Composite Posts

Composite posts are a lightweight alternative to steel for retaining walls up to 1m high. At around 90% lighter than traditional materials, they are considerably easier to handle and position on site, which matters most on jobs with no machine access: side passages, courtyards, terraced blocks and anywhere the material has to be carried in by hand.

The range

• C composite posts in 0.4m, 0.8m, 1.2m, 1.6m and 2.0m. Channel on one side, so these go at each end of a run and anywhere the wall stops against a structure.
• H composite posts in 0.8m, 1.2m, 1.6m and 2.0m. Channel on both sides, so these take the spans in between.

Sizing them

Same rule as steel: the pier depth matches the wall height, so the post is about twice the finished wall height. A 0.8m post suits a 0.4m wall, a 1.6m post suits a 0.8m wall, and the 2.0m post is the top of the range at a 1m wall. Post spacing follows the sleeper, not the post, so pick your composite sleeper length first and the centres follow from it.

Where the line sits

Composite posts are rated for walls up to 1m. Above that you are generally into engineered territory and galvanised steel posts, and in most of South East Queensland a metre is also where council approval commonly comes into it. That is not a coincidence, and it is not a limit we would encourage anyone to push. If your wall is close to the line, measure the total retained height rather than the visible face, because that is the number that counts.

A fence on top is a separate question again. It adds load, including wind load, and that belongs in the wall design rather than being bolted on afterwards. See the wall height guide for where materials sit by height band, and the guide to choosing posts for C versus H at each position.

Finish the tops with post caps, and pack each course out with composite sleeper wedges so the face sits flush.