Building a fence on top of existing wall - some questions

jmBuildExt

Hi - I orig posted this in woodcraft, might get some more action here,
I'm building a fence above existing perimeter walls in suburbia.
Exisiting wall height is approx 1.6m high and I plan putting ~600mm high fence on top.

The wall is cavity block with capping on top with a lip/overhang of about 30mm.
Constructed in the last 6 or 7 years. seems a solid construction no movement/shaking etc.

The fence itself will be lengths of larch or cedar cladding (mix of 144x18 and 94x18) configured horizontally with ~10mm gap between them.
is the gap sufficient? I want to keep it private as possible, but also want to allow wind to blow through so i don't make a sail of it.


I plan on screwing 1.2m lengths of 2x4 vertically to the wall face as battens - 600 above, 600 below.
Is this adequate contact with the existing wall?
I'd like to use 2x4 planed larch/cedar to match the fence timber, but should i be going with tanalised/treated timber?

I will use an angle grinder to notch out the overhang on the capping so the batten is flush/plum and squirt some outdoor silicon or whatever in and around where the capping now wraps the batten - so it can still do its original job.
Is that the norm?

The longest run of wall is about 10m. I plan on putting the 2x4 battens at 1.8m centres.
Will that be adequate to hold it?

Anything else I should consider?

Thanks.

PS: Just to clear up on planning - I'm aware of the planning laws, Its to the rear of the house, I don't have planning, the neighbours on the other side are looking for this, we are all in agreement. If the need arises, or I get in trouble, I will take it down or reduce the height, or apply for retention.

Lumen

Hit and miss will give you wind porosity with complete privacy.

What's the wall made of? Solid or cavity block?

jmBuildExt

jmBuildExt wrote: »

The wall is cavity block with capping on top with a lip/overhang of about 30mm.
Constructed in the last 6 or 7 years. seems a solid construction no movement/shaking etc.

Lumen

Sorry, missed that!

I was thinking, what if you removed the capping, sunk uprights into the top row of cavity blocks, cemented them into place with a bit of a slope to aid drainage, and then fixed horizontal hit and miss to either side?

Then you could have a completely flush hit and miss fence invisibly fixed to the top of the wall.

jmBuildExt

Lumen wrote: »

Sorry, missed that!

I was thinking, what if you removed the capping, sunk uprights into the top row of cavity blocks, cemented them into place with a bit of a slope to aid drainage, and then fixed horizontal hit and miss to either side?

Then you could have a completely flush hit and miss fence invisibly fixed to the top of the wall.

No worries...
Its an idea alright...
But I'm not a fan of the hit and miss style, I've an idea of what I want in my head...and I'd probably prefer T&G to be honest, but I want to leave a gap for air to pass through. The profile i will probably go for is a bevelled profile e.g. AB-24 in this pdf. http://www.abbeywoods.ie/wp-content/uploads/2016/01/Abbey-Woods-Cladding.pdf

Re: sinking the battens into the cavity -
That never actually crossed my mind. Was going to try do it with minimal fuss/interaction to the neighbour. Taking the capping off, sinking the battens into concrete etc might be a bit of a rigmarole. I had also planned on my bottom plank of the fence, covering the capping, I wont achieve that if I sink them and put the modified capping back on. The wall itself is acrylic rendered, so i want to just see that, or the nice fence.... I dont mind seeing the battens, I can taper them off and make them look nice.
But its worth considering I suppose.

Calahonda52

IMO, removing or notching the capping as asking for a lot more work and grief and tough to get vertical.

Also 600mm down and up will look crap and be very difficult to bet 100% horizontal.
I would go from ground level up, with 3 by 3 stepped out from the wall to avoid the capping.
Fix the first one and the last one and string a line between them for the rest
Be much stronger as well with a longer lever arm for the fixings against wind

Lumen

Calahonda52 wrote: »

Be much stronger as well with a longer lever arm for the fixings against wind

...and if the wind blows strong enough the wall will come down too.:D

Calahonda52

Lumen wrote: »

...and if the wind blows strong enough the wall will come down too.:D

Indeed, nothing like shearing it off at the DPC much less mess