Garage foundation wall

[Pete]

Got to build new garage rear wall 12m long running parallel to an  old victorian wall which is built using random limestone walling. The new wall will be approx 1 metre away when built but the problem is whether to pour the footings in sections so as to avoid undermining the older wall. I have not dug down to expose the existing wall and see the construction but it looks like it is on large stones under ground before using smaller face stone above ground. 

I realise I may have to see a S/E but just wondered what people thought may be the way to do this without weakening the older wall. If i poured the footing in sections I could place re bar in between the sections and place an angled timber also on the joint to be removed when set to create a kind of jigsaw effect between sections? I may add the ground is perfect for building on so that should make the case of doing the footing in sections more viable.

[Mr Punter]

Not sure what the issue is.  If the bottom of the new footing is less than say 500mm below the footing of the old wall and the ground is stable there will be no problem.  If it is a lot lower or dodgy ground, then you can do it in sections, like you would if you were underpinning.

 

If the land and old wall are yours, no probs.  If they are owned by other you will need to look at party wall agreements.

[Brickie]

A trial pit is your first move,I'd say. I know it might seem like s lot of hard work for nothing but if it saves you having to do it in sections it'll be time & money well spent. 

[Pete]

So once I have done a trial pit what am I looking for? My concern is obviously digging a 12 metre trench with the possibility of the old wall coming down or creating movement and weakening it. I assume you are thinking if there are large stones it will not matter as much? Or if the old wall is built deeper than I need to go for the new wall then that also makes doing the trench easier?

Really appreciate your advice

[Declan52]

Dig 2-3 trial holes along the length of the old wall. Only need to be wide enough for a shovel,1ft, and go down until you can scrape under what's at the bottom. Once you know how deep the old wall is at a few points along the wall then you can make a more informed choice on how to proceed. Take pictures and measurements.

[bassanclan]

If there are other buildings etc on the other side of the wall which may be damaged by the wall giving way then you have to rethink things.

 

How tall is the limestone wall?

What depth foundations are required?

 

Could get the trench dug one day and then the concrete poured the next day?