Build A Retaining Wall

  • DIY, handyman magazine, renovation, install a retaining wall
  • DIY, handyman magazine, renovation, install a retaining wall

DIY expert Frank Gardner needed to find a simple system for installing a retaining wall in a just a day.

‘The wall had to go up before the house extensions blocked access to the yard so I had to move fast,’ says Frank.
‘I found the Retain-iT system at the hardware store and liked how the galvanised posts would look with pine sleepers. I added pine capping and a set of wide steps.’
To start, establish the line of the wall, excavating 200mm behind it, then use a laser level or dumpy to set the finished height of the wall either end, setting out a stringline as a guide. 
‘Be sure to install drainage behind the wall using geotech filter cloth, agflo pipe and gravel,’ says Frank.
TIP Check local council regulations as many allow a wall up to 1000mm high to be built without approval.

Calculating the materials

‘I went three sleepers high and opted for a sleeper thickness of 75mm for strength and less timber flexibility.
‘The posts were concreted into the ground at a maximum of 2400mm apart on the sandy site,’ says Frank.
Measure the length of the wall, setting the posts to match the sleeper sizes. Multiply the spacings between posts by the number of vertical sleepers to find how many you need.
‘I worked out I need 15 sleepers 2400mm long plus six each of 1200 and 1800mm for about 16 metres of wall with steps set in one panel.’

How to install a retaining wall

Step1. Concrete end posts
Excavate two 550mm deep holes for the end posts, pour in concrete to 600mm from the top, use a spirit level to check for plumb in both directions then check the post is the right height. 
TIP A 20kg bag of cement, $8, mixed with gravel and sand fills three holes.
Step 2. Install joiner posts

Set up a stringline to use as a guide then position a base sleeper in each end post. Position the joiner posts then dig 550mm deep holes and concrete them into position using a spirit level to plumb, aligning them with the stringline and leaving to dry.

Step 3. Build the corners

Position and concrete the corner posts, using a builder’s square to install the sleepers at 90° to the wall.
TIP To build steps later we added a 1200mm deep and 2400mm wide recessed area, incorporating four corner posts. 

Step 4. Slot in the sleepers

Position the base sleepers, levelling and packing them to leave exactly 400mm of post above then install the middle and top rows.
TIP Check the height of the top sleeper matches the post so the capping sits flush along the wall.

Step 5. Install the drainage

Position geotech filter cloth behind the wall and fold it over the sleepers. Install 20m of 100mm agflo pipe with clear exits at the ends then cover with 20mm gravel to 300mm deep, folding the cloth back to separate the drainage and backfill.

Step 6. Add capping & finish

Square cut and mitre the capping, apply construction adhesive to the ends and secure to the sleepers with 75mm x 14g galvanised bugle screws then use a router with a roundover bit to remove splinters and trim the edges. Apply two coats of decking stain.

Click on the diagram

Follow the labelled diagram to build the retaining wall. It has the name of all the parts and the measurements to help you cut the components and assemble the retaining wall.  

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