Retaining wall and fencing checklist

Retaining wall installation checkpoints, Brisbane to the Sunshine Coast

Most of the cost and nearly all of the approval risk on a retaining wall is decided before a single sleeper goes in. These seven are the ones that change the number.

1. 1. Measure the full retained height, not just the visible face

   Approval in Queensland turns on height above natural ground level, so a wall that looks 0.9 m from the low side can still cross the 1.0 m trigger once the fill behind it is counted.

2. 2. Check what sits above the wall

   A surcharge - a driveway, building, pool or a second wall bearing down on the wall from above - generally triggers building approval at any height, and it changes the engineering, not just the paperwork.

3. 3. Measure the distance to the nearest building or other retaining wall

   Within 1.5 m of a building or another retaining wall, approval is generally required even where the wall is under 1.0 m and carries no surcharge.

4. 4. Ask whether subsoil drainage is included in the quoted price

   Queensland's residential design code (QDC NMP 1.7) requires subsoil drainage behind retaining walls, and inadequate drainage is a leading cause of wall failure. Agi pipe (the slotted flexible drainage pipe), drainage gravel and a geotextile wrap are often left off a headline price.

5. 5. Confirm excavation, spoil removal and backfill are priced

   These sit outside most per-square-metre rates and are one of the biggest reasons two quotes for the same wall land thousands of dollars apart.

6. 6. Ask who arranges the engineered design and certification

   An engineered wall is designed to AS 4678 and certified on a Form 15, normally by a registered professional engineer. Form 16 is the building certifier's inspection certificate and Form 12 covers installer certification. Know which forms your job needs and who is paying for them.

7. 7. Walk the access route before you ask for a price

   Narrow side access, steps, a locked-in backyard or soft ground change plant selection and labour hours more than the choice of material does, and a contractor who has not seen it will price defensively.

Fencing and boundary checkpoints

Fencing looks like the simpler half of the job until a neighbour, a pool or a retaining wall is involved. These seven cover where fencing jobs actually go wrong.

1. 8. Confirm the QBCC licence class matches the job, not just that a licence exists

   Licensing is triggered by the value of the work - $3,300 or more including labour and materials on residential land - rather than by height, and the right class differs across carpentry, structural metal fabrication, glass and aluminium, concreting and structural landscaping. The same threshold brings written domestic building contract requirements with it.

2. 9. Check whether the fence will sit on top of a retaining wall

   Where a fence sits on a retaining wall and the combined height reaches 2.0 m, the approval position generally changes, and the wall below has to be designed to carry the fence's wind load.

3. 10. Settle who benefits from the retaining wall before the cost conversation

   Retaining walls are not dividing fences under the Neighbourhood Disputes (Dividing Fences and Trees) Act 2011, so they are not automatically split 50/50 with a neighbour. This is the single most common misunderstanding we see.

4. 11. Agree in writing what a sufficient dividing fence means for your boundary

   Queensland treats a sufficient residential dividing fence as between 0.5 m and 1.8 m high in prescribed materials. Adjoining owners generally contribute equally to that, and the owner who wants something beyond sufficient pays the difference.

5. 12. Start the cost-sharing process with a written notice and a quote

   A notice to contribute with a quote attached is how the process formally begins. Matters that stay unresolved go to QCAT, so an informal fence-line handshake is worth converting to paper early.

6. 13. Ask the installer to confirm a pool barrier is built to the Queensland standard

   A compliant barrier must achieve at least 1200 mm height, a gate latch release at least 1500 mm above ground, a 900 mm non-climbable zone and gaps no wider than 100 mm, with a self-closing self-latching gate, under QDC MP3.4 and AS 1926.1. Compliance is confirmed by a licensed pool safety inspector, never by a self-check, and a certificate is needed when selling or leasing.

7. 14. Ask what post spacing, footing depth and hardware rating suit your site

   Solid panel fences carry the full wind load, so footings and post spacing follow the wind classification for your block. Near the Broadwater or the Sunshine Coast beaches, salt air attacks under-rated fixings and rails long before the panels give out.