Concrete garage floor

[jstrong]

I'm removing an old 'L' shaped shed which has a 3" thick base with membrane below. I am wanting to construct a new base to erect a timber double garage. The question is would it be ok to concrete over the old base and if so what would be the minimum thickness I could lay over the old base?

Also any tips on the size timber to use would be appreciated. (The roof will probably be 18mm OSB with a rubber membrane glued to it). Any advice appreciated.

Also the garage will be 1M away from the neighbour due to it being timber construction. What is the max ridge height I could have? Is it 2.5 meters or could I go higher as the apex will be 4 meters away from the neighbour or does it not work that way? (I'm intending to build to the max 30m2).

 

[noseall]

I take it that from your description you intend sitting the shed on a concrete slab rather than strip footings?

If so you need to prepare the slab well and dig down to a suitable depth, thus removing the old concrete and much more.

I personally would use strip footings. Slabs are prone to leak water back into the structure in particular if they have a large 'toe' all around the building.

There are about a billion posts on DIY-not complaining about leaking garages/sheds due to poor construction methods.

 

[jstrong]

Many thanks for your reply Noseall.

I was intending to lay a slab over the old L-shaped slab squareing it up to the 5.5m x 5.5m size I need. I was also going to place a membrane down before concreting thus keeping any damp out. The framework of the garage would be exactly in line with the slab and clad in loglap dropping down say an inch past the concrete slab. Would that suffice in keeping moisture and rainwater out? Please let me know your thoughts, cheers.