break up base for garden shed?

[john west++++]

hi, we have a small wooden garden shed on a cast concrete base. the shed is pretty rotten so we want to replace with a larger breeze block construction shed ( that's if breeze block is the cheapest kind of shed to build, that's not wood. [guess breeze blocks will work out cheaper than the pre fabricated kind of concrete sheds you can buy anyway?])

my question is; since i am going to need a larger concrete base, should i smash up the existing one or is there a satisfactory way to 'key in' a piece of new larger concrete base onto to the existing one. many thanks for any advice. yours, john west

[BigWallop]

This has been posted before hasn't it ?

The difference in weight between the old wooden shed and a new block work one will be enormous, so it is better to start afresh with a new base. You'd need to work out the weight of the new building to give you an idea of what depth your new foundation should be, and to what kind of mixture your concrete will need to be.