2. The reflective surface is only on one side of the sarking.
BTW, I'm fascinated by the explanation of why ventilating the roofspace doesn't help to cool the house.
This was discussed on envirotalk as well.
What is not intuitive is that a heat reflective surface also doesn't radiate heat well either (look up the terms reflectivity and emissivity). Therefore the backing of the foil gets heated up but it can't actually send that heat out the other side. The heated backing however will begin re-radiating the heat back towards the source. Therefore, the foil seems to be 'reflecting' heat back out again. Foil up or foil down doesn't affect its function (as long as the shiny side faces an air gap). If the shiny side touches something than heat no longer travels by radiation but by condution. Since foil is highly conductive, it WILL transfer the heat readily.
The convective flow rates need to be extremely high to remove the radiant heat from the roof. Remember that every 1m2 of the roof surface heated by solar radiation is equivalent to one bar radiator. Can you imagine how much air you need to blow on this to remove the heat.
The second point is that heated air doesn't contain actually much heat energy (look up the term specific heat capacity). It won't warm up the ceiling (which has a higher heat capacity) much at all.