Lindaloo asked how a radiant barrier would work under the siding on your house - herewith (after a long pause!) is the answer:

How the barrier is mounted on the side of the house is critical. Basically, you start by putting the radiant barrier material over the main structural material of your house: plywood if it's a frame home, or block.

Then - and this is the key part - you add furring strips on top of that to make an air gap, then attach the siding to the furring strips. So you wind up with plywood (or block) + radiant barrier + furring strips (air gap) + siding.

What happens is that radiant heat from the sun is absorbed by the siding, re-radiated into the "gap" between the siding and radiant barrier, and then the barrier bounces it back away from the house.

Needless to say, that air gap can get pretty hot, although the siding itself isn't air tight, so the hot air can escape.

Interestingly enough, in the specially designed "OPERA" houses designed by Horizon Energy Systems, this principle is used to heat water circulated through copper pipes on the south facing wall for the home's hot water, and if I recall correctly the water temp in the pipes was measured at 170F - and all that heat is for free from the sun!