Actually, it’s more like the aluminized mylar that’s used to make the “emergency blankets” that we see in camping goods stores and which emergency workers use to keep accident victims warm. So a space suit with five layers of aluminized mylar only has to be five millimetres thick instead of seven feet thick.
Utilizing similar technology, housing industry manufacturers now make thin sheets of material (about ½” thick) that have an effective R-value of almost 20. A rigid insulating foam is sandwiched in between two reflective layers, and this can be attached to the outside of any wall.
This system serves a dual purpose. Of course, the extra R-20 is nothing to sneeze at, but now, the heat loss out of the studs is also halted. So the 2 x 6 wall is once again an effective R-18 barrier. Add the two together, and you’ve got R-38 – almost the required R-40 for the superinsulated house.
Of course, the siding must be removed to accomplish this. But if you have the crappy plastic siding that tends to catch fire in neighbourhood conflagrations, or tends to get shredded in major hailstorms, you may want to upgrade anyways.
The only potential problem now is that the window and door sills may need to be extended outwards to accommodate the extra width of the insulating/reflecting layers. We had a recent estimate done on our house and found that even with the addition of a tiny 3/8” layer, this needed to be done.
Finally, the contractor must also have a thorough knowledge of the dangers of condensation. The last thing you want is for that additional layer to start trapping moisture in the wall.
We haven’t actually had the work done yet, since it’s not a cheap option. However, I’d like to get it done before next winter, since I’m not convinced that the price of natural gas will stay down where it is now (but that’s another column entirely).