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Building over a sewer or easement — the approval nobody budgets for

From Modular Living Australia — the independent knowledge base Last updated: 8 Oct 2026

Building a granny flat or other structure over or near a sewer, water main or easement needs written approval from the water authority, not the council.^[1] In Victoria approval is needed to build over an easement or within one metre of a water, sewerage or recycled water asset under the Water Act 1989; in Queensland the work is assessed against Queensland Development Code MP 1.4; and some authorities will not approve any habitable structure within an easement.^[2][3][4][5]

There is a category of approval that sits outside the planning system entirely, is decided by an organisation most people never think of as a regulator, and can move a proposed granny flat three metres to the left or kill it outright. It is the water authority's consent to build over or near its assets.

For a backyard second dwelling this is the single most common cause of a design being redrawn late. The pipe is invisible, it is often not where people assume, and the approval runs on a separate track from council.

It is a separate regulator, on a separate track §

Sydney Water requires written approval before you build over or adjacent to its assets, and requires plans certified by a suitably qualified, competent and experienced person confirming the building is independently structurally supported so the asset is protected^[1].

In Victoria the requirement is statutory. Section 148 of the Water Act 1989 deals with structures over works and provides that a person must not allow a structure to be built, or filling to be placed, over a water corporation's easement without consent^[3]. South East Water states the practical trigger plainly: approval is required to build over any of its easements or within one metre of water supply, sewerage or recycled water assets, and doing the work without permission is illegal^[2].

Queensland takes a codified approach. Building work over or near sewers, water mains, stormwater drains and combined sanitary drains must be assessed against the Queensland Development Code MP 1.4, which provides consistent standards across the state along with a range of default building solutions^[4].

The common thread is that a planning approval does not carry this consent with it. They are decided by different bodies against different tests, and getting one does not get you the other.

What triggers an application §

The trigger is not "on top of the pipe". It is proximity, and the thresholds are tighter than most people expect.

Queensland's referral triggers are worth reading closely because they are the most explicit published example of what "near" means in practice. Unitywater states that an application is required where the clearance from its infrastructure to a fence, building or other structure would be reduced to less than 1.2 metres; where driven piles or piers are located within 5 metres of infrastructure; or where any building, structure or bored excavation for piers or footings falls within the zone of influence of the infrastructure^[6].

That last concept — the zone of influence — is the one that catches modular and transportable installations. It is a notional wedge of soil extending outward and downward from the pipe. A footing that lands inside it can transfer load onto the pipe even though nothing is physically touching it. Screw piles and bored piers, both common on off-site builds because they suit fast installation, are exactly the footing types most likely to intersect it.

What the authority can require §

Where approval is granted, it usually comes with conditions rather than a simple yes. Published requirements across authorities include:

• Structural certification that the building is independently supported and does not load the asset^[1].
• Structural engineering design drawings of the footings showing the infrastructure, and elevation views of the proposed work^[6].
• CCTV inspection reports of the pipe, at the owner's cost, both before and after construction^[3].
• Written consent from the easement holder where the easement is not held by the authority assessing the application^[6].

Some things are simply refused. Lower Murray Water states that approval will not be considered under any circumstances for a habitable structure within an easement, for any structure over or within an easement containing an existing or planned urban water main, or for any structure that blocks access to a sewer maintenance hole or house connection point^[5].

A granny flat is a habitable structure. On a block where the easement runs along the rear boundary — the standard configuration in a great many Australian subdivisions — that is the end of the conversation about putting the second dwelling there.

And if you damage it §

The financial exposure is straightforward and sits with the owner. South East Water states that if its assets are damaged as a result of your works, you are responsible for the cost of repairs^[2].

That risk is amplified by off-site construction. A module arriving on a truck and being craned into position involves point loads, outrigger pads and heavy vehicle movements across ground that was never assessed for it. Delivery-day damage to a shallow sewer is not a hypothetical.

Where this belongs in your sequence §

Before design, not after. The order that avoids the expensive version of this problem:

1. Obtain the asset locations for the property from the authority. Most publish a mapping tool or a property information request process^[2][3].
2. Have the assets located physically on site if anything is close. In New South Wales this is commonly done through a sewer peg-out.
3. Give that information to the designer before the siting is fixed.
4. Lodge the build-over or adjacent-asset application in parallel with the planning pathway, not after it.

For a factory-built dwelling the cost of getting this wrong is not the same as for a conventional build. A site-built house can be shifted on paper. A module is manufactured to a footing layout, and a footing layout that has to move after fabrication has started is a far more expensive change.

What is not covered here §

• Your property's assets. Nothing here tells you what is under your block. Only the authority's records and a physical locate will.
• Western Australia, South Australia, Tasmania, the ACT and the Northern Territory. No authority-specific requirements for those five were located in the sources compiled here, and none are inferred from the three above. Each has its own water authority with its own process.
• Fees and timeframes. These vary by authority and are not published here.
• Clearances by pipe size. Required clearances generally increase with pipe diameter and depth. The figures quoted above are the published triggers of particular authorities, not a national standard.
• Non-water easements. Easements for electricity, gas, drainage held by a council, and rights of carriageway each have their own holders and consent processes.
• Removing or relocating an easement. A separate legal process not addressed here.
• Connection costs. Connecting a new dwelling to water and sewer is a different matter, covered in the service connections guide on this site.

References §