Building a house, cabin, shed or garage is a rewarding experience. You get to determine the floor plan, building materials, finishes, and roof structure. When selecting the roof framework, though, which is better, trusses or rafters.
Rafters and trusses serve similar purposes. They form the roof structure and slope of the roof deck. Trusses are engineered and manufactured off-site to exacting standards and are quick and easy to install as they are freestanding. Rafters are one component of a stick-framed roof structure and are individually measured, cut, and installed, and require other components for support.
In this article, we’ll explain what roof trusses and rafters are, identify their similarities and differences, and explore different types of trusses. We’ll discuss the pros and cons of trusses and rafters, compare trusses to joists and beams, and rafters to joists, and then identify which is better, rafters or trusses. Hopefully, you’ll develop a better understanding of roof frameworks available, and which is best suited for your project.
Contents (Jump to Topic)
- What Is a Roof Truss?
- What Is a Rafter in Construction?
- Trusses vs Rafters: Key Points
- What Is the Difference Between Trusses and Rafters?
- Types of Trusses
- Truss Pros and Cons
- Rafter Pros and Cons
- Truss vs Joist
- Joist vs Rafter
- Trusses vs Beams
- Which Is Better Rafters or Trusses?
What Is a Roof Truss?
Roof trusses are engineered roof frameworks that provide aesthetic and structural shape to a roof. They are pre-ordered, manufactured offsite, and delivered to the building site. Roof trusses typically are stand-alone frameworks composed of horizontal, diagonal, and vertical struts that form triangular shapes made of wood with steel plates fastening components together.
Roof trusses are constructed to span specified distances at a set spacing to sustain calculated loads. Trusses are usually fastened to each other at specified points and rest upon the wall structure so the load is transferred vertically or in a downward, not outward direction. The end roof trusses typically are designed to be both a truss and to form the gable end wall.
What Is a Rafter in Construction?
Rafters are the traditional stick framing method used for roofing buildings, they run from the ridge or hip to the supporting exterior wall. A rafter is the angled component of a roof’s structural framework that sets the slope of the roof deck and is manufactured onsite and in place. Rafters are measured and cut individually and installed one at a time, so they are more labor-intensive.
A rafter can’t stand alone and requires other components, like a ridge board or beam, oppositional rafters, purlins, purlin props and cleats, struts, collar ties, ceiling joists, etc. to share and spread the load down and outward to the support walls. Rafters also provide support to gable end walls, and may be partially carried by a ridge beam supported at each gable end, and also elsewhere along the beam.
Trusses vs Rafters: Key Points
Trusses and rafters are similar in that they form the slope and support the roof deck of a roof structure. However, there are numerous differences between the two as shown in the table below.
|Design||Designed and engineered to span greater distances using triangular-shaped webbing. The top chords set the slope.||The slope and span determine the rafter thickness and depth. The span also determines additional support requirements.|
|Aesthetics||Simple rooflines.||Greater design freedom for more complex roof lines|
|Materials||Manufactured using 2x3, 2x4, and 2x6 dimensional lumber fastened with metal gussets.||2x6 to 2x12 lumber or larger 4”, 6”, 8”, or wider timbers of greater depths.|
|Complexity||Each truss is comprised of one or two sloping top and bottom chords, plus internal geometric bracing of diagonals and or verticals. Strapping is used to brace, space, and level trusses to form the roof.||A rafter roof requires two opposing birdsmouth notched and plumb cut rafters with a collar tie and a ceiling joist spaced accordingly along a ridge board or beam, plus purlins, props, cleats, and struts spaced as required.|
|Support||Enhanced support for the roof structure.||Rafters provide low levels of support to the roof structure.|
|Load||Support greater loads over longer distances. The loads are transmitted horizontally outward and then downward to both exterior bearing walls and the foundation.||Load and span depend on rafter dimensions – larger cross-sectional dimension timbers support more over longer distances. Loads are often shared between gable end walls, intermediate support posts or walls, and exterior support walls.|
|Installation||Fast and easy. Manufactured off-site and delivered to the building site. May require a crane or boom/lift truck to place on walls. Finished roof system installed in a day or less.||Labor and time-intensive. Each component is individually measured, cut, and installed. Can take several weeks or more to complete.|
|Expertise||Low expertise required to install.||Accuracy of measurement, cuts, and installation requires higher skills.|
|Best Uses||Medium to larger roof spans and those seeking simple or classic roof lines, or coffered, sloped, or cathedral ceilings. Offer larger internal rooms or spaces too.||Sheds, cabins, garages, and small to medium-sized homes, or those seeking greater attic storage. Ideal for more complex roof deck designs too.|
|Cost||More expensive to purchase, but 25% to 40% cheaper overall as a roof structure due to faster and easier installation.||Labor and time factor to make a rafter roof structure 25% to 40% more expensive than a truss roof structure.|
|Quality||Computer-generated accuracy of measurements and cuts. High quality-control.||Quality depends on the accuracy and care of those doing the work onsite.|
|Spacing||12”, 16”, 19.2”, and 24”||12”, 16”, 19.2”, 24”, 32”, 36” and 48”|
|Ease of Modification||The structural integrity of the truss makes modification difficult.||Easy to remove one or more rafters without compromising the integrity of the roof structure.|
What Is the Difference Between Trusses and Rafters?
Roof trusses and rafters have a similar purpose, they generate the slope and structural base for the roof deck. Today, roof trusses are more commonly used in roof construction, but rafters are still the preferred method for creating roofs with multiple or complex rooflines. It is their differences, however, that is important when determining which is best for a build.
Trusses are designed and engineered triangular webbed roof structures that are built off-site to ridged specifications. They are designed to stand alone and to move roof loads to the exterior support walls in a downward direction.
Trusses can be designed to provide interior storage or attic space, but usually have a uniform or simple roofline. Trusses are designed using chords (similar to a rafter), beams, and ties to form geometric triangular shapes that distribute the load and form the roof shape and structure.
Rafters are built on-site and typically comprised of two diagonal outer beams resting on a horizontal central beam or against each other and two opposing exterior support walls. The roof forces are outward and downward, so the two diagonals require additional members or bracing to prevent the roof from collapsing or pushing the exterior support walls outward.
Rafters often provide open space underneath for storage or additional living area and may be punctuated with dormer window openings to provide light and more headroom.
Trusses are typically manufactured using 2×3, 2×4, or 2×6 lumber and barbed metal plates or gussets. Rafters are one component of a roof structure and can be 2×6 or deeper depending on the distance spanned. Rafters and their supports may be nailed, bolted, pegged, or screwed together, and may be 4”, 6”, 8” or wider timbers from 6” to 16” or deeper. Metal plates are often used when bolting the components together.
A truss is composed of 3 main parts, a top chord that angles upward from both ends of a bottom chord that spans the distance between support walls. The triangular-shaped top chord and horizontal bottom chord are joined at strategic spots using diagonal or vertical boards or runners that form a web of triangles that brace and support the framework, making them stronger.
Joints are reinforced using barbed metal plates. Being made off-site, they arrive fully assembled and ready to install.
Rafters are one component of a roof system. They can’t stand alone and require other bracing members to spread the load and to prevent wall spreading and collapse.
To span distances, rafters need to be of greater dimensional lumber, require notching to create a birdsmouth at the support wall, and bracing with purlins, props, cleats, struts, and collar ties, plus the ceiling joist to carry the load. Although rafters are cut and used to make a roof structure on-site, it is more involved and complex to install.
Trusses can span greater distances than rafters and support greater loads. Trusses use a geometric triangle design of interconnecting top and bottom chords and internal triangular web structure that provide a durable, solid, stable roof structure. The load is shared and spread or transmitted to both exterior bearing walls.
Trusses offer greater strength and load-bearing while using smaller dimensional lumber. They require fewer or no interior support walls, allowing for larger more fluid interior design options.
Rafters form the slope of the roof and require more structural support the longer their span. A rafter may share the load along a central ridge beam and intermediate support beams that transmit some of the load to gable end walls.
If a ridge board is utilized instead of a beam, the rafters share the load with opposing rafters, transferring the loads to exterior support walls down to the foundation. Rafter loads are both outward and downward, so more internal wall or post support is required for longer spans.
Roof trusses are manufactured off-site in a quality-controlled factory to engineered specifications and delivered to the building site. Typically, their delivery coincides with the time the walls are up and the structure ready to roof. The size and weight of each truss, the build timeline, and access to machinery affect the installation.
Trusses are often delivered bundled together and lifted or hoisted into place using a small crane or zoom-boom type forklift. Individual trusses can also be lifted and slid into place by hand. Each truss spans, usually without intermediate supports, from one exterior support wall to the opposing one. Use of roof trusses is much faster than rafter construction and can be completed in a workday or less.
Rafter construction involves the installation of a ridge beam or board, gable end walls, and or internal supports. Each rafter is individually placed and only spans from wall to ridge. Additionally, each rafter has to be angle cut at each end and a birdsmouth notch cut where it rests on the support wall. Plus, purlins, props, cleats, struts, collar ties, and even ceiling joists must be cut and installed to support the rafter structure. Since the rafter structure is labor-intensive, it often takes longer to fashion the roof framework.
Trusses are commonly made of readily available 2×3 to 2×6 lumber and are manufactured in a controlled setting to engineered specifications. Their purchase price includes labor and material costs, time to build, and delivery; and if the timing is right, placement on top of the structure’s walls.
The type of truss and any special features will affect the costs too. If the trusses are delivered and not placed on the structure’s walls, then a boom truck, zoom-boom lift, or crane will need to be hired to place the trusses, unless the construction crew carries and place them manually.
Depending on the roof design, rafters are only one component of a roof structure. The roof may be a single slope shed, lean-to, or Skillion type that requires only single member rafters. More complex hip, gable, mansard, or gambrel and any other roof types require more structural members. A narrow roof for small structures requires smaller dimensional lumber similar to that used in truss construction, while larger spans require larger lumber.
To span greater distances and support heavier loads, the lumber needs to be deeper and often wider or thicker. Roof design complexity and lumber size affect the roof cost. Additionally, rafter roofs are very labor-intensive, which is reflected in the finished roof structure more so than in the material costs.
Typically, trusses will range from $50 to $500 each, or $3 to $12 a square foot. On average, an installed roof truss system ranges from $5,000 to $18,000 for a 1,500 ft² to 2,000 ft² roof deck. A similar-sized roof structure using rafters usually ranges from $5 to $16 a square foot, or $7,500 to $24,000. So, a finished rafter roof structure or frame will cost between 25% and 40% more than a similar installed roof truss system due to labor and time factors.
Types of Trusses
Engineered roof trusses have become common in residential construction due to their ease, convenience, speed of installation, spanning and load potential, overall cost savings, and design opportunities. Truss designs can be simple, complex, or combinations of designs unique to a build. Incorporating different truss designs can produce a variety of ceiling heights, storage spaces, and roof deck slopes.
The basic types of roof trusses are Gable, Mono, Hip, Attic, Scissor, Gambrel, Flat, Parallel Chord, Cambered, Polynesian, Bow, and Barrel or Quadrangular trusses, plus numerous styles or combinations within each type.
Trusses are commonly manufactured off-site today, although the first two in the list below were originally and are still crafted on-site. Although there are over 100 types of truss styles or combinations, here are 17 of the most common roof truss designs:
King-Post trusses are a simple design and one of the oldest gable roof structures. They consist of two top rafters or cords, a bottom chord or ceiling joist, a central vertical post known as the king post, and two diagonal web chords that brace the rafter chords against the king post.
Often fabricated on-site in the past using large squared timbers to span greater distances, today they provide the open beam look for aesthetics as well as structural integrity. Typically used to span distances of 16 to 26-feet.
Queen-Post trusses are another simple gable roof design from the past. Comprising of two rafter chords, a bottom or ceiling joist chord, a horizontal straining beam or collar tie, and two vertical queen posts; one at each end of the straining beam. The queen posts support and transfer the roof loads to the bottom chord and support walls. They also provide a larger usable attic space and can span 26 and 40-feet.
Fink Trusses are among the most common gable trusses and have two top chords and a bottom chord separated and supported by a web of triangle-forming cross pieces. The Simple Fink truss, the ‘W’ Fink or Common Fink, and the Double Fink are some variations of the Fink Truss. The Simple and ‘W’ provide greater spaces between the webs for storage and access. These trusses span to 46-feet and are inexpensive to build and provide a simple roofline.
Howe Trusses are also common to form gable roofs. They have two top chords and a bottom chord with webbing that looks like a blend of vertical king and queen posts with diagonal members forming ‘M’s or ‘N’s to connect and spread the loads. Howe Trusses, including the Double Howe trusses, are gable trusses and span distances between 18 and 100-feet.
Pratt Trusses have an interconnecting web of vertical posts and diagonal braces resembling a continuous ‘N’ webbing pattern between a single- or two-piece top chord and a single bottom chord. These trusses are heavier and may be flat-topped or gable shaped and typically span between 18 and 32-feet.
Fan Trusses have a simple construction of vertical posts with diagonal web members between the top and bottom chords. The diagonal web members connect at the bottoms of the posts to form an advanced purlin support system. Fan trusses are often used for gable roofs and usually span from 30 to 45-feet.
Mono Trusses create a single sloped lean-to or Skillion style roof deck and are used for porches, sheds, garages, homes, and warehouses or factories. Comprising of one top chord or rafter, a bottom chord or ceiling joist, and a supportive webbing of vertical and or diagonal chords connecting the top and bottom chords. Their span determines the number of internal web triangles to support and transfer the roof loads.
Slope and distance or span affect the height or space of the open-end between the top and bottom chord. They are also available as Mono Scissor, Dual Ridge Mono, Dropped Mono Gable, Mono Cap, and Inverted. They can typically span from 4 to 40-feet but can span up to 80-feet.
Hip Trusses shed precipitation and wind forces in four directions and offer a low-profile look roof that is highly stable. Hip trusses may be dual-slope, half, hipped, and flat-top. They are commonly built today using a mix of gable and mono trusses and typically are used to span shorter distances of 40-feet or less.
Attic Trusses are similar to queen-post trusses but provide greater space between the vertical posts and have webbing support between the straining beam and queen-posts, and the top chords. They can span up to 80-feet.
Scissor Trusses are more costly but allow for a vaulted ceiling with a lesser slope than the roof deck. Made up of two top and two bottom chords, they commonly have vertical and diagonal webbing members to transfer the loads. Scissor trusses can span between 18 and 75-feet.
Gambrel or Barn Trusses are used for sheds, outbuildings, and residential roofs as they provide greater interior attic, storage, or living space. Gambrel trusses provide greater vertical space the wider the roof span is. Spans commonly range from 8-feet on sheds up to 40 plus feel for barns and homes.
Flat Trusses are similar to floor trusses with a single top and bottom chord, and a web of diagonal braces that form a zig-zagging ‘W’ pattern of triangular support.
Made of wood for most residential applications, they are usually made of steel to span larger commercial and manufacturing structures. Since they don’t have any slope to shed precipitation, they often require additional supports along their span. Flat roof trusses of wood commonly span to 40-feet, while steel can span significantly further.
Parallel Chord or Girder Trusses have two top and two bottom chords running parallel to form a cathedral ceiling parallel to the roof deck but separated and supported by vertical posts and horizontal beams that form a step-style webbing. They are very strong and durable and can span distance up to 100-feet or more.
Cambered Trusses create a low slope roof with two top chords and a cambered bottom chord. The camber or slight curvature in the bottom chord allows for calculated deflection based on loads. The webbing between the top and bottom chords has vertical posts and diagonal braces from top to bottom to spread the load forces. Often used for arenas and warehouses, they can span 100-feet or more depending on materials used in their manufacture.
Polynesian Trusses have an integrated dual slope and often look like a witch’s hat. They initially were designed to shed heavy rainfall quickly away from a building’s structural supports or foundation. They typically have a horizontal bottom cord and two top chords at a low slope merging with two other top chords at a greater slope.
The internal support webbing consists of vertical posts and diagonal braces forming an ‘N’ pattern. A flat-top modification is a common choice by many restaurants. The trusses typically span between 40 and 80-feet.
Bow or Bowstring Trusses have a horizontal bottom chord and a curved or rounded top chord. The web pattern typically is sawtooth-like with a central vertical king-post. Often used for arenas and industrial buildings, they can span 100-feet or more.
Barrel or Quadrangular Trusses have compression vertical and tension diagonal webbing between a sloped top chord and a ‘curved’ bottom chord. They are often used for arenas, auditoriums, bus stations, and railway structures, and can span more than 100-feet.
Truss Pros and Cons
Trusses, whether premade engineered or DIY, offer a great many roofing options. Premade saves all the measurement, angle cuts, calculations, time, and ladder climbing. They arrive ready to install.
Making your own trusses is more labor and time-intensive, but by doing all the cutting ahead of time, laying out, measuring, and fastening with plywood or metal gussets on a flat surface at or near ground level, a lot of ladder time is avoided. Check out the pros and cons of roof trusses.
Pros of Roof Trusses
- Designed and engineered for the task
- High-quality construction
- Digitally measured and cut pieces for consistent and accurate fabrication
- Greater strength and longer spanned distances
- Numerous roof deck slopes and options
- Larger interior spaces
- Wide choice of ceiling configurations from flat, scissor, cathedral, coffer, bow, or barrel, or combinations
- Quick and easy to install, usually in a day or less
- Easy to insulate
- 25% to 40% savings on overall roof construction
Cons of Roof Trusses
- The larger they are, the heavier and more cumbersome
- May need to rent a semi to deliver and a crane or boom truck to lift, adding to the expense
- Good building site access required
- Ceiling slopes and design limitations
Rafter Pros and Cons
Rafters are one component of a roof structure and must be individually measured, cut, and placed, so they are very labor-intensive. They are referred to as stick framing and are usually manufactured on the job site. The rafter performs a similar role to the top chord of a truss.
Smaller rafter spans require fewer supports than broader spans to prevent the rafters from sinking inward and spreading the support walls until they collapse. In place of webbing, a rafter roof relies on two rafters, a ridge board or beam and collar ties for small spans and king or queen posts, purlins, purlin props and cleats, struts, and ceiling joists for larger spans. Rafters carry and spread the load down and outward to the support walls or posts.
- Built on-site
- No hassle ordering or lead time to wait
- Greater potential for usable attic space
- Vaulted ceilings are easy
- Easier to customize
- Aesthetically more pleasing exposed roof structure
- More creative roofline options
- Can be built anywhere with basic tools
- Ideal for sheds, additions, cabins, or residences
- Possible for one person to craft and erect
- Time and labor-intensive to build
- Materials plus labor make it more costly than trusses
- Slower build time can lead to other issues due to weather damage
- More up and down ladder or scaffold work
- Complex angles and cuts require a high level of accuracy
- Less practical for long spans
Truss vs Joist
When referring to a truss, most interpret them as roof trusses. An engineered premade roof truss is designed to span greater distances and support heavier loads than a typical rafter roof structure. Roof trusses commonly have one or two top chords and one or two bottom chords, with a webbing of diagonal braces and or vertical posts that form load-sharing triangles.
A joist typically is used to support a floor or form a ceiling and is usually solid lumber or laminated veneer lumber (LVL). Joist may also be floor-trusses, but have only one top and bottom rail or chord and either an open web of diagonal dimensional lumber forming triangles in between or solid plywood or OSB. A floor truss will span further than dimensional lumber, allowing for larger open spaces underneath, and greater cost savings in time and materials.
Joist vs Rafter
Dimensional lumber or timber joists are horizontal members that form a floor above or ceiling below. They run perpendicularly from support wall to support wall or beam. The depth of the joist and spacing from other joists determines the span it can bridge between support points.
Rafters are diagonal roof members of dimensional lumber that span from the outside support wall to the ridge or apex of the structure. They form and support the ceiling on one side and the roof deck on the other. Rafters typically meet at a ridge board or beam and require a collar tie or ceiling joist to prevent them from spreading under load.
Trusses vs Beams
Trusses may be horizontal components spanning from support wall to support wall or beam to form floor and ceiling areas, or diagonal roof trusses that form the roof deck and ceiling. They commonly have two bearing points and support axial (compression and tension) loads. Depending on the span, they may or may not require intermediate support of a beam.
A beam is a frame member and carries transverse loads. They have a larger cross-sectional dimension than a truss and provide frame support to different structural components, including trusses. Beams usually have two or more support points and support shear, bending, axial, torsion, and moment stresses.
Which Is Better Rafters or Trusses?
I have used rafters, engineered roof trusses, and made my own trusses. Rafters are ideal for small or medium-sized builds but require more compound or complex cuts. They are easier to replace if something happens – like a tree falling through the roof – or if adding a dormer or an addition; you just remove the necessary components. Rafters are also cheaper if labor isn’t factored in.
Trusses are much more convenient and faster than rafters when constructing a roof. They are premade to exacting standards, and only have to be placed, leveled, fastened, and braced. I watched a crew with a crane install a roof truss system on a 2,000 ft² home in 4 hours, and have half of it sheathed before their day was done. That was faster than measuring, cutting, and installing a rafter roof or DIY truss system on an 8’x12’ shed!
Making and installing rafters is often easy for one or two people, and can be done anywhere with simple tools. However, it is also possible for one person to install a roof truss system on a 24’x36’ garage or home by themselves without the aid of a lift or crane. Speed of closing in a framed structure from the weather is usually faster with trusses than rafters too.
As for aesthetics, a cathedral ceiling can be crafted using either rafters or trusses. Exposed timber beams also add effect and can be achieved with either rafter or trust construction. Additionally, livable attic space can be created using both rafters and trusses. Exterior roof lines with trusses often are less elaborate and have fewer valleys or ridges, which, from a maintenance perspective is often better.
Time and roof span are defining factors in which method is best. For larger builds, roof trusses offer longer spans and faster builds. For small or isolated structures, rafters are an excellent choice. In the long run of a build, trusses are less expensive. From a maintenance perspective, it’s easier to replace a damaged rafter, but trusses spread the load better and are arguably more durable. As to which is best, I leave it to you to decide.