In most cases, we recommend soffit vents for intake and a ridge vent for exhaust. For homes that cannot have a ridge vent, box vents are generally the second best option for exhaust. And for homes that cannot have soffit ventilation, you will find that fascia vents to be your second best bet.
Best combination is a soffit and ridge vent, air comes in low, sweeps the attic and exits out the top. But even if you have soffit vents sometimes the insulation can restrict air flow. Their is some guidelines to attic ventilation At the least I'd keep and eye on the roof decking under the insulation for mold growth.
While ridge vents have many advantages, they are not always ideal. In cold climates, ridge vents can allow snow into the attic. They're also more expensive than box vents and won't work on all types of roofs.
Installing Rafter Vents
Complete coverage of the attic floor along with sealing air leaks will ensure you get the best performance from your insulation. Rafter vents ensure the soffit vents are clear and there is a channel for outside air to move into the attic at the soffits and out through the gable or ridge vent.
The net free ventilating area shall not be less than 1/150 of the area of the space ventilated, with 50 percent of the required ventilating area provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above eave or cornice vents with the balance of the required ...
This rule means, at least half of your attic space must be 7 feet high by 7 feet wide, with a total of 70 square feet. Keep in mind, codes vary from place to place, but for using the attic as an actual room, this rule typically applies.
It is absolutely possible the ventilation system on your roof is excessive. Maybe your home is older and prior ventilation was installed by a homeowner, or incorrect vent sizes were used in an older roof layout. Too much ventilation can negatively influence the attic's and home's insulation as well.
An attic without ventilation loses energy through ceiling fittings and leaky ducts, costing the homeowner as much as 20% in energy cost. When moisture is allowed in an attic that is unvented can lead to roofing issues. Wet roofing panels are subjective to ice dams that damage shingles.
Both types of vents are effective tools for ventilating your home, but ridge vents are more common nowadays. Box vents are more prone to leaking, letting critters into your attic and rust. The important rule to keep in mind is to install only one type of roof vent.
Positive Input Ventilation Systems (PIV) are more effective at protecting your whole home from condensation, damp, and mould than simple extractors. They do run continuously to circulate air, but thanks to their efficient design, they are quite cheap to run.
If you had to choose just one—and your attic has a great need for ventilation—an attic fan is your best bet. Attic fans in the $300 to $400 range can move upwards of 5,000 CFM. For lower capacity ventilation at a steep cost savings, a ridge vent might be your best choice.
Since there are vents on the roof, heat can escape the house naturally. It doesn't have to be vented out like a normal house would, which keeps things cool inside. Not only summers, but ridge vent helps in winter also.
Natural ventilation can generally provide a high ventilation rate more economically, due to the use of natural forces and large openings. Natural ventilation can be more energy efficient, particularly if heating is not required. Well-designed natural ventilation could be used to access higher levels of daylight.
A vented attic can heat up to 130 degrees in the summer, causing your HVAC system to work much harder than necessary. Unwanted moisture can also form as the result of condensation. These problems can be solved by applying spray foam insulation to the underside of the roof deck.
While ridge vents win for their subtle appearance and functionality, turbine vents may be better in especially hot or humid climates where more dynamic airflow is necessary. If you are not sure which to use, consult a roof professional who can examine the needs of your home and draw up a venting plan for you.
A ridge cap is also a type of baffle used for ridge vents. A cap sits on the ridge vent itself and creates an overlapping shield to prevent water from getting in. Ridge caps also create the vent system pull that sucks fresh air into the attic or roof space and expels stale air.
MYTH: Considering the problems caused by insufficient insulation, it's best to have as much air flowing through the attic as possible. Truth: Ventilation needs vary. Too much ventilation can cause leaks, encourage pest infestations, and leave your attic vulnerable to storm damage.
When calculating how much attic ventilation you need, your roofer will either use the 1/150 or 1/300 rule. The one they use determines how much Net Free Ventilation Area (open area for air to pass through) you'll need for every 150 or 300 square feet of attic space.
Maintaining adequate attic ventilation is essential for the overall health of you and your home. Without proper ventilation, you risk mold mildew growth, general deterioration of your roofing system, and even increased respiratory problems due to this moisture accumulation.
While having both types of ventilation isn't necessary, some homes need more ventilation in their attic space than others, and that's where this pair comes in. You may need to use one or more attic fans along with a ridge vent in a large, warm attic space that needs more ventilation.