The New Town Plan is not going to help people with this, in fact it is even worse.
Any development for a secondary dwelling is:
(a) a maximum of 80m2 in gross floor area;
(b) located within 20m of the dwelling house;
(c) occupied by one or more members of the same household as the dwelling house.
Household is defined as
An individual or a group of two or more related or unrelated people who reside in the dwelling, with the common intention to live together on a long-term basis and who make common provision for food or other essentials for living. The term does not include individuals living in rooming accommodation.
Looks like BCC have changed the rules again and the new plan will help.
It has a new Rooming Accommodation Code which allows 5 households in low density residential zoning.
The Household definition has also been modified to remove the Rooming Accommodation exclusion.