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I'm planning to build a Merbau privacy screen on a Colorbond fence like in the above picture and need some advice. I have three different Merbau screening wood options: 69x7x5.7m, 69x15x2.7m, 65x11x5.7m, and 65x15x5.7m. Which one would be the best choice, durable and cost effective, and what would be the ideal spacing between the posts and the screening wood? Additionally, what type of timber should I use for the posts, and how should I attach them to the Colorbond posts? Lastly, I'm looking for recommendations on the type of screws to use for this project. Any guidance would be greatly appreciated!
A warm welcome to the Bunnings Workshop community, @bboy! We're delighted to have you join us and trust you'll find the site a wonderful resource for useful D.I.Y. advice and inspiring ideas.
Thanks for your question. I'm sure our Bunnings resident D.I.Y. expert @EricL will be able to assist when he's back online later today. Let me also tag @JoeAzza, @diy_hausdesigns and @Dave-1 for their thoughts.
In the meantime, I recommend checking out experienced Workshop member @ProjectPete's guide How to extend a Colorbond fence and @Adam_W's How to build timber screening in case they help. You might also want to have a look at @Shannon's popular project: Fence extension for extra privacy.
Do keep us updated as your project progresses. We'd love to see the final result.
Akanksha
Hi there I recommend the treated losp pine it’s done an amazing job on the fence extension I installed it’s been going strong for years it doesn’t bow it looks great it’s super smooth painting is quick and easy small brush and small roller tray with short nap roller Might be worth checking out my projects hopefully it helps u decide I added plenty of pics if you work out the measurement s you can have the lengths cut down when u buy it from Bunnings which can be a great help if u haven’t got all the power tools Pre drill and countersink the screws to insure u never spilt it but this really is a great material to use in my opinion
Good morning @bboy
I like that type of screen idea, it fulfills the privacy without really building a wall. Firstly Id like to say welcome to the Bunnings community as well 
Its a nice place to hang out in.
The width of the timber pieces comes down to what you would like to see every day. When I was working out my privacy screen costs verse the different sizes I found that overall the price works out to be similar so its asthetics that comes up. I chose the 90mm x 19mm specrite merbau pre oiled decking random lengths 90mm as the one most appealing to the eyes.
With the posts I would suggest they be H4 timber and space no further apart then around the 1.5M mark (Just to keep the slats from wanting to warp over time and to make it easy to line them up at height)
Concreteing the posts in or a hole with packed rocks would both work, the advantage of packed rocks is they can be removed easier, disavantage more work for you and maybe movement.
I would not attach them to the colourbond posts as the fence is designed to carry its own weight and be able to handle winds ect. I would sugegst that teh privacy screen be freestanding, that way no issues with the neighbours saying the fence warps because you have done so and so.
Here is my project on how I attached the merabu slats to the supports. Courtyard privacy fence and gate build Part 2
It lists the tpe of scres I used to attach the timber to the posts and how I did it.
Dave
Hello @bboy
Allow me to welcome you as well to the Bunnings Workshop community. It's marvellous to have you join us, and thanks for sharing your question about installing an extension to your Colorbond fence.
It's great that you've received excellent advice from @Shannon and @Dave-1. It's important to remember that any timber that makes contact with the soil needs to be treated up to H4 otherwise it will deteriorate very quickly. Have you considered just mounting it to the Colorbond posts itself? It would save you from having to dig holes for mounting posts and concreting.
In regards to your question about which Merbau piece to use, it all depends on the distance of the posts. If for example, the Colorbond posts were 2 meters apart and you had a 2.7-meter length piece you would have a cut off of 700mm. If the posts were 1.8 meters apart then a 5.7-meter length piece would be ideal as you would only have a 300mm off cut. But if you are keen on digging new posts then I propose getting the 5.7-meters length to minimize waste.
Again, if for example you were to use a 70mm x 35mm H3 timber framing and mounting it to the Colorbond post, I suggest using Zenith 12G x 65mm Galvanised Hex Head Metal Screws. As a general guide when choosing screws, remember that you are drilling through timber then to steel. The screw must be able to anchor itself to steel and has to be strong enough to hold the timbers weight in place. This is on the condition that you'll only be using a short length of it to hold the extension in place.
I propose drawing a plan on paper or your favourite software. It will firm up your plans on how the Merbau will be attached and the type of fittings you'll be using. You'll also be able to determine the quantity of material you'll be needing.
If you have any other questions we can help with, please let us know.
Eric
Hi @EricL
Apologies for the delayed response, Eric. I was exploring various options to make the project more affordable, as I'm new to DIY projects. As you suggested, I've used an online tool to create a project plan. According to the plan, the Colorbond fence posts are 2.4 meters apart, and I intend to extend the fence by approximately 350mm. Could you please advise if attaching the H3 treated pine (70mm35mm) to the fence posts with Zenith 12g 65mm screws would be strong enough to support the Merbau at the top? I'm planning to use 2.7 meters long, 69mm15mm Merbau screening wood, given that the fence posts are 2.4 meters apart. Additionally, I plan to insert a 2 Merbau wood vertical in the middle.
Hello @bboy
If you are placing a centre support to the 2.7-meter length of screening and mounting it to the fence as well it should work. However, I would like you to take a moment and consider the amount of weight you will be applying to the fence. The extension of 350mm is not the issue, but the weight of the materials. I would like to ask you to have a look at this possible alternative - Fence extension for extra privacy by @Shannon.
They used fence extensions and aluminium angles to attach the extension to the Colorbond fence. I'm just worried that the extra weight of the 70x35 will drag the fence towards your side and creating a lean. I also suggest having a look at the Matrix Fence Extension sets. The panel is made from 100% recycled material which is UV stabilised so will last in the elements. It comes with a colour matched slimline frame top and bottom which adds support and rigidity.
I also recommend having a look at this discussion - Attaching screens to Colorbond fence by @eemrun. You can install the panel horizontally so that you get more cover and not use so many panels. Plus, it is light weight and will not put a great deal of strain on your fence.
If you have any other questions we can help with, please let us know.
Eric
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