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Roofing Terms

Roof Pitch

In roofing, the pitch of a roof is communicated as a fraction or ratio, such as “4/12”. This should be understood as rise over run. For example, if someone refers to a “4/12” pitch, that would represent 4 inches of rise for every 12 inches.

Ridge

A ridge is typically the highest point of a roof and extends horizontally, connecting the eaves and/or hips of the roof. Ridges exist only in steep slope roofing applications and often serve as the best place for outflow ventilation to be installed, as it is typically at the highest point of a structure.

Valley

Just like a mountain that has ridges, between the ridges will be a valley. It is “V-shaped” and allows water to be channeled down into drainage components such as gutters. Valleys are a high-traffic area for water. As such, valleys are often the culprits for more than 50% of the leaks in steep slope roofing applications. Roofing manufacturers take extra care when designing their roofing systems to ensure that they have products that can handle this scenario, but roof installers must take extra care when installing these products to ensure it is done correctly to avoid leaks in the future.

Hip

You can think of a hip as an inverted valley. They extend up from the eave diagonally to the ridge of the roof. Often, in steep sloped roofing, a roof may be designed to not have any valleys. If this is the case, the roof will have only hips and ridges, and they will be referred to as “hip roofs.” Hips of the roof are protected by specialty products. In shingle roof applications, “hip and ridge” shingles are used. In some cases, ventilation products may be installed on the hips of a roof where an insufficient amount of ridge may be present for ridge ventilation.

Field

The field of a roof is a plane and the largest area of a roof. Despite its size in linear square footage, it represents the simplest portion of the roof and typically is least likely to have leaks in it. Most leaks come from penetrations, valleys, or incorrectly installed or corroded flashing.

Square

A square is short-hand slang for people in the roofing industry. A square represents a unit of measure that is 10 feet by 10 feet – or 100 square feet. You shouldn’t feel required to speak in terms of “squares” as everyone will understand you perfectly fine if you communicate in lineal square footage, but nearly everyone in steep slope roofing will speak in terms of “squares” so you should be prepared.

Steep Slope Roofing

Usually refers to any roofing with a pitch of 4/12 and higher. The primary design feature of a steep slope roof is to quickly remove water from and avoid pooling. Steep slope roofing systems are the most common type of roof, statistically speaking. The roofing materials used on steep slope roofs are comprised of asphalt shingles, wood shingles, concrete roofing tiles, clay tiles and metal panels.

Low Slope Roofing

Usually refers to any roofing with a pitch of under 4/12. Low-slope roofs are often represented as “flat roofs.” Technically speaking, there should never be a “flat” roof unless there is a design flaw in the building. All roofing systems are designed to move water from one place to another, whether that is to the edge of the roof or into internal drains. Roofs in this category consist of modified bitumen, TPO, PVC and EPDM.

Decking

Refers to the substrate of a roof and applies to both low slope and steep slope roofing. The decking is often used to fasten roofing materials. In steep slope roofing applications, the decking is typically made up of either CDX or OSB plywood. In low slope roofing applications, the decking may be wood, metal pan, metal beam, structural concrete, or lightweight concrete panels such as gypsum.

Fascia

Usually made up of wood or PVC (in modern applications) and is hung to the face of the eave on the rafters of the structure. Drip edge typically protects this area of the roof.

Soffit

Attached to the underside of the eave and is typically constructed of plywood. There is often a type of outflow ventilation fastened to a soffit called soffit vents.

Eave

The horizontal area of the roof that typically has fascia and gutters attached to it. In most cases, roofers refer to eaves as being the area comprised of fascia and soffit.

Rake

The rake is structurally the same as an eave except that the rake is not horizontal, but rather follows the pitch of the roof upward towards the ridge of the roof.

Cricket

Crickets are small framed structures that essentially function as “water diverters.” They are commonly found next to chimneys. Steep sloped roofs allow water to flow towards the chimney, and a cricket diverts the water around the chimney to prevent backwash from flowing over the flashing and into the home.

Dormer

Often referred to as “eyebrows,” they represent a portion of the roof that has a framed component embedded within it. Dormers are most often aesthetic on the front elevation of the roof but may also serve as a functional area as they typically have windows attached for outward viewing. These can be challenging areas as they require a great deal of roofing components to avoid leaking. Such components are stepped flashing, apron flashing, ridges and sometimes crickets.

Underlayment

Underlayments are a fairly broad category, but in all cases, they serve as the last layer of protection before moisture reaches the decking in the field of the roof. Until recently, asphaltic felt was commonly used. Synthetic underlayments have begun to replace asphaltic felt due to their superiority in strength and functional ability to prevent water from reaching the roof decking. Probably the most important thing to know about the differences between asphaltic felt and synthetic underlayment is that felt varieties are porous. This means that given enough time and exposure to moisture, moisture will eventually make its way to the roof decking, which will cause leaks. Synthetic varieties do not allow moisture in, but not all varieties will let water vapor out (if moisture makes its way in through other areas of the roof). Having a breathable synthetic underlayment is the most expensive route but also the most healthy for your roof long term.

Eagle View

An “Eagle View” is a three-dimensional roof measurement that is typically procured by satellite imagery. A company called “Eagle View” invented this technology, and while they are not the only provider of satellite-based roofing imagery, they are dominant throughout the industry due to their reliability and the level of trust established with insurance carriers. Thus, roofing measurements are very commonly referred to as “Eagle Views.”

Inflow Ventilation

The are two flow-related components to the ventilation of buildings – inflow and exhaust. Ventilation is extremely important in all roofing applications. In steep slope roofing applications, inflow components are typically installed in the soffit, and sometimes in eaves. These components are typically at the lowest portions of the roof. The inflow of relatively cool air enters the roofing structure (typically the attic), and, with the help of exhaust components, warmer air is removed from the structure – remember that heat always rises. This is a naturally occurring convection process that relies on equal inflow and exhaust ratios to work properly.

Exhaust

The outflow ventilation or exhaust of a roof is an equally, and perhaps more important, component of roof ventilation. The most common types of exhaust on steep slope roofing applications are ridge vents. These are known as static exhaust components since there are no mechanical functions. Proper static exhaust relies on equal inflow and exhaust ratios to remove warm air from the structure properly.

Building Envelop

The building envelope, in its most simple explanation, is the physical separator between the conditioned and unconditioned environment of a building, including the resistance to air, water, and heat, light, and noise transfer. The implementation of the building envelope is a complicated subject and involves mechanical engineers, structural engineers, architects and thermal engineers. Due to the complexity of this topic, we can only offer a topical definition for you.

Roof Decking – OSB Sheathing

OSB sheathing, or “Oriented Strand Board,” is the most common form of roof decking. It is what many refer to as “particle board,” though this is not technically accurate. It was used on almost every new home built from the 70’s on. While it is touted as being more structurally sound than CDX plywood, you can watch any roofing crew tearing off an old roof and see that OSB shreds like cardboard once exposed to moisture. OSB comes in various sizes and thicknesses, but the most common for steep slope roofing is 4′ x 8′ sheets that are 5/8″ thick.

Things to Know About OSB Decking

As with any roof deck, OSB decking serves as the foundation for a roof. Though not technically part of the roofing assembly, it is critical to a roofing system as it is what all components are fastened to. Georgia does not require much in the way of fastening OSB decking. Florida, and many coastal states require hurricane clips to further reinforce the roof deck from high wind conditions. That said, rarely have we ever seen a roof deck blow off due to high wind conditions, with the exception of tornadoes.

One of the most common mistakes roofers make when inspecting roofs is not fully vetting the roof decking. With the exception of evaluating warping and ability to hold weight, it is simply impossible to evaluate issues with roof decking from on top of the roof. The ability to hold weight does not mean a roof deck should not be replaced. Any wood decking older than 20 years needs to be inspected from under the roofing assembly. The reason for this is two-fold:

1. As wood grows old, it becomes brittle. If you ever get the opportunity to hang out under a 20+ year-old roof deck while the roof is being replaced, you will likely be in a constant barrage of wood splinters. This is because the new nails are causing the old brittle decking to shatter.
2. Project Creep: Or what many refer to as hidden costs. Often, a professional roof inspector can conduct a visual inspection of the underside of a roof and determine to what degree the decking will need to be replaced. This is impossible to estimate from the top of the roof. If your contract doesn’t specifically state that the roofer must replace all “rotten” decking as part of the contract price, make sure you understand how much each piece of decking will cost to replace on a per sheet basis. While it is impossible to get an exact count of how much decking needs to be replaced, a professional roofer can get pretty close.

Asphaltic Felt Underlayment

This is perhaps one of the oldest underlayments used in roofing. It is inexpensive, easy to manufacture, and easy to install. The roofing manufacturer creates this product by embedded asphalt into 15 lb. or 30 lb. paper. The result is a slip and water-resistant underlayment which, like all underlayments, serves as an additional layer of protection against wind driven rain, which can get up under shingles. This is the recommended solution for cost effective roofs where you may not be occupying the building for any length of time, i.e. when you are selling your home.

Synthetic Underlayment

The category of Underlayment has a couple of subcategories. All kinds of synthetic Underlayment are created from plastics to give them water proofing, but vary in thickness, slip resistance, and breath-ability.

Non-Breathable Synthetic Underlayment

A non-breathable synthetic Underlayment has characteristics that resemble a tarp. This is advantageous as, like a tarp, it is completely waterproof. Unlike asphaltic Underlayment, water saturation will never pass through a synthetic underlayment’s barrier unless it makes its way in through the seams (each roll is overlapped with the previous but still represents a seam). The only downside of this type of Underlayment is that the roof must “breathe” through the seams and roof ventilation. Trapping heat in your roof is always bad for your roof, and for that reason, a non-breathable synthetic Underlayment is not the perfect Underlayment. However, it is orders of magnitude better than asphaltic felt. This is the recommended solution for all steep slope roofing assemblies where you are planning on occupying the building for 5-10 years.

Breathable Synthetic Underlayment

This is the best category of synthetic underlayment. Despite the name of this type of product, it is completely water proof. The difference is that it features technology that prevents moisture from getting in, but allows air to escape. This allows the roof to “breathe”. The most important part of this feature is that hot air can easily escape the roof, which keeps the roof’s integrity intact long term. This is a recommended product for your forever home/building.