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Building a fence on top of existing wall - some questions

  • 10-09-2019 9:55am
    #1
    jmBuildExt
    Registered Users Posts: 692 ✭✭✭


    Hi,
    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.
    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.


Comments

  • #2
    jmBuildExt
    Registered Users Posts: 692 ✭✭✭jmBuildExt


    I'll move (duplicate) this to DIY, if a mod wants to close/lock this one.
    Might get a bit more action there, thanks.


  • #3
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    I have seen many a wall pulled down by a bit of fencing added to it.
    Although usually 4" solids.

    Use full height battens (1.6m+0.6m) and fix as Low as possible to existing wall, To allow for a bit of flex.

    dont worry about sealing the capping.


  • #4
    kadman
    Moderators, Home & Garden Moderators Posts: 5,057 Mod ✭✭✭✭kadman


    Stagger the fixing points on the battens. Dont end up with a continuous row
    of fixings in the same course of blocks.

    Is the existing blockwork rendered?

    Consider closer centres for the battens to keep the cedar horizontal laths straight.


  • #5
    smelly sock
    Closed Accounts Posts: 6,820 ✭✭✭smelly sock


    jmBuildExt wrote: »
    Hi,
    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.
    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.

    Leave gaps between timber panels on fence to allow wind to pass through.


  • #6
    kadman
    Moderators, Home & Garden Moderators Posts: 5,057 Mod ✭✭✭✭kadman


    Get your neighbours agreement and conditions in writing.

    Amazing how things go pear shaped over these types of things.

    Remember you WONT get an automatic entitlement to retention after you have

    built the fence, if it needed planning before.

    Do your homework first before you waste money on materials.


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  • #7
    mobfromcork
    Registered Users Posts: 379 ✭✭mobfromcork


    I did something similar (raising a wall up a few feet) but welded up a box-steel frame which was bolted onto the top of the wall using anchor bolts. I used rectangular steel 'feet' which I drilled two holes through and then bolted down I then clad this with vertical lengths of 4x1 larch. I had a poured concrete cap so had plenty of grounds to bolt into. I painted the steel black before using tec-screws to secure each piece of larch to the frame.
    I had considered doing the uprights in wood but would have had a similar issue by notching out the caps.


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