Attic Ventilation & Roof Styles

The Importance of Proper Ventilation

Attic ventilation is the process of maintaining a steady, high volume of air movement through the attic. This unused section of the house needs to be as cool and dry as possible throughout the year.

During warm months, heat in attics can cause:

• peeling interior/exterior paint
• roofing deterioration/leaks
• wood expanding and cracking
• energy loss: a hot attic floor heats the living areas below, which increases air conditioning usage

In cold weather, furnace-warmed air circulates through the house, picking up water vapor generated by cooking, bathing, and the washing of clothes and dishes. Humidifiers, common in many homes to combat dry winter air, provides an abundant and continual source of moisture that rises. Keep in mind also that the warmer the air is, they greater its capacity to hold moisture.

During cold months, too much moisture in attics can cause:

• mold, mildew, and wood rot
• damaged insulation that needs replacing
• ice dams that can cause leaks and structural damage
• infestation of carpenter ants, termites, and other pests

Ventilation is a necessary and important part of maintaining your home, but improving ventilation conditions often can be achieved with low to moderate costs.

The Industry Standard — The recommended industry standard for proper attic ventilation is a 1/150 ratio: 1 sq. foot of ventilation for every 150 sq. feet of attic space, which is divided 50/50 in order to balance air intake (at your eaves or soffits) and air exhaust (at or near your roof ridge). This ratio takes into account that today’s homes are built with—or remodeled with—more energy-efficient materials (doors, insulation, windows, etc.). As a result, these homes are more airtight and, therefore, need more attic ventilation.

The Insulation/Ventilation Connection — Although efficient insulation that absorbs and holds heat increases the need for effective ventilation, insulation is a must during cold months. Overcoming this issue during warm months can be accomplished using an attic ventilation system that effectively compensates for the additional heat produced from insulation. In short, effective attic ventilation also helps cool attic insulation.

Determining the Most Effective System — The style of a roof on your home is one factor in determining the type of ventilation system that your home requires. For example, one of the most effective ventilation methods uses a ridge-and-soffit continuous ventilation system, but the design of this system can vary from roof to roof. There is a wide range of intake and exhaust components, allowing ventilation systems to be tailored to specific characteristics of every home. It is important to have a certified roof specialist determine your home’s individual needs.

The most common types of intake vents include:

• Undereave Vents and Continuous Soffit Vents — mounted in the soffit
• Vented Drip Edge Vents — used on homes without an eave area
• Mini-Louvers — used in combination with other larger vents

The most common type of exhaust vents include: Ridge Vents, Wind Turbines, Roof Louvers, and Gable Louvers. Some hip roofs have limited horizontal areas, and may require a power fan with a humidistat for proper ventilation.

Roof Types:

• Gable Roof — This roof has sloping planes of the same pitch on each side of the ridge, with a gable at each end.
• Cross Gabled Roof — This roof contains intersections that allow each portion of the home to have a triangular gabled roof.
• Hip Roof — This roof contains sloping planes of the same pitch on each of four sides and does not have gables.
• Gambrel Roof — This roof contains sloping planes of the same pitch on each side of the ridge, with a gable at each end. The Gambrel Roof is Dutch-inspired.
• Mansard Roof — This roof is made up of four slopes, two on each side of the home. The lower slope is a steeper, more vertical slope than the upper slope. The Mansard Roof is French-inspired.