A roof truss is a prefabricated, triangulated frame, usually built from lumber and steel connector plates, that supports the roof deck and carries that weight down to your exterior walls. Roof trusses replace the older stick-built method of cutting rafters and ceiling joists on site, and they frame most new residential roofs in the US because they're engineered to code, consistent piece to piece, and faster to set than hand-cut rafters. This guide covers the common truss types, how they compare to rafters, what drives cost, and what to watch for once they're up.
If you're comparing options for a new build or addition, the sections below will get you to a shortlist fast. If you're worried about the trusses already holding up your roof, skip to the maintenance checklist further down. If something looks off, a licensed local roofer can take a look before it becomes a bigger problem.
What Is a Roof Truss?
A roof truss is a single engineered unit, typically triangular, built in a factory from dimensional lumber connected at every joint with galvanized steel truss plates (also called gang-nail plates), then trucked to the site and lifted into place. Trusses are the roof's primary framing, one part of the larger roof system that also includes sheathing, underlayment, and the roofing material itself, and they come up in any roofing service that touches the structure, from a new build to a storm-damage replacement. A trussed roof gets its shape from these repeating triangulated units, spaced evenly across the exterior walls.
Key Parts of a Roof Truss
Every truss shares the same basic anatomy:
- Top chord: the sloped outer members forming the roof's pitch and supporting the sheathing.
- Bottom chord: the horizontal member spanning wall to wall, often doubling as the ceiling joist below.
- Web members: the diagonal and vertical pieces between the chords that triangulate the load; their pattern names the truss type.
- Truss plates: galvanized steel connector plates pressed into the wood at every joint, replacing nails or bolts.
- Heel: where the top and bottom chord meet at the bearing wall.
- Span: the wall-to-wall distance the truss covers, measured outside to outside of the top plates.
- Pitch: the roof's slope, expressed as rise over a 12-inch run (a 6:12 pitch rises 6 inches per foot).
Roof Trusses vs. Rafters: What's the Difference?
A truss is one engineered unit built off site and set in place as a whole; a rafter roof is framed member by member on site, with each piece cut, positioned, and nailed individually. That difference drives every tradeoff below.
When Trusses Make More Sense
Trusses use lumber more efficiently, since triangulated webs spread load across smaller members instead of a few large boards, and a crew can set an entire truss roof in a single day versus several days hand-framing rafters. Trusses also span farther without interior load-bearing walls, opening up floor plans below. For new construction or tight schedules, trusses are the default.
When Rafters Still Make Sense
Rafters leave the attic completely open, since no interior webs cut across the space, which matters for attic storage or a future finished attic. They're also easier to adapt mid-project for an irregular roofline, and often the only option on additions where a truss delivery and crane can't reach a tight lot.
12 Common Types of Roof Trusses
Most residential and light commercial roofs use one of a dozen named truss profiles, distinguished mainly by web pattern and interior space. Here's a quick comparison before the detail on each.
| Truss Type | Typical Span | Best Roof Pitch | Best For | Distinguishing Trait |
|---|---|---|---|---|
| King Post | Up to ~16 ft | Any | Sheds, small additions | Single center web |
| Queen Post | ~16-30 ft | Any | Garages, mid-size spans | Two webs flanking center |
| Fink (W-Truss) | ~20-36 ft | Any | Most common gable roofs | W-shaped web, efficient |
| Howe | ~20-36 ft | Any | Heavy point loads | Diagonal webs angle toward center |
| Pratt | ~20-36 ft | Any | Similar spans to Howe | Diagonal webs angle outward |
| Warren | ~20-40 ft | Any | Longer, commercial/ag spans | Alternating diagonals, no verticals |
| Scissor | ~24-40 ft | Steep, 6:12+ | Vaulted/cathedral ceilings | Bottom chord slopes upward |
| Attic | ~24-36 ft | Steep, 7:12+ | Bonus rooms, attic space | Raised bottom chord opens a room |
| Hip | Matches main roof | Matches main roof | Hip roof ends | Stepped jack trusses |
| Gable | Matches main roof | Matches main roof | Gable end walls | Vertical studs, no load webs |
| Flat / Parallel Chord | ~20-60 ft | Flat/low-slope | Flat roofs, floor systems | Top and bottom chords parallel |
| Mono | ~12-24 ft | Single slope | Additions, lean-tos | One sloped chord, no peak |
Treat these spans as illustrative. Actual capacity depends on lumber species and grade, spacing, and local snow and wind load; only a stamped engineered drawing from the manufacturer sets the real number.
Triangulated Trusses: King Post, Queen Post, Fink, Howe, Pratt, and Warren
These six share a triangular top chord over a horizontal bottom chord, with webs arranged differently. King post uses one center web for short spans; queen post adds a second for more distance. Fink, the most common gable-roof profile, uses a lumber-efficient W-shaped web. Howe and Pratt look alike but reverse which way their diagonals lean. Warren skips vertical webs for alternating diagonals on longer commercial spans.
Scissor and Attic Trusses: Built for Extra Interior Space
A scissor truss angles the bottom chord upward instead of flat, creating a vaulted ceiling with no flat ceiling below. It needs a steeper pitch, typically 6:12 or greater, and costs more to engineer than a standard Fink. An attic truss instead raises the bottom chord partway up with vertical webs on either side, opening a usable room in the center. Specify either upfront, since adding that space to a standard truss roof later usually means an engineer redesigning the structure.
Hip, Gable, Flat, and Mono Trusses
Hip and gable trusses finish the ends of a standard truss roof. A hip roof framing package uses progressively shorter "jack" trusses stepping down toward the corners, while a gable roof caps the last bay with vertical studs instead of load-bearing webs, since it only carries wall covering. A parallel chord truss keeps the top and bottom chord running the same direction instead of meeting at a peak, useful for flat roofs, porch ceilings, and floor framing. A mono truss has a single sloped chord and no peak, essentially half a standard truss, the go-to for additions and lean-tos.
How to Choose the Right Truss Type
These three factors, in order, narrow the field before cost enters the conversation.
- Span and roof pitch. The wall-to-wall distance and pitch you want rule out most profiles immediately. Longer spans (30 feet and up) need deeper trusses, parallel chord, or Warren designs; steep pitches (8:12 and up) open the door to scissor or attic trusses, while low-slope roofs point toward flat or parallel chord designs.
- Load requirements: snow, wind, and region. Local code sets a required snow load and wind exposure category for your address, and both change the lumber grade, web spacing, and plate size an engineer specifies. A truss engineered for a light snow zone won't meet code in a heavy one without a redesign.
- Interior space goals. For attic storage, a bonus room, or a vaulted ceiling, order attic or scissor trusses built for that from the start. Standard trusses fill that same space with structural webs, and there's no way to open it up later without an engineer reworking the structure.
How Much Do Roof Trusses Cost?
Average Cost Per Truss and Per Square Foot
Treat these as ballpark ranges, since lumber prices, span, truss depth, and local supply all move the final number. A standard residential Fink truss commonly runs $50 to $150 delivered, while engineered attic, scissor, or long-span parallel chord trusses often land at $150 to $400 or more per piece. Across the whole roof, factory trusses typically add roughly $2 to $6 per square foot on top of sheathing, underlayment, and roofing material.
What Drives the Price
- Span and pitch: longer, steeper designs need more lumber and deeper engineering.
- Truss type: attic and scissor trusses cost more than a standard Fink of the same span.
- Material costs: lumber and steel plate pricing is cyclical.
- Engineering and stamped drawings: required by code, sometimes bundled in, sometimes billed separately.
- Delivery and crane rigging: long or heavy trusses often need a crane truck and rigging crew.
- Order size: a full house package prices better per truss than a small custom order.
Trusses vs. Rafters: Cost Comparison
For a standard gable or hip roof, trusses usually cost less installed than stick-built rafters, since the design uses lumber more efficiently and needs less labor. Rafters can come out ahead on small, low-pitch roofs or tight-access additions, where the labor saved doesn't offset crane and factory lead time. Get quotes both ways on anything but a standard shape, since local labor rates and truss-plant proximity both swing it. A contractor quoting a full roof replacement can usually tell you within minutes which approach fits.
Roof Truss Span and Sizing: How Far Can a Truss Reach?
Truss depth drives how far it can span without extra support: a shallow, 12-inch-deep truss might top out around 24 feet, while a 24-inch or deeper truss can often clear 40 feet or more. That relationship isn't fixed, since lumber grade, spacing (16 or 24 inches on center is standard), and local snow and wind load all shift the number. A roof pitch calculator helps with pitch, but span capacity has to come from the manufacturer's stamped engineering, since it's the number that has to hold up your roof.
How Many Roof Trusses Do You Need?
Standard spacing is 24 inches on center, though some higher-load designs use 16. Rough formula: roof length in feet, times 12 for inches, divided by spacing, plus 1 for the starting truss.
Say a roof section is 40 feet long with trusses spaced 24 inches apart: 40 times 12 is 480 inches, divided by 24 is 20 spaces, plus 1, landing at 21 common trusses plus a gable end (or hip jacks) at each end. Your manufacturer runs this math against your actual plan, plus extras around skylights or chimneys.
Installing Roof Trusses: What to Expect
Setting trusses isn't a reasonable DIY project beyond a small shed. A single truss can weigh several hundred pounds, is awkward to lift, and stays unstable until braced to its neighbors, which takes a crew with the right rigging, not a ladder and a helper. This is a job for a professional roof installation crew on anything covering a livable structure.
A typical residential truss set, delivery plus crane time plus crew labor, takes one to three days depending on roof size, versus a week or more hand-framing rafters. Spans over roughly 30 feet usually need a crane truck, and the crew braces the trusses immediately per the design drawings, since an unbraced run can topple before the sheathing locks everything together.
Can Roof Trusses Be Cut or Altered?
No, not without a structural engineer's sign-off. Every member is sized for the exact loads in that design, and cutting a web or drilling through a truss plate for ductwork or a chimney chase can drop capacity well below code, even when nothing looks wrong from the ground. If you need to run mechanicals through truss-framed space, choose a profile with a designed-in chase, or get an engineer to specify reinforcement.
Roof Truss Maintenance and Inspection Checklist
Trusses rarely need routine maintenance since they sit hidden above the ceiling, but problems show up as symptoms elsewhere. During an attic walk-through or roof inspection, look for:
- A sagging ridgeline or wavy roof plane visible from the street
- Cracked, split, or delaminated wood at any joint
- Truss plates that have backed out, rusted, or pulled loose from the wood
- Water stains or streaks on chords or webs, signaling a slow roof leak reaching the structure
- Gaps opening between the bottom chord and interior partition walls (a sign of truss uplift, common in cold climates)
- Any modification, a cut web, an added chase, or extra weight hung from a chord, that wasn't part of the original design
Any of these is worth a professional look before the next storm season. If the roof surface is also leaking or storm-damaged, pair that inspection with a full roof repair assessment so a contractor checks structure and surface in one visit.
What Are Roof Trusses Made Of?
Most residential trusses are wood: kiln-dried, machine-stress-rated lumber connected at every joint with galvanized steel truss plates for a consistent, code-rated connection. Steel trusses show up more in commercial buildings, pole barns, and other metal roof systems needing longer clear spans or fire-rated construction. On homes with metal panels, purlins, horizontal members crossing the top chords, give the panels something to fasten to.
Frequently Asked Questions About Roof Trusses
What is a roof truss?
A prefabricated, triangulated frame of wood or steel members connected with galvanized truss plates. It supports the roof deck and carries that load down to the exterior walls.
What's the difference between a rafter and a truss?
A truss is factory-built off site and set in minutes; a rafter roof is framed piece by piece on site. Trusses use less lumber and install faster, but their webs limit open attic space.
How much do roof trusses cost?
A standard residential truss runs roughly $50 to $150 delivered, while engineered attic, scissor, or long-span trusses often run $150 to $400 or more each. Per square foot of roof, trusses typically add $2 to $6.
Can roof trusses be cut or altered?
Not without an engineer's sign-off. Cutting a web or drilling through a truss plate can drop load capacity well below code, even if nothing looks visibly wrong.
What is the strongest type of roof truss?
There's no single strongest design by name. Strength comes from lumber grade, web spacing, plate size, and truss depth, set by an engineer for your span and load.
New build, addition, or a roof you're already worried about, a licensed local roofer can walk your specific structure and tell you exactly what it needs. Call a licensed local roofer now for a fast quote.
FAQ & Structural Repair Guidelines
Q:What is a roof truss?
A roof truss is a prefabricated, triangulated frame of wood or steel members connected with galvanized truss plates. It supports the roof deck and carries that load down to the exterior walls, replacing the older method of cutting rafters and ceiling joists board by board on site.
Q:What's the difference between a rafter and a truss?
A truss is factory-built off site as one triangulated unit and set in place in minutes; a rafter roof is framed piece by piece on site, member by member. Trusses generally use less lumber and install faster, but their internal webs limit open attic space unless you order attic-specific trusses. Rafters leave the attic fully open and are easier to adapt for odd rooflines or additions.
Q:How much do roof trusses cost?
Ballpark, a standard residential truss runs roughly $50 to $150 delivered, while engineered attic, scissor, or long-span trusses often run $150 to $400 or more each. Looked at per square foot of roof, trusses typically add somewhere in the $2 to $6 range to a build, though lumber prices, span, and local supply all move that number.
Q:Can roof trusses be cut or altered?
Not without an engineer's sign-off. Every member is sized for the exact loads in that design, and cutting a web, notching a chord, or drilling through a truss plate can drop the truss's load capacity well below code, even if nothing looks visibly wrong. Route mechanicals through a truss profile designed with a chase, or get a structural engineer to specify reinforcement first.
Q:What is the strongest type of roof truss?
There's no single strongest design by name. Strength comes from lumber grade, web spacing, plate size, and truss depth, all set by an engineer for your specific span and load, not from picking a Fink over a Howe. Parallel chord and Warren trusses tend to handle the longest clear spans, but any profile can be engineered up for heavier snow or wind loads.