Your home’s attic ventilation system consists of intake and exhaust. In order to be effective, it must keep your attic dry in the winter and cool in the summer. This helps to protect beams and roofing materials from damage and in the end it saves you money.

Ventilation Effects in Summer

When roof ventilation is poor, the summer heat can accumulate within the attic space, easily reaching 140 degrees even when it’s only 90 degrees outside. When you combine moisture with these extreme temperatures, the damage to your shingles and roof decking can be severe and will significantly shorten the life of the materials.

In addition, built up heat from your attic can also flow into your main living spaces. The excess heat means your refrigerator, air conditioner and other cooling appliances will be run longer and more frequently. Naturally, this means your summertime energy bills will be higher.

Ventilation Effects in Winter

During winter, the warm, relatively humid air from your main living areas will travel upward and leak into your attic. This air tends to travel especially well through spaces in walls and ceilings with bypasses for plumbing and electrical systems. Once that warm air reaches the cold air of a poorly ventilated attic, physics begins wreaking havoc. The warm and cold air react with one another and cause condensation to form on the rafters, beams, decking, nails and other materials. This is a bad mixture that can result in extensive structural damage.

Moisture will soak into wood surfaces and make them swell, eventually causing them to warp or buckle. It may also cause the roof decking to rot until it is no longer able to bear weight. Furthermore, if there is ample enough condensation, water may drip onto exposed insulation, hindering its effectiveness and potentially causing water damage to your ceilings. Wet wood and insulation can also promote a serious mold or mildew infestation as well as encourage termites.

A poorly ventilated attic during winter can also promote the development of ice dams. These occur in cold weather when heat builds up in attics with poor air flow or insufficient insulation. This accumulated heat is intensified by the warm sun and quickly melts any snow that has built up on the roof, even when air temperatures outside are below freezing. The melt water seeps beneath shingles and collects at your gutters and eves. Once it re-freezes, it can cause shingles to warp, allowing water to leak into the attic space and possibly the rest of your home. When melt water freezes at gutters and eves, it can develop into an ice sheet that hangs from the edge of your roof. Due to its enormous weight, it’s capable or causing massive damage.

Image Source: www.writeforblog.weebly.com

How Roof Ventilation Works

A particular pattern of air movement is essential to proper roof ventilation. First, air flow must be established inside of the attic to facilitate the exchange process. The different parts of the ventilation system have to be the right size for the dimensions of the attic to ensure adequate and continuous air flow into and out of the space. This can be done using either mechanical means, like a fan, or natural (passive) ones, like wind-assisted exhaust vents. Whereas mechanical ventilation requires electricity to operate, natural ventilation depends on stack effect and wind effect.

What Is Stack Effect?

Warm air is lighter than cold air, so it tends to rise upward. While it’s moving up, that warm air produces an increase in air pressure near the attic’s ceiling, simultaneously lowering air pressure closer to the floor. Areas of high pressure allow air to leave the attic while the low-pressure areas allow air into the attic. A good roof ventilation system ensures that there are vents at the top of the attic as well as near the soffits.

What Is Wind Effect?

On its own, the stack effect is incapable of producing the high-volume air circulation required for proper roof ventilation. It needs to be combined with the wind effect in order for passive ventilation to work correctly. When the wind blows over and against your home, it creates pockets of high and low pressure. When it’s high, it pushes air in. When it’s low, air is drawn out.

Making Them Work For You

An effective roof ventilation system must balance exhaust with intake to accomplish the necessary rate of air flow. In most cases, your intake’s net free area will ideally be the same size as, or larger than, that of the exhaust. The term “net free” is used to describe the amount of unobstructed space for air to enter or leave and is measured by the square inch. Furthermore, the vents must be placed in locations that create a good balance of low and high. This means that half of the vent area, your intake, is placed at a low point in the attic, while the remaining half, your exhaust, is placed at a high point.

Correct location of intake and exhaust vents ensures steady, constant air circulation in the appropriate direction. These vents should be placed in such a way that they promote consistent airflow over the bottom of the roof’s sheathing. In addition, your intake vent should be placed where there’s limited ability for precipitation to enter, or where it can’t be blocked by insulation, debris or snow.

Many homeowners are unaware of the important roles played by proper roof ventilation. It helps protect materials from damage and increases their useful life, particularly when weather is harsh. By using the above information, you can enjoy a sturdier, safer and more cost-efficient roof.