Roofing and Attic Ventilation
Your roof ventilation probably isn’t something you think about very often, but it plays an important role in many aspects of day-to-day life in your home. Having the right amount of ventilation in your attic can have a positive effect on the lifespan of your roof system, the comfort and well-being of your family, your future costs for home repairs and how much you pay for heating and cooling.
How Attic Ventilation Works
Effective ventilation in an unfinished attic usually includes intake vents down low along the soffits, and exhaust vents up high at the peak or roof ridge. This allows for a continuous flow of air through the space. Cooler outdoor air gets drawn in through the soffit vents, and warm, humid air that migrates to the highest point exits through the vents along the roof ridge.
Why Adequate Roof Ventilation is Important
Proper ventilation in your attic helps address excess heat and moisture that can otherwise wreak havoc on your home. Heat and moisture buildup in an attic cause predictable but different problems in hot and cold climates; areas with hot summers and cold winters can suffer the effects of both.
When it’s hot outside, the sun beating down on the roof can increase the temperature in the attic.
Exposure to this excessive heat can warp the roof sheathing and distort and prematurely age the shingles. If the attic floor isn’t evenly and adequately insulated, that heat can radiate down into the finished living areas and make it more difficult and costly to keep the living space comfortable.
In locales where the temperature drops below freezing during the winter, warm air escaping into the attic from the heated living space below rises to the underside of the roof deck.
As the roof deck warms, the bottom layer of accumulated snow on the rooftop begins to melt, causing water to trickle down the roof. Once the runoff reaches the cold outer edge, it refreezes into ice. When this happens repeatedly, an ice dam forms along the eaves, blocking the escape of further runoff. Once the water has nowhere to go, it can back up under the shingles.
A properly installed self-adhered underlayment is a final defense against ice damming. This tear-resistant, waterproofing product seals tight around nails. It helps prevent water overflow from entering exterior walls or the attic where it can saturate the floor insulation, ruin the drywall underneath or get into the interior walls.
Read more about Ice & Water Barriers for Your Roof.
Humidity, generated from your living area or from outside, that enters a cool attic condenses into a liquid when it meets colder surfaces.
Over time, that moisture can cause deterioration of the roof system and interior structural elements or ruin the attic insulation. In a warm attic, the moisture can allow mold and mildew to flourish and put added strain on the home’s cooling equipment.
Spotting the Signs of Improper Ventilation
An inadequate attic ventilation system can cause a variety of problems that manifest themselves in different ways.
Here are some subtle and some not-so-subtle things to watch out for:
- An unexplained uptick in your household heating and cooling bills, which can happen if your attic insulation gets wet and loses its effectiveness
- More frequent HVAC repairs as heating and cooling equipment that’s under a heavier workload can become more prone to breakdowns or even premature failure
- A noticeable buildup of ice along your roof edge during the winter months
- A wavy or rippled appearance to your home’s roofline and shingles that’s caused by warping of moisture-damaged decking underneath.
- Rust and corrosion on metal materials in the attic, such as nail heads, electrical boxes, light fixtures, and HVAC system components
- Dampness, water stains or frost on the attic side of your roof sheathing, or any evidence of deterioration and decay of the roof’s structural supports
- An increase in discomforting allergy symptoms or respiratory illnesses among your family members, which may be related to the spread of fungi spores through your indoor air supply from mold growth in your attic.
If you decide to check for these signs on your roof or in your attic, be sure to keep safety in mind. Instead of climbing up on the roof, walk around the outside of your home and look up from ground level using a pair of binoculars. If you head up to the attic, make sure the space is well-lit, that you have a sturdy walking path, and are wearing appropriate protective gear.
What to Do About a Poorly Ventilated Attic
If you identify or have concerns about any of the above warning signs, it’s wise to have your attic inspected by a certified roofing contractor who can assess whether there’s enough ventilation — building codes typically require one sq. ft. of net free-vent area (NFVA) per 300 sq. ft. of space in an unfinished attic. If more is needed, they can advise you on what options exist to improve ventilation and make sure it’s effective. They’ll take various factors into account to do this, such as:
- The local climate in your area
- Your roof’s architecture
- The age of your shingles
- The condition of the decking and other roof components
- Whether your attic floor is sealed and well-insulated
If your roof is getting close to the end of its lifespan, or the decking or other components are damaged or deteriorated, repairs or a replacement may be recommended along with the following steps to properly ventilate your attic:
- Installing continuous soffit vents along the outer edge of the eaves
- Adding a ridge vent
- Insulating along the top plates to meet or exceed the R-value already in the walls
- Sealing the attic floor to make it airtight, and making sure there’s the recommended R-value of properly-installed insulation in place and that it doesn’t block the soffit vents
- Allowing one to two inches of air space between the installed insulation and roof sheathing
Owens Corning’s vent calculator can provide a general guide on the amount of roof ventilation your home needs. For a detailed assessment and expert advice, contact an independent roofing contractor in the Owens Corning Roofing Contractor Network in your area.