Support for high garden wall

[thedavidm]

Hello. As part of a decking project, I am constructing timber steps next to a part wall that forms part of the boundary of the house. The wall is approximately 7ft high and is double thickness (225mm approx). My post concerns the width and depth of the footings on our side. In places the footings are 300mm or more deep and extend 100mm or so from the wall (but not uniform, and in a few short lengths, there is just soil next to the wall bricks). I realise that many old houses only have this degree of foundations (give or take) so am not unduly worried; the wall seems to be in good condition, and shows no sign of cracking, subsidence, heave etc. My proposed solution, which is to strengthen/underpin without otherwise interfering with the wall, is to put shuttering up and use C20 concrete and extend the width of the footing in a stepped fashion, ramming dry pack in any voids between new and old and incorporating the posts for one side of the steps. Does this sound reasonable? Would some form of steel reinforcing rods or mesh be advisable as well? Any advice welcomed. Thank you.

 

[theprinceofdarkness]

Your wall is like a book standing up. So providing no one pushes it or the wind blows on it it will remain where it is as its weight would have settled the bottom edge (foundation?) hard into the earth. However, you digging the whole side up, means that the soil on the other side will be pushing it over. I can't see, but is one end keyed into the house walls? It would be good if it was.
Putting more cement on the side/top will only help a very little. What should be done is that the wall should be underpinned.
Frank

 

[thedavidm]

Thank you. On the basis that the bottom of the current foundation is a few inches above the ground level on my side, should the wall be underpinned to that level, or go further?

 

[theprinceofdarkness]

Under pinning a wall like this, means digging a trench across(2') and under the wall until subsoil is reached then putting in a foundation of concrete so its 2' wide by 12" by 6" deep then using bricks or blocks build up from this until the new "wall" is supporting the old one. when this bit has gone off, do another 12" section, this way the whole wall will have a good foundation. You can only do it in narrow strips so the wall can rest on the old earth in between. Its all a bit dodgy as you don't actually know which bit of the existing wall is being properly supported and what is sitting on loose earth.
Frank

 

[Footsoldier888]

This wall appears to be attatched to a building. Hope its not a party wall.

If it is a party wall PWA notice would be needed.