How Ventilation Affects the Longevity of Your Roof

How Attic Ventilation Works

Effective ventilation in an unfinished attic includes intake vents and exhaust vents. Usually this will include and intake down low along the soffits, and exhaust vents up high near the peak of the roof or on the ridge. This allows for a continuous airflow through the space in your attic. Cooler outdoor air gets drawn in through the soffit vents, and warmer, humid air migrates to the highest point of the roof and exits through the vents along the ridge.

Why Having Proper Roof Ventilation is Important

Having adequate ventilation in your attic greatly helps in addressing excess heat and moisture that would otherwise wreak havoc on your home. Heat and moisture in an attic can cause predictable but an array of problems in warm and cool climates; areas with hot summers and cold winters can suffer the effects of both.

  • When it’s hot outside, the sun beating down on a 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 areas 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 freeze up and 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. Three feet up the interior wall of this material is required on the eaves of all roofs in Utah.

  • 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 licensed and insured 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

**Note: Much of the information in this article is from OwensCorning.com, our preferred shingle manufacturer

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