Roof vents allow air to circulate through your attic and exit your home. In the winter the vents will cause the attic to become cold, but this should not damage your home or increase the energy use of your home, so covering the roof vents is not necessary. Blocking the vents can even harm your home by trapping moisture inside the attic.
There are many types of vents that you may have on your roof, including turbine, soffit, rafter and metal pot vents, but you should not cover any of these roof vents during the winter. All of these vents serve the purpose of creating air circulation, which is vital to keep your attic and roof from being damaged in the winter.
In the winter, moisture in your home is likely to rise into the attic. If the moisture becomes trapped there, it can cause mold problems to develop. Open vents allow the moisture to leave the attic and travel outside.
Open vents also ensure that cold air can enter into the attic during winter. This is important in colder climates with heavy winter precipitation. If the attic is too warm during the winter, the precipitation frozen on your roof will melt, drip down to your gutters, and then refreeze. This accumulation of ice can end up breaking your gutters.
The main reason that people believe vents should be covered in the winter is to prevent the loss of heat in the home. Attics should be insulated so that heat from the rest of the home cannot actually enter them easily. Even though the attic is exposed to the cold outside air, the areas of your home that are heated will not be. This means keeping your vents open will not result in an increase of energy consumption.
You can check to make sure that no heat is leaving your home through your attic by measuring the attic's temperature during the night. The attic temperature should be close to the outdoor temperature. If it is warmer, that is a sign that heat is leaking into the attic from your home.
If you do notice heat moving from your home to your attic, the correct way to fix the problem is by improving the attic's insulation. Blown insulation and insulating boards can both be used for this job. Be careful when installing the insulation not to block any of the vents. Rafter vents are particularly easy to accidentally block when installing blown insulation, so be careful not to cover their openings. Even though covering your roof vents may reduce heat loss in this situation, it will end up creating other costly problems such as mold.