Installing a swimming pool on a flat suburban block is a relatively straightforward project. Installing one on a Blue Mountains slope, where the pool needs to be excavated into a hillside, or where the surrounding terrain must be retained to create a level pool surround, is a substantially more complex undertaking.
Retaining walls are almost always required in pool installation on Blue Mountains slopes, and the combination of pool excavation loads, water loads, and soil pressures on the retaining structure creates engineering challenges that go beyond standard residential retaining wall design.
Why Pool Sites in the Blue Mountains Require Retaining Walls
The Typical Blue Mountains Pool Site Problem
A typical Blue Mountains lot falls away significantly from the house toward the rear of the property. The pool location, usually the largest flat area available, is often at the base of this slope, or requires excavating partway into the slope to achieve the necessary level area.
In either case, the pool installation creates or exposes a cut face or a fill boundary that must be retained:
Cut into slope: Excavating the pool into the hillside creates a vertical or near-vertical cut face above and behind the pool. This cut face must be retained, typically by a retaining wall along the back and possibly the sides of the pool area.
Pool on fill: Building the pool on a filled platform requires retaining walls on the downslope side to hold the fill in place against the slope below.
Level pool surround: Even when the pool itself is feasible without major cutting, creating a level surround area (paving, garden, outdoor furniture area) typically requires retaining walls on the uphill side.
Engineering Complexity: Pools and Retaining Walls
Swimming pools create two structural loads that interact with adjacent retaining walls:
Water Pressure Outward
A full swimming pool is a large, heavy water body pressing outward on its walls and floor. When a retaining wall is built close to a pool, the pool structure and the retaining wall must both be designed so that neither undermines the other’s foundation.
The setback issue: The general rule is that retaining wall footings should not be within the potential soil failure zone below the pool structure’s footings or on the pool’s water pressure influence zone. For most residential pools, a minimum setback of 1.5-2.0 metres from the pool wall to the nearest retaining wall is appropriate, but an engineer must confirm this for the specific conditions.
See [/guides/retaining-wall-swimming-pool-proximity/] for the detailed guide to setbacks and structural interaction.
Surcharge from Pool Area
The pool surround (paving, outdoor furniture, people, equipment) imposes a surcharge load on any retaining wall adjacent to or below the pool level. This surcharge must be factored into the retaining wall design, a wall that is only sized for soil pressure will be under-designed if a paved pool surround extends above it.
Geotechnical Assessment for Pool + Retaining Wall Projects
For any pool installation on a Blue Mountains slope that involves retaining walls over 1.0m, or walls within 3.0m of the pool structure, a geotechnical assessment is strongly recommended and often required by BMCC as part of the DA.
The geotechnical assessment for pool + retaining wall projects must address:
- Soil and rock conditions to the depth of pool footings and retaining wall footings
- Groundwater conditions, pools on slopes above the water table are straightforward; pools close to or below groundwater level face different challenges
- Slope stability, the overall stability of the slope with the pool excavation and retaining walls in place
- Bearing capacity for pool footings
See [/guides/geotechnical-report-blue-mountains/] for what a geotechnical report covers.
BMCC Approval for Pool + Retaining Wall
A swimming pool in the Blue Mountains requires a DA in most cases (pools are not exempt or complying development in the Blue Mountains generally). The retaining walls associated with the pool installation are typically included in the same DA.
What the DA documentation must include:
- Site plan showing pool location, retaining wall positions, pool surround levels
- Structural drawings for the pool (from the pool engineer or designer)
- Structural drawings for the retaining walls (from the engineer)
- Geotechnical report
- Drainage plan, pool backwash drainage, pool overflow, retaining wall drainage
- BASIX certificate (for the pool mechanical systems)
- Heritage impact statement if the property is heritage-listed or in an HCA
The interaction between the pool DA and the retaining wall DA means both must be assessed together. Do not build a pool without retaining walls (if they are needed) and do not assume they can be added later, separate approvals at different times create complications.
See [/guides/bmcc-council-approval-retaining-walls/] for the full approval guide.
Drainage Integration
Pool sites and retaining walls both generate significant drainage requirements. In the Blue Mountains, the drainage design must integrate:
Pool backwash and overflow: Pool water that escapes through normal filtration backwash or overflow must be directed to an approved disposal point, typically council stormwater or a soakage area. It must not discharge toward or behind a retaining wall.
Pool surround runoff: The paved pool surround collects rainfall. This water must be directed to stormwater via grade and inlet pits, not toward the uphill cut and retaining wall.
Retaining wall subsoil drain: The ag pipe behind the retaining wall drains groundwater from the hillside above the pool area. This must discharge to stormwater, well away from the pool structure.
Groundwater management: On some Blue Mountains sites, cutting into the slope for a pool releases a perched groundwater flow. This groundwater must be managed through drainage rather than allowed to pond against the pool or retaining wall.
See [/guides/retaining-wall-drainage-design/] for the retaining wall drainage design guide.
Sandstone Excavation for Pool Sites
Most Blue Mountains pool sites encounter sandstone during excavation. Sandstone excavation for a pool is expensive, it requires a rock hammer attachment on an excavator or pneumatic jack hammering, both of which are slow compared to earth excavation.
What this means for budgeting:
- Always budget for sandstone in your pool excavation costs
- Get the contractor to specify how sandstone will be handled and what the day-rate or cubic metre rate is for rock
- Broken sandstone from pool excavation can sometimes be reused as fill for the retaining wall area or in gabion walls, discuss this with your contractor to reduce disposal costs
See [/guides/cut-fill-earthworks-blue-mountains/] for earthworks cost detail.
Retaining Wall Options Around Pool Areas
Concrete Sleeper Walls
Concrete sleeper walls on H-posts are the most common retaining structure around Blue Mountains pools. They provide structural performance, clean appearance, and are compatible with the contemporary pool aesthetic. H-post foundations must be designed to provide the required setback from pool footings.
See [/services/concrete-sleeper-walls/].
Sandstone Retaining Walls
Sandstone retaining walls around pool areas are attractive, the natural stone creates a beautiful pool environment, but must be properly engineered for pool-adjacent conditions. Dry-laid sandstone must be assessed for whether the gaps between stones are a child safety concern for pool area compliance.
See [/services/sandstone-retaining-walls/].
Reinforced Concrete or Block Walls
In situations where the retaining wall is close to the pool structure and must carry high loads, a reinforced concrete wall or heavily engineered block wall may be required. These are designed as structural walls rather than gravity retaining walls.
Cost Ranges for Pool + Retaining Wall Projects (2026)
Pool installations on Blue Mountains slopes with retaining walls are premium projects. The combination of pool excavation, sandstone rock work, retaining wall engineering, and BMCC approval costs adds up:
| Cost Component | Typical Range |
|---|---|
| Pool (standard inground, 8m × 4m) | $50,000 to $100,000+ |
| Sandstone pool excavation (if encountered) | $8,000 to $25,000 additional |
| Retaining walls around pool (per lm) | $900 to $1,500/lm |
| Geotechnical assessment | $2,500 to $5,000 |
| Structural engineering (pool + walls) | $3,000 to $8,000 |
| DA preparation and BMCC fees | $3,000 to $8,000 |
| Pool surround paving | $15,000 to $40,000 |
A complete pool + retaining wall + paving project on a Blue Mountains slope can range from $120,000 to $250,000 for a well-specified project. Costs depend heavily on slope severity, sandstone depth, pool size, and retaining wall scale.
See [/guides/retaining-wall-cost-guide-blue-mountains-2026/] for detailed retaining wall cost factors.
FAQ
Do I need a separate retaining wall DA if I already have pool approval? In most cases, the retaining walls associated with pool installation are included in the pool DA. However, if retaining walls are being built separately (before or after the pool), they may require their own DA or complying development certificate. Check with BMCC.
How close can a retaining wall be to my pool? The setback depends on the depth and type of pool footings, the retaining wall footing design, and the soil/rock conditions. As a general guide, a minimum 1.5m setback from the pool wall to the nearest retaining wall footing is appropriate, but an engineer must confirm this for your specific conditions. See [/guides/retaining-wall-swimming-pool-proximity/].
Can I build a sandstone retaining wall around my pool area in a heritage zone? Yes, sandstone is generally the preferred material in heritage zones. For a pool in a heritage conservation area, the sandstone retaining wall design is typically compatible with BMCC’s heritage guidelines. Include a heritage impact statement in your DA.
My pool quote doesn’t mention retaining walls, should it? If your pool is being installed on a slope, retaining walls are likely required. If the pool contractor hasn’t mentioned them, ask specifically. Either they’ve included them in the scope or they’ve excluded them, which means you’ll need a separate retaining wall contractor. Clarify before signing.
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