More than 90% of residential roof trusses are made of wood. Timber trusses are strong, durable, and beautiful. Moreover, wood is energy-efficient, readily available, and more cost-effective than alternative materials like steel.
So, this guide explains what makes good rafter lumber and explores the best wood types for roof rafters.
What Timber is used for wood rafters?
Pine, spruce, and Douglas fir are the most common roof rafter materials. This applies to both on-site and pre-fabricated roof trusses. The three softwoods provide hard, strong, and durable timber. Moreover, all three are resistant to water and weather elements. However, hardwoods like oak are wonderful options for heavy-load applications.
What are Roof Rafters?
Rafters are the vertical roof frame members running from the ridge to the wall plate, downslope perimeter, or roof eave. Traditionally known as stick framing, they are critical framing elements without which the roof comes apart.
Roof rafters work alongside roof joists, purlins, and roof truss members, especially the top and bottom chords, webs, and chords, to form the complete roof frame.
Types of Rafters
The principal rafter and common rafters are the main rafter types. However, the roof may include various other rafter types depending on the shape and type.
- Principal rafters: Principal rafters are the longest rafters on any roof. They run diagonally from the apex of the roof to the wall plate and are solely responsible for supporting the roof purlins.
- Common rafters: The common rafter is a shorter lumber piece that runs between the principal rafter and the bottom chord to define the roof slope. Common rafter sizes increase as you approach the center of the house to define the pitch. More importantly, they are set at right angles to the wall plate and are sometimes called intermediate rafters.
- Auxilliary rafters: Auxilliary rafters strengthen the principal rafter in a truss. However, not all trusses feature auxiliary rafters.
- Valley rafters: A valley rafter is the main supporting structure directly under a roof valley. It’s mainly found in hip roofs and located where two faces of the roof coincide. However, you can also find it where two gable roofs intersect.
- Hip rafter: Hip rafters are exclusive to hip roofs or hip roof variants, such as mansard roofs. They are installed 45 degrees relative to the ridge board, forming a diagonal angle that gives hip roofs their distinctive shape.
- Barge rafters: A barge rafter is an outermost rafter at the gable end that forms the roof overhang. Indeed, the fascia board on the gable end is sometimes called a barge rafter. It extends past the eaves to hide the gutter’s end and doubles as a decorative element.
Advantages of Wooden Rafters
Although steel is a popular alternative, wooden rafters stand out for many reasons. Here are a few reasons you should pick wood rafters over other materials.
- Economical: Wooden rafters are way more economical than metal rafters. First, wood is cheaper than metal. Particularly, softwoods are very cheap. Secondly, wooden rafters are readily available, minimizing transportation costs. Also, they are lightweight. Thus you don’t require heavy machinery to hoist the rafters onto the roof.
- Energy Efficient: Wood offers excellent thermal resistance, providing superior insulation compared to steel. This is critical in metal roofing and other roofs that overheat in sunny weather as it lowers energy bills.
- Eco-Friendly: Wood is a natural carbon sink, the perfect storage for excess carbon. Indeed, 50% of dried lumber comprises carbon safely tucked away from the environment. Unfortunately, you can’t say the same about steel. Moreover, processing wood rafters consumes less energy.
- Sound absorption: Wood absorbs sound instead of reflecting or amplifying it. Therefore, wooden rafters make sense if you wish to reduce indoor noise levels. The acoustic properties also reduce echo in living areas.
- Fire resistance: There’s a common misconception that metal is superior to wood when it comes to fire resistance. This isn’t entirely true. For instance, scientific studies show that steel roof framing collapses faster than wood until you reach the critical burning temperature.
- Flexible and versatile: Wood is a flexible and highly versatile construction material. You can easily connect it to wooden components or roof materials, like glulam (laminated lumber) or steel beams. Moreover, its high strength-to-weight ratio permits long spans for beautiful open spaces.
- Strong and durable: Did you know wood outperforms steel in breaking length? This means wood supports its weight better than steel. Therefore, a steel truss is more likely to crumble under its weight than a wooden truss.
Factors to Consider When Choosing Wooden Rafters
It’s best to let a structural engineer pick your wooden rafters. However, if you must do it yourself, consider the following important factors;
- The local climate: Your climate is critical. For instance, you need heavier, denser woods in areas prone to storms and strong winds. Meanwhile, you can do with lighter woods in fair climates. Severe winter climates also require stronger wood. Otherwise, you need thicker dimensional lumber.
- Endurance/Durability: Endurance or durability is the ability to withstand harsh conditions or abuse without adverse effects. For instance, the best rafter wood can withstand light winds without splitting or cracking.
- Strength and hardness: Strength refers to the wood’s resistance to bending from external forces. Meanwhile, hardness defines the wood’s scratch and dent resistance. The best rafter wood has both. It can bear dead and live loads without cracking or bending.
- Density/Weight: The wood’s weight and density determine the dead load and the wood’s ease of handling. For instance, heavier, denser wood species exert more load on the roof, putting more pressure on the walls and foundation. They are also more challenging to transport or lift onto the roof.
- Shock resistance: Wood’s shock resistance refers to its ability to withstand sudden impact. For instance, you don’t want rafters that crack when nailing down the roof deck or shingles. Similarly, you want rafters that can withstand a few branches falling on the roof.
- Easy to form/process: All roof rafters are cut to size, shaped, and nailed or screwed into place. Therefore, the wood species must be easy to cut and form. So, avoid extra-hard woods that are difficult to nail or screw.
- Not easily deformed: Deformation refers to dimensional changes due to ununiform drying, weather, or other factors. For instance, you should avoid eucalyptus. Although strong and durable, eucalyptus is difficult to dry. It dries unevenly and is susceptible to checking.
- Availability and cost: You need hundreds of feet of rafters for a standard roofing project. So, you want a wood species that you can readily find in bulk. Also, it helps if the species doesn’t cost an arm and a leg. For instance, though strong, durable, and highly weather-resistant, redwood is difficult to find and out of most homeowners’ price range.
What’s the Best Roof Rafter Wood? (With Pros and Cons)
The following are the ten best wood types for roof rafters. We’ve included Glulams and LVL because they are wood products.
1. Best Overall: Douglas Fir
Pros
- High strength-to-weight ratio
- Highly decay resistant
- Readily available
Cons
- It’s pricier than comparable softwoods
- It requires extra weather and moisture protection
Douglas fir, also known as Oregon pine or Colombian pine, is one of the most popular softwoods. Indeed, it has the most applications of any softwood. This is because it’s abundant in Europe, New Zealand, South America, and North America. The color varies from orange to dark red-brown.
Its main attraction is the high weight-to-strength ratio. Douglas fir is exceptionally light yet one of the strongest softwoods. Thus, it makes excellent beams and roof rafters. The low moisture content (15% to 16% when dried) is another big plus. Also, Douglas fir is easy to cut, nail, and screw.
Finally, Douglas fir is chemical-free and highly decay-resistant. This makes it very durable in roofing applications.
2. Southern Yellow Pine
Pros
- It’s extremely hard and strong
- Durable and long-lasting
- Low maintenance
Cons
- Prone to bending in high-traffic
- Sensitive to high-moisture environments
Southern yellow pine is the next best rafter material if you cannot find Douglas fir. Although a softwood, it’s very hard and strong. Also, it’s a low-maintenance lumber that lasts many years without painting or waterproofing. Thus it’s common in both residential and commercial roofing applications.
The main selling point of southern yellow pine is durability. It’s among the most durable softwoods. Southern yellow pine roof rafters can last a lifetime if treated, installed properly, and well-maintained.
Additionally, it’s among the hardest softwood species. An 870 Janka rating makes it harder than mahogany (800 Janka) and very close to cherry (950 Janka). Above all, southern yellow pine is one of the most affordable softwoods in the US.
3. Cypress
Pros
- Naturally pest and insect resistant
- Naturally water and decay-resistant
- It’s very durable
Cons
- Poor workability
- It takes a long time to dry fully
Cypress is a popular building material due to its natural resistance to insects and pests. It’s also naturally resistant to decay, thanks to its natural oils. Thus, cypress roof rafters require very little maintenance. Moreover, a cypress roof structure is extremely durable.
Another big advantage of cypress roofing is availability. Cypress trees grow aplenty in Arizona, California, North America, and Europe. Therefore, it’s readily available and, more importantly, affordable.
The main downside to cypress rafters is workability. Unfortunately, a fully dried cypress is difficult to cut, nail, or screw. So, you often need to pre-drill fastener holes. Besides roof rafters, you can use cypress for roof joists, roof decks, and ceiling joists.
4. Oakwood
Pros
- High dimensional stability
- Exceptional durability
- It’s a natural insulator
Cons
- Oak wood is pricey
Oak is among the most popular building materials today. Its stability is unmatched, forming sturdy beams and roof framing members for maximum structural integrity. Thus, it’s the go-to wood type for heavy roofs, such as slate and tile roofs. It’s also perfect for floor joists or other load-bearing framing members.
We also love oakwood for its durability. Many wood types can last a few decades with good maintenance. However, they are easily tested by mild winds, storms, and ice loads. Meanwhile, an oak roof structure can bear substantial weight for a prolonged period without a hitch.
Finally, oak is a natural insulator. It absorbs heat thanks to millions of minuscule air pores within the grains, making it a great rafter wood for metal roofing.
5. Spruce
Pros
- High strength-to-weight ratio
- Excellent workability
- Affordable and readily available
Cons
- It’s not very durable
Spruce is a coniferous evergreen tree from the pine family. It’s a fairly tall tree, with some species reaching a mind-boggling 300 feet. Meanwhile, the color ranges from reddish brown to yellowish or creamy white.
The main selling point of spruce for construction site applications is its stiffness and strength-to-weight ratio. Spruce lumber doesn’t bend easily. So, you don’t have to worry about a sagging roof, provided you follow standard roofing procedures.
Moreover, its high strength-to-weight ratio results in strong but lightweight roofs that put minimal strain on the walls and foundation.
Finally, spruce is weather and rot-resistant. Its natural oils also help to repel pests and insects.
6. Larch Wood
Pros
- Waterproof and rot-resistant
- It dries easily and doesn’t shrink
- It’s pest and insect-resistant
Cons
- Allergies and toxicity
- It has a distinct resinous odor
Larch wood, especially the western larch, is another wonderful choice when constructing a wooden roof structure. Like spruce, it’s a conifer from the pine family. But it’s slightly more resistant to rot, thus an even better fit for exterior applications.
However, water resistance is the main property that makes larch wood perfect for roof rafter construction. The high density and oily surface make it essentially moisture-proof.
Therefore, a larch wood rafter can withstand long periods of high moisture exposure without signs of damage. It can also withstand roof leaks and snow damage for extended periods.
These qualities make larch an exceptional choice for principal rafters and the roof deck. Above all, it’s highly workable and doesn’t cost an arm.
7. Hemlock
Pros
- Knot-free hemlock is very strong
- Highly resistant to warping
- Ages gracefully
Cons
- Prone to splintering
- Requires pre-drilling to avoid splitting
Hemlock is a popular construction wood for many reasons. First, it’s very strong. A few species have lots of knots, making them ill-suited for construction projects.
However, smooth-grained hemlock is almost as strong as Douglas fir or southern yellow pine. The high strength makes it resistant to wear and tear. Thus it’s a good choice for heavy-load roofs.
Additionally, hemlock is highly resistant to warping. This explains why it’s the material of choice for trims and moldings. It doesn’t shift in extreme temperatures (cold or hot), maintaining its size and shape throughout.
Finally, hemlock weathers to a beautiful color, making it a great choice for exposed ceilings. The eastern hemlock, for instance, ages to a gorgeous brown-red color. This separates it from other roofing woods, such as spruce, that ages to a dull grey color.
8. Western Red Cedar
Pros
- It’s strong but lightweight
- Resists swelling, warping, and twisting
- Excellent thermal and insulation properties
Cons
- It’s a high-maintenance wood type
Cedar is a very common softwood and a popular building material. It’s used for cladding, cabinetry, ceiling, paneling, and decking. Most importantly, cedar shakes are premium roofing materials.
We recommend the western red cedar for roof rafters. Its low density makes it lightweight, thus easy to transport and lift to the roof. Moreover, it maintains its density surprisingly well while resisting shrinking, warping, swelling, cupping, and twisting, among others.
We also love the western red cedar because it’s highly resistant to decay. So, although it’s not the most waterproof wood type, moisture exposure doesn’t easily damage it.
A low flame-spread rating and the ability to dampen vibrations are other attractive qualities of a cedar roof rafter.
9. Reclaimed Timber
Pros
- Highly eco-friendly
- Very durable
- It gives you endless options
Cons
- Cost up to 50% more than new timber
Reclaimed wood, also known as antique wood, refers to upcycled wood obtained from old structures. The wood is cleaned, and the nails are removed. Then it’s dried, milled, and finished before selling to contractors and construction companies.
Therefore, reclaimed wood is a great option if you wish to go green. It’s good for the economy and better for the environment. The only challenge is potential toxicity.
Fortunately, this isn’t a major concern for roofing projects. However, feel free to speak with your structural engineer about it if you’re worried about your safety.
Again, it’s best to go with traditional rafter timber, like Douglas fir, pine, and cypress. Surprisingly, reclaimed wood rafters cost up to 50% more than freshly cut timber.
10. Glulams and LVL
Pros
- Environmentally sustainable
- Excellent strength-to-weight ratio
- Durable and fire-resistant
Cons
- Difficult to repair
- Not very easy to find
Glued Laminated Timber (glulams) and Laminated Veneer Lumber (LVL) are newer alternatives to natural timber. Both are engineered wood products comprising layers of wood glued together using strong adhesives. But they’re slightly different.
Glulam boards comprise sheets from the same log. Also, the layers are arranged, so the grains run in the same direction. This gives glulam boards exceptional strength.
On the other hand, LVL comprises boards from different logs, especially hardwoods. In addition, the boards are arranged with the grains facing opposite directions for maximum stiffness.
So, they offer different qualities but are both great choices for roof rafters. Glulam boards are stronger than steel. So, it’s best for larger roofs, high-load applications, and industrial settings. Meanwhile, LVL is perfect for standard building projects.
Rafter Wood Size
Rafter wood comes in many sizes. The most common dimensions are 2×6, 2×8, and 2×10 rafters. However, 2×4, 2×12, and 2×14 rafters are available if you need them.
Your structural engineer will help you determine the best rafter size based on location, roof type, and load variable. The correct size also depends on the intended rafter sizing and type of decking.
Rafter Wood FAQs
Is oak a good choice for roof trusses?
Yes, oak is a good choice for roof trusses and rafters. Its natural strength and hardness are valuable qualities that guarantee resistance against strong winds and other roof loads. Additionally, oak is low-maintenance and a highly renewable domestic wood. However, beware that oak is expensive and difficult to work with.
What are most rafters made of?
Most rafters are made of Douglas Fir, pine, or cedar. Southern yellow pine is the go-to material as it’s strong but highly workable. Moreover, it’s water resistant and doesn’t crack or warp due to weather. However, Laminated Veneer Lumber (LVL) is an increasingly popular choice for longer rafter spans.
What are the 3 types of rafters?
The principal rafter, common rafters, and auxiliary rafters are the three main types of roof rafters. However, several other rafter types exist, depending on the roof type. These include hip rafters, hip jacks, valley rafters, and barge rafters. Note that a roof can be complete without some of these rafters.
Do I need 2×4 or 2×6 rafters?
Roofers use 2×4 and 2×6 rafters interchangeably. But generally, it depends on rafter spacing and span size. For example, 2×4 rafters are best suited to shorter spans of up to 8.0 feet. Meanwhile, 2×6 rafters are ideal for 10-12-foot spans. Also, 2×4 rafters are best for closely spaced rafters, whereas you can space 2×6 rafters more widely.
What is the best wood to use for beams?
Douglas fir is the preferred roof beam material among professional roofers in the US. However, walnut, alder, poplar, oak, and mahogany beams are also common. Meanwhile, pine and spruce are Europe’s most common roof beam materials. The best choice often depends on strength/hardness, availability, workability (ease of cutting and nailing), and personal preferences.
Summary
Douglas fir and southern yellow pine are the best rafter woods. They are lightweight but strong, putting minimal strain on the walls and foundation while standing up against dead and live loads.
However, cypress and oak are other excellent choices. Alternatively, consider reclaimed wood or engineered rafter boards, such as glulam or LVL.