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Block Wall

Hi All , just joined, first post , look forward to hearing from you all...

This has probably been discussed untill the cows come home but just want definative advice on building a block wall to later be rendered. Its 23m long with two returns of 5 m each . The wall is 2.4m tall. 

Its retaining chalk basically with 300mm of topsoil .

As i understand it: footing at 800mm deep and twice width of block, H blocks, re bar in footing every 600mm  , fill cells with concrete .

Does the fill behind the wall need to be gravel ? Drainage holes etc ? Anything else to add? 

Thanks team 

Nick

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Replies

  • PRO

    Hi Nick 

     

    depending on length of wall and fals on ground etc you might need to put joint vents to allow water to run through and not build up behind the wall, just rememebr if rendering later on the vents will need setting so there usable once render is on.

     

    also how many skins you looking to do because even with rebar bedded in each H block cavaty that for 2.4m retaining height i think is going to need a 2 skin wall (at desk on day job so not with my bits to calculate fully so any one else feel free to correct there) but also depending on height you might need planning to check and start etc depending on structural dependance

  • PRO Supplier

    I was told that any retaining wall over 1.8m high needs an engineering drawing - not sure how true it is, or if it needs consent from Planning, but worth checking to cover yourself in the event of wall failure...our local planning are generally fine with a call to check...

  • PRO

    You may find this useful as planing guidance & building control :

    https://www.planningportal.co.uk/info/200130/common_projects/20/fen...

    We referred to it when I had an extenstion and new garden walls built in 2016.

    Fences, gates and garden walls
    Details of the planning permission and building regulation regimes for Fences, gates and garden walls
  • PRO

    Any retaining wall over 1.2 requires a structural engineer to spec. This is generally only a few hundred quid, which is a drop in the ocean compared with the potential cost of Construction.

    It also removes your liability for any movement or cracking that may occur down the line.

    Everysite has different issues and factors to take into account and a bespoke engineering is definitely required. 

    Good luck with it.

  • Just my two cents, feel free to ignore. Structural engineer might suggest a key footing with a heel and toe instead. You may not have to go quite so deep with the footings and the cantilever effect helps retain the bank.

    As mentioned already, an open drainage stone behind with a french drain at the base of the wall to remove water should reduce water pressure.

  • Hi Nick

    I would also consider puting in a Visqueen barrier to protect your render.

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