Roof Rafters

About Roof Rafters 

Building a roof is unimaginable without rafters, the most traditional elements of the roof framing and lining. A rafter-based structure is also known as stick framing, a labour-intensive process that offers many benefits in return.  

Each beam is typically built on-site, measured and cut from dimensional lumber. It consists of several elements attached together. 

Advantages of Roof Rafters

• Stick building makes rafters suitable for diverse use.
• Custom measures are ideal for hard-to-reach locations and specific design solutions. 
• Zero lead time
• Suitable for making sheds, cabins, and other small structures

On the downside, customised beams are less cost- and labour-effective than roof trusses. The preparation process that is very convenient in some cases, can be a disadvantage in others.

Roof Rafters Applications

• Customised additions of vertical space for maximising the home's functionality. 
• Vaulted ceiling creations
• Structures and building sites that cannot be easily reached.

Rafter Elements

A closed couple roof includes roof joists running horizontally to sustain the weight of a ceiling, making the structure more rigid.

Purlins are used for maximising potential roof span without compromising the stability or adding extra costs. They provide additional strength to the structure, sometimes allowing for lighter and thinner rafters. 

In modern residential construction, the most common form used is the fink or "W-trussed" rafter. The name comes from tension and compression features added to the beam, forming the shape of a W letter. Such a system can support ranges of up to 12 m with a variety of different pitch angles, enhancing the structural strength of the roof framing. 

Rafter boards create the slope of the roof. They are fastened to the ridge board at the roof's apex and the top plate where they join the wall. Ridge boards share the same width and can be replaced with ridge beams in more demanding systems. 

Collar ties are installed horizontally to provide additional strength and stability.

Types of Roof Rafters

Typical stick framing roofs consist of three to seven different types of rafters, where more elements mean the more complex structure. A simple gable roof can be assembled using only the common rafter type, while the addition of hip and hip jack rafters forms a standard hip roof framing.

Common Rafters 

These are standard elements of most conventionally framed structures. A common rafter runs between the wall and the ridge board, determining both the height of the roof and the board location. The hip and valley beams follow next. 

Hip Rafters

Stretching from the wall plate to the ridge board at a 45-degree angle, hip beams mark the structure's outside corners.  

Hip Jacks 

Hip jacks sit on the outside walls and extend up to the hip rafter, parallel with the commons.

Valley Rafters

Placed at inside corners to the ridge, these beams extend diagonally at a 45° angle. They are transferring the portion of the weight to the intersecting wall plates, to support the roof's ridge. 

Valley Jacks

Valley jacks connect the valley rafter with the ridge board.

Cripple Jacks

In situations when the hip and valley beams are placed close together, cripple jacks are engaged for connection. 

Flying Hip

Also called mystery hip, this element reaches the end of a higher ridge board.

Materials

Most beams can be cut from standard framing wood. That includes laminated veneer lumber, genuine wood, and glued laminated beams.

Steel rafters are also available and broadly used in commercial applications. 

Before buying lumber for roof framing, it's important to consider two details: the length of the boards and the number of frames. 

The roof framing needs to take a substantial yet specific weight. For that reason, the number of frames depends on the material quality, among other features. Less sturdy beams require more frames and vice versa - strong lumber can hold well in fewer numbers.

Lumber strength depends on the species used, its grade, and sawn dimensions.

Types of Rafter Cuts

There are five cuts needed to create a common rafter.

• Plumb cuts 
• Tail cut 
• Bird's mouth cut
• Seat cut
• Heel cut
• Fascia cut 

Things to Consider Before Buying Roof Rafters

Before cutting the base material, it's essential to have a layout plan. That includes the span and height of the roof, run, and line length of the frame.

• Span is the length between the two walls that will carry the roof. 
• Run is half of the span measure.
• Rise is the elevation of the roof ridge at its highest point, measured from the centre of the span.
• The line is the length of the triangle's "hypotenuse" that determines the length of the rafters. The triangle consists of the run, rise, and rafter.

The rise and line dimensions depend on the roof pitch that directs the angles and length in which the rafters need to be cut. It's the result obtained when the size of the rise is divided by the length of a run.

It's best to consider building codes before installation, to make sure that the desired roof pitch will comply with the requirements.

When buying lumber for the rafters, it's good to consider some extra lengths for additional insurance. It will provide ample space for cuts - and possible mistakes. 

If you need assistance to find the right roof rafters for your home or office, ArchiPro provides a connection to the various professionals, ready to assist with all requirements and questions. Simply click "Contact supplier" on the product's page, or visit the supplier's website directly from the product's page.