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How to add an extension to a Colorbond fence

Trusted Contributor

Difficulty: Intermediate

A fence extension can add welcome privacy for your outdoor spaces, as well as enhanced security for your property.


While the standard install height for Colorbond fencing is 1800mm, for a small investment you can add privacy and security to your boundary fencing with D.I.Y. extensions taking the finished height to 2100mm.


As with any changes to a shared boundary, remember to talk to you neighbour before starting work. It’s the right thing to do and they might even agree to share the cost. It is also wise to contact your local council.  


Step 1

Measure your existing fencing to determine your material list. Simply count the number of sheets, uprights and rails that you have. That will be the quantity of each of the items needed in the extension kit. To calculate how many plate brackets, just count how many uprights you have, halve it, and add one (for the end).


Note that some sections (from upright to upright) will be shorter or longer than the rest, so be sure to measure the rails and order the lengths required. Keep in mind you may need to cut some to fit.


1.1 Calculate the materials needed.jpg

Step 2

The plate brackets are usually 250mm long so start by marking the halfway point on all of them before hammering them all into place with your claw hammer down to the halfway point you marked. A flat head screwdriver comes in handy to create some space for the plate bracket between the top rail and the upright depending on how closely they’ve been installed.


With the plate brackets in place, slide one 300mm upright over the bracket and place a second one up against it. Now clamp them together and ensure they’re level. Then pop two of the button head screws through both uprights and the plate bracket in a diagonal configuration.


2.1 Hammer the plate bracket down halfway.jpg  2.2 Slide the uprights over the bracket and clamp them together.png

Step 3

With all your upright extensions in place, slide one end of a rail into an upright, then slide the other end in a downward direction to fit into the upright at the other end of the section. This is your new bottom rail. Once it’s in place, pop a screw in each end and one in the middle to attach it to the top rail of the existing fence. Repeat this step for each section.


3.1 Slide one end of the rail first.jpg


Step 4

Now pop your first sheet into the bottom rail and slide it into the upright. Ensure you align the profile with the existing fence below. With the first one in place, take note of how and where the sheets on the existing fence overlap each other and continue inserting your remaining sheets, keeping an eye on the alignment of your profile.


For this step, do only one section, then go to Step 5.


4.1 Pop your first sheet into the bottom rail.jpg

Step 5

With a section of sheets in place, grab another rail and insert one end into the upright (like you did in Step 4). Slowly and carefully wriggle it into place over the sheets dealing with small parts at a time. Wriggling the rail back and forth, essentially following the wavy profile of the sheets, will help get it in place.


Once it’s in place, check it’s level then screw a hex head through the uprights and into the rail (at the top) to hold it in place. Do the same on the other side of the upright (neighbour’s side). Repeat for the bottom of the uprights. Note that it’s not necessary to do the bottom of the upright on neighbour’s side.


Repeat Step 4 and 5 until all sections are complete. You have now finished your Colorbond fence extensions. Now is the perfect time to clean off any cobwebs and dirt and treat it all with pest spray.


5.1 Wriggle the rail back and forth to get it into place.jpg  5.2 Check the rail is level.jpg  5.3 Screw hex head through the uprights and into the rail.jpg  5.4 Finished extensions.jpg

Step 6

You might like to consider cladding your fence to add sophistication and style to your backyard. There are many options to consider, from quality fibre cement products from James Hardie through to pre-made and bespoke timber screening. Whichever way you go, you’re going to need to install a H3 treated pine frame to attach your cladding to and the type of framing required will depend on your chosen cladding.


An already braced premade timber panel will likely only require some 50 x 25mm treated pine fixed to the top and bottom rails with 14g x 50mm Metal Teks. Then use either colour-matched timber screws or trim head screws to fix the panels to the treated pine frame.


Fibre cement would require a more complex 70x35mm treated pine frame to be attached to the top and bottom rails along with vertical lengths at certain points (see installation guides) and noggins to ensure a strong foundation.


If you need a hand with your fence cladding project, just let us know by commenting below. Good luck and please share your project with the community. 


6.1 Adding Merbau cladding.jpg  6.2 Finished Merbau.jpg  6.3 Frame for fibre cement cladding.png  6.4 Finished fibre cement cladding.jpg  6.5 Finished fibre cement cladding.jpg



  • Tape measure
  • Spirit level (ideally 2100mm)
  • Pencil or marker
  • Clamps which open at least 150mm
  • Claw hammer
  • Rubber mallet or dead blow hammer
  • Large flat head screwdriver
  • Drill – An impact driver makes the job easier
  • Ladder (tall enough for you to safely reach a drilling point of 2100mm)
  • Angle grinder or hacksaw with a steel blade
  • Personal protective equipment


1.1 Calculate the materials needed.jpg 

2.1 Hammer the plate bracket down halfway.jpg 

2.2 Slide the uprights over the bracket and clamp them together.png 

3.1 Slide one end of the rail first.jpg 

4.1 Pop your first sheet into the bottom rail.jpg 

5.1 Wriggle the rail back and forth to get it into place.jpg 

5.2 Check the rail is level.jpg 

5.3 Screw hex head through the uprights and into the rail.jpg 

5.4 Finished extensions.jpg 

6.1 Adding Merbau cladding.jpg 

6.2 Finished Merbau.jpg 

6.3 Frame for fibre cement cladding.png 

6.4 Finished fibre cement cladding.jpg 

6.5 Finished fibre cement cladding.jpg


8 Replies
Budding Contributor

This is what I need for my fence extension. Thanks heaps!

Budding Contributor

This is my existing fence on one side.



Thank you for your tutorial, Can you point me where I can buy the materials at bunnings. I want to build 600mm extentions. I am looking for the following at bunnings:


Plate brackets to support 600mm extentions ( where can I find these)

600mm uprights


Infill sheets 600mm


I figure i would have to cut the post upright extentions and colorbond infill sheets to 600mm

Do they sell this pre-cut anyway?


Can anyone help me.



Community Manager
Community Manager

Hi @marly,


Thanks for joining in the discussion. Glad to see you have been inspired by @ProjectPete's guide. Our resident Bunnings D.I.Y. expert @EricL will be more than happy to help you with your shopping list when he's back on the site on the weekend. Thanks for your patience in the meantime, and a very warm welcome to the Bunnings Workshop community.




Bunnings Team Member
Bunnings Team Member

Hello @marly


Thank you so much for joining us and sharing your question about extending your Colorbond fence.


It's great that you've found @ProjectPete's guide useful. I can only find the COLORBOND Steel 340mm Domain Fencing Post Extension at the moment. It may be a part that will have to be specially ordered at the store. Let me make some inquiries for you about the parts that you specified and get back to you.


Should you need to cut the Colorbond Fencing Panel I recommend using the P&N Nibbler Attachment 1/4" Shank. It transforms your power drill into an easy-to-use straight or curve cutter for sheet metals, corrugated sheets, spiral ducts, plastic sheets, or laminate.





Hi, this is helpful thanks.

I can't find the 300mm solid sheets online at Bunnings. Are these available?


Bunnings Team Member
Bunnings Team Member

Hello @jacquimaria


Welcome to the Bunnings Workshop community. Thank you for joining us and sharing your question about the Colorbond extension sheets.


I'm so sorry, but the most common sheets available at the store are the Colorbond 2350mm Fencing Lattice. If you are after a specific Colorbond colour extension sheet, it will have to be specially ordered at the Special Orders Desk. I recommend ordering the extension sheet as a full set in your preferred colour. This will include the left and right extension posts and the top and bottom rails. Please make sure to bring your current fence measurements, specifically the distance between posts. It sounds like a great project, please keep us updated.


If you need more advice or information, please let us know.




Bunnings Team Member
Bunnings Team Member

Hello @marly


I've spoken to our provider about you're preferred extension. I'm so sorry but I've been informed that the maximum extension kit height is 340mm. Having a 600mm extension on top of your existing fence is not recommended as it could bend or warp your existing fence. I suggest as an option to build a vertical raised garden bed with a trellis backing. You can build this higher than your fence and have a beautiful garden at the same time. Please keep us updated.  


Here is a link to the raised garden bed project: How to build a vertical garden by @MitchellMc


Let me tag our experienced members @tom_builds and @TedBear for their recommendations.


If you need more advice or information, please let us know.




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