Putting a pool on a sloping block in Hobart

A pool on a sloping block is common in Hobart, where many backyards fall towards the Derwent or away from kunanyi. It's also where pool engineering earns its fee. On flat ground a pool is a box in the soil. On a slope it becomes a retaining structure, a load near the house and a water tank on a hillside, all at once.

Pools on sloping blocks: quick facts

Approval

Pool and barrier are notifiable work

Barrier

AS 1926.1-2012, built by a licensed builder

Shell standards

Concrete AS 2783:2025; fibreglass AS 1839:2021

On a slope

The shell and retaining walls are designed together

Near council pipes

Consent for pools over 9 m² or 300 mm deep

Our fee

Pool engineering from $850 + GST

What engineering does a pool on a sloping block need?

A pool on a slope needs a structural design for the shell, a design for any retaining walls, a check of nearby footings, and drainage that controls groundwater around the pool. Each designer gives the building surveyor a Form 35.

What are the pool regulations in Tasmania?

In Tasmania, an inground swimming pool and its safety barrier are notifiable building work: a building surveyor issues a Certificate of Likely Compliance before work starts, and a licensed builder builds the barrier.

Councils add their own detail. Clarence, for example, requires barriers for water 300 mm or deeper and for pools and spas installed from 1994. Ask your building surveyor which barrier edition applies to your approval.

Does a pool on a slope need a retaining wall?

A pool on a slope usually needs retaining in two places: the uphill cut, and the downhill side where the pool wall stands partly out of the ground. On the downhill side, the shell itself often acts as a retaining wall. That is engineering practice rather than a Tasmanian rule, and it means the shell is designed for soil pressure as well as water.

• Separate retaining wall: the slope is retained behind the pool, and the shell is designed as a normal inground pool. Simpler shell, more wall.
• Shell as the wall: the pool wall retains the slope, so it must carry soil pressure when the pool is empty and water pressure when the soil is dug away.
• Partly elevated pool: the downhill edge sits on piers or a thickened footing into firm ground, often with a deck around it.

The retaining wall rules still apply. A wall over 1.2 m, or over 0.5 m within 1.5 m of a boundary, is no longer low-risk work, and an easement or landslip band takes any wall out of low risk. See our retaining wall rules guide and retaining wall design (from $750 + GST).

What is the zone of influence, and why does it matter for a pool?

The zone of influence is the ground beside an excavation that can move if the excavation isn't supported, and on a sloping block the house is often in it. Engineers commonly draw a line up from the base of the excavation at about 45°, flatter in soft or wet ground. Footings above that line, yours or a neighbour's, need to be considered in the design.

The reverse applies too. A house, retaining wall or driveway uphill of the pool pushes extra load (surcharge) onto the pool wall, so the shell is designed for it. If the excavation would need to shore or underpin a neighbour's footings, that is protection work, which needs a building surveyor. A dilapidation report on the neighbour's house before digging starts is good practice.

Can groundwater lift a pool out of the ground?

Yes. An empty pool in saturated ground can float, because water pressure under the shell pushes up harder than the empty shell weighs down. On hillsides, water moving downslope can collect against the uphill wall and under the floor. This is engineering practice, not a local rule, and it is why designs on slopes include:

• subsoil drainage around and under the shell, with an outlet that works
• a hydrostatic relief valve, or a shell heavy or anchored enough to resist uplift
• clear instructions on emptying the pool: when it's safe, and when it isn't

Rock changes the picture as well. Jurassic dolerite forms Hobart's higher hills, and some hillside excavations reach rock. A shell that sits partly on rock and partly on clay can move unevenly, so the design either takes the whole pool onto one material or allows for the difference.

How much does pool engineering cost in Hobart?

Pool engineering in Hobart typically costs more on a slope than on a flat site, because the retaining design and ground checks add work. A national pool engineering firm publishes these indicative Hobart fees:

Our swimming pool engineering starts from $850 + GST for a straightforward pool. A sloping block with retaining walls costs more, and your fixed quote states the price and what's included before we start.

What if the pool is near a stormwater pipe, easement or landslip band?

A pool larger than 9 m² of water surface or deeper than 300 mm counts as a "prescribed structure" under the Urban Drainage (General) Regulations 2026. On a council stormwater easement, or within 1 m of a council stormwater pipe, it needs the council's consent before work starts. See building over a stormwater easement.

When should you call a structural engineer about a pool on a slope?

• Before you sign with a pool builder, so the shell, walls and drainage are priced on a real design
• The pool is close to the house or a boundary, inside a likely zone of influence
• The slope needs retaining walls over about 1 m, or the pool edge will stand out of the ground
• The ground is wet or seeps after rain, or a council pipe or easement crosses the yard
• The block is in a landslip band on LISTmap