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Home Garden

Build a sunken garden in your own backyard

Perfect for prettying-up a granny flat
Better Homes and Gardens

Don’t let a sloping garden be a downer for your outdoor entertaining. With a bit of digging and creative timber work, you can create a level outdoor area and standout feature – love a fire pit.

Gather your supplies:

• Retaining wall posts – 200 x 75mm H4 treated pine sleepers

• Floor supports – 200 x 75mm H4 Treated pine sleepers

• Floor sleepers – 200 x 75mm hardwood sleepers

• Retaining wall – 200 x 50mm hardwood sleepers

• Wall capping – 200 x 50mm hardwood sleepers

• Step sleepers – 200 x 50mm hardwood sleepers

• Step support – 90 x 45mm H3 treated pine

You’ll also need:

Hired mini excavator; tape measure; set-out paint; post-hole digger; quick-set concrete (2 bags per hole); spirit level; stringline; power plane; 100 and 150mm galvanised batten screws; reciprocating saw; power saw; decking oil; 10mm river gravel; garden edging; soil underlay; buffalo turf Note Before starting excavation, find out whether there’s any services running underground. Ring Dial Before You Dig on 1100 or visit 1100.com.au.

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Here’s how…


Step 1

Create a level area with a hired mini excavator (around $350/ day) or hire an excavation contractor. Stockpile soil for backfilling behind retaining walls (in Step 6)

sunken garden step

Step 2

Install retaining wall posts. Put a post at each end of walls and space posts 1.2m apart to match sleeper lengths. Dig 600mm-deep holes for each post. Concrete end posts first. Run stringline between them to line up posts in between, before concreting remaining posts.

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sunken garden step

Step 3

Install floor supports made up of 2 sleepers laid on edge. Top of supports should sit 475mm below height of retaining walls. Space floor supports every 1.2m to match sleeper length. Make sure they’re level along their length and with each other.

sunken garden step

Step 4

Chamfer edges of floor sleepers, lay on and across floor supports and screw down. Lay sleepers so gaps between them are uneven. Cut 900mm-dia. circle in middle of sleepers for fire pit. Support cut ends.

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sunken garden step

Step 5

Cut off top of posts to desired height and screw retaining wall sleepers to posts. Stagger joins between rows of  wall sleepers. Screw wall capping to top of retaining wall and down any visible ends. Build step.

sunken garden step

Step 6 

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Apply decking oil to hardwood as recommended and let dry. Use river gravel to fill gaps around and under floor sleepers. Backfill behind retaining wall with soil (from Step 1) and roll out turf as required.

sunken garden step

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