Garage Extension - BC Say Existing Wall Needs Underpinning

[machineage]

Hi all

I plan to extend my attached garage. One wall of the extended part of the garage will be formed from an existing 9" thick boundary wall. This wall already forms one wall of the existing garage - and it is the continuation of this wall that I planned to use. However BC have told me that the section of the wall that will form the extended part of the garage will likely need underpinning / rebuilding. I have to dig a trial pit to expose the foundations. Can someone tell me what depth / type of foundations would be deemed suitable and not require such work and what would not be deemed suitable? Thanks.

 

[freddiemercurystwin]

There ought to be a foundation about 6" thick and sticking out about 6" beyond the face of the wall, the depth will likely not be much of an issue. But he probably just wants to see some kind of foundation rather than no foundation as some boundary walls are built on little else but the earth.

 

[machineage]

Thanks

The wall actually formed a building constructed in the mid 1920s. Better get digging.....

 

[freddiemercurystwin]

Prolly built off the ground then.

 

[machineage]

Wunderbar

 

[machineage]

OK I suspect this isn't good news

I've been digging - and unearthed stepped brick footings. No sign of concrete foundations as of yet...

Footings

• machineage
• 3 Oct 2016

What would be an approximate cost to underpin a 5 metre length of wall such as this?

 

[freddiemercurystwin]

Well its a foundation albeit in brick and in essences is doing the same thing - spreading the load. And it looks pretty sound so have a word with your BCO before you get too worried/get him out.

 

[machineage]

Thanks - I'm living in hope

He's coming to have a look again this week.

The stepped footings are seven courses below the surface level and as you can see are two courses thick. The footings sit on solid clay. It's all clay around here - and you can see the clay in the photo above just a foot below the surface.

What would be deemed to be the advantages of a concrete strip foundation over these brick footings - such as to deem them a requirement (or underpinning) for using this wall as a part of the garage extension?

 

[tony1851]

That is a pretty substantial footing for a boundary wall. There are many houses around here which are built just off one offset, one-and-a-half bricks wide, rather than the two-bricks width you have.
Your BCO would have to be clueless - or peverse - to expect you to underpin that.

 

[machineage]

The wall was originally part of a substantial group of garages which were subsequently demolished leaving just this wall around the perimeter of the plot. The lowest footing course appears to be of different brick with a yellow tint.

A cross-section of the construction as I see it is as follows:

Wall Footings

• machineage
• 3 Oct 2016

Your comments are getting my hopes up here - however the BCO appeared to be pretty sure (99%) it would require underpinning / rebuilding. Oh well - see what he says later this week

I'll keep you updated - and thanks again for the comments.

 

[machineage]

It passed inspection

Phew...