Do I need to ventilate my attic?
Is mechanical ventilation necessary in a North Jersey attic?
In a nutshell: Yes.
Because Mother Nature is partially responsible for the air-exchange in all houses, it is important that we understand how she does her work. Naturally occurring pressures cause an exchange of air in houses. Keep in mind that positive and negative pressures themselves are neither good nor bad, but they can have positive or negative effects. For example, they can cause fresh air to enter a house (a positive effect) or they can cause pollution- or moisture-related problems (a negative effect).
The easiest source of natural pressure for people to visualize is the wind. The pressures from the wind cause infiltration through random holes in the house like soffit vents and gable wall vents. Stack effect is just as common a pressure in causing air to move through houses as the wind, but it isn’t as well-recognized. Stack effect is sometimes called chimney effect and is based on the principle that warm air rises. Warm air has fewer molecules per cubic foot than cool air. Thus, warm air is less dense (lighter) than cool air, so warm air rises up above cool air. If a house is airtight (no random holes), then it doesn’t matter how much pressure there is because of wind or stack effect—there will not be enough air movement between the indoors and outdoors.
Air-exchange rate is the measure of the speed of the exchange of air between indoors and outdoors. Wind and stack effect are the most significant natural pressures that cause air to move through houses. In contrast, diffusion is insignificant. Builders often use plastic sheeting in walls as a diffusion retarder, slowing the movement of water vapor through the wall. Such a retarder will also slow down considerably the movement of air. Because natural pressures are not continuous or predictable, they will only move air through a house in an equally unpredictable manner.
As with natural pressures, accidental pressures can cause pollution or moisture-related problems. It isn’t unusual for there to be a great deal of infiltration and exfiltration whenever the forced-air heating or cooling system is running. Leaky ducts provide accidental ventilation that can be excessive, resulting in high heating/cooling bills.
Diffusion is the scattering of air particles through a material, or from one area to another. In addition to all the ways air enters and leaves a house naturally and accidentally, there are mechanical systems specifically designed to ventilate houses using controlled pressures. This is controlled ventilation—in other words, ventilation on purpose – and it is the only way to exchange the air in houses that is consistent, reliable, and predictable.
Many modern building codes dictate that houses be built purposefully airtight – for comfort, energy efficiency, and moisture control reasons. Actually, a lot of the houses we inspect each week are too air tight. A great example would be a 4 year old home in Sewell, NJ that I recently inspected for mold. This house had both gable wall vents and a ridge vent in the attic, but still ended up with severe mold contamination on the roof sheathing. The problem? No mechanical ventilation. Cool air came in… and stayed in. That same cool air mixed with the warm air in the attic and cause condensation on the roof sheathing. Without proper air circulation, the roof sheathing stayed damp long enough to promote mold growth – and a $7800 mold remediation bill.
If you have an attic without mechanical ventilation, you may be asking for trouble, In my opinion, it is absolutely necessary and it could save you money in the long run on utility bills.
Seems like a no-brainer, right?