When creating an energy-efficient, airtight home through air sealing techniques,
it is very important to consider ventilation.
Unless properly ventilated, an airtight home can seal in indoor air pollutants.
Ventilation also helps control moisture,
another important consideration for a healthy, energy-efficient home.
Your home needs ventilation—the exchange of indoor air with outdoor air—to reduce indoor pollutants, moisture, and odors. Contaminants such as formaldehyde, volatile organic compounds, and radon can accumulate in poorly ventilated homes, causing health problems. Excess moisture in a home can generate high humidity levels. High humidity levels can lead to mold growth and structural damage to your home.
To ensure adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) says that a home's living area should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per person per minute, whichever is greater.
Where and How Much should I Vent?
The answer to this question is determined by the total square feet of your attic. Normally one square foot of vent (net free) is needed for every 300 square feet of your attic area. If you do not have a vapor barrier installed (the paper backing on blanket insulation is commonly referred to as a vapor barrier), the amount of vents you will need could be doubled. Use a combination of vents, half located on the roof and half higher up, so air flow can go in one and out the other. For example, use soffit and ridge vents, and then install proper vent baffles (see below) to prevent insulation from blocking air flow.
Always try to keep your vent screens clean, especially when repainting your house do not allow the painter to paint over the screening. Painting over the screening will diminish the effectiveness of the air flow from 50% to 100%.
Baffles (commonly referred to as Proper Vents)
It is recommended to install baffles whenever any type of insulation is installed in an attic. The vents prevent the insulation from blocking the air flow from the outside.
One baffle should be installed in each rafter space 6" into the overhang or past the wall plate.
Vents are openings in the attic area that allow moisture to escape. If you don't have proper ventilation in your attic, water vapor can condense and collect on insulation and in rafters. This will reduce the effectiveness of the insulation you have installed and could damage your house. Also, without proper ventilation, attic heat could penetrate into living areas during the summer.
NOTE: When installing Ridge Vents, existing Gable vents need to be closed off from the inside or the Ridge Vent will not work. This is to maximize the high-low principal of the ventilation system.
For additional information on attic ventilation and the proper method of installing vents, go to http://www.ronhungarter.com/ventilation_repairs.html