Common Rafter Length Table for Roof Framing Projects

If you're working on a roof framing project, you'll want to make sure you have the right rafter lengths. A common rafter length table can be a huge help in determining the correct lengths for your project.

For a simple gable roof, the rafter length is typically determined by the roof's pitch, which is the ratio of the rise to the run. A 4:12 pitch, for example, means the roof rises 4 inches for every 12 inches of horizontal distance.

In a common rafter length table, you'll often see tables for different roof pitches, such as 4:12, 6:12, and 8:12. These tables provide the rafter lengths for each pitch, making it easy to choose the right length for your project.

For a 4:12 pitch, a 12-foot rafter length is a common choice for many roof framing projects.

Calculating rafter length is a crucial step in building a roof, and fortunately, there's a calculator that can make it easy. You can use it to calculate the rafter length based on the rise and run of the roof.

To start, you need to choose one of the two options: "rafter length" or "truss count". If you picked the rise, you just need to input its value and the roof's run, and the calculator will return the rafter length.

The calculator works both ways, so you can also use it to calculate the rise or the run. If you already know the rafter length and want to figure out any of the other dimensions, simply input the two you know, and you will get the third one.

For example, if you know the rafter length and the roof's run, you can use the calculator to calculate the rise. Similarly, if you know the rise and the rafter length, you can use it to calculate the run.

Here's a summary of the variables you need to fill out in the calculator:

Don't worry if you're unsure what some of these terms mean – the calculator comes with an illustration that explains them.

Roof span is the horizontal distance between the two end walls of a roof, and it's essential to calculate it accurately to determine the length of your common rafters. This is done by subtracting the thickness of the ridge from the total span, then dividing the answer by two.

The roof pitch, on the other hand, is the angle of the roof and can be expressed in various ways, but is most commonly measured in rise over a standard 12-inch run. You can use the formula angle = arctan(pitch / 12) to calculate the angle in degrees.

Common roof pitches range from 4:12 to 9:12, with ratios like 6:12 and 8:12 also being common. These ratios indicate the relationship between the horizontal distance (run) and the roof's vertical rise.

To determine the horizontal span of a common rafter, you'll need to calculate the individual rafter span by subtracting the thickness of the ridge from the total span, then dividing the answer by two.

Here are some common roof pitches and their corresponding angles in degrees:

Understanding roof span and pitch is crucial to determining the length of your common rafters.

Before diving into roof work, it's essential to ensure you have the necessary safety gear and equipment. A hard hat, safety glasses, and gloves are must-haves to protect yourself from potential hazards.

Make sure the roof is clear of debris and obstructions, especially if you're working with a ladder. Always maintain three points of contact with the ladder, whether it's two hands and one foot or two feet and one hand.

Check the weather forecast to avoid working during strong winds or heavy rain, which can compromise the stability of the roof and the ladder.

To work out roof rafter lengths, you can use a scientific calculator and trigonometry, but that's complicated unless you're a math whiz.

A simpler method is to draw and set the rafter lengths out on a sheet of plywood - just a straight edge and a good strong bevel are needed.

For larger roofs, a roofing ready reckoner is a handy tool. It's essentially a rafter length calculator, a book full of tables that help you work out rafter lengths quickly and easily.

A good ready reckoner like Goss's Roofing Ready Reckoner can be bought for around £20 and has probably paid for itself a hundred times over.

To use a ready reckoner, you'll need an adjustable Stanley quick square. This allows you to measure the run of a rafter and then look up the right table in the ready reckoner for your roof pitch angle.

Here are some of the things you can find in a good ready reckoner:

Using a ready reckoner saves a ton of time and trips up/down the ladder, as you can cut the whole roof on the ground and assemble it in one go.

Before you start working on your roof, you'll need to access it safely. You should ensure the wall plates are squared, levelled, and fixed down onto the brickwork.

The first thing to do is to determine the horizontal span of the rafter by subtracting the thickness of the ridge from the total span, then dividing the answer by two. This calculation will give you the individual rafter span.

You'll also need to get a long tape measure to get the span, as it might be quite a distance. The total span minus the ridge thickness, divided by two, equals the individual rafter span.

The roof pitch or angle is another crucial factor to consider. It should be specified on your technical drawings, or if you're deciding on it yourself, make sure it's suitable for your roof covering.

To find the right rafter length, you'll need to calculate the roof pitch in degrees. The angle in degrees is equal to the inverse tangent of the pitch of the roof, or you can use a table to find the angle for your roof pitch.

A common way to calculate rafter length is using the formula: rafter length = run√(pitch + 1). This formula is useful when you know the roof pitch and run. For example, if you have a 4:12 pitch and a 12 feet span, you would need a rafter that is 6 feet 4 inches long.

Here's a quick reference table to help you find the rafter length for different roof pitches:

Remember to also consider the overhang when measuring the roof span, and use a rafter length calculator or a ready reckoner to simplify the calculations.

To measure the roof span, you'll need to add the width of the building to the overhang on each side. This will give you the total length of the roof.

The overhang is the part of the roof that extends beyond the building on either side. Make sure to account for this when measuring the roof span.

You can use a tape measure to get an accurate reading of the building's width. Then, add the overhang on each side to get the total roof span.

If you're working with a complex roof design, you might want to consider using a roofing calculator to help you determine the number of shingles needed.

Here's a simple formula to calculate the roof span:

Roof Span = Building Width + Overhang (Left) + Overhang (Right)

For example, if the building is 20 feet wide and the overhang on each side is 1 foot, the roof span would be 22 feet.

To find the right rafter length, you need to determine the horizontal span of the rafter by subtracting the thickness of the ridge from the total span, then dividing the answer by two.

The total span is calculated by getting the span with a long tape measure.

The roof pitch or angle is also necessary, which should be specified on your technical drawings for the job.

If you're deciding on the pitch yourself, make sure it's suitable for your roof covering, as some tiles require a minimum roof pitch to stay in place.

You can use a rafter length calculator to simplify the process.

To start, choose one of the two options: "rafter length" or "truss count".

If you picked the rise, input its value, the roof's run, and the calculator will return the rafter length.

The rafter length calculator works both ways, so you can also use it to calculate the rise or the run.

If you know the rafter length and want to figure out any of the other dimensions, simply input the two you know, and you will get the third one.

To calculate rafter length using pitch, follow these steps:

1. Remember that pitch is the ratio between rise and run.

2. Use the rafter length formula: rafter length = √((run × pitch) + run).

3. Simplify the formula: rafter length = run√(pitch + 1).

4. Substitute the known values for pitch and run to calculate the rafter length.

Here's a quick formula reference: