Introduction
This guidance provides information on the Building Code Regulations 1992 (the Building Code) and Building Act 2004 (the Building Act) requirements that relate to retrofitting insulation in external walls of buildings.
The guidance highlights the main considerations when assessing work for compliance. It lists the relevant Building Code performance criteria for common types of insulation retrofits.
Purpose
Decisions on retrofitting insulation in external walls can be complex. Insulation is usually retrofitted into older houses that have stood the test of time but are now too cold and draughty for modern lifestyles. Older houses often have simpler designs and are built of naturally durable native timbers.
The increase in more complex designs and use of untreated pine during the 1990s increased the risk of moisture problems. Insulation retrofits deliver tangible benefits, but there can be unintended problems if the insulation or its installation is unsuitable.
This guidance does not provide solutions or recommend installation methods for particular types of insulation or building construction. Insulation specialists should be consulted if you have doubts about how best to retrofit insulation.
What the law says
Schedule 1 – the Building Code — legislation.govt.nz
Building Act 2004 — legislation.govt.nz
Who is this guidance for?
The guidance is intended for territorial authorities (TAs) and building consent authorities (BCAs) assessing building consent applications and applications for discretionary exemptions for retrofitting wall insulation.
Territorial authorities may use this guidance to assist them in decisions as to whether to exempt retrofitting of wall insulation from a building consent, which can be done under exemption 2 of Schedule 1 of the Building Act – Territorial and regional authority discretionary exemptions. Designers and installers may also find the document a useful guide to the relevant Building Code requirements for retrofitting wall insulation.
What the law says
Clause 2 of Schedule 1 of the Building Act – Territorial and regional authority discretionary exemptions:
Any building work in respect of which the territorial authority or regional authority considers that a building consent is not necessary for the purposes of this Act because the authority considers that—
- (a) the completed building work is likely to comply with the building code; or
- (b) if the completed building work does not comply with the building code, it is unlikely to endanger people or any building, whether on the same land or on other property.
Check if a building consent is required
Retrofitting insulation into an external wall cavity is not exempt building work under Schedule 1 of the Building Act. It either requires a building consent or a specific exemption from a TA that a building consent is not required.
Refer to the Territorial and regional authority discretionary exemptions
Building consent applications for retrofitting wall insulation will need to cover all the associated building work, show that the building work will comply with the Building Code and that it will not adversely affect the performance of the existing building.
Note that exemption 13 of Schedule 1 of the Building Act exempts underfloor and roof insulation retrofits from requiring building consent. Home or building owners can still seek a building consent for this work should they choose to.
What the law says
Schedule 1 – Building work for which building consent not required — legislation.govt.nz
Why retrofitting external wall insulation is not included in Schedule 1
Retrofitting insulation to walls involves more work than simply placing or injecting insulation in walls. All the associated work must be assessed to see if it complies with the Building Code, whether it is as small as drilling and repairing holes in interior linings or as significant as removing and reinstating exterior claddings. Even if the building work is relatively simple, the effects on the existing building may be complex and potentially problematic.
Retrofitted wall insulation may affect moisture transfer inside timber framed walls and change drying rates, which in turn may cause moisture to accumulate in the wall and affect the durability of timber framing and cladding. Poorly installed insulation may also affect the fire and electrical safety of buildings. Buildings must be assessed on a case-by-case basis to determine if they are suitable for retrofitting wall insulation and if the proposed methods and materials are appropriate.