Concrete Foundation top Level

5 Oct 2012
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United Kingdom
just wondering what is the best way to know how much lower than the finished floor level to have the top of the foundation pour. we have 150mm block/beam, and about 75mm insulation, 50mm screed, leaving 25mm for floor finishes, so is it best to have the top of the finished foundation pour, -450mm from the current finished floor level.

any advice will be welcome

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Any drainage to go out of the area? If so work out invert level at foundation top.. but normally about 600mm below slab level will give enough space..
no drainage at all, -600mm seems like a big amount?? as we will have to excavate a bit for the block and beam either way, how would i build up the 600mm,
150mm block, 75mm insulation,75mm screed. ? what about the other 300mm?

With no drainage it may well just fall down to min void requirements.. so between 200-300mm.. take 300mm then so a block and brick depth below the beams..
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so the build up would be 75mm for floor finishes, 75mm insulation, 150mm block/beam, which makes 300mm, and then as im using 215mm blocks if i allow mortar would make it 250mm, so 550 in total, that would allow one block under the beams?? am i understanding that right?

what is the minimum ground clearance between the underside of the beam and the earth? i have heard you have to have the ground treated with weedkiller? or have a concrete base?

Nope, i am saying 300mm below the beams.. which can be made from one block and one brick.. that is assuming you have clay type soil.. you dont put the beams directly onto the concrete foundations..

Then you have the 150 beam/block over followed by insulation and screed.. also consider a DPM in there somewhere..

A concrete oversite under the floor or weed kill the area.. either is fine..

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