Rafters Vs. Trusses: What Are The Major Differences?
Installing a roof is not as simple as assembling a pyramid of boards and dropping it on your house frame. There are things to consider as far as time constraints, cost, and aesthetics when drafting plans for a new build. Unless you’re using a single layer flat roof, two construction frame options are available to you: rafters or trusses.
Rafters and trusses differ primarily in their method of assembly: trusses are often preassembled, and rafters are typically created on-site. Each building method has its merits and drawbacks and determines ceiling height as well as structural stability. Choosing which method is best for your project will depend on several variables that line up with your vision.
Rafters and trusses have many similar components, and both help transfer the roof load to the outside walls. Pros typically fashion rafters from seasoned pine, red cedar, or yellow pine for optimal strength and durability. Recent developments in materials and structural framing have steel as a viable alternative to using wood.
What Is a Rafter?
Rafters are likely the oldest and most traditional method used for roof framing. A rafter is a part of the internal roof framework of a house or building. Each rafter reaches from the eaves of the framework to the peak of the roof.
It’s the presence of rafters that gives the roof its slope and supports the sheathing, membrane, and shingles. Builders lay rafters side by side at set distances to distribute the roof’s weight through the building walls evenly. You can conceal rafters to enclose the living space or leave them open as their own design element.
Workers build rafters on-site from the selected building materials, usually long wood planks that connect to the main framing. These planks form beams that run on an angle from the roof’s peak to the joists in the outside walls. When constructed, it ties to the base to make one interconnected structure.
What Is a Truss?
A truss is similar to a rafter, as it is an assembly of beams that form a solid support construction. Workers can build a truss structure for a roof in the same way they build a rafter. The difference is that a truss is assembled as a single unit, then placed and attached to the base foundation.
Trusses come in many varieties and slopes–a truss can even be built for a flat roof. The truss framework is a series of interconnected materials that offer stronger support than a single flat layer. Professional take measurements on-site so they can put together the truss elsewhere before bringing it in for installation.
As trusses are typically built in a factory under ideal conditions, it lends itself to automated processes and precision cuts. Regular, more abundant 2x4s replace the wider, longer boards that rafters require. You’ll need more materials to compensate, but your overall materials cost will be significantly lower.
When Would I Use a Rafter or a Truss?
While rafters and trusses perform the same basic functions, they are not necessarily interchangeable. Conditions surrounding building type and function can greatly influence which option is more suitable. Builders choose between rafters and trusses based on location and project requirements.
Since trusses are pre-built structures hauled to the job site, they have a fixed design. Because these builds don’t require custom assembly, they are very budget-friendly. However, you need to figure out the logistics of how to move the truss site for installation.
Rafters tend to be the best choice for specialty projects. They allow for more custom features within the building design, such as vaulted ceilings and attic storage. There’s little difficulty transporting materials, a task that’s much more manageable than moving a prebuilt unit.
Pros of Using Rafters
Rafters are pretty versatile structures, and you can use them just about anywhere. They work just as well for small projects as they do for big, dramatic design elements. There are a lot of advantages to using rafters in your roof design.
Rafters Have Zero Lead Time
The contractors assembling the house form rafters on-site. Since the materials are not previously assembled, construction can begin as soon as the materials are on site. Meanwhile, workers build trusses off-site, which can take time, and waiting for the finished product may cause delays.
Rafters Are Ideal for Small and Specialized Projects
Rafters are a great choice for small and specialized construction projects. Building these roof supports allows contractors to be flexible with their dimensions, like high vaulted ceilings and built-in attic storage. Any adjustments upward or downward in scale are easy to do on the fly.
Cons of Using Rafters
There are some drawbacks to using rafters that you should keep in mind when choosing your support method.
Rafters Take Longer to Complete
Constructing rafters is a “build as you go” project; you measure, cut, and install the lumber piece by piece. The individualized nature of building rafters means that the building process will take longer to complete.
Rafters Require Professional Skills
Rafter builds may appear to be a simple process, but it’s not something you want to do yourself without expertise. Because the process requires extensive carpentry skills, you will need trained labor–which will add to your overall costs.
Rafters Have Higher Overall Costs
All of the above disadvantages can greatly increase the projected cost of the project. Since a successful build requires specialized labor, those are labor costs you can’t avoid. Inclement weather can interrupt an already slow construction project, generating even more overtime and racking up higher labor costs.
Pros of Using Trusses
Trusses will work on most building projects as long as you settle all the details regarding logistics and code specifications. They are most ideal for a larger roof span since there are more support connections spread throughout the structure. Using trusses has its own set of positives to keep in mind.
Trusses Save Time and Reduce Error
Trusses have excellent accuracy, strength, and span due to being pre-built to the contractor’s measurements. The truss factories employ automated production processes, greatly increasing precision cutting and assembling materials. With the truss completely fashioned off-site, it saves time on installation and even lends itself to do-it-yourselfers.
Using Trusses Means Less Exposure to the Elements
The prefabricated truss also considers environmental variables–shorter installation times means less likelihood of building in inclement weather. It also reduces the time and possibility of extended exposure to weather conditions that could warp or damage the framework.
Trusses Have Lower Overall Costs
The most important plus for trusses is that it’s the least expensive option to build. The upfront, out-of-pocket cost of building the truss can be larger than securing rafter materials. However, labor costs are lower with fewer hands and man-hours involved in both the pre-built and on-site installations.
The Cons of Using Trusses
When it comes to construction, everything has upsides and downsides. Trusses are no exception and have a few negatives worth noting.
Trusses Equal a Fixed Design
Unfortunately, trusses come with their own set of complications. Their prefab nature means planning the specifications in advance to begin the manufacturing process. Therefore, trusses lock you into your design and space allowances; design changes mean starting a whole new build.
Trusses Have Weight, Size, and Transport Complications
Once built, the truss is a sizable piece to lift and transfer from the factory to the job site. The truss weight and size directly affect how you lift it and how–and whether–you transport it to the job site. Something a few workmen might typically do will now require the use of a crane and an 18-wheeler flatbed.
Another consideration with truss size and transport is whether or not the road is accessible for that transport. A flatbed truck will find it difficult or impossible to move a truss down a narrow or steep road. A truss unable to navigate an area without causing significant damage proves impractical and impossible.
Can I create attic storage on a truss support?
Ideally, a truss has a series of webs built in to support the roof and connect it to the dwelling structure. These webs often take up the open space for attics that rafters can provide, making ease of movement difficult. However, creating usable seasonal attic storage is achievable depending on the style of truss you use.
How do I insulate my attic space?
Once you’ve gotten your roof in place, it’s a good idea to help protect it from the elements. There are several materials available to insulate the interior from excessive heat and cold and conserve utilities. You can install insulation along the attic floor and use foam core and sheathing for exposed beam ceilings.
What We Have Learned?
Both rafters and trusses support the weight of the roof securely. Trusses have a more spread out network of structural webbing that gives them greater stability. Conversely, rafters offer stability as well as versatile functionality in the living spaces.
Mathematically, trusses tend to be the most economical choice in the long run under ideal conditions. As a homeowner, you need to decide if you will fare better with form or function as your central goal. Closely examine when and where you can spend, then ensure you’ll be able to get what you pay for.
Stacy Randall is a wife, mother, and freelance writer from NOLA that has always had a love for DIY projects, home organization, and making spaces beautiful. Together with her husband, she has been spending the last several years lovingly renovating her grandparent's former home, making it their own and learning a lot about life along the way.
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