Rafters for roof

Types of Roof Rafters

Roof rafters are located on sloped roofs and support the roof’s weight. They differ from roof trusses, which are pre-built triangular structures that evenly distribute a roof’s weight and are typically placed almost parallel to one another.

Roof rafters come in several varieties based on structural requirements:

• Common rafters

  Common rafters are installed on angled portions of sloped roofs. They extend from the building’s walls to the roof’s peak or ridge where they connect with similar rafters. When arranged together, common rafters create a framework that provides roof support known as the rafter framework. Between the angled common rafters, rectangular horizontal pieces called purlins are installed that help support roof materials and serve as attachment points for insulation, sheathing, or shingles. The dimensions of common rafters vary depending on the roof’s pitch and the weather conditions expected in the area.

• Hip rafters

  Hip rafters are unique because they run diagonally from the building’s corners to the roof peak. They combine the functions of common rafters and ridge rafters. By connecting every roof side and forming a stable framework, hip rafters are mainly used in roofs with a hip design that slopes in four equal sides. Such roofs are called hip or pavilion roofs. Hip rafters transfer the roof’s weight evenly down to the walls, improving stability and making them ideal for areas with harsh weather.

• Valley rafters

  Valley rafters are integrated between hip rafters. They run diagonally along the lower angles where two roof sections meet.

• Couple rafters

  A couplet is when two common rafters are used together and separated by a horizontal member called a purlin rafter. A purlin rafter is attached halfway up each rafter where it meets another purlin at a right angle, creating a square frame supporting the roof. This simple couple construction is economical, especially on roofs with small to moderate pitches, reduces the number of rafters needed by half, and is commonly used in sheds or garages. Extra stabilization is required since the load is not as evenly dispersed as with other rafters.

• Jack rafters

  Jack rafters are shorter than other rafter types. Like valley rafters, they are installed parallel to the roof slope but unlike valley rafters, they connect to a ridge or peak instead of two adjoining hip rafters. Jack rafters fill the space between a hip or valley rafter and the last common rafter, creating a level, uniform roof surface.

Rafter Material

The following materials are used to make roof rafters:

• Wood

  Wood is the traditional material for rafter construction due to its good balance between strength and lightness. Wooden rafters provide flexibility to withstand pressure without breaking. They are easy to work with. Most commonly, wooden rafters are made from timber, with frames cut on-site from 2x4 or 2x6 pieces of wood. Another type of wooden rafter uses prefabricated assemblies made from engineered wood products like laminated veneer lumber or glulam. These engineered rafters offer uniform strength that natural wood can’t match and can be designed to carry heavier loads or span wide openings.

• Steel

  Steel rafters are a durable choice for modern structures. Steel boasts outstanding strength-to-weight ratio, allowing longer spans and greater distances between supports than wood. While heavier, steel’s rigidity provides exceptional resistance to bending or warping under heavy loads. Compared to wood, it requires less maintenance, doesn’t rot or be affected by pests, and lasts longer. Steel rafters, popularly galvanized or coated, offer protection from rusting. Due to its durability and suitability for large open interiors, steel rafters are commonly used in industrial buildings, contemporary homes, and commercial complexes.

• Concrete

  Reinforced concrete rafters are commonly found in demanding construction settings. Concrete offers unbeatable durability and long lifespan. Concrete rafters hold up enormous loads, withstand adverse weather, and resist rot and pests unlike wood. Usually, they are cast in place or pre-made and fitted. They are often heavier and more difficult to install than other types. The concrete roof is ideal for providing unmatched fire protection in heavy-load applications. Frequently used in conjunction with steel reinforcement bars to increase tensile strength, concrete rafters are staples of commercial buildings, parking garages, and homes.

• Fiberglass

  Fiberglass rafters are lightweight and highly resistant to rot, rust, and corrosion. Built from a mixture of glass fibers and resin, these rafters hold their shape exceptionally, flexing without breaking under stress. Although not as strong as wood or steel, fiberglass rafters provide sufficient support for residential structures. They can cut to length easily on-site, simplifying installation. Although typically more expensive than other rafter materials, fiberglass provides an appealing low-maintenance solution ideal for coastal areas prone to extreme weather conditions and designed for long-lasting build.

Commercial use of rafters for roof

Roof rafters are widely used in various construction applications, especially when the desired aesthetic is pronounced.

• Residential rooftops

  Common rafters are widely used in residential roofs. Since they give the roof structure support that holds the weight of roofing materials, snow, and any other elements, they are crucial in roofing. This ensures the entire house is stable and that the roof doesn’t sag or collapse over time.

• Garages

  The couplet purlin rafter design is economical and perfect for garages and storage sheds, which typically have low to moderate roof pitches. By using two rafters per frame and inserting purlins as cross braces, the roof is simple yet strong enough to hold light to moderate snowfall and rain.

• Workshops

  Jack rafters and purlins create level, flat areas ideal for skylights or other design features in workshops. This practical framework supports the roof while functional and attractive to workspaces.

• Outbuildings

  Hip rafters link every side of a pavilion roof, ensuring stability and strength for outbuildings like gazebos or pool houses. This broad shape efficiently handles adverse weather and provides long-lasting shelters.

• Marketplaces

  Rafter construction is often open and allows for flexible layouts and designs that accommodate various vendor stalls while providing a durable shelter from the elements, promoting a lively outdoor market atmosphere.

• Parking garages and carports.

  Avalanche rafters are widely used and designed to drain rainwater or snow melt efficiently, providing reliable weather protection for vehicles in garages and carports.

• Workshops and barns

  The purlin rafter design is often seen in barns and work sheds. Purlins give extra strength and a handy place to attach boards or metal for the roof over barns and workshops.

The construction of rafters for rooftops

Building a rafter framework begins with careful planning and taking important measurements to determine appropriate rafter lengths and angles for adequate roof support.

• Cutting rafters

  After the measurements, wood or other material is obtained and brought to a workshop to be cut into specific rafters. A special cutting machine is used to cut the end of each rafter at the required angle to fit perfectly on the ridge and walls.

• Building the framework

  The remaining framed rafters are placed on the ground and nailed together. A ridge board is used at the top and attached to the rafters, then other pieces nailed between the rafters called rafter ties. This frame is then raised onto the walls of the building.

• Raising the frame

  The team constructs the frame by holding and nailing the rafter ties to the upper wall, ensuring everyone has their own few sets of rafters tied together to make the standing frame strong and sturdy for the roof.

• Installing purlins

  Horizontal cross supports called purlins are now added between the rafters lower ties. These help evenly distribute the roof’s weight to make it stronger and prevent it from sagging under pressure.

• Attaching roofing materials

  Plywood sheets, metal, tiles, or shingles are attached to the purlins on top of the rafters to create the roof. This acts like a cap that protects from rain, heat, and gives the building a nice look.

Q&A

What are the advantages of using purlin rafters over conventional purlin?

Purlin rafters save time and money since they eliminate the need for extra supports by acting as both the rafter and purlin. The roof can be built faster with fewer materials. It also allows wider spaces between columns for open designs. Roof construction is simpler with purlins on rafters that fasten the roof and wall together for stability. They provide roof framing that is cheaper and faster for modern and industrial buildings with attached porches or lofts.

What factors should be considered when selecting a roofing rafter?

The key considerations include the rafter material - whether wood, steel, concrete, or fiberglass - for strength, weight, and compatibility with the structure; the roof pitch or slope angle, as steeper roofs require different rafter lengths and more complex junctions; local weather patterns, including expected snow loads, rain, and wind, to ensure the rafter framework adequately supports any external forces; building codes compliance based on regional construction standards; aesthetic roof design - gabled, hipped, or valley - that determines rafter configuration; and cost and availability based on the project budget and sourcing.

What are the common mistakes to avoid when building a rafter framework?

The typical errors to avoid include failing to calculate the correct rafter length and angle, ignoring local building codes, inconsistent spacing, inadequate support misalignment, neglecting to consider additional load factors like snow or wind, cutting corners on material quality, lack of proper bracing, and not allowing for expansion and contraction.