If you have ever looked into replacing old timber or aluminium windows, you have probably heard some version of this:

‘It’s like-for-like, so it doesn’t need building consent.’

That may be correct as far as the building consent is concerned. But it does not answer the more important question:

Will the new installation comply with the Building Code?

Those are two separate issues. A building consent is the council approval process. The Building Code is the performance standard the completed building work has to meet.

No building consent does not mean no Building Code requirements.

Does replacing a window require building consent?

In many cases, no.

Schedule 1 of the Building Act provides an exemption for building work connected with windows and exterior doorways in existing dwellings and outbuildings of no more than two storeys.

There are exceptions. For example, the exemption does not apply where the window being replaced failed to meet the Building Code durability requirements, such as a premature failure caused by external moisture. It also does not apply where the work modifies or affects a specified system.

You can read the current requirements in Building Performance’s guidance for windows and exterior doorways.

One useful distinction is that ‘like-for-like’ is largely industry shorthand.

The general repair and replacement exemption elsewhere in Schedule 1 refers to using a comparable component in the same position. However, there is also a specific exemption dealing with windows and exterior doors. Simply asking whether a replacement is ‘like-for-like’ therefore does not tell the whole compliance story.

No building consent does not mean no Building Code requirements

This is the part homeowners need to understand.

Section 17 of the Building Act states that all building work must comply with the Building Code whether or not a building consent is required. Section 42A, which deals specifically with Schedule 1 work, reinforces the same requirement: exempt work must still comply with the Building Code.

Building Performance’s exempt-work guidance also warns that non-compliant exempt work may affect insurance cover or the future sale and purchase of a property.

There is an important practical difference with exempt work. Because there is normally no building consent, there generally is not a council inspector checking the installation during construction. That does not create a loophole allowing lower-quality work. It simply means more responsibility sits with the owner and the people carrying out the work.

What does E2 External Moisture actually require?

For windows, one of the most important Building Code clauses is E2 External Moisture.

E2 requires external walls and openings to resist moisture entering or accumulating in a way that causes undue dampness or damage.

That means the window installation needs to work as part of the entire wall system — not just as a piece of aluminium or uPVC sitting inside an opening. Depending on the wall construction, that can involve consideration of:

• the window flange and cladding interface;

• sill and jamb flashing;

• head flashing;

• flexible flashing tapes;

• wall underlay;

• drainage paths;

• air seals;

• the condition of the framing around the opening; and

• how the existing cladding was originally constructed.

Simply removing the old window, inserting a new one and sealing around the outside does not by itself demonstrate that the completed installation complies with E2.

Does every replacement window have to follow E2/AS1 exactly?

This needs some care.

E2/AS1 is not the Building Code itself.

It is an Acceptable Solution published by MBIE. Following an Acceptable Solution provides an accepted way of demonstrating compliance, but using it is not mandatory. Building work can instead comply through an appropriate alternative solution.

That distinction matters with older homes. BRANZ notes that replacing windows in existing openings can make literal compliance with current E2/AS1 detailing difficult. Its replacement-window guidance provides practical methods for dealing with existing direct-fixed and cavity-clad walls.

For an older direct-fixed wall, for example, the framing and wall underlay should be inspected once the original window is removed. Depending on the existing construction, the replacement detail may involve flexible flashing tape around the opening, sill flashing, a continuous air seal and a suitable head flashing.

So the accurate position is not that every replacement window must be installed exactly to a current new-build E2/AS1 detail. It is that every replacement window still needs a defensible installation detail that achieves the required Building Code performance.

Why older Wellington homes can be difficult

This is where replacement windows can become more involved than expected.

Many older Wellington, Porirua and Hutt Valley homes were built with timber windows and direct-fixed weatherboards. When those windows are removed, the opening may look very different from a modern E2/AS1 construction detail.

Older direct-fixed walls commonly do not have wall underlay folded into the window opening in the way a modern installation would. The installer therefore needs to assess what is actually there and develop an appropriate replacement detail rather than simply assuming the existing junction will work with the new window.

That inspection can also uncover rotten framing, damaged underlay or historic moisture entry that was hidden behind the original window. Those are not reasons to avoid replacing the windows. They are reasons to involve someone who understands how the window, cladding and wall assembly work together, particularly when the work forms part of a wider renovation.

When a replacement may actually require building consent

There is another part of Schedule 1 that is often overlooked.

The exemption does not apply if the existing window has failed prematurely to meet the Building Code durability requirements.

MBIE gives the example of a window installed within the previous 15 years that has rotted out. That type of premature failure can indicate a durability or weathertightness problem, so replacing it may require building consent rather than relying on the Schedule 1 exemption.

By contrast, an older window that has simply reached the end of its expected service life may normally qualify for the exemption. The cause of the failure therefore matters.

What should you ask before your windows are replaced?

Before approving a replacement-window job, ask for clear answers to these practical questions:

• How will the new window be integrated with the existing cladding and wall underlay?

• What flashing detail will be used at the sill, jambs and head?

• Will the opening be inspected for moisture damage or rot once the old window is removed?

• How will the internal air seal be completed?

• What happens if damage is discovered behind the existing window?

• What Building Code compliance approach is the installer relying on?

• Who is responsible for making good the surrounding cladding and flashings?

A reputable installer should be able to explain the system rather than simply say ‘it doesn’t need consent.’

Frequently asked questions

Do I need building consent to replace windows in New Zealand?

Usually not for window work in an existing dwelling of no more than two storeys, provided the Schedule 1 exemption applies. There are exceptions, including replacement of a window that failed prematurely to meet Building Code durability requirements and work affecting specified systems.

Does a like-for-like window replacement have to meet the Building Code?

Yes. Section 17 of the Building Act requires all building work to comply with the Building Code whether or not building consent is required.

Does a replacement window have to comply with E2/AS1?

The replacement must comply with the performance requirements of Building Code Clause E2 where applicable. E2/AS1 is one accepted means of demonstrating compliance, but it is not mandatory and an appropriate alternative solution may be used.

What happens if rot is found when the old window is removed?

The cause and extent should be assessed before it is covered by the new window. If the original window failed prematurely due to a durability or external-moisture problem, the Schedule 1 exemption may not apply.

Does council inspect window work done under Schedule 1?

Normally there is no standard building-consent inspection process for exempt work. The people responsible for the project still have to ensure the work complies with the Building Code.

The practical takeaway

Schedule 1 is useful. It allows relatively straightforward building work to be completed without putting every minor alteration through the full building consent process. But it does not remove the standard the work has to achieve.

When an existing window is replaced, the installer still needs to think about how water is kept out of the wall, how any water that does get behind the cladding can drain or dissipate, and how the replacement interacts with the existing building.

For homeowners, the important question is therefore not just ‘Do I need a building consent?’ It is ‘How is this replacement being detailed so that it remains Building Code compliant?’

Planning window replacement as part of a renovation?

If you are replacing windows while renovating a home in Porirua, Wellington, Lower Hutt, Upper Hutt or Kāpiti, Newport Construction can help assess the existing wall construction, identify issues around the openings and coordinate the work as part of a properly planned renovation.

Talk to Harvey before the work starts and make sure the whole wall system — not just the new window — has been considered.