New Project for a novice

[darrenh]

Hi all - I'm building an extension. Not neccasarily to save money (although I don't have much so that helps), but because I want to learn!

Anyway - I am stage 0 in the endeavour and have a few questions i was hoping to leverage your experience on.

Foundations: existing house has one course of concrete block and then 3 courses of brick before I get to the DPC (you can only see 2 course of brick at ground level as the rest are below the soil). I am going to mirror this.

My question is that the Building Inspector has asked me to dig down 1.5m. If I did this, I'd actually only need to fill with concrete about 1.3m worth to mirror the block/brick base.

Is this fair - or should I be going down 1.7m to get 1.5m of concrete?

Clearly going digging 1.7m is less desirable! I figure he will come round and put a tape from top to bottom so I may get away with only buying the 1.3m of concrete....

thanks

Darren

 

[foxhole]

Why not ask the Building Inspector ?

 

[^woody^]

Why not ask the Building Inspector ?

Probably because the BCO does not read this forum?

Why do you need to go down that deep?

If you have been asked to dig 1500mm then you go 1500mm below ground level, not more so as to get 1500mm of concrete

Anyway if mass filling, you would fill the trench to 150mm below ground level and then just have four course of engineers externally, and a concrete block and one course of brick internally

 

[darrenh]

I think the issue is the definition of 'ground level'. 150cm down from the ground level would leave me 20cm higher than the existing concrete foundation level.

Less concrete means less cost

 

[^woody^]

150cm down from the ground level would leave me 20cm higher than the existing concrete foundation level.

Your existing foundation level is irrelevant.

As you are learning, all that you need to know is that the foundation depth is the crucial factor, and then what you construct the foundation of is up to you

For the sake of a bit of extra concrete, then you wont have the hassle of building in a trench and you can deduct the cost of the bricks/blocks/sand/cement/ties/cavity fill in the ground

 

[darrenh]

Woody - this makes sense - I'll top up to 150mm below gorund level and use 4 courses up to DPC.

Another silly question - but I intend to get premixed concrete pumped in. Already got a good quote.

Question is, will this be 'self levelling' ie will it naturally be uniform in level around the footings or will I need to mark a level around?

If so, what is the best way to do this? Thanks

 

[noseall]

Peg it.

 

[darrenh]

Peg it.

My novice status allows me to ask... Do you mean peg the internal side of the trench and use a long piece of baton and level to find a line? Then peg with string across the line etc?

 

[Alastairreid]

Peg the trench out approx 1.2m apart and level through, then pour your concrete and tamp to top of pegs.

 

[darrenh]

The trench is on a slope so levelling the ground level will be hard.

 

[Alastairreid]

google stepped foundation.