire or smoke control, or is automated, changing it can affect a specified system under the building’s compliance schedule.
• Changing the opening. MBIE’s guidance treats widening an opening as exempt in a dwelling of up to two storeys: its worked example replaces French doors with wider bifolds and a new lintel. The lintel and bracing must still meet the Code’s structural requirements, so get a designer or engineer to size them.

Exempt is not the same as unregulated

All building work, consented or not, must comply with the Building Code. For windows that means, among other things, safety glass where people could fall against or walk into glass, weathertight flashings, and openable windows in habitable rooms. A glazier who knows the Code will handle this, but on exempt work there is no council inspection to catch mistakes.

Planning rules are separate

Building consent is about the Building Act. Heritage listings and character overlays in a district plan are about the Resource Management Act, and some councils require resource consent to change windows on scheduled buildings or in character areas, especially on street-facing walls. Check the district plan for your property before you change joinery on a listed or character house; see villa and timber windows.

This week: Palmerston North

Single glazing in an aluminium frame runs below the dew point about 2,430 hours a year in Palmerston North (H1 zone 3); clear double glazing cuts that to 350. A low-E retrofit of 25 m² saves $190 a year heated mornings and evenings with a heat pump, or $569 heated all day. Fastest payback here: DIY magnetic secondary glazing, 17 years.

Cheap fix. EECA estimates that closing curtains before dark saves $80–90 a year. Lined, full-length curtains with a pelmet work best. Read more

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