The source is section 0.5 of the Building standards technical handbook 2022: domestic. It applies to a building warrant submitted on or after 1 June 2022, and to building work which does not require a warrant commenced from that date.
What the handbook says
Regulation 5 and schedule 3 set out work that can be done without a warrant. That work must still meet the building standards. The handbook says type 1 is any work to or in a house, with exceptions.
One exception is any work which increases the floor area of the house. An extension adds floor area, so it sits outside that exemption. That is why an extension normally needs a building warrant from the council.
Other exceptions include demolition or alteration of the roof, the external walls, or an element of structure. The handbook gives examples such as forming a dormer, or slapping a new window or door. Underpinning, work that harms a separating wall, and a change in how wastewater is discharged are exceptions too. A house with a storey above 4.5 metres has a further limit on the exemption.
The handbook also says some small jobs on a house do not need a warrant, such as certain non-loadbearing partitions, or a patio or fence within the sizes it describes. An extension is not one of those small jobs.
What can be priced
Drawings already prepared are enough for a price on the stonework and blockwork. Many clients use an architect or designer for the warrant. The council can confirm whether a particular job needs one.
Recent extensions are a stone and block job in Bonkle, and an extension in Hamilton.
What to do next
Source: Building standards technical handbook 2022: domestic, section 0.5.