Homeowners · Builders · Landscapers
Retaining wall engineer for Hobart's sloping blocks
In Tasmania a retaining wall stops being low-risk work once it retains more than 1.2 m, or more than 0.5 m within 1.5 m of a boundary. We design block, concrete, sandstone, gabion and timber walls, with the drawings, calculations and Form 35 your builder and building surveyor need.
Engineering only
We design and certify the wall. Any licensed builder can build it.
Fixed quote in 1–2 business hours
Get a fixed quote for your retaining wall
Send a photo of the slope, the height and length of wall you need, and anything above it such as a driveway, house or pool.
From $750 + GST. No obligation. Or call 03 6146 4747
In short
A retaining wall in Hobart needs an engineer's design once it retains more than 1.2 m, or more than 0.5 m within 1.5 m of a boundary, road or right of way. Walls up to 1.8 m can then be built by a licensed builder. Taller walls, and walls in an easement or landslip band, are not low-risk work. Our designs start from $750 + GST.
- Fee
- From $750 + GST, fixed before we start
- Low-risk limits
- 0.5 m near a boundary, 1.2 m elsewhere
- You receive
- Drawings, calculations and a Form 35
Tasmanian rules
When does a retaining wall need an engineer in Tasmania?
A retaining wall needs an engineer's design in Tasmania once it is outside the owner-built low-risk limits: more than 0.5 m retained within 1.5 m of a boundary, road or right of way, more than 1.2 m elsewhere, or closer to a building than its own height.
| The wall | Category | Who can build it | Engineer's design |
|---|---|---|---|
| Retains up to 0.5 m, within 1.5 m of a boundary, road or right of way | Low risk (Category 1) | Owner, competent person or builder | Not required by the category |
| Retains up to 1.2 m elsewhere, set back at least its own height from any building | Low risk (Category 1) | Owner, competent person or builder | Not required by the category |
| Retains up to 1.8 m | Low risk (Category 2) | Licensed builder | Required |
| Retains more than 1.8 m | Notifiable (Category 3) | Licensed builder, with a building surveyor's Certificate of Likely Compliance | Required, with a Form 35 |
| Any height in an easement or a landslip hazard band | Not low risk | Licensed builder, with a building surveyor | Required in practice |
Director's Determination, Categories of Building and Demolition Work (items 1.3.14, 2.3.2 and 3.1.3). A planning permit may also apply. Your building surveyor confirms the category for your wall. More detail in our guide to retaining wall rules in Tasmania.
Check your wall in four steps
Is the wall in an easement or a landslip hazard band?
Check the title for easements and LISTmap for Landslip Hazard Code bands.
Yes: not low risk, needs a design and a surveyorNo: go to 2Is it within 1.5 m of a boundary, road or right of way?
That sets the owner-built height limit.
Yes: limit 0.5 mNo: limit 1.2 mIs it within that limit and at least its own height from any building?
Measure the height of soil retained, not the height of the blocks.
Yes: low risk, owner can buildNo: go to 4Does it retain more than 1.8 m?
Above this, the wall is notifiable building work.
Yes: design, Form 35 and a surveyorNo: licensed builder and engineer's design
Retained height limits for low-risk walls
Wall types
Which type of retaining wall suits your block?
The right wall depends on the height, the soil, what sits above it and how much room there is for a footing. This comparison reflects general engineering practice; your design specifies the details.
| Wall | How it holds the soil | Often used for | Engineering notes |
|---|---|---|---|
| Sandstone | Heavy blocks resist the soil by their weight (a gravity wall) | Traditional garden and boundary walls, and rebuilding old ones | Old walls can bulge when drainage behind them clogs; new walls need a footing and drainage |
| Concrete block | Reinforced, core-filled blockwork on a reinforced footing, or interlocking blocks with geogrid | Taller walls, boundary walls, walls beside driveways | Reinforcement, footing size and drainage are designed; geogrid length sets how far back the wall reaches |
| Concrete sleeper and steel post | Precast sleepers slotted between steel posts concreted into the ground | Residential walls where space is tight | Post size, depth and spacing depend on the soil and height; galvanising matters |
| Gabion | Wire baskets filled with rock, acting as a gravity wall | Landscaped slopes and walls that need to drain freely | Needs enough width and a firm, level base; flexes more than a rigid wall |
| Timber sleeper | Sleepers between timber or steel posts | Low garden walls | Shorter life in contact with soil; best kept to low walls |
What's included
What does a retaining wall design include?
A retaining wall design gives your builder everything needed to price and build the wall, and your building surveyor what they need to approve it.
- A review of the site from photos, a survey or a site visit, and of the soil, with a soil test where the design needs one
- The loads behind the wall: the slope above, a driveway, a house footing, a pool or a fence on top
- Wall type, footing, reinforcement and posts
- Drainage: free-draining backfill, an ag pipe and where the water goes
- Drawings and calculations for the builder
- A Form 35 for notifiable walls, and inspections and certification where your surveyor needs them
Retaining wall design
A typical residential wall in Greater Hobart. Taller, longer or heavily loaded walls are priced in your fixed quote, and design from photos and plans is available anywhere in Tasmania.
Council rules
What council rules apply to retaining walls in Hobart?
Besides the building category, three local checks can apply to a retaining wall in Hobart: a planning permit, council consent near a stormwater pipe, and the landslip code.
Planning
A planning permit may be needed as well, for example on a heritage-listed place. Check with your council's planning team before you build.
Stormwater pipes
Building on an easement or within 1 m of a council stormwater pipe needs the council's consent under the Urban Drainage Act 2013. See stormwater and drainage.
Landslip bands
In a Landslip Hazard Code band a wall is no longer low risk and may need a landslip report. Rosetta and Taroona are documented landslide areas.
Digging near the boundary or building a pool?
Cutting into a slope near a neighbour's house can undermine their footing, and underpinning or shoring a neighbour's property is protection work that needs a building surveyor. A pool beside or above a wall adds load to it. See pool engineering and our guide to a pool on a sloping block.
Related services
Often needed on a sloping block
Landslip reports
Landslip hazard reports for building in a Landslip Hazard Code band, prepared to AGS 2007 with an AS 1726-2017 site investigation.
Learn more
Stormwater & drainage design
Drainage plans, stormwater reports and on-site detention designs for houses, units and subdivisions, with the Form 35 council needs.
Learn more
Swimming pool engineering
Concrete shell designs and site engineering for pools on slopes and near footings or boundaries, with the Form 35 your building surveyor needs.
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