Trusses are the reason a timber frame has a roof overhead. Beyond holding up the ceiling, they shape the look of every great room, from a cathedral-style hall to a cozy cottage. A truss is the timbered unit made of vertical posts, girts, main rafters, struts, and knee braces joined with pegs into a single section of frame called a bent. Bents are assembled on the ground and raised by hand or crane, then joined by ridge beams, girts, and purlins to form bays, the spaces between bents.
Before choosing a truss style, it helps to understand the materials and engineering behind the whole frame, from sawn lumber to glulam and cross-laminated timber, and a structural timber engineering reference covers that ground in one place. The five styles covered here, common, queen post, king post, hammerbeam, and scissor, account for nearly every timber frame built today.
How a Timber Frame Truss Works
A truss works as a triangular web of members that transfers roof loads down to the walls and foundation. The vertical posts carry compression, the rafters and struts brace the roof plane, and the knee braces stiffen the joints where posts meet beams. Every peg in a timber frame does real work: it locks the joinery so the frame acts as one unit instead of a collection of sticks, and a frame with tight joints stays square through decades of settling and snow loads.
The same joinery logic scales down to small projects. A garden shed wall built with half-lapped 4x4s shows how lap joints and through-pegs transfer load in a miniature frame, which makes it a useful hands-on introduction before committing to a full house.
Bents and Bays: The Frame’s Vocabulary
Two terms explain how a frame goes together. A bent is a complete cross-section of the frame, usually with two posts, a tie beam or collar, rafters, and bracing, assembled flat on the ground. A bay is the space between two bents, typically 8 to 12 feet wide in residential work. Trusses define the bent, and the bent defines the rhythm of the room, so truss spacing is one of the first decisions a timber framer makes.
The Five Truss Styles in Modern Timber Homes
Five basic truss types dominate modern timber homes: common, queen post, king post, hammerbeam, and scissor. Each style works for one story or two, depending on load capacity, window placement, and room layout, and the table below summarizes how they compare.
| Style | Profile | Typical span | Best for |
|---|---|---|---|
| Common | Vertical posts with a tie beam and rafters | Up to about 24 ft | Everyday great rooms and gable roofs |
| King post | One central post under the peak | About 16 to 24 ft | Open living areas with a single ridge |
| Queen post | Two posts flanking the center | About 24 to 36 ft | Wider rooms needing a clear center |
| Hammerbeam | Short beams with curved braces projecting inward | 30 ft and up | Cathedrals, great halls, dramatic ceilings |
| Scissor | Rafters that cross like open scissors | Varies with pitch | Vaulted and shed-style ceilings |
The common truss appears most often in modern timber frames because it is strong, straightforward, and suits the proportions of a typical house. The other four trade visual drama for different structural geometry, and each changes how the ceiling reads from the moment you walk in.
Rafter and truss spacing also interacts with the rest of the roof assembly, especially where insulation goes. Curtain trusses with cellulose insulation show how a double-truss detail keeps the thermal envelope continuous in a timber frame, a detail worth discussing with your framer before the roof is closed in.
What Each Style Looks Like in a Room
- Common truss: a clean A-frame profile with vertical posts at the walls; reads as classic timber frame.
- King post truss: one post rising from the tie beam to the peak, often with angled struts; reads as simple and strong.
- Queen post truss: two posts with a horizontal span between them; opens the center of the ceiling.
- Hammerbeam truss: curved braces and short horizontal beams; the most theatrical of the five.
- Scissor truss: rafters that cross and continue past each other; makes a vaulted ceiling feel taller.
Choosing a Truss Style for Your Floor Plan
Room layout drives the choice more than any other factor. A king post truss in the middle of a 20-foot living room gives the eye a natural anchor, but the same truss blocks sight lines if the room is arranged for conversation across the center. A queen post keeps the center clear, which is why it shows up in great rooms with an open plan behind the kitchen.
Ceiling height changes the math too. In rooms with low walls, a timbered ceiling that combines timber frame aesthetics with stick frame efficiency can deliver the look without the full structural system, which keeps both cost and thermal complexity down.
Window Placement and Load Paths
Windows belong between posts, not through them. If the plan puts a window where a truss post wants to land, either the window moves or the truss changes. This is why truss selection happens with the floor plan open on the table, not after the layout is locked, and why framers ask for window schedules before they cut any joinery.
One Story or Two
Each of the five styles can be built for one-story or two-story applications. A two-story great room changes the proportions: posts get taller, braces get longer, and the truss reads more like sculpture than structure. Load capacity, not style, usually sets the limit, and your timber framer will calculate member sizes for the actual roof load, including snow, before the design is final.
Curved and Custom Trusses
The five standard styles cover most homes, but timber framing also rewards custom work. Curved braces, arched tie beams, and scalloped rafters turn a standard king post into something unique, and the joinery is the same, just cut to a curve. Custom work also lets a frame respond to an unusual floor plan instead of forcing the plan to fit a catalog shape.
Curved members need different milling, and curved timber techniques explain how curves are cut, joined, and braced so the frame stays true over decades of seasonal movement.
When Custom Is Worth the Cost
Custom trusses pay for themselves in signature spaces: a curved hammerbeam over a stair hall, an arched scissor in a lake house great room. In ordinary rooms, a standard style with well-chosen proportions delivers most of the effect for less money, so budget the custom work for the one or two rooms people remember.
Engineering, Loads, and Connections
Every truss transfers three kinds of load: dead load from the roof and frame itself, live load from snow and maintenance traffic, and lateral load from wind. Snow load dominates in northern climates, so a truss sized for a warm region may be undersized there, and the reverse is also true. Local building codes set the design values, and the framer sizes every member against them.
The roof system also includes purlins, ridge beams, and sheathing that work with the trusses, and a timber roof truss reference covers how those members interact and how span tables are read.
Joinery and Pegs Carry the Load
Timber frame connections are not nailed; they are cut and pegged. Mortise-and-tenon joints with oak pegs resist both compression and racking, and the size of the peg and the depth of the mortise are engineering decisions, not decoration. A well-made joint transfers load across the full bearing surface, which is why a century-old barn frame can still carry a roof long after its nails would have loosened.
Working With Your Timber Framer
Truss selection is a conversation, not a one-way decision. Bring your floor plan, your ceiling heights, and photos of rooms you like, and let the framer show which styles fit the structure and the budget. Most framers have built all five styles and can explain the trade-offs in the context of your actual house.
Connections extend below the trusses too. Posts bearing on concrete block walls need designed connections and load transfer details, because the frame is only as good as the foundation it lands on.
Questions to Ask Before You Commit
- Which truss styles fit the span of each room?
- How do window placements affect post locations?
- What member sizes does the roof load require?
- Which styles add cost, and where does the money go?
- Can a custom curve be milled from local timber?
There are no wrong answers when the structure is sound, only different characters. A truss frames the life in a home the way a picture frame surrounds a painting, so choose the one that fits the rooms you will actually use.