Roof ventilation isn’t the most interesting topic to talk about. Even experienced roofers and civil engineers say that sometimes it’s difficult to design efficient and affordable ventilation system. No matter what professionals think, we will still try to explain you, how your attic ventilation affects the roof, house itself and it’s owners.
How is Roof Ventilation System Built?
First and foremost, it’s worth noting that nearly every roof should have intake as well as exhaust vents installed. Even though IBC (International Building Code) requires only exhausts, adding soffit vents lowers the risk of heat spot forming, because fresh air cools all the roof area more efficiently.
Intake Vents
Intake roof vents are mainly located in roof’s eave, i.e. in fascia and soffit panels. Their main goal is to distribute fresh and cold air to the attic. The air movement is possible, as warm air creates vacuum (negative pressure) when moving through ridge vents or other exhausts in the upper part of the roof. Mechanical intake vents are hardly used. It’s worth noting, however, that gable vents are also used sometimes.
Exhaust Vents
On the other hand, the achieve proper ventilation of the attic, exhaust vents are required too. As fresh air usually comes also from the house interior, regardless of the intakes presence, we can admit that exhaust vents are more important part of roof ventilation system. It’s worth noting, however, that IBC allows roofers to ventilate entire attic area only with ventilated ridge caps or box exhausts. The only requirement is to use twice as much of them.
How Do Roof Ventilation Systems Work?
The main role of attic ventilation is always to achieve constant airflow under the roof, what undoubtedly drives to hot air removal, for example through ridge vents. In practice, fresh air is sucked through intakes in soffit vents (perforated soffit panels), flows up closely to roof sheathing, purlins and rafters, and then it escapes the attic space through ridge vents The bigger the difference between the temperature of exhaust and intake air is, the higher is the volume of air transported.
No matter you have asphalt shingles, cedar shakes or slate tiles, ventilation of every roof works generally the same. Thus it’s always important to create proper attic ventilation during the roof assembly. It can be achieved not only by locating more intake ventilation devices at roof eaves – you can also insulate attic floor, add a/c units downstairs or install fans. What’s incredibly important, even the presence of objects in attic floor space may affect the efficiency of ventilation. Maybe it’s a good reason to tidy an attic a little bit?
What Happens if Proper Attic Ventilation is Missing?
As cedarroofing.com mentions, improper attic ventilation lead to several problems.
Reduced Lifespan And Increased Risk of Damage
Poor ventilation affects the roof by increasing it’s temperature and shake humidity. It’s definitely dangerous, as shakes or shingles are more likely to rot, and if hailstorm comes, ice nuggets shell wet shakes easily. With efficient roof ventilation, mold doesn’t grow that quickly, thus time to next roof replacement gets prolonged.
It should be also said that also interior walls, furniture, floors and susceptible to moisture damage – high humidity is dangerous for nearly everything in your home, as it leads to mold and mildew growth and water condensation. The only solution is to force air movement inside the building (what wisely installed attic ventilation system generally does).
Ice Dams Are More Likely to Develop
Poor ventilation, especially combined with low-quality attic insulation, leads to ice dam forming. This phenomenon occurs, when hot air accumulates in the attic, heating the sheathing and shakes up, melting the snow lying at the roof. While formation of icicles is completely normal and it’s a result of sun radiation, it’s worth to avoid that. The density of melting snow is higher, what results with sheathing overload. Ice dams create roof leaks pretty often too.
Heating And Cooling Costs Rise
It’s worth noting that broken roof vents often increase the energy bills. If functioning properly, intake ventilation devices provide cool air. Airflow, apart from removing moisture from attic space, decreases the temperature inside the building. However, if roof vents are clogged with debris or their area is insufficient, problems arise. With low r value and poor ventilation, your attic space may warm up to 130 Fahrenheit degrees. As interior walls aren’t insulated at all, the temperature rises also in bedrooms and toilets upstairs, so they need to be air conditioned.
You Will Feel Worse
Without proper ventilation system, air inside the building is getting saturated with carbon dioxide and monoxide, water vapor, ammonia and sulfur compounds. Each of these chemicals affects your health and well-being negatively. With continous flow of air inside the house, toxic gases escape the room quickly, letting fresh air come.
The most popular symptoms of breathing with low-quality air are:
- Head aches;
- Feeling dizzy;
- Feeling sleepy;
- Allergic symptoms (due to the dust and mold in the air).
How Efficient The Roof Ventilation System Should Be?
An IBC (International Building Code) doesn’t strictly regulate the amount of air that attic space ventilation should transport. Instead, the law requires a presence of vent area equal to at least 1/150 of roof area or 1/300, if at least 40% of the vent area are box or ridge vents. In practice, roofing contractors recommend to install ventilation with area comparable with 1/100 of total roof area. It translates to roughly 1,700 cubic feet per minute, which allows you to keep comfortable, continuous flow of fresh air inside.