Houses built before the late 1970s are unlikely to have any insulation in the walls unless major alterations or renovations have been carried out.
Insulation only became mandatory nationwide in 1978, although there were regional exceptions, such as Christchurch, where a bylaw made insulation mandatory in 1972.
This Good Reapir Guide explains options for retrofitting insulation into existing residential timber-framed walls. Insulation materials covered include fibreglass, polyester, wool and mineral wool (and blends of these) and rigid sheets such as polystyrene and PIR/PUR foam.
This guide does not cover blown-in and injected foam insulation or retrofitting insulation to: