Extension foundations?

[chicd4]

Can anyone tell me what is the minimum thickness for concrete footings for a ground floor kitchen extension.

 

[Static]

Depends on foundation width.. for absolute minimum would be distance from wall to foundation edge or 150mm.. whichever is greater..
That said i wouldnt do a mass concrete strip of less than 1/2 width in depth without reinforcement.. so 225mm depth of concrete for a 450mm wide strip footing..

Course most would do trench footings to avoid all the extra brick/blockwork below ground..

 

[freddiemercurystwin]

Static, For all domestic jobs with trad construction I've been specifying 600x200 (750 to U/S) unreinforced foundations since I don't know when, never had it rejected by BC and nothings fallen down AFAIK should I be worried?

 

[Static]

Static, For all domestic jobs with trad construction I've been specifying 600x200 (750 to U/S) unreinforced foundations since I don't know when, never had it rejected by BC and nothings fallen down AFAIK should I be worried?

Doubt it.. only if you have a single skin wall with a high load.. extremely rare on single dwellings.. all to do with 45deg line from point of load needs to be outside the base area or you need to check for punching shear..

 

[freddiemercurystwin]

Fair enough

 

[^woody^]

I think the OP is confused.

Footings don't actually have a thickness - they are the structure below ground level

So does he mean the depth of footings, or the thickness of the concrete strip foundation?

 

[chicd4]

I have dug down 1100mm to reach compacted sandy gravel (bigish pebbles)
and would like to do a strip foundation with trench block to come out of the ground.

 

[amwc]

It needs to be wide enough to spread the load evenly to the allowable bearing of the ground they are sat on.

 

[r896neo]

I think what you are trying to ask is how deep should the concrete be? If that is the case 9 inches would be fine.

 

[noseall]

I think what you are trying to ask is how deep should the concrete be? If that is the case 9 inches would be fine.

agreed.
225mm deep (at 600mm wide) is the thinnest i have ever seen specified for standard domestic.