How to Check Attic Ventilation

Look, feel and smell your attic for signs of moisture. Poor ventilation may show up as condensation on the ceiling, rust around the vents, soggy insulation or simply a moldy smell throughout the attic. Issues like these are more than likely a result of poor ventilation.

Clear away all dirt and debris from the attic vents. Ensure that you have not blocked any vents with boxes or other storage. Check the area for bird's nests or damage from rodents, as these creatures often take refuge in the attic during the winter.

Open all attic vents, regardless of the season. Many homeowners are under the false impression that attic vents should be closed during the winter to prevent cold drafts from entering the attic and cooling the house. In actuality, a properly ventilated attic should be drafty during the winter. If you experience a chill in your house when the attic vents are open, add more insulation instead of closing the vents.

Check any attic fans to make sure the blades turn freely. Always use a wooden rod or stick to check the blades, as many fan blades can be very sharp. The blades should turn easily.

Do the math. Attics need 1 square foot of free ventilation space for every 150 square feet. If the attic ceiling has a vapor barrier, this need is reduced to 1 square foot of space for every 300 square feet. Compare the square footage of your attic with the square footage of the ventilation to see if it measure up to the standard. Keep in mind that vents rarely provide 100 percent free space---vent screens and covers often reduce the free space by 25 to 50 percent of the vent's measurements. Check with a local contractor or the vent manufacturer information to find out.

Determine the probable path of air flow through your attic by examining the placement of the vents. Keep in mind that air usually enters through the lower vents and exits through openings higher up. For example, many attics have vents along the eaves of the house and a second set of vents along the ridge of the roof. In this set up, air enters through the lower vents and leaves through the vents in the ridge. Since air always follows the path of least resistance, vents placed to closely together may allow air to enter through one vent and exit through the other without ventilating the rest of the attic.

Call a home inspector if you have concerns. While you may be able to save a few bucks by checking your attic yourself, undetected problems may cost you dearly in the long run. If in doubt, have a home inspector check your attic to ensure the ventilation is adequate.