Complying with the Building Act
Retrofitting insulation into the external walls of an existing building is “building work”4 and therefore must comply5 with the Building Code. When a building consent is required (see previous section), it should not be granted until it is shown that the alteration (i.e. the insulation retrofit) will not reduce the extent to which the existing building meets the Building Code performance criteria6.
It is important to distinguish between the need for “building work” (i.e. retrofitting insulation) to comply with the Building Code (as required by section 17 of the Building Act) and the need to ensure retrofitted insulation does not reduce the extent to which the existing building complies with the Building Code (as required by section 112(1)(b)7 of the Building Act). These two requirements relate to different parts of the building (i.e. new part versus existing parts); the extent of Code compliance is different; and they can relate to different Building Code performance criteria.
Complying with the Building Code
When buildings, or parts of buildings, are constructed or altered they must meet Building Code performance criteria8. Retrofitted insulation material, sitting within the wall cavity, is required to meet relevant Building Code performance criteria. The associated building work, such as repairing cracks in claddings, fixing holes that have been drilled and reinstating linings or claddings must also comply with the relevant Building Code performance criteria.
Performance criteria that relate to the existing building (particularly the wall framing, cladding and internal lining) and with which the building must continue to comply to the same extent9, may or may not be the same as those relating to the insulation retrofitting work. The Building Code performance criteria relevant to the retrofitting work and the Building Code performance criteria relevant to the existing building are analysed in Appendix A and B.
How do I show the work complies?
There are no acceptable solutions or verification methods specifically for retrofitting insulation into wall cavities. The current acceptable solutions provide useful benchmarks when deciding if relevant performance criteria are met, in some instances. However, not all the performance criteria relevant to retrofitting wall insulation have corresponding acceptable solutions, which means judgements will need to be made on each ‘specific design’.
Decisions on the Code compliance of retrofitting wall insulation, in particular the effects of the retrofit on the existing building, can be complex. These decisions are not easily distilled into a one-size-fits-all solution. Appendix A and B highlight relevant factors to consider when deciding whether insulation retrofits comply with the Building Code. A number of different approaches may be used to support claims that work complies with the Code including Determinations, compliance with Standards, test results, expert opinion, appraisals or in-service history10.