Definition of an Owner Builder - NSW

Masterbuilders:
An owner-builder is a person who is not a registered builder and who proposes to carry out all building work over $12,000 or when a building permit or approval is required limited to a single detached dwelling for the proposed work.

Home Building Act 1989 - SECT 3:
A person who does Owner Builder Work (and who is issued an owner-builder permit for that work.
Owner Builder Work means residential building work:
(a) the reasonable market cost of the labour and materials involved in which exceeds the prescribed amount, and
(b) that relates to a single dwelling-house or a dual occupancy:
(i) that may not be carried out on the land concerned except with development consent under Part 4 of the Environmental Planning and Assessment Act 1979 , or
(ii) that is complying development within the meaning of that Act.