Treated pine posts vs hardwood posts, vs steel posts when building fences

Hardwood and treated pine are the two traditional types of timber posts used in fencing. Being a natural material, both types of wooden post will eventually rot and require replacing but the speed at which this disintegration occurs depends on many different factors. There is a growing trend in the use of steel posts for timber fencing in Sydney. Steel posts have much greater longevity and strength but a higher cost. The question I commonly get asked is does the increased cost of steel posts represent good value in the long run?
Treated pine is treated to withstand rot for longer and also protects against termite attack. In the past, fence posts were commonly put in the ground without concrete so it makes sense that these posts should last longer than hardwood posts. However, concrete is almost always used for fence posts today which means a hardwood post doesn’t come into contact with the wet soil. The speed of rot is dramatically reduced and if built correctly, hardwood posts can have a long life too.
For this reason, I believe that hardwood posts will outlast treated pine posts as long as dirt is not allowed to build up around the base of the concreted area. This doesn’t protect hardwood from termite infestation, so if there is a high risk of termite attack in your area then take the treated pine option as this will minimize this risk.
Steel posts are stronger than both hardwood and treated pine posts when heavy gauge (2.5mm thick) steel is used. They are galvanised against rust so they will outlast timber posts by quite a long time if built correctly and will not bow like timber may so the posts will remain straight. Although they are galvanised against rust, in salty areas near the coast the posts will rust eventually, and sometimes in less time than a timber post may rot.
We can also look at the longevity of a post on a time scale. Taking into consideration the Sydney climate, a well maintained treated pine post would roughly last 15-25 years, hardwood 20-30 years (if un-infested by termites), and steel posts 35-100 years depending on the thickness of the steel.
Although steel posts may last 100 years, the timber on the posts won’t and will require replacing eventually. The advantage of steel posts is that when this happens it’s simply a matter of removing the timber and replacing it with new timber. The advantages of this is you avoid the labour cost of digging holes, concreting posts in and dealing with boundary disputes the second time around!
So how much money does the additional cost of steel posts save you and over how long?
As a rough estimate a basic closed paling fence 30m long may cost you $2400 including the cost of demolition and removal of the old fence. Steel posts will increase the cost by $21 per post and since there are 10 posts the additional cost would be $315, bringing the total cost of a steel post fence to $2715. In 20 or so years when palings and rails need to be replaced, we can re-use the existing steel posts, and the cost of replacing the fence again would be approximately $1650. This is a saving of $750, when compared to re-purchasing an all timber fence at the cost of $2400. Multiply that saving by the 3 fences you share with your neighbours and you can see that over time you’d be getting great value from your choice of steel posts!

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