Roof Trusses: Types, Span, Cost, and When to Choose Truss vs Rafter

Roof trusses are prefabricated triangular wood framing assemblies that span the entire width of a home with no internal load-bearing walls required. Because they are built in a plant and set as finished units, trusses usually go up faster than stick-built rafters and can clear-span a typical house without interior bearing walls; whether they also cost less depends on the span, the design and current lumber prices, so price both options on the same plans. Here is the breakdown of truss types, span limits, costs, and the decision framework for truss vs rafter construction across new builds and additions. Related: Roof truss cost and types.

By The Roofing Brief Team. Last reviewed: October 2026.

The Short Answer: Why Trusses Dominate New Construction

Roof trusses are the common framing method for new single-family homes in the United States. Three factors drive that: material efficiency (the web-and-chord geometry lets small 2×4 and 2×6 members carry loads that would need larger rafters), install speed (a crane can set a full house of trusses in a day on many jobs, where cutting rafters on site takes longer), and span (trusses can cross the full width of a typical house without interior load-bearing walls, opening up the floor plan below). The clear span is the architectural feature that makes great rooms, vaulted family rooms, and open kitchen-to-living-room layouts buildable on a typical wood-framed budget.

Truss vs Rafter: The Engineering Difference

A rafter is a single dimensional-lumber piece (typically 2×10 or 2×12) running from the top plate of the exterior wall to the ridge board at the peak. The load path goes from the roof deck down through the rafter, into the ceiling joist that ties the two rafters together at the bottom, and into the wall plates. A truss is a triangular assembly of smaller dimensional members (typically 2×4 or 2×6) connected by toothed metal connector plates (MTC plates) at every node, engineered to act as a single structural unit. The web members inside the triangle take tension or compression depending on geometry, distributing the load across a much more efficient material profile.

The framing decision affects the floor below in subtle ways. Trusses do not provide attic floor space unless designed as attic trusses. Rafters do, because the ceiling joists become the attic floor structure. The structural elements that connect every roof type are covered at parts of a roof.

King Post Truss: The Simplest Form

The king post truss is the oldest engineered truss form, with documented use dating to the medieval period. The geometry is simple: two top chords, a bottom chord, and a single vertical king post running from the bottom chord midpoint up to the peak. King post trusses suit short spans and a simpler look, and are used today on garages, porches, small additions, and rustic-style timber-frame applications. The visible king post timber-frame style is a premium architectural feature priced as custom timber work.

Queen Post Truss: Mid-Range Spans

The queen post truss extends the king post geometry with two vertical posts spaced symmetrically and a horizontal tie beam connecting them. The geometry reaches longer spans than a king post and is the historical predecessor to the modern Howe truss. Queen post trusses appear in barn frames, traditional church construction, and architectural timber-frame work. For commodity residential framing, the geometry has been displaced by the Fink truss because of cost.

Fink Truss: The Residential Workhorse

The Fink truss is the W-shape pattern of internal web members that is the standard profile for ordinary residential gable roofs. The web pattern, with two diagonals running up to the peak and two short diagonals near the heel, distributes load efficiently across common residential roof widths. The standard Fink truss uses 2×4 top and bottom chords with 2×4 web members, MTC plate connections, and Southern Yellow Pine or Spruce-Pine-Fir lumber, with the exact sizes set by the truss design drawings.

Scissor Truss: Vaulted Ceiling Option

The scissor truss creates a vaulted interior ceiling by sloping the bottom chord upward toward the peak, with the bottom chord pitch often about half of the top chord pitch. A 6/12 top chord with a 3/12 bottom chord gives a partial vault, while a 12/12 top with 6/12 bottom gives a dramatic cathedral feel. Scissor trusses usually cost more than equivalent Fink trusses because of the more complex web geometry and the longer lumber lengths required. Headroom-restricted bonus rooms over garages use modified scissor or attic geometries.

Attic Truss: For Usable Floor Space

The attic truss is engineered with a clear-space center bay flanked by web members, allowing the homeowner to finish out usable floor area inside the truss zone; the room width and height are set in the truss design. The web pattern locates load-bearing chords at the outside walls of the attic room, with the bottom chord serving as the attic floor joist. IRC Table R301.5 sets a 30 pounds per square foot live load for habitable attics and attics served with fixed stairs, versus 10 for uninhabitable attics without storage, which is why attic trusses use heavier bottom chords. Attic trusses cost more than Fink trusses but can add living space without a separately framed second story.

Howe Truss: Heavy-Load Applications

The Howe truss has vertical web members in tension and diagonal web members in compression, the inverse of the Pratt truss configuration. The Howe pattern suits heavy loads and longer spans and appears in industrial, commercial and post-frame buildings. In homes it is chosen where the truss designer needs the extra capacity, such as high snow loads.

Cost: Trusses vs Stick-Built

We could not find a primary source that publishes national installed costs for trusses versus stick-built rafters, so this guide does not quote a per-square-foot range. The cost comparison depends on four things you can price directly: the truss plant’s quote for the package (which reflects span, truss type, loads and current lumber prices), delivery and crane time, the framing crew’s labor, and, for rafters, the lumber sizes the span requires. Longer spans tend to favor trusses, because stick-built rafters at longer spans need larger dimensional lumber (2×12 instead of 2×10) and, beyond the IRC span tables, an engineered design. For more on truss pricing by type, see roof truss cost and types.

Span Ratings and Engineering

Every roof truss is built to a truss design drawing. Under IRC Section R802.10 (2024 IRC text, as carried in the 2025 California Residential Code), the design and manufacture of metal-plate-connected wood trusses must comply with ANSI/TPI 1 and the drawings must be prepared by a registered design professional; check the code edition your jurisdiction has adopted. The design package specifies the maximum span, the dead load (the roof material weight), the live load (snow and wind), the pitch, the lumber grade and species, the plate type and size at every connection, and the deflection limit. The Truss Plate Institute (TPI) publishes that design standard, ANSI/TPI 1, which the IRC references in Section R802.10.2.

Truss drawings list four design loads, which IRC Section R802.10.1 requires on the drawings: top chord live load (often labeled TCLL; under ASCE 7 snow is its own load type, separate from live load), top chord dead load (roofing material plus sheathing), bottom chord dead load (insulation plus drywall), and bottom chord live load. The code sets the minimums: IRC Table R301.6 requires a roof live load of 12 to 20 pounds per square foot depending on slope and tributary area, or the ground snow load, whichever is greater (Section R301.6), and IRC Table R301.5 sets 10 pounds per square foot for uninhabitable attics without storage and 20 for attics with limited storage. Higher-snow regions and tile-roof applications drive the design loads upward. The roof snow load starts from the ground snow load for the site, taken from the IRC ground snow load map (Figure R301.2(3) in the 2024 IRC, which maps allowable stress design ground snow loads), the ASCE Hazard Tool or the local building department, since many mountain areas are mapped as case-study zones that need site-specific values. Under IRC Section R301.2.3, homes in regions with a ground snow load above 70 pounds per square foot must be designed under accepted engineering practice rather than the prescriptive code tables. The 2018 and 2021 editions apply that threshold to the mapped ground snow load; the 2024 IRC text (as carried in the 2025 California Residential Code) keeps the 70 psf threshold but states it as the allowable stress design ground snow load, p_g(asd), from Figure R301.2(3). Check which edition your jurisdiction has adopted.

Truss Spacing: 24-Inch On Center Standard

Standard residential truss spacing is 24 inches on center, which works with common roof sheathing and roofing materials. Per IRC Table R503.2.1.1(1), a 24-inch roof span needs a wood structural panel with at least a 24/0 span rating (3/8-inch nominal) when the panel edges have edge support such as panel clips or blocking, or a 24/16 panel (7/16-inch nominal) without edge support. Panel options are covered at roof sheathing. Tighter spacing of 16 inches on center may be specified where the design calls for it, such as heavier tile dead loads or high snow loads. Going from 24 to 16 inches on center means about 1.5 times as many trusses (24 divided by 16), which raises the cost of the truss package.

Engineered Truss Stamping

IRC Section R802.10.1 requires the truss design drawings to be provided to the building official and approved before installation, and to be delivered to the job site with the trusses, so the inspector can check them at framing inspection. The drawing package includes the truss layout (showing every truss location, type, and identification number), the per-truss design sheets (with span, load, and material specs), and the bracing requirements. Missing drawings can hold up the framing inspection until they are produced.

Installation: Crane-Set vs Hand-Set

Crane-set installation is the dominant method, with a boom crane or telehandler lifting trusses from a delivery truck and setting them on the top plates in sequence. A crew of 3 to 5 framers ground-handles, ties, plumbs, and braces each truss as it lands. Crane time is usually billed separately, so ask whether the truss supplier or the framer is providing it. Hand-set installation (no crane) is used on small additions, remote sites, and small budgets, with trusses carried up, walked into position, and tilted up by the crew. Hand-setting is slower and practical only for trusses light and short enough for the crew to handle safely.

Truss Bracing: The Safety-Critical Step

Trusses are stable in their plane but unstable out of plane until permanent bracing is installed. The temporary bracing during setting (2×4 lateral restraints nailed across the top chords at the spacing the truss drawings and the industry BCSI guide call for) prevents domino collapse if a single truss tips. The permanent bracing per the engineered drawings includes diagonal web bracing, lateral chord bracing at specified web members, and ceiling diaphragm action through the drywall and sheathing. Missing or wrong bracing can let trusses buckle or collapse, so install it exactly as the drawings show.

Modifying Trusses: Almost Always Voids the Engineering

Cutting, notching, or drilling a truss chord or web member almost always voids the engineered design. The truss is designed as a single load path, and removing material from any member changes the load distribution unpredictably. Electricians and HVAC contractors are the most-common offenders, drilling holes for wiring runs and ductwork through chords. Any field modification requires an engineer-stamped repair detail (typically a plywood or LVL gusset bolted across the modified member) before drywall close-up.

Truss Damage Repair

Damaged trusses (from fallen trees, fire, water rot, or sagging from inadequate bracing) require engineered repair details. The repair package is specific to the damage location and the original truss design. Common repair details include lap-spliced sister members, plywood gusset reinforcement, and steel strap reinforcement at MTC plate joints. The sag identification, severity assessment, and contractor decision framework is at sagging roof repair. Trusses showing visible sag, separated MTC plates, or chord splits should be inspected by a structural engineer, not a general contractor.

Truss vs Rafter Decision Framework

Choose trusses when: the design includes longer spans, the floor plan benefits from no interior load-bearing walls, the truss quote comes in below the rafter quote, and the schedule benefits from a fast crane-set install. Choose rafters when: the design requires a finished attic with conventional ceiling height, the roof shape includes complex multi-plane geometry (Mansard, complex hip), the project is a small addition where crane access is impractical, or the homeowner specifically wants exposed timber framing for aesthetic reasons.

Most major roof shapes (gable roof, hip roof, gambrel roof) can be built either way. Mansard roof geometry is rarely trussed because the steep lower slope and shallow upper slope require complex truss profiles. Cathedral ceilings without an interior space above can be built with scissor trusses or with stick-built rafter-and-ridge construction.

Truss Manufacturing: Who Builds Them

Trusses are built in fabrication plants by regional manufacturers and delivered by truck, so the nearest plants set your lead time and delivery cost. Well-known names in the industry include MiTek (engineering software and plate supply to independent fabricators), Builders FirstSource (in-house truss plants serving its lumber yards), and Eagle Metal Products (plate supply and design software).

MTC Plate Connections: The Engineering Detail

The metal truss connector plates that join chord and web members at every node are an engineered component, not a generic fastener. The plates are stamped from galvanized steel with rows of teeth bent at right angles to the plate face; MiTek’s plates, for example, are 16 to 20 gage G60 galvanized steel with 4.6 to 8 teeth per square inch, per ICC-ES ESR-1988 Table 4. The teeth are pressed into the adjacent lumber to their full depth by hydraulic-platen or roller presses at the truss plant. Design values for each plate model are published in the maker’s ICC-ES evaluation report under ANSI/TPI 1, and they come in two different units. Per MiTek’s ICC-ES ESR-1988, allowable lateral (tooth-holding) resistance runs about 64 to 266 pounds per square inch of plate contact area per plate, depending on plate model, lumber species and grain direction, while tension and shear are rated in pounds per inch of plate width, about 509 to 2,522 pounds per inch for a pair of plates. MiTek, Eagle Metal, Alpine Engineered Products, and Cherokee Metal Products dominate the plate supply market.

The published design values assume plates pressed to full tooth depth by plant presses, as ESR-1988 describes, so plates hammered in on site are not covered by those values. That is why engineered repair details typically specify plywood gussets or bolted steel plates rather than field-driven MTC plates. A truss that arrives with a plate visibly backed out (one or more teeth not fully embedded, gap visible between the plate and the lumber surface) should be rejected and replaced rather than installed.

Lumber Species and Grade Selection

Truss design specifies lumber species and grade because the reference design values vary significantly by species, grade and size. For 2×4 Southern Pine, the Southern Pine reference design value table (SFPA, based on SPIB grading rules, effective June 1, 2013) lists a reference bending value (Fb) of 1,650 psi for No.1 Dense, 1,500 psi for No.1 and 1,100 psi for No.2, with Select Structural grades higher. Spruce-Pine-Fir and Douglas Fir-Larch have their own published values in the American Wood Council’s NDS Supplement. The truss design package specifies the species and grade explicitly, and substituting at the truss plant or on site invalidates the engineering.

Roof Sag Diagnosis on Truss Roofs

Visible sag on a truss-framed roof typically indicates one of three problems. First, missing or inadequate permanent bracing, allowing trusses to rack and twist under live load. Second, attic storage beyond what the trusses were designed for; IRC Table R301.5 sets 10 pounds per square foot for uninhabitable attics without storage, and the truss drawings show the actual bottom chord live load. Third, water damage at one or more truss heel locations, with the MTC plate slipping or the lumber rotting at the connection point. The sag inspection sequence, severity grading, and contractor decision framework is at sagging roof repair.

Energy Heel and Raised Heel Trusses

The energy heel truss (also called the raised heel) is a Fink or similar truss with the heel raised above the standard heel height to allow full insulation depth at the eave without compression. Standard trusses pinch the insulation at the eave where the top chord meets the wall plate, leaving only a few inches of usable insulation depth there instead of the full attic depth. Raised heel trusses cost more than standard trusses because of the taller heel and extra material, so ask the truss supplier to quote both versions; in return they allow full-depth insulation across the entire ceiling area, including over the wall plates. The energy code rewards that detail: the 2021 IECC (Section R402.2.1) lets a builder install one step less ceiling insulation (R-38 in place of R-49, or R-49 in place of R-60) over 100 percent of the ceiling when the full, uncompressed insulation height extends over the wall top plate at the eaves, as summarized by the Delaware Division of Climate, Coastal and Energy and the WSU Energy Program.

Truss Delivery Logistics

Truss bundles are heavy and need a truck with a piggyback forklift or a site with crane access. Delivery fees depend on distance and access, so get them in the truss quote. Trusses are often delivered shortly before the crane arrives or staged at a yard until needed. Trusses stored on site should be kept off the ground, supported and covered as the manufacturer and the BCSI guide describe, since lumber left lying in wet conditions can warp and take on moisture.

Snow Load and Wind Load Adjustments

Truss design loads vary by location. The IRC ground snow load map sets the base for snow, with mountain areas often mapped as case-study zones that need site-specific values. Wind load follows the ASCE 7 design wind speed maps, which run highest along the hurricane-prone Gulf and Atlantic coasts; the ASCE Hazard Tool gives the values for a specific address. Trusses for high-wind zones include heel hurricane-strap connection details, with the strap connection from the truss heel to the top plate engineered for the uplift load.

Inspection Checklist for Buyers Reviewing Truss Roofs

Buyers reviewing a home with truss roofing should check for six conditions during the home inspection. First, visible sag in any roof plane, particularly mid-span between supports. Second, separated or backed-out MTC plates visible in the attic (a flashlight inspection identifies these quickly). Third, evidence of field modification (cuts, notches, drilled holes through chords or webs), with no engineered repair documentation. Fourth, missing or inadequate permanent bracing per the original truss layout. Fifth, water staining on truss chords or MTC plates indicating active or historical leaks. Sixth, attic storage loading that exceeds the design live load. The full inspection process and cost expectations are at roof inspection cost.

Renovation Implications: Removing Walls Below Trusses

Many truss-framed roofs clear-span the full width of the home, so interior walls often carry no roof load. That is not guaranteed: some truss layouts bear on interior walls, girder trusses can bring point loads down to interior posts, and in two-story homes an interior wall may carry floor joists. Before removing any wall, confirm it is non-bearing from the truss design drawings (which show the bearing locations) or have a structural engineer inspect it. Trust the engineering documentation, not field assumptions.

Roof trusses dominate North American residential framing because the engineering, the install economy, and the architectural freedom all favor the prefabricated approach. The Fink truss covers the bulk of typical single-family work, with scissor, attic, and Howe variants available where the design calls for them. For the sheathing layer that installs on top of the trusses, the breakdown is at roof sheathing, and the pitch chart that drives every truss-design conversation is at roof pitch chart.