2.2. Single-storey detached buildings between 10 and 30sqm in floor area, using lightweight material

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Before you begin, please read the notes for single-storey detached buildings (particularly District Plan requirements and disposal of stormwater).

Any buildings that include bathroom facilities cannot be built using these exemptions. A building consent is required.

If you are providing sleeping accommodation in such a building, note that the facilities (such as potable water) of an existing dwelling must be readily available and used for sanitation, and the building cannot include cooking facilities because of the risk of fire.

The net floor area of a single storey, detached building is limited to a maximum of 30 square metres. If you are extending an existing single storey detached building, the maximum combined net floor area cannot exceed 30 square metres.

To qualify for this exemption, only lightweight materials such as light timber or steel framing and cladding must be used for the construction of the walls and roof of the buildings and the structural components must be designed and built in accordance to Building Code compliance document B1/AS1. Currently, NZS 3604:2011 and National Association of Steel Framed Housing standards cited in the Building Code are used as an Acceptable Solution.

NZS 3604:2011 Timber-framed buildings which is used as Acceptable Solution (B1/AS1)

National Association of Steel Framed Housing Inc

If you have difficulty with understanding how to apply the technical requirements of B1/AS1 to a particular building, professional advice of qualified people should be sought.

Where B1/AS1 (NZS3604:2011) is being used as a means of compliance for detached buildings, bracing lines should not exceed 6 metres in any direction for ground floor construction and be no more than 5 metres apart for subfloor areas. These requirements help to evenly distribute bracing throughout the building and avoid a disproportionate concentration of bracing in any one area.

What is exempt

1. The owners of a commercial property intend to construct a 20 square metre detached building to serve as a garage. The proposed building will be more than its own height away from the boundaries, it contains no potable water supply, and no facilities for cooking or sanitation. The owners want to construct the building from the lightweight materials in accordance with the technical requirements of the Building Code as specified in B1/AS1.
2. A 28 square metre sleepout is constructed in the backyard of a residential dwelling. It is more than its own height away from all boundaries and the associated residential dwelling, and does not contain cooking or sanitary facilities, or a potable water supply. The design complies with the technical requirements of the Building Code for the lightweight material per B1/AS1. Subsequently, the construction is carried out in accordance with that design.
3. A 26 square metre detached single garage is constructed on a concrete slab of a property with a residential dwelling. It is more than its own height away from all boundaries and the associated residential dwelling, and does not contain cooking or sanitary facilities, or a potable water supply. Plans and specifications comply with the technical requirements of the Building Code for the lightweight timber material per B1/AS1. Subsequently, the work is carried out in accordance with that design.

What needs consent

1. A homeowner decides to erect a sleepout with a net floor area of 33 square metres on a property that has a residential dwelling on it. This sleepout would require a building consent as its floor area is greater than 30 square metres.
2. A homeowner intends to construct a sleepout with a net floor area of 29 square metres on a property that has a residential dwelling on it. Heavy concrete masonry units are proposed for construction of perimeter walls. This sleepout would require a building consent because the proposed material for the construction is not lightweight material (If the homeowner had the proposed building constructed or supervised by a licensed building practitioner under exemption 3B (section 2.4), then a building consent would not be required).
3. A homeowner intends to construct a storage shed with a net floor area of 20 square metres on a property that has a residential dwelling. Reinforced concrete panels are proposed for construction of this building. This shed would require a building consent because the proposed material for the construction is not lightweight material (If the homeowner had the proposed building constructed or supervised by a licensed building practitioner under exemption 3B (section 2.4), then a building consent would not be required).
4. A homeowner wants to construct a sleepout with a net floor area of 20 square metres on a property that has a residential dwelling. The owner also wants to construct an elevated loft of 8 square metres 1.2 metres above the ground level. This sleepout would require a building consent because the proposed level for the loft area is more than 1 metre above the ground.

What the law says

3A. Single-storey detached buildings exceeding 10, but not exceeding 30, square metres in floor area, constructed of lightweight material

1. Building work in connection with any detached building that—

(a). is not more than 1 storey (being a floor level of up to 1 metre above the supporting ground and a height of up to 3.5 metres above the floor level); and

(b). exceeds 10 square metres in floor area, but does not exceed 30 square metres; and

(c). is built using lightweight wall and roof materials, and in accordance with Acceptable Solution B1/AS1 for timber or steel buildings; and

(d). does not contain sanitary facilities or facilities for the storage of potable water; and

(e). does not include sleeping accommodation, unless the building is used in connection with a dwelling and does not contain any cooking facilities; and

(f). if it includes sleeping accommodation, has smoke alarms installed.

2. (2) However, subclause (1) does not include building work in connection with a building that is closer than the measure of its own height to any residential building or to any legal boundary.