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Building a fence on top of existing wall - some questions

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  • 11-09-2019 12:06pm
    #1
    jmBuildExt
    Registered Users Posts: 692 ✭✭✭


    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.


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    #2
    Lumen
    Registered Users Posts: 31,020 ✭✭✭✭Lumen


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

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


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    #3
    jmBuildExt
    Registered Users Posts: 692 ✭✭✭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.
    :)


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    #4
    Lumen
    Registered Users Posts: 31,020 ✭✭✭✭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.


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    #5
    jmBuildExt
    Registered Users Posts: 692 ✭✭✭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.


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    #6
    Calahonda52
    Registered Users Posts: 12,240 ✭✭✭✭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

    “I can’t pay my staff or mortgage with instagram likes”.



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    #7
    Lumen
    Registered Users Posts: 31,020 ✭✭✭✭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


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    #8
    Calahonda52
    Registered Users Posts: 12,240 ✭✭✭✭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 :)

    “I can’t pay my staff or mortgage with instagram likes”.



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