Increasing slab

[bolst3r]

I have a slab in my garden 3x3m which has two sheds standing on it, I previously increased it to enable it to host the extra shed however I now need to remove the smaller shed and increase the slab by a further 1.5m as I want to build an office in the garden. I guess in an ideal world I would cast a new complete base but budget is against me and I'm worried about part of the base sinking and causing an issue with the new building. So how should I increase the slab to cater for the new office? Current the base is 8 inches thick and is set on another 8 inches of compressed hardcore. Wondered about increasing the slab by a couple of inches and running steel reinforcing over everything as its crucial the footings don't move...

Any suggestions appreciated.

 

[pinenot]

The base you have explained is good at 8" conc on 8" compressed hardcore, so far so good, but the bit that needs explaining - [I'm worried about part of the base sinking] needs a bit of explaining.
Also what's the building to be built of, design etc. and where are the walls being located on the old/new base. What's the make up (apart from 8" on 8") lay of the land etc. ...pinenot

 

[bolst3r]

Yes, more information is needed – sorry about that. I've created a small image below to show how the slab is divided up and a pic of the sort of thing i'm going to build, as you can see it's quite a bit more than a 'shed'. The ground is flat and seems stable, there are a few trees nearby so the ground stays quite dry all year. As you can see the new building will span all three areas of concrete but I wondered if I should try and tie them all together as I'm paranoid one will drop thus causing my lovely new office to bend and buckle... I know adding steel and more concrete to the job is probably another £250 which I would rather not spend but I will if necessary. I was considering drilling 20mm holes in all the bases, inserting steel rods then overlaying with a steel frame and tying it all together before covering in 2 inches of new much but is this overkill?

Untitled

• bolst3r
• 10 Jun 2013
• 1

 

[bolst3r]

Ok, been doing lots more research on this and think i'm best to just drill a few holes in the exiting base, add rebars then another decent slab next to it to create one big base. The structure i'm building is timber so won't be heavy like brick and the roof will be rubber which is considerably lighter than felt and i'll be able to position the floor timbers to bridge the joints making sure to spread the load so hopefully this should do the trick

 

[pinenot]

I would agree with your proposal, but would put debonding sleeves on the new concrete end of the pins (rebar) to allow for any horizontal movement, like this - View media item 62366 ...pinenot