StandAId › NCC explained › Smoke alarms in a house: where they go, mains power and interconnection
Every new house (Class 1a) needs smoke alarms, and the NCC is specific about where. The short version: on any storey with bedrooms, alarms go in every corridor or hallway that serves a bedroom — or, where there's no hallway, between the bedrooms and the rest of the house. Any other storey gets at least one alarm too, so a typical two-storey home ends up with alarms on both levels.
The alarms themselves have to comply with AS 3786, be wired to the consumer mains power (where mains is available), and be interconnected so that when one goes off, they all go off. Positioning on the ceiling matters — keep them clear of the wall/ceiling corner dead-air space and follow the sloped-ceiling rules.
The clauses below are from the ABCB Housing Provisions (the deemed-to-satisfy pathway most houses use) plus the Volume Two performance clause they sit under. NSW has a state variation to the location rule — if you're in NSW, read the NSW entry as well.
This page is a plain-English guide written by StandAId, followed by the actual NCC 2025 clause text. It is not professional advice and StandAId is not endorsed by the ABCB — always check the current edition on ncc.abcb.gov.au and your state's requirements.
(1) Smoke alarms must—
(a) be located in—
(i) a Class 1a building in accordance with 9.5.2 and 9.5.4; and
(ii) a Class 1b building in accordance with 9.5.3 and 9.5.4; and
(b) comply with AS 3786, except that in a Class 10a private garage where the use of the area is likely to result in smoke alarms causing spurious signals, any other alarm deemed suitable in accordance with AS 1670.1 may be installed provided that smoke alarms complying with AS 3786 are installed elsewhere in the Class 1 building; and
(c) be powered from the consumer mains source where a consumer mains source is supplied to the building; and
(d) be interconnected where there is more than one alarm.
Explanatory information: A smoke alarm can give spurious alarms if the atmosphere contains particles which obscure vision, such as could occur in a Class 10a private garage part of a building. 9.5.1(b) therefore allows the use of a more suitable alarm, such as a heat alarm, in these locations. 9.5.1(d) requires alarms to be interconnected where there is more than one alarm. This only applies within a single dwelling. Therefore, alarms in a Class 1a dwelling need not be interconnected with alarms in another dwelling or a private garage which does not belong to the Class 1a dwelling.
State variation: this clause is varied in New South Wales. Check the state schedule on the ABCB site, or set your state in StandAId to get the right version.
(1) In a Class 1a building, smoke alarms must be located in—
(a) any storey containing bedrooms, every corridor or hallway associated with a bedroom, or if there is no corridor or hallway, in an area between the bedrooms and the remainder of the building; and
(b) each other storey not containing bedrooms.
Note: Figure 9.5.2a and 9.5.2b illustrates requirements of this provision.
[See Figure 9.5.2a — Class 1a building where all bedrooms are grouped together and served by a hallway]
[See Figure 9.5.2b — Class 1a building where bedrooms are located in separate areas]
Figures referenced (view on the ABCB site — images aren't reproduced here):
(1) Smoke alarms required by 9.5.2 and 9.5.3 must be installed on or near the ceiling, in accordance with the following:
(a) Where a smoke alarm is located on the ceiling it must be—
(i) a minimum of 300 mm away from the corner junction of the wall and ceiling; and
(ii) between 500 mm and 1500 mm away from the high point and apexes of the ceiling, if the room has a sloping ceiling.
(b) Where (a) is not possible, the smoke alarm may be installed on the wall, and located a minimum of 300 mm and a maximum of 500 mm off the ceiling at the junction with the wall.
Explanatory information: Smoke alarms need to be located on (or near) the ceiling for optimum detection of smoke in a fire situation with special care taken to avoid dead air spaces. A dead air space is an area in which trapped hot air will prevent smoke from reaching the alarm. This space generally occurs at the apex of cathedral ceilings, the corner junction of walls and ceilings and between exposed joists etc. (see Explanatory Figure 9.5.4). Smoke alarms may be located on the wall in accordance with 9.5.4(b). Explanatory Figure 9.5.4 provides location criteria and the dimensional relationship to building elements and the associated dead air spaces. [See Figure 9.5.4 (explanatory) — Installation of smoke alarms to avoid dead air space]
Figures referenced (view on the ABCB site — images aren't reproduced here):
(1) Compliance with Part 9.5 of the ABCB Housing Provisions satisfies Performance Requirement H3P2 for smoke alarms and evacuation lighting.
(2) For the purposes of (1), a Class 1 building includes a Class 10a private garage located above or below the Class 1 building.
Explanatory information: Performance Requirement H3P2 and the Deemed-to-Satisfy Provisions of Part 9.5 of the ABCB Housing Provisions require automatic warning on the detection of smoke in buildings, so that occupants may be alerted to a fire in order to evacuate to a place of safety.
Explanatory information: Part 9.5 of the ABCB Housing Provisions specifies different smoke alarm requirements for Class 1a and Class 1b buildings. The main difference is that a Class 1b building is required to have a greater number of smoke alarms, i.e. smoke alarms must be installed in all bedrooms, and a system of lighting must be installed to assist evacuation. This is due to Class 1b buildings generally being used for more transient purposes and the occupants being less familiar with the building layout.
Explanatory information: Clause 9.5.1(b) of the ABCB Housing Provisions requires a smoke alarm(s) to comply with AS 3786. AS 3786 contains the requirements for the design and performance of electrically operated smoke alarms containing both detection and alarm facilities. Types of smoke alarms prescribed in AS 3786 include photoelectric, ionisation or a combination of the two.
Explanatory information: Clause 9.5.1(c) of the ABCB Housing Provisions requires that a smoke alarm be connected to the consumer mains electricity source where a consumer mains source is supplied to the building. A smoke alarm complying with AS 3786, that is intended for connection to an external power source, is required to be provided with a secondary power source i.e. a source of power to supply the smoke alarm in the event that the primary power source is unavailable. Generally, the requirement is met by providing mains powered smoke alarms with a battery back-up.
Explanatory information: Clause 9.5.1(d) of the ABCB Housing Provisions requires that alarms be interconnected to provide a common alarm so that if one alarm in the dwelling activates, the other alarms automatically activate, which will increase the likelihood of sleeping occupants becoming aware of the detection of smoke. Alarms of a Class 1 building need not be interconnected with alarms in another Class 1 building or a private garage which does not belong to the Class 1 building.
Explanatory information: When deciding on the position of smoke alarms it is important to remember that they are intended to detect smoke before it reaches the sleeping occupants of a building. The ensuing alarm is designed to wake the occupants and give them time to evacuate the building.
Explanatory information: In addition to a smoke alarm being required to be provided on storeys containing bedrooms, a smoke alarm is also required on each other storey that is not already provided with a smoke alarm even if those storeys consist of only carparking, bathrooms, laundries and the like. “Storey” in this context differs from the definition contained in the NCC which excludes such spaces from being considered as storeys. Reference to “storey” only applies within a single dwelling. For example, if a storey contains a private garage belonging to the Class 1a dwelling in addition to a private garage which does not belong to the Class 1a dwelling, smoke alarms must be installed in both private garages. Where the other storey is a Class 10a private garage, clause 9.5.1(b) of the ABCB Housing Provisions permits the use of any other alarm deemed suitable in accordance with AS 1670.1 provided smoke alarms complying with AS 3786 are installed elsewhere in the Class 1 building.
Explanatory information: Smoke alarms are extremely sensitive and may detect smoke and moisture created by common household activities such as burnt toast or steam from a bathroom. Accordingly, to reduce the likelihood of nuisance alarms, it is preferable that smoke alarms are not located near cooking appliances and bathrooms. However, if it is necessary to locate alarms in these positions, the type of alarm installed may need to be considered as some alarm types may be more suitable in certain locations.
Explanatory information: The options described in the ABCB Housing Provisions are not the only means available for complying with this Part. The performance-based nature of the NCC provides flexibility to develop alternative methods if it is preferred to meet the Performance Requirement in some other way. This added flexibility may be utilised when considering the location of smoke alarms.
Got a follow-up? StandAId answers questions on the text of the NCC 2025 — Volumes One, Two, Three and the Housing Provisions — with the clause linked. Free account, 3 questions a day; upload your own standards for more.
Ask the NCC in StandAId — free, 3 questions a dayYes — where consumer mains power is supplied to the building, the NCC requires smoke alarms to be connected to it (with battery back-up as per AS 3786). See Housing Provisions 9.5.4.
Where more than one alarm is installed in a house, the NCC requires them to be interconnected so they all sound together. See Housing Provisions 9.5.4.
At least one on each storey: on the bedroom storey they go in hallways serving bedrooms (or between bedrooms and the rest of the house), and every other storey gets at least one. See Housing Provisions 9.5.2.
The National Construction Code 2025 was provided by the Australian Building Codes Board under the CC BY 4.0 licence. © Commonwealth of Australia and the States and Territories of Australia 2026, published by the Australian Building Codes Board. Licence: CC BY 4.0. NCC text on this page was extracted from the ABCB's NCC 2025 dataset (v1.2) and reformatted; figures, diagrams and photographs are not reproduced (they are outside the licence) — follow the links to view them on the ABCB site. The ABCB publishes the NCC without warranty and it is not legal or professional advice.
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