House Works: Your questions on adding exterior insulation, attic frost

Adding Exterior Insulation
Q: What’s the best way to add insulation to the outside of my house? My friend is planning to apply vertical vinyl siding and wants to upgrade energy performance as part of the job. What’s the best plan of attack?
 
A: Assuming your friend is working from bare wall sheathing outwards, the best approach I know of is to apply extruded polystyrene foam to the outside walls, then the siding.
This kind of foam is completely waterproof and retains insulation