MATERIALS AND PERFORMANCE
Roof rafters and trusses can look similar, especially when built with dimensional lumber. They may have the same basic shapes, but roof rafters can use a variety of different sizes of lumber. Trusses are generally fabricated by using 2”x4” dimensional lumber.
Roof rafters can use 2”x4” lumber on small projects, but larger roofs often require thicker materials up to 2”x12” boards of various lengths. For open, dramatic ceiling structures, timbers 6”x6” to 12”x12” can be employed. When hand-hewn, they deliver a rustic or Western appearance.
When larger timbers are used, rafters can be spaced further apart than the customary 16” (most common) or 24” that trusses require.
Even though trusses are built using 2”x4” lumber, their web-like design and closer spacing makes them strong and durable.
Rafters, which are built on site, are more versatile and allow for more creativity in roof design. They don’t have to be built with a horizontal member connecting the base of the rafters on each side. This allows for an open ceiling design for aesthetic purposes or to maximize use of the space (see next).
Homes built using trusses usually have flat ceilings or ceilings that are minimally vaulted. The trusses are rarely exposed because they don’t have the pleasing appearance timber rafters possess.
Small projects – those with a roof span of less than 16 feet – are usually fitted with rafters. Larger projects up to 48 feet or so can be framed with either. Very large roofs are usually built with trusses – the largest spanning more than 60 feet.
Rafters and trusses are used for the same primary purpose – to frame and support a home’s roof. The main difference is that rafters don’t require base members and web-like cross members, and this gives you more design options such as spectacular vaulted ceilings with open framing or closed-in attic space.
Standard trusses with a horizontal member at the base of the truss are used in homes with flat ceilings; Scissor trusses employ slightly angled base members for use in low-slope vaulted ceilings. Trusses are also used on big homes or pole buildings.
CONSTRUCTION AND INSTALLATION
Trusses are built in a factory. You need to order your truss package two to six weeks in advance of when they’ll be needed. During the busy building season, advance time might stretch to eight weeks or more.
One key benefit of trusses is their dimensional uniformity. All the measurements, angles and cuts are digitally calculated and made by an automated precision saw.
Installation takes a day or more on most homes. They are either hand-lifted to the roof or raised by a mechanical lift. A team of two or three receives them on the roof, fits them, and nails them to the top-framing of the walls.
There’s no lead time for rafters when the materials to build them are readily available. Roof rafters can take a week or so to construct on a 2,000 square foot home, depending on the construction crew size, the timber dimensions and the roof slope. During this time, the home’s framing is often exposed to the elements, which can result in water and storm damage in severe weather.
When building roof rafters on site, a concern is that the cuts might not be as accurate. Calculating the angles properly is a challenge for even the most experienced builder.
Tip on Terms: Rafter construction is also called stick framing when dimensional lumber (2”x4”’s, etc.) is used, since the rafters are hand-built “one stick at a time.” Knowing the term might help you discuss your construction project with a builder. Of course, trusses are built with “sticks” too, but in a factory setting using automated means, so that term doesn’t “stick” to trusses.
Trusses cost 20% to 50% less than roof rafters. On the low end, you’ll save about 20% to 30% when comparing trusses vs rafters built with 2”x4” dimensional lumber. As the width of lumber used to build rafters goes up to 2”x10” or 2”x12”, the cost rises quickly. The upper end of 50% savings is achieved when comparing 2”x4” truss packages with rafters built from hand-hewn 6”x6” beams or similar high-priced timbers.
What does that mean in real dollars? You’ll find information on rafter truss price per linear foot of truss and also in cost per square foot. Let’s use the second metric – per square foot cost. Per square foot of what? Roof. So, a home with a 1,500 square foot footprint, whether it is a ranch or two-story, has 1,500 square feet of roofing – or a little more if the trusses have one-foot overhangs. A 30 x 50 house with 1-foot eaves on the long side would have 32 x 50 feet of roof coverage, so 1,600 square feet of trusses or rafters.
Truss Price: $4.35 to $5.85 per square foot, or about $6,950 to $9,360 for a truss package covering 1,600 square feet per our example.
Rafter Price: $5.25 to $8.00 per square foot, or approximately $8,400 to $12,600 for the 1,600 square foot roof. Again, the width and thickness of the lumber used, plus higher labor costs for trusses, are the primary reasons for higher costs.
Both truss and roof rafters are very durable, as long as they were not exposed to any adverse weather during the construction process that might lead to damage or rot. When properly constructed, both types of roof framing can be expected to last for a century or more. To achieve maximum durability, the roofing must be maintained in good condition to prevent leaks.
ROOFING TRUSSES VS RAFTERS – THE BOTTOM LINE
About 80% of wood-framed buildings employ trusses due to the pros and cons of each. Trusses are cost-effective, have outstanding load-bearing ratings and are easy to install. Just remember to get them ordered well in advance to prevent construction delays waiting for the truss package to arrive.
Rafters are a better choice for spur-of-the-moment projects like a weekend project building a shed in the backyard. They’re also ideal for buildings with short spans. DIY is a challenge unless you know how to use a roofing square and can make exacting, uniform cuts rafter after rafter.
You’ll also want to consider rafters if you desire open ceiling framing, especially using visually appealing timbers. Rafters are also employed with the area below the roof will be an enclosed attic used for living space or to maximize storage