Retaining walls over 1 metre highJune 29, 20150
Does your landscape project require a retaining wall higher than 1 metre? If so you there are some things that you will need to be aware of, such as; the wall will require a building approval; the wall will require an engineering drawing; the contractor you engage to build the wall will need to be licensed with the QBCC as a Builder Restricted to Structural Landscaping. The contractor you engage should be aware of these things and be able to include the costs for the engineer and certifier in quotation for the works to be done.
Engineers details will vary on a site by site basis. Therefore every retaining wall should have it’s own specific engineering detail. your contractor should have an engineer that they work with regularly and can discuss the best solution for your particular project. This will ensure that your retaining wall is properly engineered to last without expensive over engineering.
Building approvals are usually dealt with by a private certifier. If your contractor has a working relationship with a certifier it will reduce the time taken for the building approvals to be completed. Some of the more tricky approvals can take weeks or even months if they require things such as; build over sewer; build over stormwater; relaxation. The quicker all these things are sorted out the quicker your project can be started.
The contractor you engage should be able to tell you who they use for their engineering and certification. They should be able to provide you with more than one option for the construction of the retaining wall, i.e concrete sleeper, timber sleeper, besser block, linkwall block. Each product has its own method of construction and design features that will be either better suited or not suited at all for your landscaping project.
options for retaining
Concrete sleeper/steel post
A very durable option that takes up a minimum amount of room. Fencing can also be attached to the wall posts meaning the wall and fence are all in alignment. This is a very structurally sound way of building a retaining wall/fence combination. Many of the concrete sleeper options now come coloured and/or patterned, this means that the aesthetic appearance of the product has improved greatly.
Similar to concrete sleeper walls in the construction method however timber does not have the durability of concrete and steel. Timber walls are one of the cheapest forms of retaining so if budget is your main concern they may be worth looking at. One option to consider is the use of galvanised steel posts with timber rails, this way the posts are reusable when the timber perishes, making the cost of repair/replacement of wall much cheaper. The timber used should be a minimum of 75mm hardwood sleepers, this will ensure that you get the best longevity out of your timber retaining wall.
Link walls are a very durable retaining wall system. Being a masonry product they last for a very long time. There is a great selection of block styles and colours to choose from so that you will be able to choose something that compliments your landscaping. Link walls are very good where a curve is required and can also be used for straight lines. Because link walls are a gravity system of retaining wall the weight of the blocks aids in the retaining, allowing for smaller footing than many other retaining wall systems. This can be very useful if the footings for your retaining wall are going into rock or large excavations are not possible. Link walls are not always the answer though because they require some room to be constructed properly, generally around 500 – 800mm.
Besser blocks are great for formal retaining areas front fence/retaining wall combinations or any situation that requires a truly vertical wall. Usually finished with render or stone cladding they add aesthetic value to any landscaping project. A core filled block retaining wall that has been constructed properly is one of the most durable systems of retaining. Two things that should be considered are that block walls are very expensive to construct and they require large footings, meaning extensive excavation is required.
Remember to check your contractors details and their class of license, it should be Builder Restricted to Structural Landscape for walls over 1m high. Ensure that your contractor can deal with all aspects of the project, including the engagement of certifiers and engineers. Make sure that your contractor provides you with all your options so that you receive the best possible finish both structurally and aesthetically for your landscape project.