The big one is site coverage. According to Medium Density Residential Standards, the maximum area of a property that buildings can cover is 50%. In some residential zones, it may be even less – 30% or 40% of the total site area.
The site coverage rules apply to most residential zones. They are designed to strike a balance between the need for housing and the provision of open space, sunlight, and effective stormwater management.
Building coverage includes:
- The main building footprint.
- Accessory buildings (sheds, garages, sleepouts).
- Overhanging or cantilevered parts of the building that extend beyond the main structure.
- Eaves and spouting that project from exterior walls.
While adding additional buildings on a traditional kiwi quarter-acre residential section might be feasible, doing so on smaller sites is likely impractical.
Council oversight
Other factors that may hinder plans for adding a granny flat or secondary building include local council regulations and guidelines. For instance, many councils have expressed concerns that increased site coverage may exacerbate stormwater and flooding issues, especially in smaller areas.
While building consent may not be required for certain granny flats and some other secondary buildings under the proposed changes, the council will, in many cases, need to be notified before and after construction.
For a granny flat, you will need to apply to the council for a Project Information Memorandum (PIM) before work starts. A PIM application must have detailed information on the site and the proposed building work, including site plans, floor plans, scaled drawings, building dimensions, and information on potential hazards, storm and waste water disposal provisions, vehicle access and parking.