‘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 step 1. 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.