Do Attics Have to Be Ventilated?

Benefits

• In cold climates, the primary benefit to ventilating the attic is to keep the roof cooler in winter to prevent ice dams, or the melting and refreezing of water into dense, heavy layers of ice over several weeks. In hot climates, attic ventilation helps disperse excessive heat and lower the building's cooling needs. Roof vents, in any climate, also allow any moisture from inside the building to leave, preventing condensation. Ideally, a roof and attic are completely sealed off from the interior living space, creating a buffer of air that can move between the attic and roof to the outside.

Code Regulations

• The decision to vent the attic in any location may be made moot by local building codes. To prevent property damage and mitigate risk to building inhabitants, laws may dictate that certain styles or ventilation specifications be met in the attic or roofline, based on materials used or the structure's design. Consult with licensed architects and experienced contractors as well as contacting local code-enforcement agencies to learn about minimum ventilation requirements.

Use

• Homeonwers can prevent ice build-up, overheating and moisture accumulation/condensation using either ventilated or unventilated attics and roofs. The ventilated attic allows air movement from the soffit to the peak of the roof, often in a cupola or capped ridge. It's vital that there are no air leaks from the home into the attic space, such as from an open attic door or unsealed areas around ceiling lights. Venting allows both heat and humidity that leads to condensation to escape, reducing the potential for mold and mildew growth. Unventilated attics are sealed unto themselves. Heat, humidity and condensation are prevented because of the sealed insulation, and the air layer around the walls and ceiling within the attic.

Special Circumstances

• Some circumstances warrant the use of certain venting systems. In regions with lots of snow, ventilated roofs are best. In windy, humid areas near the ocean, unventilated attics may be better since they lack soffit vents that can catch wind-driven rain that can enter the attic. If the attic is conditioned -- heated and cooled -- and is used as a living space or for mechanical systems, the roof deck must be ventilated, according to provision R806.3 of the International Building Code. The roof deck is the space from the back of the roof covering, such as the shingles, to the top of the insulation layer.

Options

• While creating vented roof peaks and soffit spacings is the most straightforward approach to attic and roof ventilation, a sealed space is doable. The sealed attic can't be used for storage or as a "bonus room." On vaulted ceilings with exposed beams or where the roof line is full of many peaks and valleys, a sealed roof diminishes the need for vents since there is much higher quality buffering and layering of wood and insulation between the interior space and the outside roof shingles. However, in regions with high snowfall, ventilation is still needed to prevent ice damming, according to Joseph Joseph Lstiburek, building engineer of the Building Science Corporation in Westbrook, Massachusetts.