Building question - Must be some builders on here :)

[Paul]

Hi all.

I have some walls in a square configuration - Front and back are Cinder block Retaining walls based around the mid-section of my garden... side walls are just simple graduated blocks...



I want to lay a concrete slab accross the entire area (4-6" depth)... Front to back, left to right, inside of the walls. There is a french drain behind the rear wall, along with seepage holes in it to aleviate any water pressure that might be behind it.
The slab will run off front to back... which in itself would be fine, but eventually my block-built games room will be built on the slab.

Questions :

1. Guessing i would need drainage between the rear retaining wall and the gamesroom to run off any water, rather than it just sitting there?
2. Where would (if needed) the slab need to be tied into? I was initially thinking rebar into the rear and front walls which went into the slab itself - however it doesnt give any scope for movement and also runs the risk of pulling the whole thing about.
3. Expansion joints between all walls and the slab?

Any thoughts appreciated

 

[Tilt_Birmingham]

1. Ideally, you'd need the french drain to be deeper than the lowest point of the wall and lay a perforated pipe to collect and carry the water away. Make sure the wall is well tanked when you construct your games room.

Are you going to build directly onto the existing brickwork? or building from scratch?

If you building onto existing, dig a test pit and see what foundations they sit on, and work out your structural loads. and if good those would be your foundations and the slab simply would be a concrete floor

If you building from scratch and leaving a gap between those walls and new... I wouldn't tie them into existing walls as you'll want them to move separately to avoid cracking as the building settles

Btw not a builder but I have a degree in building surveying but a little rusty