Need advice - fixing a timber privacy fence on top of a brick wall

[Sideways]

The wall / fence is about 3m long to provide a little privacy between my house and a neighbour in a residential housing estate.
The wall is only about 2ft high, double brick with concrete capping.
On top of this is a 3 ft high "screen" of those patterened concrete blocks that were popular back in the 70's and have been there for 40 years.
We want to remove the screen and replace it with a 4ft tall timber fence, as a refresh and for slightly greater privacy.
The fence would have timber uprights and horizontal planks that alternate on either side of the fence. It makes for a visual screen but very "breathable".
It's my wall but the neighbour is proposing this for their privacy and has a local tradesman lined up for the job. Conscientious chap but I know he doesn't have experience of putting a fence like this on top of a wall like this.
I'm onboard with the plan, but very aware that a 4ft wooden sail needs something more than a few angle brackets to attach it to the dwarf wall if it's to stay upright and not damage the wall.

Does anyone know of any proprietary fixing products or methods that will do this job properly ?

I'm not averse to putting an 18" long drill down through the capstones and grouting some rebar, inch dia heavy wall pipe or whatever into the wall to get a decent anchor. I don't want to get into rebuilding the wall to incorporate new pillars or anchors just at the moment.

Relations with our neighbour are good. The job needs doing I just need to make sure it will stay up

 

[Spectric]

If you stick it on top of that wall you may well find the whole thing ends up horizontal and no longer vertical, any fixings would need to get down into the footing otherwise you will just be changing the point at which the wall breaks. What you need are post on one side attached to the ground with the fence attached at the top and sitting on the wall but the post taking all the load.

 

[phunky]

Provided the wall is build with cement mortar (grey colour) rather than lime (no grey tones normally), Im not convinced that you need to go into the footing. Cement has good bonding properties. How about some brackets like this.

https://www.wickes.co.uk/Wickes-Bolt-Down-Post-Support-for-Fence-Posts---100-x-100mm/p/218589
Then either take the cap stones off, attach them with 6 x 150 screws. Drive 2 or three brown plugs down through the hole with the screw so they anchor the screw at its deepest part. Then cut cutouts in the cap stones to go around the brackets which will hide most of the bracket from view and mean the weight of the capstone is acting in your favour.

Or you can go the chemical anchor route. Drill holes as deep as you desire. I’d have thought 300mm/12in would be plenty. Then squirt this down the hole:

https://www.screwfix.com/p/rawlplug-r-kem-ii-styrene-free-polyester-resin-300ml/32863
and push threaded rod down the hole. It sets quickly. Put the bracket over with washer and nut and tighten up. Chemical anchors are used in structural work such as holding floor joists and steel uprights to their bases for steel framed buildings. I’d be happy with chemical anchors even without the capping stones removed but obviously you’ll see the brackets.

 

[Spectric]

Cement has good bonding properties.

But once mixed with sand to make mortar then a different story, have you not seen garden walls that have been pushed over by the local have nothing better to do's ?

 

[deema]

I would suggest your neighbour digs in fence posts to take the fence panels so that it’s an independent screen and does not affect your wall. With posts dug in against your wall, and not attached the screen will look good from your side. On their side, if they can trellis below for plants to climb against. I did the exact same thing for my parent’s house. This ensured that both parties had clear responsibilities of who owned what when at some point either property is sold and avoided any issues of the screen causing the wall to fail.

 

[phunky]

But once mixed with sand to make mortar then a different story, have you not seen garden walls that have been pushed over by the local have nothing better to do's ?

Not where I live. Personally I don’t think a wall constructed with a decent mix and buttressed at the appropriate points should be possible to push over by human strength alone. If the footings were poor and there’s been movement leading to cracking then maybe. I’m happy to defer to you on this though. Clearly sinking posts is a belt and braces approach but a pig of a job assuming the footing extends out past the side of the wall as it should.

 

[Sideways]

Helpful observations everyone, thank you.
There is no possibility of sinking posts adjacent to the wall (on either side) to support this screen. There isn't room.

It sounds like we would either need to agree to modify the wall or rebuild it incorporating uprights for the screen.

 

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I think if the wall is sound and in good condition then avoid disturbing it anymore than necessary after removing the screen blocks . A short 2 or 3 ft fence should be fine if the posts can be fixed top and bottom - the only issue is who has the posts on their side of the wall . Sounds like all is amicable between you so shouldn’t be too difficult . The other option is the fence supports that hold a 3 or 4 inch post but there’s would be drilled into the concrete capping and would most likely crack or damage the concrete . Also the post is then only supported at the base leaving the ( sail ) exposed to any high winds . Hope this helps

edit.. A combination of the two types of fence supports should work ..

 

[Inspector]

Is it possible to leave the "breeze blocks" and attach the boards to either or both sides the blocks? Perhaps painting the blocks black or an agreeable colour before adding the boards. The boards can stick above the blocks as much as desired. This is assuming the blocks are sound and not falling apart.

Pete

 

[MikeJhn]

These may give some inspiration.

https://www.amazon.co.uk/Post-Buddy...words=Fence+post+repair&qid=1696976412&sr=8-5
https://www.amazon.co.uk/Changsheng...62&sprefix=fence+supports,aps,107&sr=8-6&th=1

 

[MikeJhn]

I'm not averse to putting an 18" long drill down through the capstones and grouting some rebar, inch dia heavy wall pipe or whatever into the wall to get a decent anchor. I don't want to get into rebuilding the wall to incorporate new pillars or anchors just at the moment.

Get a longer drill bit, 20mm galvanised conduit and these : https://www.amazon.co.uk/Pergola-Shaped-Galvanised-Support-Concrete/dp/B0B3Y49FNN/ref=sr_1_24?crid=4UNQ3AYTNNHS&keywords=Fence+post+support&qid=1696976616&sprefix=fence+post+support,aps,88&sr=8-24

 

[Tris]

Is the wall freestanding? How exposed is it? Do you know how well the two skins are bonded? What supports do the patterned concrete blocks have? Some of these walling systems had precast pillars that would be dropped over rebar and filled with mortar or concrete.

In my landscaping days I'd have recommended taking the whole lot down and putting a new hit and miss fence on posts on concrete repair spurs angled so they are within the fence unless it was possible to span the length of the dwarf wall and fix to a new post one end and a building at the other. Once you've got secure fixings either end you could use a post shoe on the dwarf wall for a single central support.

If the skins are well bonded and tied then you could chance drilling down and putting rebar through the wall. Being a bit of an overengineer I'd probably want to drive the rebar a foot or so out of the bottom of the footings then weld or bolt on a shoe like MikeJhn posted. Better still would be a steel plate that fits into a slot in the post. Once bolted in it will hold the post clear of any moisture.

 

[Terry - Somerset]

Many of the suggestions made seem a little overengineered with cost and effort implications.

This is a short length of fence probably largely sheltered on most sides on a housing estate, not an exposed structure on a hillside, or subject to coastal storms and waves.

Assuming the existing dwarf wall is free of obvious defects I would be inclined to use just bolt down post supports.

Rebuilding the wall on proper foundations (if they don't already exist) and/or drilling down below the base of the wall to reinforce it seems overkill. If that concerned remove the wall and simply replace with a 6ft fence with all new uprights.

 

[davethebb]

Sideways, I had a similar problem but with a very old stone wall with a small, 2 ft fence on top which I inherited from the previous owner. The wooden fence was constructed with posts secured to the top of the wall with standard post brackets bolted into the stonework and small wooden lightweight panels.

In the wind, the fence would move and over time I noticed the ongoing movement started to stress the bolted fixings. The fence panels eventually gave up and I replaced the fence.

I realized that the light weight of the fence contributed to the problem as it was easy for the wind to move it so I decided to make the fence as heavy as possible. I used hardwood posts and two arris rails (the fence is only 2ft high) per bay and then a thick weatherboard secured vertically in place. To date, this has held up very well and it doesn't move even though it is an exposed area.