Building close to boundary wall

metricspaces

I am wondering how close I can build to my boundary wall. The boundary wall is hand built stone. The land outside the boundary wall is about 1m lower than the land inside the boundary wall. See pic below.

I have about 3m between the side of my house and the boundary wall. I am thinking of building a shed in this area, and would like to take advantage of as much of the 3m width as possible.

If I want to build as close as possible to the boundary wall can I use normal foundations\block work? Or would I need to get additional work done to make it stable e.g. dig down to at least below the level of the land outside boundary, which would be over 1m deep foundations?

BryanF

Structural eng

Gumbo

Talk to your engineer. You may be able to build right up against it subject to the condition of the wall, and possible suitable underpinning.

metricspaces

Thanks. I will talk to an engineer. I am just wondering, in general based on my description what is possible or what would need to be done.

If I am going to get an architect to design this shed for me (I will need planning permission), should I talk to the engineer before I get the architect to come up with proposals?

My concern is that the architect comes up with some proposal, I submit planning application, get approved, then go to builders for quotes and find out there's a significant cost in underpinning as the architects proposal is too close to the boundary wall for standard foundations to be used.

metricspaces

kceire wrote: »

Talk to your engineer. You may be able to build right up against it subject to the condition of the wall, and possible suitable underpinning.

Thanks. I think my description may not have been that clear. I don't want to actually use the boundary wall itself, I just want to build another wall as close to it as possible. See image below. In this scenario, where I am not touching the boundary wall, is it still possible that it may need to be underpinned?

Gumbo

metricspaces wrote: »

Thanks. I think my description may not have been that clear. I don't want to actually use the boundary wall itself, I just want to build another wall as close to it as possible. See image below. In this scenario, where I am not touching the boundary wall, is it still possible that it may need to be underpinned?

No, your post was perfectly clear. Building up against an existing structure (wall in your case), you have to design where the pressure from the new foundations will go. It’s possible the new foundation will cause the existing wall to loose its stability and fall to the ground. So building close to the wall will/may require underpinning.

Is the shed big enough to warrant planning?
If so, budget for underpinning, get your Planning then get engineer on site to details the structural design.

metricspaces

kceire wrote: »

Building up against an existing structure (wall in your case), you have to design where the pressure from the new foundations will go. It’s possible the new foundation will cause the existing wall to loose its stability and fall to the ground. So building close to the wall will/may require underpinning.

Thanks! That makes sense. I couldn't see the reason boundary wall would need to be underpinned.

kceire wrote: »

Is the shed big enough to warrant planning?
If so, budget for underpinning, get your Planning then get engineer on site to details the structural design.

Yep, I'll definitely need planning. Would the architect know how close I can build to the boundary wall without underpinning required, or it is only an engineer that could tell me this?

Paullimerick

Apoligies if this is not what you want. But why not put down let's say 4" of concrete and put up a good quality steel tech shed on it. No foundations. No pressure on wall. And not so sure you.would need planning for one of them sheds. It would definitely cost less. And removable at any time to use else where.

Lumen

If you want a search term for finding more info it's "retaining wall surcharge".

I dimly remember from researching garden terracing a rule of thumb that you can't add surcharge within 2x the drop of the ground level without reinforcement.

Presumably the worst case is that you'll need 1m of foundations, i.e. imagine that the earth is capable of taking no weight at all.