A: Insulating contractors I have spoken with recommend removing the insulation on the floor before adding insulation to the sloped sides of a roof. This makes sense if the insulation has mold growing or has mice living in it. But other than that, I do not see what harm in having more insulation. Often, the reason people are insulating the sloped sides of a roof when the floor of the attic is already insulated is because they are adding a heat pump air handler unit to the attic. It is essential to insulate the sloped parts of a roof when adding an air-handler unit to an attic or the heat from the air handler in winter will melt the snow and cause icicles or ice dams. The only circumstance that I could see that would warrant removing the insulation on the floor would be if the attic now gets warmer in winter than the house below it. Then it would make sense to allow the heat from the air handler to be conducted down into the house. These circumstances would be quite likely if you were adding a very thick layer of spray foam to the sloped parts of the attic.