Ventilation is one of the most important elements to a proper roofing system, but unfortunately this part of the roof is often overlooked. There are many reasons for this – some of which include contractors placing less importance on this factor and sometimes it is based in simply a limited understanding of the entire building envelope system. Ventilation cannot be applied with a one-size-fits-all approach as each roof structure is different and may require different types of ventilation systems and technologies.
Proper ventilation ensures air in the attic space moves effectively, such that it moves water vapor and excess heat away from the attic space. Due to everyday household use, activities such as showering, running humidifiers, furnace use, etc moisture is created that eventually makes it’s way into the attic. If there is not enough ventilation, condensation may occur on the roof deck or other surfaces due to humidity in the air which is not able to escape the attic cavity and condenses on the cooler surfaces.
When this occurs, over time damage can occur such as mould growth, rotting wood, or the insulation and ceiling drywall can become physically damp. This type of damage may show up immediately, but in some cases may not be discovered for many years. If this is the case, the damage discovered may potentially be very severe and end up costing thousands of dollars of damage.
Another side-effect of insufficient ventilation can be premature aging of shingles. According to many roofing manufacturers and the industry in general, if you cannot allow the buildup of heat to escape the attic space via proper ventilation, the shingles on the roof deck reach higher than normal temperatures. When this occurs in the summer months and happens over an extended period and over many years, shingles of many compositions can experience accelerated aging. The shingle material may become brittle and lose granules many years sooner than they should otherwise.
In fact, due to these issues many roofing manufacturer warranties become void if proper ventilation is not applied. Finally, the other major potential risk with insufficient ventilation is ice damming that occurs due to heat not buildup in the attic if warm air is unable to escape. This occurs because of the snow melting over warmer parts of the roof. When that happens in colder temperatures the water runs down the roof slope and freezes by the colder eaves. This “dam” of ice can trap newly melted water which can potentially infiltrate the roof system.
Roofs must be designed to let new fresh air in and allow it to vent warmer air out. In a standard roof structure the air intake is near the bottom of the roof (at or near the soffits) and is released at the top of the roof. For standard roofs, the ratio required is 1 square foot of unobstructed vents for every 300sq ft of insulated ceiling space.
Low slope roofs require double the amount of ventilation to ensure proper air movement. To achieve this, there are many different types of vents available in the marketplace but they must be applied properly to different roof structures to be effective. Vents can be passive or powered and there are many different styles. Some are larger and more effective at moving large volumes of air given a relatively low footprint on the roof deck, whereas others are better at spreading out an even amount of air movement over an attic space. Installing a new ventilation system on your roof must take into account these considerations. Make sure your chosen roofing contractor understands these elements and can explain why they are installing these types of vents to be the most efficient and effective for your home.