Will existing concrete slab take the weight of concrete block garage?

The existing concrete base should be suitable for your new block built garage. I’d preferably use Fibralite Blocks which are a lighter concrete block (3.5n) with supporting pillars halfway down each side. 7” Timber flat roof with EPDM rubber and plastic trim kit, with guttering to the rear. You’ll need ‘furrings’ to get your fall from front to back.

Personally I would start again and put in a foundation that you know is sufficient to take new garage . If you’re spending the money then do it right .

Yes will be fine I’ve just build a house on a 300 slab

It does not sound deep enough to be used as a footing. As you suggested I recommend cutting the slab back and digging down and por a footing with the correct strength thanks

The old slab won't be good enough unfortunately you will need a minimum of 500mm strip footings or a slab that has been reinforced with steel. Also contact building control on the local council website and apply for a building notice. This will cover there visits throughout the job and get you a certificate at the end. Building control will also give you there recommendation for the depth of the footings and any other regulations you must follow. Hope this helps Mark

I would have to say no. It is always best to dig footings. With the money you spend it isn’t worth the risk. If it was me I would take up the concrete. Never cut corners. Hope this helps

I would always err on the side of caution, just because a concrete slab looks OK doesn't mean what's underneath is. You could leave the slab in place if you're happy with it's appearance but cut around the perimeter so that a normal footing can be dug. You could save a few bob by going down this route and if the slab should fail at a later date you could easily replace it but not if you have built on it. If the garage is separate from the house and is classed as an outbuilding you don't need building control to get involved which will save you more money but make sure you hire a builder that knows what he is talking about. Trying to save money in the short-term can cost you much more in the long term.