Understanding Roofing Construction Diagram Basics

A roofing construction diagram is a visual representation of the various components and layers that make up a roof.

It typically includes the roof's structural elements, such as rafters, trusses, and beams.

The diagram may also show the roofing material layers, including underlayment, insulation, and waterproofing membranes.

These diagrams can help homeowners and contractors identify potential issues and plan repairs or replacements.

Rafter roofs are a simple and classic choice for many buildings. They consist of rafters that rest on horizontal wall plates on top of each wall.

The top ends of the rafters often meet at a ridge beam, but may butt directly to another rafter to form a pair of rafters called a couple. Heavier under purlins or purlin plates are used to support longer rafter spans.

Tie beams, which may also serve as ceiling joists, are typically connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart.

Rafter Construction is a fundamental aspect of building a roof. A simple rafter roof consists of rafters that rest on horizontal wall plates on top of each wall.

The top ends of the rafters often meet at a ridge beam, but may butt directly to another rafter to form a pair of rafters called a couple. This design allows for a sturdy and secure roof structure.

Heavier under purlins or purlin plates are used to support longer rafter spans. This is crucial for maintaining the integrity of the roof.

Tie beams, which may also serve as ceiling joists, are typically connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. This helps to keep the structure stable and secure.

Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength. This adds an extra layer of support to the roof.

Truss construction is a crucial aspect of building design. Pre-manufactured roof trusses come in a variety of styles, each designed by the manufacturer for a specific building.

Heavy timber rafters are typically spaced 240 cm to 370 cm apart and are called principal rafters. Principal rafters can be mixed with common rafters or carry common purlins.

Pre-manufactured roof trusses are designed to meet specific building requirements.

A valley is an inward joint where two sloping roofs meet, and your roof will likely have multiple valleys.

In a typical roof, these valleys are where the two roof types intersect, creating a complex system of joints and connections.

As you inspect your roof, you might notice that the valleys are often reinforced with additional support to ensure they can withstand various weather conditions.

Roofs with multiple valleys require careful planning and execution to ensure they are structurally sound.

Design and loads play a crucial role in roofing construction. Building codes in the United States specify loads in pounds per square foot, which vary by region.

Roof framing must be designed to hold up its own weight and the weight of the roof covering, known as the dead load. This includes the weight of the roofing materials, such as shingles or tiles, and the roof deck itself.

Environmental loads like snow and wind also need to be considered when designing a roof. In areas prone to heavy snowfall, the roof must be designed to withstand the added weight.

Flat roofs may also need to be designed for live loads if people can walk on them. This means the roof must be able to support the weight of people and any equipment or furniture they may bring.

The load and span, or distance between supports, define the size and spacing of the rafters and trusses. This is why it's essential to consider the specific loads and spans when designing a roof.

A roof's slope is typically between 4:12 and 9:12, depending on the climate and local building codes. This slope helps water to run off the roof more easily.

The average roof pitch is around 6:12, which is a good balance between water runoff and structural integrity.

Roofing materials are often categorized into three main types: asphalt shingles, metal roofing, and clay or concrete tiles. Each type has its own unique characteristics and advantages.

Asphalt shingles are the most common type of roofing material, accounting for over 80% of all roofs. They're relatively inexpensive and easy to install.

Metal roofing is a popular choice for its durability and resistance to weathering. It can last for 30 to 50 years or more, depending on the quality of the material.

Clay or concrete tiles are a premium option, offering excellent durability and weather resistance. They can last for 50 years or more, and some even come with a 100-year warranty.

A roof beam is a typically squared length of timber that spans an area of a building, intended to be a primary load-bearing part of the roof framing.

Roof beams can be categorized into two types: Through Beam, which is a single length of beam that goes through the entire space, and Spliced Beam, which is a beam with the illusion of being a single length but is spliced in the interior of a wall or above a post.

The part of a roof beam that extends out past the roof-edge framing is referred to as its projection, which is usually the only part of a structure not protected by the roof covering, making it highly vulnerable to wood-decay fungi.

The following table breaks down the anatomy of a roof beam:

A gable roof, like the ones commonly found in Arizona, has a ridge at its peak, eaves at its lower edges, and a gable at the A-shaped side wall that forms the peak of the roof.

A gable roof is a classic design that's easy to spot, with two sloping sides that meet at a peak. The peak of the roof is called the ridge, which is the highest point on a sloped roof.

The eaves are the lower edges of the roof that overhang the home's exterior walls. This is a common feature on many homes.

The A-shaped side wall of the home that forms the peak of the roof is called the gable. In fact, most homes have two gables, one on each end of the home.

The rake of the roof is the part that ends over a gable end. This is a distinctive feature of gable roofs.

Here's a summary of the key parts of a gable roof:

A hip roof is a unique type of roof where the ends are also sloped, replacing the traditional gable end. This design provides additional structural support and can be more resistant to high winds.

The hip end is a distinct feature of a hip roof, characterized by a sloped side with a peaked top. It's an essential component that helps distribute the weight of the roof evenly.

A hip roof still has a ridge, just like a traditional peaked roof. The hip ridge is the sloped, diagonal ridge between two sections of the roof. It's a crucial element in maintaining the structural integrity of the roof.

The following parts make up a hip roof:

Proper ventilation is crucial to prevent condensation in the roof space, which can cause serious structural damage and ruin insulation. Without adequate ventilation, humidity can lead to interstitial condensation.

Tighter building envelopes with high-performance windows and doors have reduced ventilation, making condensation a bigger problem. This is especially true in the UK, where building regulations require roofs to be ventilated.

Most building materials are permeable to water vapor, making them susceptible to interstitial condensation. This includes brick, concrete, plaster, wood, and insulation.

The UK requires roofs to be ventilated using soffit vents, ridge vents, or replacement ventilation slates or tiles. Ventilation of the roof deck speeds up the evaporation of water from leakage or condensation.

A properly insulated and ventilated roof is called a cold roof. This design has a higher r-value insulation installed between the ceiling joists or rafters.

In contrast, a warm roof is not ventilated, with insulation placed in line with the roof pitch. A hot roof has no ventilation and uses air-impermeable insulation to prevent condensation.

A roof beam is a crucial part of your home's structure, spanning an area and serving as a primary load-bearing part of the roof framing. It's typically a squared length of timber.

There are two main categories of roof beams: Through Beams and Spliced Beams. Through Beams are a single length of beam that goes through the entire space, while Spliced Beams are beams that are spliced in the interior of a wall or above a post, giving the illusion of being a single length.

The part of a roof beam that extends out past the roof-edge framing is called its projection. This exposed part of the beam is highly vulnerable to wood-decay fungi that exploit weather-related dampness.

Old-growth lumber, like the type used in Mid-century Modern homes, has superior strength, stability, and decay resistance due to its tight ring patterns. However, if your roof beams no longer resemble their original appearance, look for signs of dry rot.

Here are the two main types of roof beams:

As you learn about the different parts of a roof, you may come across some other terms that can be helpful to know. Fascia is a horizontal board that's fastened to the lower ends of roof rafters, and it's where rain gutters are typically attached.

Soffits are actually the underside of the eaves, and they play a crucial role in keeping your home dry. I've seen soffits get damaged during strong winds, so it's essential to keep them in good condition.

Drip edge, on the other hand, is metal flashing along the edges of the roof designed to divert rain away from the house. If you take a closer look at your roof, you might notice a white line where the drip edge would be if it were installed.

Here's a quick rundown of these terms:

Flashing, which wasn't pictured in our example, is metal used to help stop water from penetrating the junction of a roof with another surface, like a chimney or flue pipe. It's an essential component in keeping your home watertight.