General Foundation Digging Query

[Neo Cortex]

Dear forum, my builder has quoted me too much money to dig the foundations for an outbuilding that I recently gained planning permission for and I am considering digging them myself. Have never done anything like this before.

The building is 5.5m wide, 8.7m long and 2.45m high. It will be built out of blocks, cladded in wood with a flat felt roof. The ground type is clay.

Could I get some guidance on how deep to dig them and how wide to dig them pls? Appreciate it depends on the ground type but general rule of thumbs for each ground type would be fab.

I have paid for the building inspector to come and inspect them before they are filled. Can anyone advise what he is likely to ask me about it? And what would be the correct way to repond with the necessary information? Can I just say its block built with a flat roof to this size and he will be OK with that?

Really appreciate your help with this.

 

[cwhaley]

I can absolutely not recommend doing it by hand! I did 5.5m x 3m and had to draft in help. If you're not used to shifting such a large amount of soil/clay it can be very exhaustive. Unless there's an army of you, machinery is the only way.

Depending on access, hire costs, labour hours, insurance, etc. -- his quote might not be as expensive as you think.

 

[johnny2007]

Ask BC how deep they want you to dig; they'll have the last word anyway, so better take their advice before starting digging.
A mini digger costs around £300 for a weekend hire and it will take you a day to do your project, including a bit of practice.
Best money you'll ever spend.
Make sure nobody is within the digger action radius and be extra careful with anything that can be broken (plant pots, shed, etc.)
I hope you have a skip and someone helping with a wheelbarrow.

 

[mikeey84]

And if you do hire a digger, try and work out where cables, gas pipes and drains run  before you start digging, so you at least know where to be careful

 

[matlob]

You could also also dig a test hole by hand and get BC out to look at the ground

I did this and dug down to 1m and the BC said that 700 was fine so saved a lot on concrete and spoil!

Are you able to repurpose the spoil anywhere else?

 

[noseall]

Dear forum, my builder has quoted me too much money to dig the foundations for an outbuilding that I recently gained planning permission for and I am considering digging them myself. Have never done anything like this before.

The building is 5.5m wide, 8.7m long and 2.45m high. It will be built out of blocks, cladded in wood with a flat felt roof. The ground type is clay.

Could I get some guidance on how deep to dig them and how wide to dig them pls? Appreciate it depends on the ground type but general rule of thumbs for each ground type would be fab.

I have paid for the building inspector to come and inspect them before they are filled. Can anyone advise what he is likely to ask me about it? And what would be the correct way to repond with the necessary information? Can I just say its block built with a flat roof to this size and he will be OK with that?

Really appreciate your help with this.

1m deep is a standard spec'. My experience with clay digs is that once you hit the clay layer, the conditions are unlikely to change. What is crucially important however, with a clay substate is proximity to (water demanding) trees and shrubs. This affects the depth and sometimes width of the trench massively.

 

[HERTS P&D]

Hire a man with a digger.

Andy

 

[jono_h]

I’ve just done 9x4m by hand. I went out to dig a test hole, found it was easy digging down to shale at 600mm, so just carried on.
BC wanted 750mm deep so I had to kango out another 6” of shale.

I hand planned to get a mini digger in, but in hindsight I almost certainly would have taken out the oil feed pipe to my boiler.

 

[Hugh Jaleak]

Founds in Clay, assuming an 11" cavity wall, used to have to be 600mm wide and a metre deep if memory serves me correctly. BCO will just check they are deep and wide enough, if he/she is happy, they'll tell you to concrete.

Just bear in mind though, if you're thinking of DIY and hiring a Mini Digger, they are not the easiest of things for a novice to get the hang of, can fall over very easily, and any damage or loss will be your responsibility. Hit a service, and suddenly your Builder's quote will seem cheap.