High wall - Shoring up foundations

[davidm]

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 some areas, there is just soil). Reading the text on garden walls in the main site, I am concerned that this is inadequate and would not be built this way these days. However, 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 rammed into the voids and extend the width of the footing, perhaps by another 100mm. Does this sound reasonable? Would some form of steel reinforcing rods or mesh be advisable as well? Any advice welcomed. Thank you. Not sure how to post an image from my laptop desktop...?

[seanandruby]

Any walls over 1.2 in height should be designed by a structural engineer. Underpinning is not for a diyer and should be left to professional tradesmen. underpinning is done in strips and the concrete left low for dry packing. Please seek advice from an engineer.