Digging footing next to neighbours wall

[Jim589]

Hi all,

I plan to put a single storey extension in, down the side of my house, with the wall being as close as it can be to the boundary to maximise the internal size.
The boundary is effectively a 3ft high garden wall, I haven't dug a trial pit but i'd be amazed if there was more than a foot of footings. Now this is not too bad, except sometime in the past someone clearly thought it would be OK to build a lean-to (my neighbours) on top of this garden wall. It's all lightweight. Rotten timber and a polycarbonate roof.
I spoke to my neighbour on the other side, who has put an extension in recently and he said his footings kept collapsing as the soil was loose.
So I guess my fear is digging along this wall, and it sliding into my footings.
I have not really come across this before, I vaguely remember once using a digger to drive plates into the soil between a nearby house and footing, but in my case here, I wouldn't have the room and if I did, they would have to be pretty deep as i'd be excavating next to them.
The wall in question is about 6m long.
Has anyone any advice please? I haven't gone through building control yet and aware of the PWA notice that needs serving, but I am currently planning this and this is really bugging me.

The solutions I thought of, were shuttering the sides as I dig it (by hand I guess) with OSB and bracing across the footing to the other side. Then pulling the braces out whilst pouring. I.e. dig 600mm worth of the footing (I guess it will be 600 wide and then 1m deep) brace it, then dig the next 600mm etc. Its fairly lightweight, single skin wall etc, so wouldn't require too much.
Or I guess, dig a section, pour it, then the next day do another etc until I have done it (I could work from the ends)
Finally I could replace his lean-to. But spending a couple of grand on a new upvc conservatory and then the footings for it, for my neighbour really really doesn't appeal

Any help or advice would be really appreciated as things like this keep me awake hahaha

Many thanks

 

[noseall]

How long is the proposed section of wall on this elevation?

I was kinda thinking that you could have three points of support (foundation pads) for a pair of steel beams (to support your wall), i.e. one abutting the house, one on the return foundation and one in the middle. Sounds convoluted but it may work. Have you spoke to the neighbour?

Pads

• noseall
• 18 Sep 2015

 

[^woody^]

It's all in here

www.diynot.com/diy/threads/neighbours-extension-foundations-or-lack-of.441025/

 

[theprinceofdarkness]

As I see it, you mark out your 600 X 600 section then go down 1m, with shoring to hold his foundations and soil back. Then you pour your 300mm slab section somehow pulling the shoring out as you go, but you still have to support 700mm of his foundations and soil?. Or you fill the hole to the soil level, which is a lot of concrete! Another point is that the garden wall might have a spread foundation, so three courses under the soil step out to 18", which will make your digging awkward. Yet another point if you manage to shore up the soil and support the wall foundations and build of your own foundations, you will have to fill the gap between your wall and the soil, else it will fall out into the gap and the garden wall will lean over towards you.
I am wondering rather then all mucking about, if you just bracket his woodwork of your house wall and remove that section of the garden wall, it depends what he has done on his side of it, and finally bracket his woodwork back to your new side wall and paint the bottom of it white or screw back his paneling if required.
Frank

 

[KenGMac]

Jim 589 Hi.

Suggest you have a look @ Shire piling? a method of in effect screwing a big drill bit into the ground on a steel post, right down to a load bearing strata, getting over several problems.
1/. No deep dig.
2/. No shoring of the Boundary wall and no chance of its sliding into your excavation, even if you do a hit and miss foundation dig.
3/. Fast in and out in one day.
4/. No vibration to cause damage to the boundary wall, or the neighbours shack as termed by Noseal.

All you then need is a relatively shallow found, the reinforcing of which is attached to the steel poles on the shire collars, and assisted by the reinforcing in the collar

It would be accepted by the BCO with no problems, and your insurer when you come to get cover for the new extension will have no doubts about it

Ken

 

[noseall]

It's all in here

www.diynot.com/diy/threads/neighbours-extension-foundations-or-lack-of.441025/

Where's the fun in that Woodbarrel. Options, options dear boy.

 

[Jim589]

Guys, thanks!
This really is a great response.
Cheers woody, somehow I didn't see that haha. The corrugated steel was what I was on about. But I would have to go quite deep with that. You can see from my pic that I'm limited with room so very keen to go as close as I can. Really just for a toilet and small utility room.
Yes theprinceofdarkness, sort of what I mean. I was thinking of doing the whole 6m trench, pouring it and using the hydraulic pressure of the concrete to hold in in place. Although very much doubt I'd get the osb out from his side of the footing.
I notice the other thread recommends digging and pouring it on sections

Ken, I did some research and they are quite clever and simple. What's the rough costing?
I'd still have to dig a trench albeit a small on but I presume even that will undermine his wall. The idea of not having to excavate all that soil is appealing haha

 

[Jim589]

Agh noseall. Apologies I thought you were talking crap! I'm really sorry. I get it now! That's a good idea!!!
How do you finish under the steel? I was aiming for a suspended floor.

 

[KenGMac]

Jim589, hi again.

Sorry but, any prices I have are from Insurance Claims.

This means that any costs are Probably, nudge, nudge, higher than can be obtained by a Private Individual, such is the way of the Insurance Industry?

As an aside, where is it you reside? and is there a history of Subsidence in your area? or do you live in an area of Shrinkable Clay, all of the above will dictate whether Shire piling can be used? There are a couple of Apps, for Apple and I think Android that are free and can be down loaded as regards the geological conditions, and the soil conditions in the area where you live.

Shire also do a system that is designed for small specifically for "relatively light Extensions"

Ken.