Key takeaways
- Split system coordination is a frame-stage problem, because the outdoor unit position, the wall penetration and the drain route must all be locked in before the wall is closed up.
- Electrical connection is licensed work, so the builder’s job is to sequence the electrician and the refrigeration mechanic rather than to have anyone improvise a supply at handover.
- Every head needs a continuous fall to a lawful discharge point, and a condensate drain that runs uphill or terminates under the house will show up as a stain or a complaint within the first cooling season.
- Because the unit is chosen late, often by the owner, the rough-in must be sized for a range of capacities rather than the one model that happens to be quoted at contract.
- Defects in split system work are almost always latent — they appear after practical completion, when the builder has lost the leverage of retention and the owner has the certificate in hand.
A single-head split system looks like the least complicated trade package on a new home. One head on a wall, one outdoor unit on a bracket or a slab, a pipe run between them. Owners like them because they are cheap to buy and cheap to run a single room, and builders like them because they do not eat ceiling space the way a ducted system does.
The complication is not the equipment. It is the sequencing. The decisions that determine whether a split system looks like a considered part of the house or an afterthought bolted on at the end are made at frame stage, when the wall is still open and the pipe route can still be cut cleanly. By the time the installer arrives with the head and the outdoor unit, every one of those decisions has already been locked in by someone else.
This article is about coordinating single-head splits on new residential work — how to sequence the trades, where the risks sit, and what to check before the wall is sheeted. If you are weighing up a ducted system instead, the design and installation issues are different and are covered in our article on ducted air conditioning design and installation.
Why the split system decision belongs at frame stage, not fit-off
A split system has three physical interfaces with the building: the head on the internal wall, the penetration through the wall or roof, and the outdoor unit position. All three are set by the frame. Once plasterboard is on and the external cladding is fixed, the only remaining option is to run pipework on the surface, which is where most of the ugly split system installations you see on new homes come from.
There is a second reason to settle it early. The unit is often not chosen by the builder at all. On many new homes the owner buys the split system themselves, sometimes months after contract, sometimes on a sale weekend. If the rough-in has been sized for one particular model and the owner turns up with a different capacity or a different brand with different pipe sizes and a different wall bracket, the rough-in is wrong and someone is paying to redo it.
The practical answer is to rough in generously. Confirm the wall type and the head height with the owner at frame stage, agree where the outdoor unit will sit, and make sure the penetration, the cable route and the drain are all sized for a range rather than for a single unit. Record the decision in the contract documentation, including who supplies the unit and who is responsible for the connection.
The electrical connection is licensed work, and the sequencing follows from that
Electrical work is a licensed activity, and the safety obligations that attach to it are set out by the regulator rather than by the builder. Safe Work Australia’s guidance on electrical safety is clear that electrical equipment and installations must be safe, that only competent and licensed people work on them, and that the risks of shock, fire and arc flash are managed at the source.
For a builder, that translates into a sequencing rule rather than a technical one. The electrician installs the circuit, the isolator and the supply point. The refrigeration mechanic connects the unit to that supply, or the electrician does, depending on how the two trades are licensed and how the contract is written in your state. What the builder must not do is let the split system be connected by whoever is on site when the unit arrives, on the assumption that it is a plug-in appliance.
There is a variation risk here that is easy to miss. If the electrical rough-in was priced as a standard allowance and the owner later adds a split system, the circuit, the isolator and the cable run are all additional work. That is a variation, and it should be documented as one before the electrician starts, not argued about at the end of the job.
Lead in. The mistake that costs the most is roughing in a split system without agreeing the outdoor unit position and the drain route first. Moving a drain after the wall is sheeted and the paving is laid means cutting finished surfaces, and the cost lands on the builder, not the owner.
Condensate drainage is the defect that appears after handover
Every cooling head produces condensate, and it has to go somewhere lawful. The drain is the least glamorous part of the installation and the most common source of callbacks, because a drain that is wrong often looks fine on the day of commissioning and fails a season later.
The rule to work to is continuous fall. A condensate drain must run downhill from the head to its discharge point without any section that rises, sags or runs level. In practice the failures come from three places: a drain that has been run through a wall cavity with a horizontal section to get around a stud, a drain that terminates under the floor or into a garden bed where it saturates the soil, and a drain that has been joined with a fitting that creates a lip the water cannot get past.
Decide the discharge point at frame stage. If the head is on an external wall, the drain can usually run straight out and down. If it is on an internal wall, the drain has to travel to a suitable point, and that route needs to be planned while the frame is open and the fall can be checked with a level. Photograph it before sheeting. When a stain appears on a ceiling six months after handover, the photograph is what tells you whether the drain was right when you closed the wall in.
Sealing the penetration matters too, and it is the same principle that applies to any hole in the envelope. Our article on building envelope air sealing in residential work covers why an unsealed penetration undermines the thermal performance of the whole wall, and a split system pipe is a large one.
Coordinating the trades so the rough-in is cut once
The electrician and the refrigeration mechanic both need access to the same wall at the same point in the programme. If they arrive separately, you get two sets of penetrations, a cable run that conflicts with the pipe route, or a pipe that has been installed across the position the electrician needed for the isolator.
Book them into the same window. The refrigeration mechanic sets the pipe route and the drain, the electrician runs the supply and the isolator to a position that suits the finished wall, and both agree the penetration before anyone drills. This is a single morning of coordination that saves a day of rework later.
There is an apprenticeship dimension to this that is easy to overlook on a residential site. Changes to the Australian Apprenticeships Incentive System from 1 January 2026 affect how apprenticeship support is structured, and electrical and refrigeration trades are among those that rely on apprentices to keep crews staffed. If you are running apprentices through your site, the practical implication is that supervision arrangements and the paperwork that supports them are worth confirming with your training provider rather than assumed.
Coordinating a single-head split system across the build programme
- 1Design and contract stageConfirm whether the unit is supplied by the owner or by the builder, and record the answer in the scope so no one assumes the other.
- 2Frame stageSet the head height against the room layout, note the wall type, and confirm the outdoor unit can sit where the plan shows it.
- 3Rough-in stageGet the electrician and the refrigeration mechanic on site in the same window so the cable, the pipe route and the drain are cut once.
- 4Pre-line inspectionWalk the rough-in before sheeting, checking penetration positions, drain fall and the isolation point.
- 5Fit-off stageInstall heads and the outdoor unit after painting, then commission and record the settings.
- 6HandoverDemonstrate the controls, hand over the manuals, and note the filter cleaning interval for the owner.
Outdoor unit position: clearance, fixing and access
The outdoor unit is where the split system meets the neighbours, the fence line and the building surveyor. Three things determine whether it is acceptable: clearance, structural fixing, and access for service.
Clearance is set by the manufacturer, and the figure matters because the unit has to move air through its coil. A unit pushed into a corner or boxed in by a fence will struggle, run hot, and fail early. Check the installation manual for the clearance the manufacturer specifies for the model being installed, and check it against the position on the plan before the bracket goes on. Where the position is tight, the answer is usually to move the unit rather than to hope.
Fixing is a structural question. A wall bracket carrying an outdoor unit imposes load and vibration on the frame, and on lightweight cladding the fixings have to suit the substrate. A ground-mounted unit on a manufactured slab is often simpler, provided the slab is stable and the unit is not sitting in a drainage path.
Access is the one that gets ignored. Service technicians need to reach the unit, open it and work on it. A unit installed behind a fixed screen, under a deck with no clearance above, or on a bracket two storeys up with no safe access is a maintenance problem for the life of the building. If the position cannot be serviced safely, it is the wrong position.
The commercial reality: who pays when a split system goes wrong
Split system defects are almost always latent. They appear after practical completion, when the builder has lost the leverage of retention and the owner is living in the house. A condensate stain on a ceiling, a unit that ices up because the gas charge was never verified, a head that was mounted too high to throw air across the room — none of these show up at the pre-handover walkthrough.
On a project where a head contractor holds retention, the rules about how retention money is held and released are set out by the NSW Government, and they affect how much protection you actually have when a defect emerges late. The point is not the mechanics of retention; it is that a split system defect surfacing in the first cooling season is usually a cost you carry rather than a cost you recover.
That is the argument for doing the coordination work up front. The time spent at frame stage confirming the head position, the pipe route, the drain fall and the outdoor unit clearance is a fraction of the cost of returning to a finished house to move a drain. If you are pricing the job and want to understand where those costs sit in your margin, our article on pricing and margin for residential builders is a useful companion.
Pre-line rough-in checks for a split system
- Head position set at the height and wall agreed with the owner, not the default on the plan.
- Pipe route runs inside the wall or in a ducted cover, with no exposed run across a finished face.
- Condensate drain falls continuously to a lawful discharge point and is not run uphill at any point.
- Wall penetration is drilled, sleeved and sealed against weather and air movement.
- Electrical supply, isolator and cable route confirmed by the licensed electrician.
- Outdoor unit position checked for clearance, structural fixing and access for future service.
- Photographs taken of the rough-in before sheeting, filed against the lot.
Worked example: a single-head split that had to be moved
A builder in western Sydney was completing a four-bedroom project home. The contract included one split system in the main living area, with the outdoor unit shown on the plan on an external wall beside a paved courtyard. The owner had not chosen the unit at contract, and the plan showed the head in a position that suited the furniture layout drawn at sales stage.
At frame stage, the head position was set and the pipe route was cut through the wall to the outdoor unit position shown on the plan. The drain was run through the same penetration and turned down the outside face of the wall to discharge onto the paving. Nobody checked the fall across the horizontal section inside the wall.
The unit was installed at fit-off. The owner ran it through the first summer. Water pooled on the paving next to the outdoor unit rather than draining away, and by late summer a damp patch had appeared on the internal wall below the head. The horizontal drain section inside the cavity had a slight backfall, and the condensate was finding its way out through the plasterboard rather than down the pipe.
The fix required opening the wall, re-running the drain with continuous fall, and re-sheeting and repainting the affected area. The paving had to be lifted to change the discharge point. The owner had already taken possession, the defect was reported as a building defect rather than a maintenance item, and the builder carried the cost of the rectification and the disruption. All of it traced back to a decision that was not made at frame stage.
The lesson is not that the drain was installed badly. It is that no one checked it before the wall closed, because the drain was treated as part of the installer’s scope rather than as part of the builder’s rough-in. On the next job, the same builder added the split system rough-in to the pre-line inspection list and photographed it.
What to put in place on the next job
The coordination work is not complicated, but it has to be deliberate. Confirm at contract stage whether the unit is owner-supplied or builder-supplied, and record it. At frame stage, walk the head position with the owner and agree the outdoor unit position. Book the electrician and the refrigeration mechanic into the same window for the rough-in. Add the split system to the pre-line inspection and photograph the pipe route, the drain fall and the penetration before sheeting. At fit-off, make sure the unit is commissioned and the settings are recorded, and demonstrate the controls to the owner at handover.
None of that requires a specialist. It requires the builder to treat the split system as a coordinated trade package rather than an appliance that turns up at the end. Builders working in NSW also need to keep their continuing professional development current, and our guide to how NSW builder CPD works explains what counts and how to record it. If you are looking for courses that cover coordination, compliance and contract administration, the PointCPD course catalogue is the place to start.
Single-head split systems compared with ducted air conditioning on a new home
| Single-head split | Ducted system |
|---|---|
| One outdoor unit per head, positioned near the room it serves | One outdoor unit serving a network of ducts and outlets |
| Pipe and drain penetrations through individual walls and roofs | Bulkhead or ceiling void taken up by ductwork and outlets |
| Head position is a wall and furniture decision made at frame stage | Outlet and return positions are a ceiling plan decision made at design stage |
| Owner can add or change a unit later with less disruption | Capacity and zoning changes are far harder to retrofit |
| Trades are the electrician and the refrigeration mechanic | Trades include sheetmetal ductwork, insulation and ceiling works as well |
Questions builders ask
Who is responsible for the split system rough-in on a new home?
It depends on how the contract is written, and the ambiguity is where the problems start. If the split system is an owner-supplied item, the rough-in is usually excluded from the builder’s scope unless it is added as a variation. The safe approach is to state in the contract who supplies the unit, who cuts the penetration, who runs the drain and who connects the electrical supply.
When should the electrician be booked for a split system rough-in?
Book the electrician and the refrigeration mechanic into the same window at frame stage, before the wall is sheeted. Running them separately produces duplicate penetrations and cable routes that conflict with pipe routes. One coordinated morning at frame stage is far cheaper than reworking a finished wall.
Can a split system condensate drain discharge onto paving or into a garden bed?
It should discharge to a lawful point, and dumping condensate onto paving or into a garden bed creates a nuisance and can saturate the soil. The drain must also fall continuously to the discharge point with no horizontal or rising sections. Decide the discharge point at frame stage so the fall can be checked while the wall is open.
What clearance does an outdoor unit need?
The clearance is set by the manufacturer for the specific model, so check the installation manual rather than working from a rule of thumb. The unit has to move air through its coil, and a unit boxed in by a fence or a screen will run hot and fail early. Confirm the clearance before the bracket goes on.
Why do split system defects often appear after practical completion?
Most split system faults are latent. A drain with a slight backfall, a unit that was never properly commissioned, or a head mounted too high to throw air across the room will all pass a pre-handover walkthrough. They show up in the first cooling season, when the builder has less leverage and the owner is already in the house.
Does a split system affect the thermal performance of a new home?
A split system conditions one room rather than the whole house, so the building envelope matters more, not less. An unsealed penetration for pipes and cables lets air move through the wall and undermines the insulation around it. Seal the penetration as part of the rough-in and treat it as part of the envelope, not as a separate trade detail.
Sources
- Electrical safety · Safe Work Australia
- Retention money held by head contractors · NSW Government
- Changes to the Australian Apprenticeships Incentive System from 1 January 2026 · Apprenticeship Support Australia · 2025-12-01
Published 13 July 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.
