The Main Components of a Roof

Note: As of 2026, Rainshield is exclusively focusing on roof replacement in Bellingham. If you found this page and were looking for any other service, please feel free to give us a call for a recommendation. If you need Bellingham roof replacement done right, you've come to the right place.

To discuss roof components, key terms are essential. The roof plane is the flat, pitched surface of a roof. Where planes meet, we find the ridge (the highest point), hips (outward-projecting junctions, not at the peak), and valleys (inward-projecting junctions). A dormer is a roof projection, often with a window, adding space or light indoors. The gable, while not part of the roof, is the triangular wall section between pitched planes.

Understanding these terms helps clarify how residential pitched roofs are built.

Structural Layers of the Roof

Just like the rest of the house, the roof starts out as a frame. The frame is usually constructed of lumber. It incorporates joists, trusses, and rafters. Together, these three types of beams make up a framework that gives the roof its shape. The frame needs to be strong enough to support the weight of the roof. With a standard asphalt shingle roof, this is not much of a concern. But if you plan to use heavier materials like tile or slate, you may need to add extra supports at this stage.

Once the frame is in place, it is covered in decking. Decking is the skin that covers the frame and creates the base that the rest of the roof will be built upon. The most common material for decking was once plywood. However, in recent decades oriented strand board (OSB) has taken over as the most common material for load-bearing planks in residential construction. OSB is similar to particle board, but instead of tiny bits of wood, it is made up of thin strips of wood. The strips are held together with resin and a small amount of wax to form a very strong plank.

Underlayment

Roof underlayment, installed directly on the decking, is a critical barrier beneath shingles. It absorbs resin from the decking, enhances water resistance, and prevents "picture framing"—bumps caused by decking expansion and contraction that can disrupt a roof’s flat surface and water resistance.

Traditional tar-saturated felt remains popular, but modern synthetic options offer improved water resistance and lower heat absorption. In cold climates, specialized water and ice barriers protect against ice dams, often self-adhering and sealing around nails for a watertight fit.

These may cover entire roofs in harsh climates or just vulnerable areas like valleys and edges in milder ones.

Flashing

We have covered flashing in detail in some earlier posts, but it is still important to mention here. After the underlayment is installed, flashing is installed in areas of the roof that collect a lot of water. Valleys, where water from multiple roof planes is directed into a gushing stream, are always covered with flashing. The flashing is generally a thin layer of sheet metal that protects a vulnerable joint and directs water away from the area.

Flashing is also used anywhere the decking is cut open for some type of penetration. For example, a chimney requires flashing all around it. The flashing prevents water from seeping through the seam where the chimney walls meet the roof. Other roof penetrations such as vents and skylights also require flashing and may come with flashing as part of the finished product.

Another common place to put flashing is around dormers where the vertical walls of the dormer meet the pitched roof. Similar to a valley, this area can collect a lot of water and requires extra protection.

Shingles

Asphalt shingles remain the top choice for residential roofing, unchanged for over half a century. Among them, three-tab shingles dominate due to their durability and affordability.

These flat, three-foot strips feature two slits for a triple-shingle look, available in various colors with heat-activated adhesive for enhanced wind and water resistance. For high-wind areas, premium options offer extra adhesive. 

Meanwhile, architectural shingles, a newer innovation, add a layered, three-dimensional effect, mimicking natural materials with irregular shapes. Popular in luxury homes, they boost curb appeal and may increase property value, making them a favorite for new roofs or upgrades.

New Roof Installation

When it comes to installing a new roof, Rainshield Roofing has your back. We can peel back your roof all the way to the decking. We then ensure that the decking is in good condition and install a whole new roof, from underlayment to shingles. Whether you need a new roof or just some repairs, we’re ready to take on your job.

Call Rainshield for a quick no-obligation estimate to find out what it will cost to address your unique roofing needs. 888-858-7663