Most District and Unitary Plan have a beneficial omission, because they were written before the affordable housing crisis, thus they do not speak to mobile homes (residential box trailers). Almost all rules regarding residences include the word “structure” in their meaning. RMA s2 says “structure means any building, equipment, device, or other facility made by people and which is fixed to land…“
This distinction is not incidental. It lies at the foundation of property law. This was extensively examined by Sir John W Salmond, former Solicitor General of and Supreme Court Judge in NZ, who in 1902 wrote Jurisprudence. In §155. Movable and Immovable Property, Salmond explains the elements of immovable property (i.e. land), where he wrote
…all objects placed by human agency on or under the surface with the intention of permanent annexation. These become part of the land, and lose their identity as separate movables or chattels; for example buildings, walls and fences. Omne quod inaedificatur solo cedit [Everything which is erected on the soil goes with it] said the Roman Law. Provided that the requisite intent of permanent annexation is present, no physical attachment to the surface is required. A wall built of stones without mortar or foundation is part of the land on which it stands. Conversely, physical attachment, without the intent of permanent annexation, is not in itself enough. Carpets, tapestries, or ornaments nailed to the floors or walls of a house are not thereby made part of the house. Money buried in the ground is as much a chattel as money in its owner’s pocket. Footnote 2: Unlike a chattel, a piece of land has no natural boundaries. Its separation from the adjoining land is purely arbitrary and artificial, and it is capable of subdivision and separate ownership to any extent that may be desired.
Mobile homes are not structures because they are not fixed to land. As such they can be interpreted as a permitted use, provided they remain mobile and can be towed away. As chattel, they do not commit land the way a building does. They are low impact solutions, provided the councils say yes.