Extending a garage base

[Sombrero]

I currently have a concrete sectional garage sat on a concrete base in my back garden.
The front of the garage leads onto the driveway. The sides are flanked by turf. But behind the garage, the ground drops away at about 45 degrees by about 3 feet.

I want to take down the concrete things and build a workshop - probably our of block or brick... but my main problem is that I want to move the whole thing back by about 4 feet, so now over the lower bit of garden.

Is this a huge undertaking?

Can I just make a framework of concrete posts or steels? Or do I need to add to the concrete base? Would it be ok to form the shape out of OSB and just fill it with concrete? if so, how do I tie it to the existing base? how far down do I go?

 

[Corazones]

Hi Sombrero,

If you extend the base within shuttering alone as you suggest, you will have an edge at the bottom of the slope which will be easily undermined. At the very least, you will need to dig deeper at that end.

I would be inclined to build a retaining wall at the end with slabs on a good footing, and then fill in the rest with consolidated rubble and oversite concrete.

Ideally you should lock the two slabs together, but that would involve more work and is probably unnecessary if both sections are properly built.

Alec