That's 0.0082677165 inches for Americans, and really thin in either unit.
One of the great advantages of Passivhaus design is that they don't require much heating, in even the coldest of climates. When you don't need a lot of heat, you get some really interesting options, like this Carbontec heating film, seen at the North American Passive House Network conference in New York City. It's a carbon fibre polymer film in 2 foot wide strips, with a copper conductor on either side. Hook it up to a 24 volt transformer and it pumps out 22 Watts per square foot.
Many people get sold on radiant floors because of all the advertising that shows babies and puppies looking happy on a toasty floor. But as Alex Wilson has noted in his book Your Green Home, “it's a great heating option for a poorly designed house.... For the radiant floor system to provide enough heat to feel warm underfoot (the feature everybody likes with this system) it's going to be cranking out more heat than the well insulated house can use, and it will likely cause overheating."Radiant floors also usually have the heating buried below the flooring material (which can act as an insulator) or in concrete, which has to warm up, causing thermal lag.
That's why Carbontec is so interesting; you can bury it in the floor if you like, but you can also put it on the ceiling or walls like wallpaper. It is so thin (.21mm) that you can paint right over it. This makes it 98 percent efficient and almost instantaneous. Being radiant heat, it will warm the floors and the walls, and your body. As Robert Bean has explained:
Radiant heating systems provide comfort by warming the interior surfaces which reduces the temperature difference between your clothing and skin and the interior surfaces which in turn reduces the loss of body heat via radiation. You see it's not necessarily the radiant energy you are absorbing - it is the heat you are not losing which results in perceptions of comfort.
Once people realise what thermal comfort really is, the mix of interior temperature and wall temperature, then Passivhaus and radiant heating become very attractive. Instead of fancy furnaces and heat pumps and expensive plumbing in the slab, you get a few panels of radiant fabric that you just stick on and paint over. It is a simple, maintenance free solution that, combined with the warm walls and windows that come from Passivhaus design, could deliver real comfort.
Of course, being electric, it can run carbon-free. In a Passivhaus design you could run them off solar panels and it would probably stay warm all night, as your home becomes a thermal battery. Another step in the path to Electrify Everything.