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The Basics of Roof Framing and Construction

by Nov 25, 2024

Did you know the most common roof in the U.S. is the gable roof? It’s known for its triangular shape.

There are five basic roof designs used in homes. Knowing how to frame and build a roof is key for a strong, weather-resistant, and good-looking roof.

Roof framing can be done with trusses or rafters. Trusses are made in a factory and are easy and affordable. Rafters are better for smaller homes and custom builds because they save space and cost. The roof must support the weight of the materials, have good ventilation, and be well-insulated.

The roof’s pitch is very important – it’s how steep the roof is. For example, a 3 in 12 pitch means for every 12 inches horizontally, the roof goes up 3 inches. Most roofs need a 3/12 pitch, but in cold places, it’s often 8/12 or more to handle snow.

To build rafters, you need to know the span, rise, run, and line length. These help figure out the rafters’ length and angles. You’ll also need tools like a framing square, measuring tape, and saw. Knowing these basics helps build a roof that’s strong, saves energy, and lasts long.

Key Takeaways

  • Gable roofs are the most common roof design in the United States
  • Trusses and rafters are the two main options for roof framing, each with their own advantages
  • Roof pitch is determined by the rise divided by the run, with a minimum pitch of 3/12 for most roofing materials
  • Key measurements for building rafters include span, rise, run, and line length
  • Understanding the basics of roof framing and construction is crucial for creating a sturdy, weather-resistant, and energy-efficient roof

Understanding the Types of Roofs

Knowing about different roof types is key in roof framing and construction. Each style has its own look, benefits, and fits certain climates and designs. Let’s look at the main roof types: gable, hip, gambrel, mansard, and flat roofs.

Gable Roofs

Gable roofs are the most common, with two sides that meet at a ridge. They offer lots of attic space and are great for cold, snowy areas. Even though they’re a bit harder to build, their classic look and function make them popular.

Hip Roofs

Hip roofs have four sides that meet at a peak. They’re very stable and work well in windy areas. Their modern look and efficient water drainage make them a favorite.

Gambrel and Mansard Roofs

Gambrel roofs, like those on barns, have two sides with different slopes. The lower slope is steeper than the upper slope, adding extra space. Mansard roofs have four sides, with a nearly vertical lower slope and a gentler upper slope. Both add a special touch to buildings.

Flat Roofs

Flat roofs aren’t really flat; they have a slight slope for drainage. They’re good for hot, dry places and are used in modern buildings. Thanks to better waterproofing, flat roofs are now trendy for their clean look.

Rafters vs. Trusses: Choosing the Right Framing Method

When it comes to roof framing, we have two main choices: rafters and trusses. Each has its own benefits and is better for different projects. Knowing the differences helps us choose the best option for our homes.

Advantages of Rafters

Rafters are framing boards that go from the ridge to the wall plate. They are built on-site. This makes them great for unique designs or complex roof shapes.

Rafters also allow for open attic spaces. These can be used for storage or even as extra living areas.

Benefits of Trusses

Trusses are made off-site in a triangular webbing frame. They are cheaper and faster to install than rafters. This makes them ideal for big projects with spans up to 60 feet.

Differences Between Rafters and Ceiling Joists

Rafters are diagonal roof boards, while joists are horizontal ceiling boards. Rafters are built on-site, which can be more expensive. Trusses, on the other hand, are made beforehand and installed quickly by a smaller team.

Cutting and Sizing Rafters for Your Roof

Building a strong roof starts with cutting and sizing rafters right. You need to know how to figure out the roof’s span, rise, and pitch. This helps make sure your roof framing is both correct and efficient.

Calculating Roof Span, Rise, and Pitch

First, measure the roof span, which is the distance between the walls. Our example shows a building width of 6 ft. 3/4 in. After subtracting 1 ½ in. for the ridge beam, we get an adjusted run of 5 ft. 11 1/4 in. Then, divide this by 2 to find the rafter’s actual run, which is 2 ft. 11 5/8 in. The roof’s pitch is 6/12, which is its angle.

Determining Rafter Length and Angles

With the pitch and run known, we find the diagonal for layout, which is 3 ft. 3 13/16 in. The rise, or vertical distance to the ridge, is 1 ft. 5 13/16 in. These figures help us figure out the rafter’s length and angles for our project.

Making Plumb, Bird’s Mouth, and Tail Cuts

Now, we make the cuts needed for the rafters. A 4-in. seat cut is made for each rafter. The model roof has a 4-in. HAP for the rafters. Use a rafter square to mark the plumb and bird’s mouth cuts. Lastly, make the tail cuts for a perfect fit and overhang.

Roof Framing: Step-by-Step Guide

After choosing between rafters or trusses, we start placing them. We align them at the ridge board, which is at the roof’s peak. To keep the walls stable, we nail rafter ties to the rafters and walls. This makes the roof strong and steady.

Installing Ridge Boards and Rafter Ties

Attaching Sheathing and Fascia Boards

With the rafters or trusses set, we attach the roof sheathing. We use framing nails to secure the sheathing, like OSB or plywood, to the frame. This makes a solid base for the roofing.

Then, we cover the rafters’ ends with fascia boards. They give the roof a finished look and support the gutters.

Applying Waterproofing Underlayment and Shingles

Before putting on shingles, we add a waterproof underlayment. It stops water from getting to the roof sheathing and damaging the house. We lay out the underlayment carefully, making sure to seal around vents and chimneys.

Finally, we put on the roofing shingles, starting at the eaves and moving up. We always focus on safety, using the right tools and following best practices.

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