# Forum Home Renovation Fences & Screens  Adding fence / screen on top of block work wall

## Sir Stinkalot

Hi Folks, 
Just after some input to see if this idea is viable before I plunge in. 
I have a small 150 series "U" block wall that I would be keen to add a screen to the top of to help shield the neighbours. The wall is a planter box and the rear side is higher - I want to add the screen to the high side. The wall is core filled, but I would suspect that the extent of the core fill is only to the height of retaining and not the full height of the high side - leaving about 3 courses empty.  
The screen I was looking at putting up was the Bunnings Matrix 2400 x 600mm Charcoal Sahara Fence Extension set into the Matrix C-Channel Frame Kit (Bunnings links below). Ideally I would like to start the screen about 300mm above the top of the fence - so the top will be 900mm above the top of the fence. 
As for the supports I was thinking about removing the capping from the block work and inserting a 50x50 powder coated steel post into the block work cavity and then locally core filling around the post. I would then replace the capping around the posts. How does this sound? 
Images: 
1. Structural Design
2. Construction
3. Current conditions on high side (and photo on side)        https://www.bunnings.com.au/matrix-2...nsion_p0029254 https://www.bunnings.com.au/matrix-2...-sky-_p3041114

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## Uncle Bob

Sounds good to me.

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## Marc

You will be adding a 'sail' to the top of the wall. You need the post to go deep in the wall cavity next to the existing reo for this to work out. 
As for sourcing the materials, i would check prices from alternative sources. Bunnings is very convenient but can at times be extraordinary expensive.

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## cyclic

[QUOTE=Sir Stinkalot;1116546]Hi Folks,   
The wall is core filled, but I would suspect that the extent of the core fill is only to the height of retaining and not the full height of the high side - leaving about 3 courses empty. ???? 
Not according to the design which shows the bar should be almost to the cap which would mean core fill to the top.
I would be making sure of that first.

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## Marc

If the top 3 rows are empty, you can drill into the bottom core fill and Chemset 101 new reo in it and up to the top, then concrete frame post and reo in one.

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## Sir Stinkalot

Thanks folks ..... 
I will need to pop off one of the capping blocks before I know 100% what I am dealing with, but thought I would throw up my thought process to see if there were any issues.  
The structural does show additional reo between all 6 courses and then the bottom three being tied back to the footing. The photos I have clearly show the reo out of the footing, but I wasn't around when the core filling was done so cant be certain if it is fully filled without popping off the cap - it does sound a little more hollow when doing a tap test towards the top. If it is fully filled I will need to go for a base plate to the posts. 
If it is empty, I'm not sure how I would go trying to drill into the bottom core fill for additional reo. I'm not even 100% sure of the cavity size to be able to get a 50x50 post in. It would come close to 570mm depth which isn't too bad if I can get the post in and core fill again, the cold joint between the original core fill and the new isn't ideal, but not much I can do. The original thoughts were to run the posts externally to the wall and attach into the side of the core filled section, but it's not an attractive solution, and if done from inside the planter means removing the plants. 
Agree Bunnings isn't the cheapest / best in most situations - to be fair their website is somewhat handy for doing research (app is even better). They seem to be the only supplier of the screen, but will certainly be looking elsewhere for the posts. In the past I have always found steel and aluminium profiles are much better sourced from the specialists. 
Before rushing out - first step is to knock off a capping section. I will keep all informed of the progress.

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## Sir Stinkalot

Well credit to the builders - they did core fill to full height.    
Makes my job a little harder now as I will need to go for a flanged bolt down post. The plates seem to be either 100x100 or 100x134 - holes seem to be 70mm centres apart. 
Im thinking about base plate directly on the core fill and then trying to fit the cap back over to conceal the plate. Might be testing my skill levels  :Smilie:

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## cyclic

As Marc mentioned in #3 you are adding a sail to the top of the wall and 
You only have 70 mm of core fill to bolt to and any bolt should be no closer than 50 mm from the edge of the fill so it does not bust the face of the block, meaning a base plate bolted to the core fill will have to be bolted centre of the core fill and even then is only 30 each side to the block. 
 I very much doubt it will be strong enough to stop a reasonable wind from pushing the panel either way. 
This means the sideways movement of the fence panels is only limited by the flat of the plate held by 2 bolts centre of the core. 
It may work ??? but placing the plate under the cap means even the slightest movement in wind will loosen the cap off the block.  
Two ways you might get away with 
1) A U bracket upside down with the legs of the bracket going down each side of the block and bolted about 100 mm down the side of the block with the post welded to the bracket and gusseted each side of the post for strength. 
(ugly IMO) 
2) Diamond drill probably a 65 dia hole into the concrete core through the cap down about 250, remove the drilled core and use a 40 x 40 post epoxied into the concrete up to top of block, then expansion caulking around the post at the cap.

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## Marc

Or ... you can build a hinged fence spring assisted so that if there is a bit of wind it folds out of the way. A bit like a sailboat that reduces sails in a storm. 
If it is a spinnaker it would be called a letterbox drop  :Smilie:

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