How to extend height of existing timber fence with steel posts?

Question

Existing seriously compromised wooden fence (round 4-5’ height) has been constructed using (I assume) the uprights from an old chain wire fence. Provided I can remove the bolts/ nuts or screws without compromising the uprights… and everything is sufficiently plumb / level - can I 1. Add H4 treated cross beams (rookie terminology) secure them and then 2. Add palings.

If so - am I limited in the height I can extend past the height of the steel posts? The fence is really very short.

Should I attempt to use the existing steel posts and add uprights next to / in front of them somehow to allow me another maybe 1-2’ of height?

Skill level - never built a fence before but can access some muscle and guidance from a friend…

And what I lack in skill I usually make up for with bloody-mindedness and ability to adapt!

Should add - I’m in FNQ - so massive rainfall and always possibility of a cyclone. Apologies for the imperial measurements- I can guesstimate in feet and inches but never in mm unless it’s rain we are discussing 😂

thank you brains trust

Nailbag · Answer

Hi @jmcavoy1

Due to the condition of the fence I would be inclined to replace it with a taller one that’s designed to carry the weight of the extra height. Alternatively as with @JacobZ suggestion,  of install new posts and rails to support the extensions.

Nailbag

Dave-1 · Answer

Good Morning @jmcavoy1

Mmmm and interesting question and also a ahhh question.

I love the idea of reusing the pots and also like the idea of making the fence higher. It comes down to how far the posts go into the ground (To stop the fence leaning) The fence looks like its been carrying the timber load for years so I dare say the posts are solid :) And there is no lean on them which is even nicer.

I would pretty much be bolting a new post directly to the old steel post (and yep make it 600mm higher) I wouldnt go over that 600mm tho.

Just know the further out from the post the more force will be applied to the fence. So -

* post plus timber post, including rails, plus palings.

You could go for a post either side of the metal post to keep weight centered but think that will be overkill.

I would use a grinder and cut off the bolts when you go to do the fence, no point in wasting a huge effort trying to undo old bolts.

Dave

JacobZ · Answer

Hi @jmcavoy1,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I'll just start with some basic fencing terminology, as this should make it a bit easier to find suitable products and guidance. The vertical members coming out of the ground are your posts, the horizontal timbers running between them are generally called fence rails, and the vertical timber boards attached to the rails are your palings. Anything above the ground needs to be H3 treated and anything in direct contact with the ground needs to be H4 treated.

You can certainly have the palings extend a little higher than the top of the posts, but the further they extend beyond their highest mounting point, the less support they have and the more susceptible they become to twisting and movement. As a general guide, I wouldn't want to go much more than around 200–300mm above the top of the posts.

There is actually a very similar situation at my parents' place, where an existing fence had steel posts that weren't tall enough for the new fence. The neighbour's fencer attached new timber posts directly to the existing steel posts using bolts like your rails have. This allowed the rails and palings to be installed at the required height. That being said, we are in Brisbane, which is far less prone to cyclones than you guys up north.

Being in FNQ is an important consideration though. As mentioned, cyclones are a possibility, and increasing the height of the fence also increases the surface area exposed to wind. I wouldn't want to recommend simply extending the existing arrangement significantly higher without knowing that the posts and their footings are capable of handling those additional wind loads.

Considering you're looking to gain potentially another 1–2ft (300–600mm), ideally, I'd be looking at either removing the existing steel posts and concreting in new, taller fence posts, or installing new posts in the spaces between the existing steel posts. This would give you proper support for the additional height rather than relying on a substantial unsupported section of paling.

Given your location, I'd be much more inclined to recommend you simply replace the fence. This will help guarantee that the structure is capable of supporting the additional height and the additional loads that that height brings.

Check out

https://www.bunnings.com.au/diy-advice/building-construction/fences-gates/how-to-build-a-fence

and the associated articles for some guidance.

Also, allow me to tag @Dave-1, @Nailbag and @TedBear for their thoughts.

Let me know what you think.

Jacob