Deck/sheathing: The surface, usually plywood or oriented strand board (OSB), to which roofing materials are applied. Dormer: A small structure projecting from a sloped roof, usually with a window.

There are a number of things to consider when selecting a new roof system. Of course, cost and durability head the list, but aesthetics and architectural style are important, too. The right roof system for your home or building is one that balances these five considerations. The following roofing products commonly are used for steep-slope structures.

A roof system's performance is affected by numerous factors. Knowing about the following will help you make informed roof system buying decisions:

One of the most critical factors in roof system durability is proper ventilation. Without it, heat and moisture build up in an attic area and combine to cause rafters and sheathing to rot, shingles to buckle, and insulation to lose its effectiveness. Therefore, it is important never to block off sources of roof ventilation, such as louvers, ridge vents or soffit vents, even in winter. Proper attic ventilation will help prevent structural damage caused by moisture, increase roofing material life, reduce energy consumption and enhance the comfort level of the rooms below the attic. In addition to the free flow of air, insulation plays a key role in proper attic ventilation. An ideal attic has: A gap-free layer of insulation on the attic floor to protect the house below from heat gain or loss. A vapor retarder under the insulation and next to the ceiling to stop moisture from rising into the attic. Enough open, vented spaces to allow air to pass in and out freely. A minimum of 1 inch between the insulation and roof sheathing. The requirements for proper attic ventilation may vary greatly, depending on the part of the United States in which a home or building is located, as well as the structure's conditions, such as exposure to the sun, shade and atmospheric humidity. Nevertheless, the general ventilation formula is based on the length and width of the attic. NRCA recommends a minimum of 1 square foot of free vent area for each 150 square feet of attic floor—with vents placed proportionately at the eaves (e.g., soffits) and at or near the ridge.