Smoke alarms in renovations and alterations: what NSW builders must do

A builder is asked to replace the kitchen in an older house in the inner west of Sydney. While the work is being priced, the homeowner asks whether the smoke alarms need upgrading as part of the job. The usual answer comes from the room in front of you. The kitchen is being stripped, the alarm sitting over the bench is not part of the design, so the alarm is not in scope. That reasoning is where the trouble starts, because the rule that brings smoke alarms into an alteration does not care which room the tradesman is standing in.

Smoke alarms are there to wake the people who are asleep when a fire starts, usually in the kitchen, the lounge or the hallway, and to give them enough time to get out. An older home may have a single battery alarm in a hallway, or units installed years ago that have never been tested. When work changes the building, the question becomes whether the protection the building relies on still meets the current standard, and whether the new work has turned an old gap into something the certifier must sign off. Answering that question late is expensive. The builder ends up reopening finished ceilings, paying for a second electrician visit and explaining to the owner why the handover is delayed.

The organising idea of this article is simple. An alteration makes you responsible for the warning system that protects the people sleeping in the building, not only for the work you can see. The sections below show how to work out the scope, which areas it reaches, how the alarms must be powered and connected, and what to record so the upgrade can be shown to a certifier, a building inspector or a future buyer. The requirements are described here in words. Where the detail matters, the article tells you what to check and where to check it.

Why an alteration can bring smoke alarms into scope

The fire safety rules for existing homes are triggered by building work rather than by a decision to renovate. When work that needs approval is carried out on a dwelling, the approval and the certifier decide how far the upgrade reaches. The governing instrument is the Environmental Planning and Assessment Regulation, and the certifier will normally put the smoke alarm requirement into the conditions attached to the development consent or complying development certificate. Read those conditions before you price the job, not after the first inspection.

Whether an alteration triggers the upgrade depends on a combination of factors: the type of work, its value, whether it changes the structure or the layout, and whether the work is confined to one part of the dwelling or spreads through the whole of it. Two jobs of similar size can land in different places. A new bathroom in one corner of a house may leave the rest of the alarm system alone, while a rear addition that changes how people escape can bring the whole building into the upgrade. You do not need to memorise the detail. You need to ask the certifier, get the answer in writing and keep it with the contract.

The commercial reality is that this question is cheapest to answer at the quote stage. An alarm upgrade is a small line on a quote, but it can involve an electrician, an opening in a finished wall or ceiling and a reinspection. If the owner agrees to it after the walls are closed, the cost is paid in lost time and in a difficult conversation about a variation nobody priced.

Which areas the upgrade reaches

The purpose of the alarm layout is to wake people who are asleep. That is why the areas that matter most are the sleeping areas and the route people take to leave the building. A smoke alarm in each sleeping area, or in the corridor or space immediately outside it, will wake a person in bed when smoke reaches the hallway. An alarm over the kitchen bench will sound when someone is cooking, but it will not necessarily wake a person asleep on the far side of the house. The layout therefore follows the bedrooms, not the kitchen.

The upgrade also reaches each storey of the building, because smoke rises and a fire on one level can cut off the stairs before anyone on another level knows about it. Where the alteration changes the layout of a storey, the certifier may ask for the alarms on that storey to be checked against the new arrangement, even if the work itself sits in one room. The practical test is whether the new layout has moved a sleeping area, closed off a route to the exit or added a room that needs its own cover.

Be careful with the places that look like they should be covered but are not, and with the places that should not be. Alarms should be kept out of the kitchen and bathroom where cooking and steam will set them off, and the manufacturer specifies the clearance from those spaces. A reasonable alarm placed in a sensible position is more useful than an alarm in the room everyone expects, which the owner takes down after the third false alarm. Place each alarm where the standard and the manufacturer’s instructions put it, and write the position down so the next person can check it.

How the alarms must be powered and connected

A smoke alarm that depends on a single battery is a weak link. The usual expectation for an upgrade in a dwelling is a mains-powered alarm with a battery backup, so that the alarm keeps working through a power cut and the battery is there when the mains supply is interrupted. Connecting the alarm to the building’s electrical supply is the usual route for an alteration, because the units can then be interconnected and the owner has no battery to forget.

Interconnection is the feature that most often gets missed. When one alarm in a building detects smoke, every other alarm in the interconnected group should sound. That is what makes the system useful in a house with a bedroom at the far end of the building. A set of unconnected alarms, each with its own battery, will wake the person nearest the fire and leave everyone else asleep. The wiring between the units, the way the alarms are linked to one another and the product selected must all match what the certifier has accepted.

Wireless interconnection is sometimes offered as a way to avoid running cable through a finished house. Whether it is acceptable depends on the product, the building and the certifier’s view, so ask before you order anything. Do not assume that a product sold as interconnected meets the requirement for the building you are working on. Get the certifier’s written acceptance of the product and keep the data sheet with the handover documents.

All of this wiring is electrical work. Only a licensed electrician may carry it out, and the electrician must issue the certificate of compliance for electrical work. The Building Commission NSW advisory note on requirements for that certificate should be read before the electrician is booked, not after the wall is closed. The builder does not need to become an electrician, but the builder does need to know which work is electrical, who signs for it and what the certifier will want to see. For a related point on replacing existing electrical equipment, see the advisory note on like-for-like electrical replacement.

Working out the scope before the price goes out

The sequence below keeps the scope question in front of you before the price is sent. Most of the trouble comes from skipping the first step and going straight to the quote.

Each step produces something you can file. The first produces the certifier’s answer, the second produces a sketch of where the alarms go, and the third produces the electrician’s booking and the certificate. Keeping those three documents together is what turns a difficult question into a routine handover.

Putting the upgrade into the quote and the programme

An alarm upgrade should be a named line in the quote, with the number of alarms, the work it includes and the exclusions stated plainly. If the certifier’s answer is not in hand when the quote goes out, say so and make the upgrade a provisional item. The owner should understand that the alarms are a condition of the approval, not an optional extra. That avoids the argument at the end of the job about who should have seen it coming.

Describe the variation in plain words. A line that says alarms, with no reason, invites an argument about who should pay. Attach the certifier’s letter, or refer to it by date, so the owner has the same document the builder relied on. The owner then sees that the cost comes from the approval and not from a builder’s preference, which is a much easier conversation to have before the wall is opened.

Check how the upgrade affects the programme. The electrician works to a different schedule from the carpenters, and the alarms often have to be in place before the ceiling is closed, so a missed alarm in the first fix can hold up the plasterboard. Put the electrician’s inspection point into the programme and make sure the certifier’s inspection is booked against it. A late alarm is one of the most common reasons a finished ceiling gets reopened.

What to record for handover

The handover file is the part of the job the owner is least likely to read and the certifier is most likely to ask about. A clear record makes the upgrade provable years later, when the house is sold or the next builder opens the ceiling for an unrelated reason. The record should show what was installed, where, by whom and how the owner can test it.

Keep the photographs with the record. A picture of each alarm in place, with the model label visible and the ceiling position clear, is worth more than a sentence in the file. Put the handover documents in a single folder, give the owner a copy and include a short note on testing the alarms and replacing them at the end of their life, which is the period the manufacturer states.

A worked example from a western Sydney alteration

A builder in western Sydney takes on an alteration that opens the rear wall of a two-storey house to create a larger kitchen and family room. The bedrooms are upstairs, and the existing alarms are single battery units in the hallway and the kitchen. The builder asks the certifier before the quote goes out. The answer is that the upgrade applies to the storey with the new work and to the hallway that serves the bedrooms, and that the certifier wants to see the product before it is installed.

The builder adds a line to the quote for interconnected, mains-powered alarms in the hallway outside the bedrooms, a unit in the ground floor corridor, and the kitchen unit moved to a position away from the cooking area. The electrician is booked for the first fix, ahead of the plasterboard. The certifier inspects the alarms before the ceiling is closed, and the electrical certificate of compliance goes into the handover folder with the photographs.

When the owner later asks for the file ahead of a sale, the builder can answer the buyer’s questions in minutes. The job cost the builder an afternoon of extra planning and one line on the quote. Without that record, the same house would have been a question mark at settlement.

Keeping the evidence that stands up to scrutiny

A builder who keeps good records is protected on more than one job. The same habits serve the business when a licence is reviewed or when a dispute about the work arises. The general principle behind the Australian Taxation Office’s guidance on record keeping applies here too: keep the original documents, keep them in order and make sure they can be found when they are needed. For the wider set of records an NSW builder should hold, see the records an NSW builder must keep.

Continuing professional development is part of the same picture. If the question ever turns to what the builder knew about the alarm rules at the time, a record of the course completed on the topic is useful evidence. The PointCPD guide to how NSW builder CPD works explains which learning counts and how it should be recorded. Keep the CPD record in the same system as the job file, not in a separate drawer.

Finishing the job properly

The smoke alarm upgrade is the sort of work nobody notices when it is done properly and everybody notices when it is missed. Treat it as part of the building, not as an add-on. The questions to ask at the start are the same questions the certifier will ask at the end: which areas are caught, how the alarms are powered and connected, who signed for the electrical work and where the record is kept. Answer them early and the upgrade becomes a routine line in the programme.

Questions builders ask

• Electrical
• NSW Compliance
• Renovations

Published 3 October 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.