Level for Foundations

[Chandler]

I am building on a sloping bush block, using steel piers for the subfloor. But to make best use of the space under this floor, I intend to place a half concrete slab on the lower side (that is, cut into the slope where necessary to create an extra couple of rooms).

I want to know at what level to excavate, allowing for the concrete slab, and subflloor beams and joists?

I plan to get an excavator to do the main cut, then a bobcat for tidying up and dig footings, etc. I DO NOT plan to do a "cut and fill" - I have enough space to dispose excess soil, so will cut only.

My plans show, say, 100mm thick concrete slab (with deeper footings), 200mm beams, 200mm joists and a wall height of 2400mm.

Does this mean I mark the level of the cut at 2900mm (100 + 200 + 200 + 2400) below the finished floor level?

[Barry_White]

Chandler

You wouldn't allow for the the beam depth only to the ground level under your slab. The beams would be below your ground level.

But you really should be having your plans drawn up first and have an engineer detail for your concrete slab because it will depend on what type of structure you are having as to what size the beams will be. e.g. Brick or timber construction, tile or steel roof etc.

[Chandler]

Thanks for your reply Bazza, but I am not sure what you are saying.

The plans have been drawn and approved by a structural engineer, but in regard to levels he just advises the builder to check on the ground.

I want to avoid excavating too much (or too little) soil for the slab, so want to establish a level for the excavator to cut down to.

I have included a drawing of the cross-section (level.jpg) which may explain how far below the proposed (first) floor level I should cut the platform for the slab.

Maybe its not a big deal, because I can alter the height of the piers on the upper slope when I build the steel subfloor.

[ausdesign]

As I read it your joists are 200mm
The beams [bearers] supporting the joists are 200
from the underside of the beam to the top of the slab is 2400
if this is correct - from underside floor level to excavation is 2900 plus 50mm for packing sand under the slab.

[Tools]

If you are lining the ceiling below you need to consider the battens and lining as well.

Tools