When Trenching Happens on Your Build
Trenching sits in a narrow window between the completed site cut and the slab pour. Your plumber and electrician specify where services run — under the slab, around the perimeter, or out to the street connection — and an earthmoving operator opens the ground to the required depth and width.
On new homes across Melton, Cobblebank, Weir Views, and Brookfield, most under-slab trenches are cut into the prepared clay pad after compaction. External trenches for sewer and stormwater connections may run through the front yard to the authority's junction point in the nature strip or easement.
Plumbing Trenches: Depths and Standards
Plumbing trenches in Victoria must comply with the National Construction Code and AS/NZS 3500 plumbing standards. Typical requirements include:
Sewer and Drainage
Sewer pipes generally require a minimum cover of 300 millimetres below finished ground level, with adequate fall (gradient) toward the connection point. Under a slab, pipes sit in a bed of sand or fine material with clearance from the concrete above. Your licensed plumber designs the layout; the earthmover cuts to their marks.
Stormwater
Melton properties must manage stormwater on-site or connect to council drainage infrastructure. Trenches for agi drains, strip drains, or underground pipes need correct falls — usually a minimum of 1:100 — and may require inspection by a building surveyor before backfill.
Water Supply
Incoming water mains from the street meter to the house typically run in a separate trench, often at 450 to 600 millimetres depth depending on local water authority requirements. In Melton, Western Water (now part of Greater Western Water) sets connection standards that your plumber follows.
Electrical Trenches: What Is Required
Electrical conduits carrying mains power from the street pit to your switchboard need trenches dug to the depth specified by your electrician and the distribution network service provider. In many Melton estates, underground power is standard — meaning conduits run in trenches rather than overhead lines.
Typical electrical trench depths range from 450 to 600 millimetres for domestic supply conduits, with warning tape installed above the conduit before backfill. The electrician pulls cable through after the trench is prepared; the earthmoving contractor may backfill once the plumber and electrician sign off.
Separate trenches are usually required for electrical and plumbing services — they should not share the same trench unless specifically designed and approved. Your trenching contractor in Melbourne coordinates multiple parallel runs in a single visit to minimise machine mobilisation costs.
Dial Before You Dig — Non-Negotiable
Before any trenching begins in Melton or anywhere in Melbourne, lodge a free enquiry with Dial Before You Dig (call 1100 or use the online portal). This alerts gas, electricity, water, and telecommunications providers to mark their assets on your site.
Plans alone do not show every underground cable or pipe. Striking a gas main or high-voltage cable is dangerous and expensive. Professional earthmoving contractors will not excavate until locates are confirmed and any required potholing is done to verify depths.
Allow at least two full business days for locate marks to appear. Factor this waiting period into your build schedule between site cut and slab pour.
Call 1100 before you dig — no Melbourne earthmoving contractor should excavate until service locates are confirmed on site.
Council and Authority Requirements in Melton
Melton City Council building permits cover the overall construction, but service connections involve additional authority approvals. Sewer connections require inspection by the relevant water authority. Electrical connections need coordination with the network provider for pit-to-house conduit installation.
If your trench crosses a footpath, nature strip, or road reserve, a council permit for excavation in the road reserve may be required. Traffic management and reinstatement of surfaces are additional costs your builder or earthmoving contractor should flag early.
Who Digs the Trenches?
Responsibility varies by contract. On many Melbourne builds, the earthmoving contractor who completed the site cut also opens service trenches because they already have the machine on site and understand the pad levels. On other projects, plumbers dig their own trenches with small equipment.
Using one earthmoving team for both site cut and trenching usually saves money and reduces coordination errors. The operator knows the soil conditions, has the right bucket widths, and can backfill and compact immediately after the plumber and electrician install their services.
Backfill and Compaction
After pipes and conduits are laid and inspected, trenches must be backfilled in layers and compacted to prevent future settlement beneath the slab or driveway. Sand bedding protects pipes from sharp rocks. Clay backfill is compacted in 150-millimetre lifts where specified.
Poor compaction in plumbing trenches is a common cause of slab cracking and driveway subsidence. An experienced Melton earthmoving operator compacts as they backfill rather than leaving loose material for the concreter to deal with later.
Typical Costs and Timeline
Under-slab trenching on a standard Melton home typically takes half a day to one day with a skilled operator, assuming locates are clear and trades are on site to mark out. External sewer and stormwater runs add time depending on distance to the connection point.
Costs depend on total trench length, depth, soil conditions, and whether spoil removal is needed. Expect trenching to be quoted as part of your earthworks package or as a separate line item — ask for clarity upfront.
Tips for Melton Homeowners and Owner-Builders
Book your plumber and electrician to mark trenches on the same day the earthmover arrives. Confirm all service locations on your plan before the site cut. Keep photos of every trench before backfill. Choose a local contractor who knows Melton estate layouts and typical soil conditions.
Professional Construction Services provides trenching alongside site cuts and truck work across Melton and greater Melbourne. We coordinate with your licensed trades, work from their marks, and backfill to specification — with team members who speak English, Arabic, and Turkish.