NCC 2019 Volume Three
Part A7 United buildings

Part A7 United buildings

Introduction to this Part

This Part explains how multiple buildings can be considered as a united building. Where adjacent buildings are joined through openings in walls, they need not meet additional requirements if they jointly comply with the NCC as if a single building.

A7.0 United buildings

Buildings are deemed united when two or more buildings adjoining each other are connected and used as one building.

Application 1:

Application 1:

For A7.0, two or more buildings are a united building if they are connected through openings in the walls dividing them and together comply with all the requirements of the NCC as though they are a single building.

Application 2:

Application 2:

A7.0 only applies to Class 2 to 9 buildings.

A7.1 Alterations in a united building

If, after alterations or any other building work, two or more of the buildings in A7.0 cease to be connected through openings in the dividing walls, each of those buildings not now connected must comply with all the requirements for a single building.

Explanatory information:

Explanatory information:

It is not unusual for authorities to receive plans proposing the connecting of two or more buildings. Connecting buildings could be achieved by breaking openings through walls, or by joining the buildings by a tunnel, bridge or covered walkway.

When connected, if the buildings jointly comply with all the requirements of the NCC applying as if they were a single building, they become a united building.

United buildings are not required to comply with additional NCC provisions. For example, any new openings do not require any form of fire protection not required of a single building.

Note, however, an external wall, which as a result of an interconnection becomes an internal wall, must comply with the requirements for an internal wall.

Interconnected buildings that do not jointly comply with all the requirements applicable to a single building, remain as separate buildings.

This raises the possible need for fire doors, or other forms of protection to be fitted to connecting openings.

Multiple allotments or ownership

The NCC does not concern itself with actually prohibiting or permitting the uniting of buildings in separate ownership or on separate allotments. Such matters are dealt with by the relevant local bodies.

Example of connection by bridge

In this example, Building A is connected to Building B by bridge C. There are four different options for designing such a proposal.

The first is a united building

A, B and C are considered as a single structure and comply with the NCC.

The second is three separate buildings

A, B and C are a fire-source feature to each of the others, and are separated by fire walls with the openings protected at the points of connection. In this case, C may require independent support and separate egress to a road or open space, that is not through Buildings A or B. In this case, attention should also be paid to the length of the bridge, as regards distance of travel to an exit.

The third option is the bridge as a portion of Building A

In this option, A and C are one building, meeting all requirements of the NCC as a single or united building. B is a separate building, with suitable fire separation, including fire-doors at the point of interconnection. Bridge C could be supported off Building A, but not off Building B.

The fourth option is having the bridge as a portion of Building B

In this option, B and C are one building, meeting all requirements of the NCC as a single or united building. A is a separate building, with suitable fire separation, including fire doors at the point of interconnection. Bridge C could be supported off Building B, but not off Building A.

In some cases, C will link A and B across a public road, including laneways and the like. Special approvals may be required from various appropriate authorities. However, in such cases—

  • if C is supported by means other than off A and B, such support will generally only be permitted if there is no obstruction of the public road; and
  • care will need to be taken in calculating the distance of travel to an exit if travel is required to be over C and the road is wide; and
  • fire-separation may be necessary at each end of the bridge.

If the last stipulation is the case, the following matters need consideration:

  • The bridge would probably need to be of fire-rated construction because combustible construction could provide a ready path for the transfer of fire, and non-combustible construction could, in a major fire, distort and collapse onto the road.
  • The designer needs to take care that the bridge does not negate the fire separation between the storeys of the building.