The roof structure is the frame for the roof. Think of it as the bone structure of your body. Depending on the structure of your home, it’s either made of rafters, trusses, or beams and defines the shape of the roof. There are many types of roof structures, gable end, hip, mansard, dormered, gambrel to name a few. Most residential roofs in this area are made of wood lumber (as opposed to steel used on commercial projects). The floorplan of a home and the final roof covering determines the roof’s structure. For instance, a house with concrete tiles is different than one with asphalt shingles because the roof structure must support the extra weight. Also, it is the roof structure that determines what the slope of the roof will be.

When you drive by a home under construction and see bare sheets of flat material on top of the house, that’s the roof sheathing. It sits on top of the roofing structure and is secured directly to it. The most common material used is oriented strand board (OSB) because it’s lightweight, affordable, and available. Plywood is also used but mainly for roofs that will hold more weight, such as concrete tiles. Older homes (1900 and older) usually have skip sheathing. Skip-sheeting, or spaced sheathing, is just as it sounds: sheathing with gaps between. Traditionally, skip-sheathing consists of 1 inch by 4 inch boards nailed to the rafters with gaps between the boards. Spacing between boards is optimal for wood shakes but cannot support asphalt composite shingles. By RI Building Code, this sort of roof must be re-sheathed with plywood to support the new system.

In a perfect roofing world, every roof would have a small slope without any obstructions. But that’s not the case. Roofs have joints and structures like chimneys and ventilation. Flashing is what’s used to protect the roof around these areas. Its main job is to keep water from entering. Most flashing is a thin strip of material, generally metal. It’s placed in the valleys and around protrusions so water can be deflected and run off the roof. The roofing company typically decides the exact type of flashing. Appliances such as boots (around pipes) vents, chimney re-leading and step and valley metal are all features of flashing.

Your roof ventilation system is critical. When done correctly, it extends the life of the roof, reduces energy bills, and lowers indoor temperatures. There are two parts to roof vents – the exhaust function and intake vents. Many roof vents are installed underneath the roof covering at the roof ridge and roof edges, so you don’t even see them from the street level. When designed well and working correctly, the ventilation system allows hot air to leave the roof area while cool air enters.

The top layer of the roofing system is your roof covering. Looking around, it’s not surprising asphalt shingles are the most popular roof covering in the United States because of cost, fire protection, ease of installation, and durability.