When discussing ventilation, the term "Net Free Area" or NFA is used to describe the amount of space available in any type of vent that can be used to freely pass airflow. This is essentially the empty spaces you see in the installed screens and louvers on most passive vents.
Your venting should come from soffit vents and a ridge vent. That is the best way for air to circulate in the attic and keep down on moisture. Your local fire code will dictate whether or not they should be open to each other. In most cases they must be open for ingress/egress of fire personnel.
Venting products are normally rated with a Net Free Area (NFA). The NFA is the open area that exists for air to pass through. The key to effective venting is to balance air intake (at your eaves, soffits or fascias) and air exhaust (at or near your roof ridge).
There are two types of attic ventilation systems (active and passive) that get their name from how they move air through your attic. Active attic ventilation actively pulls fresh air with a drawing effect while pushing out the trapped air.
Ridge vents: These are installed on most homes, since this type of exhaust vent is effective and fairly easy to install at the highest point of the roof: the ridge or peak. It's the ideal location to allow hot air to escape the attic.
There are three methods that may be used to ventilate a building: natural, mechanical and hybrid (mixed-mode) ventilation.
According to the International Residential Code (Section R806. 2) and International Building Code (Section 1202.2. 1), attics require a minimum of 1/150 of NFA but can be reduced to 1/300 if certain conditions are met.
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.
Ridge Vents: What You Need to Know
They are considered one of the most effective types of roof vents due to their design and positioning. Ridge vents work by creating a continuous air channel, allowing hot air to escape and fresh air to enter through intake vents located at the lower parts of the roof.
This means that for every 300 square feet of enclosed attic space, 1 square foot of ventilation is required – with half at the upper portion (exhaust vents) and half in the lower portion (intake vents). This formula is traditionally used for static roof vents which are rated for Net Free Area in terms of square inches.
Talk to a therapist or a neutral person
While venting is not the way to go, sometimes you need to get a frustrating experience off of your chest. If that's the case, talking to a therapist or a third party you know will stay neutral can be beneficial.
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.
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 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.
In the summer, natural air flow in a well-vented attic moves super-heated air out of the attic, protecting roof shingles and removing moisture. The insulation will resist heat transfer into the house. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves.
For hot-humid climates, attics should not be vented, and you should not install any vapor retarders in the assemblies interiors. In hot-dry climates, your attic can be vented, though, like, in hot-humid climates, you should not install any vapor retarder or barrier.
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.
For most homes, a rule-of-thumb is to just multiply the total square footage of the attic by 0.7 to find the minimum ventilation rate in cubic feet per minute (CFM). For homes that have dark shingles and/or steep roofs, the multiplier is increased by 15%, to 0.805.
The NFVA is calculated by dividing the total attic square footage by 300, the minimum recommendation for a balanced ventilation system, or the number stipulated by local codes. In our example, we divide 1,200 by 300 to get 4 sq. ft. NFVA needed for attic space.
Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically.
Ventilation can, therefore, make or break the outcome of an incident. Successful execution requires strict fireground discipline, which is achieved by adhering to the three operational principles of communication, coordination, and control.
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.
Cross ventilation (single spaces): Being unsophisticated and efficacious, this type of ventilation is a horizontal process that is driven by pressure differences between the windward and leeward sides of the occupied indoor environment.