Save Energy — Attic Ventilation

You attic can be like an oven over the top of your ceiling. Your roof is essential in keeping out the rain and weather. In the summer, the sun will beat down on the roof adding considerable energy. Without proper ventilation the attic will become much hotter than the outside temperature. In the winter any moisture in the attic could condense causing water damage. Proper ventilation in the winter keeps the space dry.

Your Home Energy Living Plan

  • Maintain all openings. Keep clear of obstructions and debris.
  • Add insulation above ceiling. See insulation for more information.
  • Make sure whole house fan frame, attic access door/stairs, light housings are sealed tightly.
Impact of Your Energy Saving Actions

Cooling is 11% of the average US home’s annual utility bill. Of that about 14% is through the roof, also some of the infiltration losses are through the ceiling. If your ceiling is poorly insulated these numbers are much higher. Adding insulation to poorly insulated ceilings will have a major impact. Sealing ceiling openings can save energy with little investment.

Changing or modifying your attic ventilation can be expensive. Measure the temperature in your attic during a hot day in the afternoon. If the temperature is greater than 50 degrees above the outside temperature, then you should consider modifications.

Any ductwork running in the attic space is affected by the high temperature. See air distribution for energy saving actions for ductwork.

How Energy is Lost

Your attic is a large volume of air. In the summer, the sun beats down on the roof. Heat is absorbed by the roof and flows into the attic. It is not uncommon for the attic to be 50 degrees hotter than the outside temperature. Heat gain within your home is based on the temperature difference. For your ceiling there could be a much larger temperature difference than for your walls. This and the large amount of area are the reasons ceiling insulation levels are so high compared to your wall. More insulation slows down the heat gain into your house. Also trying to minimize the temperature increase in the attic can help. The more air flowing through the attic, the closer it can get to the outside temperature.

While it can be dry in your home in the winter, it has more moisture than the outside. In some cases humid air from the bathrooms and kitchen is exhausted into the attic. If this moisture is allowed to build up, then condensation will occur. The winter attic can be almost as cold as the outside temperature, especially at night. The best way to prevent moisture climbing to damaging levels is to ventilate the attic. As air moves through the attic, water vapor will mix and move along with the air. The amount of ventilation is much less than for summer ventilation. Therefore calculations to determine proper ventilation is based on summer conditions.

Attic Ventilation Characteristics

Attic ventilation can be from natural means. Since warm air rises, openings along or near the top of the roof can let out the hot air. The air is replaced through openings as low as possible. This is usually in the roof overhang or soffit. Another factor that can help is the wind. Air on the windward side can enter the soffit vents and flow out the leeward side.

The air inlets should be as open as possible. Inlets are either slots or perforations in the soffit of the roof. They have screens to keep unwanted visitors out. There should be as many as possible and kept clean of debris.

The air outlets should be at or near the top of the roof. These can be continuous ridge vent, roof vent, or turbine(wind) vents. They should be placed to allow ventilation of the entire attic space. In the case of the turbine type vent, the wind will spin the turbine drawing air from the attic.

With attic ventilation, the more the better. Natural ventilation may not be enough. Powered vents in the roof or high on the gable ends can increase airflow. The power to run the fan is offset by savings in air conditioning from a cooler attic. With powered vents, the inlets must be kept clear. The powered vent will draw air from within your house if the inlet vents are obstructed.

Energy Solutions Explained

Any blocking of the vents will slow or stop airflow regardless of whether it is natural or powered. If powered, air can be pulled from inside your house.

The problem of summer attic heat is greater if the ceiling is poorly insulated. Since adding more vents in your roof can be expensive, then adding more insulation may be more economical. Any work to add or change attic ventilation should be performed by a licensed contractor. This may be more expensive unless your own modifications result in a leaking roof.

Air leakage through the ceiling can waste energy. Ceiling infiltration can often go unnoticed. The attic access panel should be sealed tightly and insulated. If you have a whole house fan, it must seal tightly when not in use. The whole house fan will not be in use on hot summer days if you have air conditioning. Lights recessed into the ceiling can leak air. Consider replacing with Energy Star qualified fixtures.

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