>If I'm understanding it correctly its basically a space dug down and left empty to keep the walls ~60cm away from the foundation?
Exactly.
There is no actual need of 60 cm, which is only a "sane" width to allow inspection, the external wall and "air chamber" can be much smaller, see as an example:
and if there is not enough space for the above (25-30 cm) a wall of porous/hollow bricks (thickness 10-15 cm) will still do better than waterproof membrane alone.
>In most places, but especially SF, there isnt space for an extra meter on each side of the houses
I know, and I am not at all saying that it is a universal solution, and - besides - it costs a lot more than plainly applying to the house foundation and earthed walls this or that kind of non permeable membrane (there are bitumen based, PVC based, synthetical/chemical liquid compounds, bentonite, etc.).
Still if you are building a house and have the needed space, it is money well spent, I have seen tens or hundreds of recently built houses using membranes notwithstanding the availability of space (because it is easier and cheaper) with humidity/mould problems that cannot simply be resolved without mechanical ventilation (besides when needed repairing the waterproof layee(s)).
But you might be pleased that the most modern system at least in Finland actually has little of the same features than the romans had. If you look at the same membrane I posted earlier, it has little knobs that hold it little bit away from the wall:
I don't know the English word for it. It's not perfect, but lot better than couple decades ago. They used to paint the concrete with tar. This "patolevy" is cheaper, easier to install and allows little bit of ventilation.
Yes, I know those, though - technically - they are not a waterproofing membrane, they are intended (at least here) to be only a mechanical protection and a separation layer, and the height of the knobs is anyway too small to have an actual ventialtion.
Besides - usually the "top" of the layer is not properly sealed/protected so - over time - the space (at the bottom)is filled with fine sand/dust brought by wind/rain, of course preventing any ventilation where it is more needed.
Exactly.
There is no actual need of 60 cm, which is only a "sane" width to allow inspection, the external wall and "air chamber" can be much smaller, see as an example:
http://docplayer.it/docs-images/41/9277133/images/page_8.jpg
and if there is not enough space for the above (25-30 cm) a wall of porous/hollow bricks (thickness 10-15 cm) will still do better than waterproof membrane alone.
>In most places, but especially SF, there isnt space for an extra meter on each side of the houses
I know, and I am not at all saying that it is a universal solution, and - besides - it costs a lot more than plainly applying to the house foundation and earthed walls this or that kind of non permeable membrane (there are bitumen based, PVC based, synthetical/chemical liquid compounds, bentonite, etc.).
Still if you are building a house and have the needed space, it is money well spent, I have seen tens or hundreds of recently built houses using membranes notwithstanding the availability of space (because it is easier and cheaper) with humidity/mould problems that cannot simply be resolved without mechanical ventilation (besides when needed repairing the waterproof layee(s)).