Your home’s roof sheds water, but a raindrop that starts out on the top of your roof doesn’t just encounter shingles on its way down. There’s a series of roof components that protect your home from the rain, wind and snow. It is critical to understand all of the parts of a house roof in order to explain a problem to a roofing professional and understand what he or she is talking about when he or she is doing repairs.
Architectural Parts of a Pitched Roof
Roofs come in all sorts of shapes and sizes, but you only need to know a handful of terms to describe their essential architectural features. These are the parts of a house’s roof:
- Roof plane: This is the pitched face of a roof.
- Ridge: This is the peak of the roof, where two roof planes meet.
- Hip: This is where two roof faces connect and project outward.
- Valley: This is where two pitched roof faces connect and project inward.
- Dormer: This is a roof feature that projects out from the roof face. It usually houses a window and adds extra space and/or light to the room inside.
- Gable: This is the triangular wall underneath where two roof planes meet.
The Anatomy of a Residential Pitched Roof
The anatomy of a roof, or the layers of a roof, give it structure and protect the home. Let’s begin at the bottom.
1. Roof Frame: Joists, Trusses, Rafters and Decking
When a home is being built, the first part of your roof to go up will be a wooden frame. The components of this frame include joists, trusses and rafters. These project above the house to make the structure on which the rest of the roof will be built. This skeleton is covered by the roof’s decking, a thin piece of wood that will be the platform for everything else. The material chosen for the decking can vary, but the most commonly used materials are plywood or oriented strand board (OSB).
- Underlayment protects the shingles from any resin that the decking might release.
- Underlayment serves as a secondary water barrier if water gets beneath the shingles.
- Underlayment may help prevent “picture framing.” Picture framing is generally the result of the expansion/contraction of the wood panels used for the roof deck. As they move, the deck panels create ridges or bumps in the surface of the roof which look unappealing and may interfere with the water shedding function of the roof.
- Underlayment also contributes to fire resistance.
Synthetic underlayments have become more popular over the last several years because it is lightweight and easy to install. Additionally, synthetic underlayments may have features you can’t get in traditional asphalt saturated felt. For example, IKO’s RoofGard-Cool Grey is a lightweight underlayment designed to absorb less heat, providing a more comfortable surface for the shingle applicator.
Another type of underlayment is ice and water protector. This underlayment defends a roof from ice dams and wind-driven rain, which can drive water up between shingles. IKO’s ice and water protectors are self-adhering and made of modified bitumen. This material closes around nails, providing a watertight seal. Some, like ArmourGardTM, also act as vapor retardants, which means they allow very little water vapor to pass through them.
In some climates, it makes sense to use an ice and water protector over the entire roof deck, particularly in high wind and hurricane-prone portions of the country. However, if the attic does not have proper ventilation, the ice and water protector could make them worse. Even in climates with less severe weather conditions, ice and water protectors can provide an added water barrier for vulnerable areas of the roof, like valleys, the roof’s edge or around roof features like skylights.
Of all roof components, flashing seems to be the least clear to the homeowner. To understand the need for flashing, think of a chimney. Chimneys don’t have shingles or underlayment, and they punch right through the roof decking into your home below. Chimneys have protection to keep water from rushing in through the top (a chimney cap); but what about the sides? What’s to stop water from running down the exterior of the chimney, wiggling right past the edge of the shingles, underlayment or decking and into your home? Flashing is the answer.
Flashing is a thin sheet, usually made of metal, that a roofing professional installs around any vertical surface that intersects with the roof plane, such as the surface of a chimney. Flashing installed around a chimney is bent approximately 90 degrees so that one plane rests against the face of the chimney while the other extends out horizontally above the underlayment, but below the shingles.
There are many roof flashing applications. You will see flashing installed around other residential roof features, including:
- Skylights: Some skylights manufacturers include built-in flashing with their product, especially for deck-mounted skylights or those that are installed right on the roof deck. If the skylight does not come with built-in flashing, the roofing professional will need to add flashing around it.
- Plumbing vents: The plumbing vent provides ventilation for your home’s plumbing.
- Roof vents: A roof can have several other kinds of vents projecting through the roof face, all of which will need flashing. There are attic vents, gable end vents, ridge vents and soffit vents (which we will discuss below). Vents help keep the attic space properly ventilated. Soffit vents, combined with ridge vents, will allow for air to flow freely through the attic space.
It’s often necessary to install flashing around a roof’s architectural features, the design elements that create the shape of the roof. Architectural features that need flashing include:
- Valleys: These are the indented spots where two roof planes meet. In the open valley style, valleys are flashed with a long flat piece of metal with a “v”- or “w”-shaped center. You can cover a valley with shingles, in woven or closed-cut styles, but these are usually less effective than open valleys with metal flashing.
- Dormers: Where dormers connect with the main roof face, they create a valley, which needs flashing for protection. Also, roofers must add flashing to the side and front surface of the dormer.
Finally, the roof is topped off with the most recognizable of roof components: the shingles. In the past, wooden and slate shingles were typical, but, for the last 100 years, asphalt shingles have become the most common residential roof covering in North America. Generally speaking, there are three styles of asphalt shingles:
- Traditional or 3-tab shingles maintain a uniform look on the roof because the shingles all have the same size and shape. They are a budget-friendly option that will protect your roof for years to come.
- Laminate or architectural shingles are distinguished by their dimensional appearance, with accent tabs of different sizes and sometimes deep shadow bands to add character. To learn more about what shingles are made of, read our article describing shingle composition.
- Premium shingles are available that offer aesthetic enhancements beyond those provided by laminated shingles. There are a variety of looks and styles available. IKO’s ArmourshakeTM, for example, mimics the look of a wood shake roof while providing Class A fire protection.
- Asphalt shingles are offered in an array of colors to match or enhance your home’s style. To consider which kind of shingles are right for you, use our guide.
After being applied, shingles need to seal to one another. Though the roofing professional will first secure the shingles to the roof with nails, IKO’s shingles have a heat-activated sealant that will help achieve better wind resistance. After sufficient exposure to warm weather, the sealant will bond the shingles to the course below them.
If your roofing professional applied your shingles in cold weather, he or she might have manually sealed the shingles to provide wind protection until warm weather arrives. Also, IKO offers a special high-wind application procedure, which a roofing professional can use to provide an added measure of protection to help meet the challenges of high-wind conditions.
There is also a special type of shingle, which a roofing professional installs along a roof’s hips and ridges. Hip and ridge cap shingles are specially manufactured to conform to the shape of the roof’s hip or ridge. A premium version of hip and ridge shingle, such as IKO’s UltraHP®, has an enhanced profile that will complement the look of many roof designs.
Shingles can also be designed to serve other functions on the roof or to create a unique look.
- Solar reflective and thermal emissive shingles: Manufacturers can produce shingles that reflect or emit heat, like IKO’s CambridgeTM Cool Colors. Installing these shingles can help keep your home cool.
- Mock slate shingles: Manufacturers design some asphalt shingles to mimic the look of slate shingles, like IKO’s Crowne SlateTM.
Learn more in our guide to the different shingle patterns.
The Parts of the Roof’s Edge
The basic layers of a roof that we’ve covered so far aren’t enough to protect your home. Water can’t just roll off your shingles and down the face of your house, or your bricks or siding would be damaged. Plus, the water would collect around the base of your home, which could cause foundation issues. So, at the roof’s edge, a series of roof drainage components are installed to protect your home from these potential problems.
First, you have to understand that there are two types of edges on a roof: eaves and rakes. An eave is the horizontal edge where the roof hangs over the exterior wall. A rake is the sloped edge where a roof hangs over the exterior wall. It is essential to handle the drainage from a roof at the eave properly and protect against wind-driven rain at the rake.
Here are the parts of a roof edge:
1. Drip Edge
When water reaches the eave edge of a roof, it meets the drip edge, also called the eaves flashing. This is a thin metal strip that directs the water into the gutters. In most cases, the roofing professional should install the drip edge before the underlayment on the eaves and after the underlayment on rake edges. Without a drip edge, water may not properly drain and could flow down the wall surface, or worse, into the home.
A fascia is the topmost vertical component of the exterior where it meets the roof edge. The roofing professional places the drip edge at the top of the fascia, and the rain gutter is attached to the fascia.
3. Gutters and Downspouts
Gutters are the plastic or metal troughs that take the water away from the edge of the roof. They connect to downspouts, which bring the water down and direct it to drain away from the home’s foundation. Without the downspouts to direct the water away from your home, you could develop foundation issues or other damage.
Many roof styles include a soffit. When the eave edge of a roof extends past the exterior wall, the soffit is the horizontal underside of this extension. Often, soffits are perforated or have built-in vent openings to provide ventilation for the attic space. Soffit vents, coupled with ridge vents at the top of the roof, can be a very effective way to achieve proper roof ventilation.
All of these roof components work together as a system to drain water away from your home and protect it from the elements. There’s more to learn about the shape, structure and edge of residential pitched roofs; discover it by visiting IKO’s Roofing 101.