Terracing is the most practical and visually appealing way to make a steep Blue Mountains slope into a usable, productive garden. Rather than one tall retaining wall trying to hold back the entire hillside, terracing uses multiple lower walls, each creating a level planting bed, stepping up or across the slope.
The practical advantage beyond aesthetics: multiple walls under 600mm each are generally exempt development in the Blue Mountains, avoiding the DA process entirely. A single wall over 1.0m requires a DA. If your garden slope rises 2.0 metres over 15 metres of length, four 500mm walls almost always work better than one 2.0m engineered wall, and they cost less to approve.
Why Terracing Works for Blue Mountains Gardens
Approval Advantages
BMCC’s exempt development threshold for retaining walls is 600mm. Multiple walls under 600mm each, with adequate horizontal spacing between them, are generally exempt development, no DA, no certifier, no approval fees. This is a genuine planning advantage that terracing provides over a single tall wall.
Important qualification: If the walls are so close together that they effectively act as a single structure, BMCC may consider them a combined wall and apply the overall height to the approval threshold. Space walls adequately, a rule of thumb is that the horizontal spacing between wall bases should be at least equal to the combined height of the walls. Confirm with BMCC for your specific situation.
Drainage Benefits
Multiple low walls manage water better than one tall wall. Each terrace level acts as a catchment basin, slowing rainfall runoff and giving it time to infiltrate rather than flowing rapidly downslope. This reduces erosion, reduces the volume of fast-moving water at the base of the slope, and improves soil moisture for planting.
Each terrace level should have its own drainage path, a slight backward slope toward the uphill cut face, with overflow to the terrace below via weep holes or notches in the wall capping.
Structural Advantage
Lower walls carry less load per wall than a single tall wall. A 500mm wall retaining 500mm of soil has less than half the lateral pressure of a 1.0m wall retaining 1.0m of soil. Multiple lower walls are structurally simpler and less prone to catastrophic failure.
Planting Opportunity
Each terrace level creates a distinct planting area with its own microclimate. Lower terraces may be moister and shadier; upper terraces drier and sunnier. This diversity supports a wider range of plants than a single flat lawn or garden bed would.
Terrace Layout Design
Determining Wall Spacing and Height
For a given total slope height (H) and terrace wall height (h), the number of terraces needed is approximately H/h, and the horizontal spacing of each terrace depends on the desired terrace width.
Example calculation:
- Total slope: 2.5 metres rise over 12 metres horizontal run
- Desired terrace width: approximately 2.0 metres each
- Wall height: 500mm per wall
- Number of walls: 5 walls of 500mm each = 2.5m total rise
- Total horizontal coverage: 5 × 2.0m + 5 × (wall thickness ~200mm) = approximately 11m
This roughly matches the available 12 metres, giving one terrace level approximately every 2.2 metres of run.
In practice, vary the terrace widths for design interest, wider lower terraces for outdoor use, narrower upper terraces for planting, rather than making them all equal.
Moving between terrace levels usually means building stairs into or alongside one or more of the walls. See our guide on stairs through retaining walls for rise and going proportions, materials, and drainage detailing around a stair opening.
Not every terrace wall needs to run in a straight line either, a curved wall can follow the natural contour of a slope rather than cutting an arbitrary straight edge across it. See our guide on curved retaining walls versus straight runs for which materials curve well and what the cost difference looks like.
Where a terraced garden sits either side of a driveway that also needs to be levelled, it’s worth designing the terrace walls and the driveway’s own wing walls and gatepost piers together, so the material, height stepping, and line all read as one coherent scheme from the street. See our guide to driveway gateposts and wing walls at entry for how we approach that design brief.
Wall Face Options
For a terraced garden, material choice affects both the look and the build cost:
| Material | Aesthetic | Typical Cost (per lm, 500mm high) | Heritage Suitability |
|---|---|---|---|
| Sandstone (dry-laid) | Traditional, natural | $500 to $800/lm | Excellent |
| Concrete sleeper | Modern, clean | $350 to $550/lm | Limited (rear garden OK) |
| Split-face concrete block | Contemporary | $400 to $650/lm | Moderate |
| Timber sleeper (hardwood) | Rustic | $250 to $400/lm | Limited in upper Mountains |
| Gabion basket | Natural, textured | $400 to $700/lm | Good |
| Boulder/rock | Natural, informal | $300 to $550/lm | Excellent |
For most Blue Mountains gardens, sandstone or boulder walls for the terraces create the most natural integration with the landscape. Concrete sleeper terraces work well for vegetable garden areas where a neat, clean look is preferred.
A terrace wall at the lowest level, closest to the house or entertaining area, is also a natural candidate for built-in seating rather than a purely structural profile. See our guide to seating walls and fire-pit terraces for seat height, coping width and clearance detail specific to that use.
If you’re planning lighting for a terraced garden, raise it before construction rather than after. Conduit for step lights, up-lights or coping-mounted fixtures needs to be run through the backfill zone as each wall is built, well before panels or stone courses are finished and covered. See our guide to lighting retaining walls and wiring during construction for how we plan conduit placement around the drainage system on a multi-level terrace.
Costs are indicative 2026 rates per lineal metre installed, including drainage and basic earthworks. See [/guides/retaining-wall-cost-guide-blue-mountains-2026/] for the full cost guide.
Drainage Design for Terraced Gardens
Drainage in a terraced system needs to manage water at each terrace level:
Approach 1, Back drain with outlet at wall base: Each terrace level has an ag pipe along the back wall face (at the base of the cut), discharging through weep holes or a pipe through each wall to the terrace below. Water flows level by level down the slope to the bottom outlet.
Approach 2, Stepped ag pipe: A continuous ag pipe runs the full length of the terraced slope at the base of each wall, with a fall gradient running along the length of the terrace. Each terrace’s ag pipe connects to a single outlet at the end.
Approach 3, Terrace surface drainage: Each terrace surface is graded slightly backward (toward the cut wall) so surface water runs to the back, infiltrates, and enters the ag pipe drain. The terrace surface doesn’t flow forward over the wall face. This is the neatest approach for garden terraces but requires accurate grading of the terrace surface.
In the Blue Mountains, all three approaches are used. The choice depends on wall length, terrace width, and the amount of upslope catchment area.
See [/guides/retaining-wall-drainage-design/] for the detailed drainage design guide.
Soil and Planting in Terraced Gardens
Each terrace level needs adequate topsoil for planting. The cut-and-fill process of creating terraces often exposes subsoil (the topsoil was on the original slope surface and ends up in a mixed state after earthworks). Plan for:
- Minimum 300-400mm topsoil depth in each terrace for ornamental planting
- Minimum 400-600mm topsoil depth for vegetable gardens
- Compost and organic matter addition to improve soil structure after earthworks disturbance
For vegetable gardens on terraces, see [/guides/retaining-walls-vegetable-gardens-raised-beds/].
Plant recommendations for Blue Mountains terraced gardens:
Lower terraces (moister, possibly shadier):
- Native ferns (Blechnum spp., Doodia spp.)
- Native violets (Viola hederacea) as ground cover
- Lomandra longifolia (mat rush) as border
- Ginger plants and shade-tolerant natives
Mid terraces:
- Native grasses (Microlaena, Themeda)
- Grevillea and Hakea species
- Small Acacia species
Upper terraces (drier, sunnier):
- Drought-tolerant natives
- Mediterranean herbs (rosemary, lavender)
- Perennial plants and ornamental grasses
See [/guides/landscaping-after-retaining-wall-planting-drainage/] for post-construction planting guidance.
Trees in Terraced Designs
Terracing around existing trees is one of the most common design challenges in Blue Mountains garden terracing. The key rules:
- Never raise the soil level against a tree trunk, this causes crown rot and ultimately kills the tree
- Never excavate through significant roots, identify the root protection zone before setting terrace levels
- Build a tree well around the trunk to maintain the original soil level immediately around the tree while the surrounding terrace changes
See [/guides/retaining-wall-tree-preservation/] for the detail on tree root protection during retaining wall work.
Council Approval for Terraced Gardens
As discussed, multiple walls under 600mm are generally exempt development in the Blue Mountains, which is the main approval advantage of terracing. Exceptions:
- Heritage conservation areas, even low walls may need approval if visible from the public domain
- Near drainage lines, check BMCC mapping; setback requirements apply
- Near protected trees, see above
For heritage properties or those near drainage lines, discuss with BMCC before starting work. See [/guides/bmcc-council-approval-retaining-walls/] for the approval guide.
Cost of Terraced Garden Retaining Walls
Terracing is generally cost-effective compared to single tall wall alternatives:
Comparison for a 2.5m high slope, 15m wide:
| Approach | Approx. Installed Cost | DA Required? |
|---|---|---|
| Single 2.5m engineered concrete sleeper wall | $22,000 to $38,000 (including engineering and DA) | Yes |
| 5 × 500mm sandstone terrace walls | $18,000 to $30,000 (no DA needed) | No (exempt) |
| 5 × 500mm concrete sleeper terrace walls | $12,000 to $20,000 (no DA needed) | No (exempt) |
These are indicative 2026 costs. Actual costs depend on access, earthworks volume, drainage complexity, and material specifications. See [/guides/retaining-wall-cost-guide-blue-mountains-2026/].
FAQ
How many retaining walls can I build without council approval in the Blue Mountains? Each individual wall under 600mm height is generally exempt development (with conditions, not near drainage lines, not in HCA visible from road). There is no limit on the number of exempt walls, but if they are so close together they form a composite structure, BMCC may assess them as a single wall. Get advice from BMCC or us if you’re planning more than 2-3 walls.
What’s the best terrace wall material for a Blue Mountains cottage garden? Dry-laid sandstone or boulder terraces create the most naturalistic cottage garden look and are consistent with the heritage character of many Blue Mountains properties. They are excellent performers in frost and high-rainfall conditions.
Can I use terracing for a vegetable garden on a steep slope? Yes, terracing is ideal for vegetable growing on steep Blue Mountains slopes. Each terrace becomes a raised bed with level soil, good drainage from the terrace walls, and sun access. See [/guides/retaining-walls-vegetable-gardens-raised-beds/] for specific advice on raised bed terraces for food growing, and our dedicated guide on terraced vegetable gardens on mountain slopes for wall sizing, materials, and drainage specific to food-growing terraces.
Do I need drainage behind low (500mm) terrace walls? Technically not always required for very low walls, but in the Blue Mountains we recommend at least a basic ag pipe drain behind any terrace wall that retains more than 300mm of soil. The high-rainfall environment means waterlogged soil behind walls is a real risk even for low structures.
Can Blue Mountains Retaining Walls design and build a terraced garden for my property? Yes. Complete terraced garden design and construction is available through the contractors we refer to, including wall construction, earthworks, drainage, and topsoil placement ready for planting. Contact us at [/contact/#quote] for a design consultation.
Get a terraced garden design and construction quote, /contact/#quote