It certainly has gotten cold here. As I write this, it is 17 degrees outside and the high for tomorrow is in the 30s. This sudden change in weather has certainly hit me hard. I hope you are staying warm. Speaking of staying warm, is your house comfortable? Do you have enough of the right kind of attic insulation in the right places?
Over the years I have been in a LOT of attics and most of them do not have the right kind of insulation and certainly not enough of it. Even worse, there is often duct work running in the space on the wrong side of the attic insulation, the cold side, with very little insulation around the ducts. Code says you need R-38 insulation in the attic as a minimum. I would say that is about half what you should have for your attic in our climate if you are using fiberglass insulation or cellulose. Think of it as adding a second blanket to your entire house.
In areas where duct work penetrates the conditioned space at the supply points, there is no insulation. Having the duct work inside the thermal envelope would fix this problem. So if you have the chance, insulation on the underside of the roof sheathing, open cell spray foam, is certainly a better solution than fiberglass or cellulose on the floor of the attic (when duct work is in the space). Spray foam is air tight and when installed in the appropriate places will make your home both comfortable and energy-efficient.
Other holes that exist in the insulation envelope can be can lights and eave ventilation that does not have baffles. These holes and air leaks from improper sealing of the thermal envelope all combine to diminish the effectiveness of your installed insulation. Finding ways to stop air leakage and installing the proper amount of attic insulation will help on these cold days.
If you have fiberglass insulation, add more to achieve R-72. If you have cellulose, add more to achieve R-72. However, if you want to get it right insulate with an air tight solution, open cell spray foam is the easiest method to create a home that will be comfortable and energy-efficient for many years.