Roof Vent

No matter what type of roof vent you choose, a properly installed exhaust system in your attic will make an enormous difference in the ambience in your home as well as in your home cooling bills. Attic vents are an economical way to prevent the build-up of heat in your attic during the warmer months. Did you know that in summer the air temperature in your attic could reach as high as 150 degrees Fahrenheit? That's more than uncomfortably hot!
Proper attic venting allows the hot air rising from the living areas into the attic to escape outside through the roof fans or roof vents. Most homes nowadays have a system of attic vents, but it may not always be adequate for the size of the home.

The most common attic vents are “passive” in that they are operated by the movement of air around them. These would include ridge, soffit, flat or “pot” roof vents, and turbine roof vents. Attic roof vents operated by electricity or solar power are often called “active ventilation devices” and include exhaust fan vents and electrically powered roof ventilators.

Roof vents help extend the life of your roof, make the house more comfortable and, very importantly these days when there is a lot of concern about allergens, help prevent the growth of mildew, mold, and fungi in your attic area. These are caused by a build-up of moisture, and a roof vent system is designed to keep a flow of air through the attic, which stops the creation of the right “climate” for these allergen-causing growths.

It isn't just for summer weather that you need an attic vent system – roof vents will also help stop the build-up of ice in the roof, which results in roofing damage and costly repairs.

Probably not! Your roof fans or vents work hard all year round. Not only do they exhaust hot air in the summer and bring in cooler air; they exhaust potentially damaging moisture from your attic. In the winter, a properly vented attic will help prevent damage from ice dams and so increase the lifespan of roofing shingles.

It is important to get a proper balance for ventilation in your attic. For example, if you have a good inward air flow, but not a good exhaust flow, then the cooler air will find its way into the living areas and you'll have drafts.

Professional installers work with a rule of thumb for a good balance of incoming and out flowing air, which determines the number of roof or attic vents needed. This is called a “net free area” and is determined by the size of the vent opening, after taking into account blockages caused by screening or slats in the attic vent opening. Ask your local building supply or hardware store that supplies roof vents about the “net free area” required for the type of attic vents you want to install.

Attic vents work by encouraging a flow of cooling drying air through the attic space. As the hot air is pushed outside through the roof vents, the cooler air moves in and replaces it. This kind of ventilation keeps your attic cool and dry, preventing a build-up of hot air in summer and stopping condensation and dampness which can lead to the growth of potential allergens such as mold and mildew. These also cause damage to your roof timbers, such as rot and ice build-up.

It isn't just the attic that gets hot if there is no proper attic vent system; the hot air that becomes trapped after rising from the living area will eventually be compressed and forced back down through the wall cavities to increase the uncomfortable heat in the living areas and bedrooms. This problem can be particularly bad in older homes where moist warm air may leak around bathroom exhaust fans and light fixtures into the attic. It can also be a problem in newer homes, despite the use of vapor barriers, because the flow of heated air from the living area will still find its way into the attic. Once there, it condenses on the cooler roof structures and eventually causes damage.

No matter what kind of roof vent system you choose to install, the experts agree that encouraging a flow of air through the house by ventilation is the best and most energy efficient way of cooling.

This is something your supplier will be able to help you with, but the general rule in many municipal building codes is that there should be one square foot of vented area for each 300 square feet of attic. Remember that vented space is determined by the amount of space of your attic vents minus the barriers such as screening or slats. If you have 1500 square feet of attic space, you will need about five square feet of vented space. This vented space should be equally divided between intake and exhaust vents. This applies whether you are using turbine, ridge, or flat vents.

Probably the most common of all attic roof vents, the flat vent is a passive system and looks like a small square box on the roof. It is easily installed, usually from the outside, and fastened to the roof with shingles overlapping it to prevent leaking. Inside the box there is usually screening material or slats to allow the air to pass through without letting in other materials, or allowing snow or water inside the attic in bad weather conditions. If, once the square flat vents are installed, you find that there is wind infiltration or a lot of drafts in the house from the attic, it is probably an indicator that the flow of air is unbalanced, and the hot air is not being expelled fast enough. The solution is to add one or more vents to allow a faster movement of air outside the house rather than down into the living area.

These “curly” roof vents are sometimes called “whirligigs” because of the way the curved slats turn around like the child's toy of the same name. These are long-lasting vents that are powered by the wind – the breeze catches the slats, turning the vent mechanism, which then pulls hot air from the attic or pulls in cool air. Homeowners are occasionally advised to stuff these vents with insulation during the winter months, but the manufacturers advise against this because water vapor cannot be expelled from the attic if these vents are blocked, and will cause problems in the roofing area.

It is recommended – and some municipal building codes insist – that soffit vents are installed with the turbine attic vent system, so cool air is pulled in over the tops of the walls. This is to prevent the turbines pulling heated or conditioned air from the living areas of the house.

The older model turbine roof vents have been known to rust, so the wise consumer would probably look to buy vents made from aluminum, as these won't rust. It's a good idea to check the specifications on the box before buying your attic turbine exhaust fan – as not all models can be used on all roof pitches. However, many are adjustable, so the moving part can be set level even on a steep roof.

One major complaint there has been about the turbine roof fans is that they can start to make an annoying squeak, as they get older. This can be cured with a spray of oil, and the newer turbine roof vents have a built-in lubricating system to prevent the squeaking.

This is a very unobtrusive style of attic vent, which is installed along the peak of the roof and so is almost unnoticeable from the ground. It is claimed to be the most efficient roof venting system that can be installed when combined with external baffles, under eaves attic vents, and an internal filter. Ridge vents work all year round and evenly distribute the air along the length of the roof peak. Because of this, there is a high flow of air through the vent system and, unlike some of the other passive systems, this vent is not affected by changes in wind direction.
The external baffle is necessary to deflect snow, rain, and other weather variables away from the attic and to aid in exhausting the air through the vents. It is recommended that ridge roof vents be installed along the entire roof ridge, and there may be some limitations to the efficiency if installed on a steep or hip roof.

This type of vent is sometimes referred to as a “whole house” vent. These exhaust fan vents require an electrical connection and are powered by the house power supply. These roof vents look very unobtrusive on the roof, as they are installed slanting away from the front of the house. They are operated by a thermostat, which senses heat and humidity build-up in the attic.
You can mount your attic exhaust fan in the gable end of the house or on the roof close to the peak. As with a flat or turbine vent, you will have to cut a hole in the roof and replace the shingles to overlap the vent panel. These attic exhaust fans operate by a thermostat, which switches the fan on when the temperature inside the attic reaches a certain preset level, and then turns it off again when the temperature has dropped.

Before installing an electrically powered attic vent, be sure to ask your local municipal offices or check the building codes, as a permit and inspection are required in some jurisdictions. You will need to install electrical wiring and service to your attic – and many attics do not have these facilities. It is also wise to check the electrical codes and your electrical authority to get the exact specifications. They may require that the work be inspected.

Like so many other aspects of home building and maintenance, attic ventilation systems are going “green” with the arrival on the market of solar powered roof vents. These can only be described as a cross between the electrically powered exhaust fan roof vent and the passive attic vent models, because the solar powered attic fans are operated by the wind but also require solar power. This solar power is stored and so the vent keeps operating even after the sun goes down.

Solar powered attic roof vents are powerful enough that you only need one to ventilate the entire attic space, and most are rated as very efficient. Some models can lower the temperature in the attic by up to 50 degrees Fahrenheit or more, so less heat is able to slip back into the living area of the house. Manufacturers claim this can result in savings on air conditioning of up to 30 per cent. Because the sun powers them, the solar exhaust fan offers more savings in electricity costs over conventional electricity powered roof exhaust fan ventilating systems. Solar attic vents are usually accompanied by a solar panel, which collects the heat from the sun and delivers it to a DC motor inside the roof vent, where it is then used to power the ventilation system.

Like conventional attic vents, the solar operated roof exhaust fan continues to work in the winter, balancing the air temperatures inside the attic and outside in order to prevent moisture build-up turning to frost inside the attic or creating ice-jams in the roof, which can seriously damage the roofing materials.