Most shed electrical work in Australia gets done after the shed is built. The cabling runs are surface-mounted, the conduit is added after the fact, and the work is more expensive and uglier than it needs to be. Planning the electrical at the rough-in stage — before the slab is poured and the walls go up — costs less and produces a better result.

What rough-in means

Rough-in is the electrical work that happens before the visible finishes are in place. For a shed, this includes the underslab conduit runs, the cable routes through the wall framing, the outlet positions, and the entry point for the main supply.

Done properly, rough-in produces a shed where the electrical work is invisible — cables run inside walls and under the slab, outlets and switches sit where they were planned, and adding new circuits later is a matter of pulling cable through existing conduit rather than running new conduit.

What to plan before the pour

The main supply entry point is the foundational decision. Underground supply from the main board into the shed is standard for serious sheds. The trench depth, the conduit size, and the entry point into the slab need to be coordinated with the slab pour.

The internal underslab runs are the second decision. Conduit runs under the slab to the workshop areas where you want outlets that are not near a wall — workbenches in the middle of the shed, equipment positions, machinery — let you have power where you need it without surface conduit running across the floor.

The earth grid is the third decision. A proper shed earth grid bonded into the slab reinforcement provides better protection than a single earth stake added after the fact.

What to plan before the walls

The outlet positions and switch positions should be marked before the walls go up. Cable runs inside the wall framing are tidy and protected. Cable runs surface-mounted after the walls are up are ugly and vulnerable.

The lighting circuit is the obvious internal wall work. The often-missed work is the conduit for future runs — empty conduit from the main board area to the various corners of the shed lets you add circuits later without opening walls.

The ventilation and air conditioning power requirements should be considered at this stage. Air conditioning units that get added later often end up on undersized circuits and the rework is significant.

What to plan for the workshop specifically

Workshop sheds need more outlets than residential rooms. The standard density is one double outlet per metre of bench top, plus dedicated circuits for high-current equipment.

Three-phase power is worth running into the shed if you are anywhere near needing it. Adding three-phase later is expensive. The cost difference at the rough-in stage is modest.

EV charger preparation, even if you do not have an EV now, is cheap to add at rough-in. A dedicated circuit and an outlet position near the door is small money. Retrofitting an EV charger circuit later is not.

What the licensed work costs

A licensed electrician for a serious shed rough-in costs $3,000 to $8,000 depending on size and complexity. The work has to be done by a licensed person and the certifications are required for insurance and resale.

The cost is meaningfully lower at the rough-in stage than the retrofit stage. A retrofit on the same shed costs $5,000 to $15,000 because the cable runs are harder and the patching of walls and slab is messy.

The mistakes I have made

Skimping on conduit sizes. The conduit costs almost nothing. Larger conduit at rough-in saves you from having to pull a second conduit through later. Always go one size up from what you think you need.

Forgetting future circuits. The conduit runs I added without specific circuits in mind have all eventually been used. The conduit runs I did not add have all eventually been needed.

Not coordinating with the slab pour. The conduit penetrations through the slab need to be placed before the pour, in formwork, with proper sealing. After-the-fact penetrations are a compromise.

A note for first-time shed buyers

If you are buying a shed and you have any intention of doing serious workshop work, talk to the electrician before the slab is poured. Forty minutes of conversation at the right time saves thousands of dollars of rework and produces a shed you will be happier with for decades.