A timber frame is more than a collection of heavy beams. Every member has a name, a position, and a job, and the terms show up constantly in drawings, bids, and site conversations. Understanding the vocabulary lets you read a floor plan, talk to a framer about a change, and spot the difference between decorative wood and structure that is actually carrying load. The components belong to the larger field of structural timber engineering, which spans sawn lumber, glulam, cross-laminated timber, and heavy timber construction.
The classic frame starts at the foundation and works upward: posts rise from post pockets, plates and girts tie them together, and a roof system of rafters, purlins, and a ridge beam sits on top. Braces lock the joints against movement. Walking through the parts in the order they meet makes the terminology stick, from the post pocket in the foundation to the common rafter at the ridge.
Posts: The Vertical Skeleton
Posts are the columns that carry the frame’s weight down to the foundation. In the standard vocabulary, the simple vertical member is called a post, while a post that flares wider at the base is a gunstock post, named for the shape of a rifle stock.
Gunstock Posts and Tapered Profiles
The gunstock profile flares at the bottom to spread load over a larger bearing area and to give the base of the column a heavier, grounded look. A smaller cousin appears in garden structures: half-lapped 4×4 walls give a shed the visual rhythm of a timber frame, though the engineering is much simpler than a full post and beam system.
How Posts Carry Load
Posts sit in post pockets, recesses cut into the beams or the subfloor assembly, or bear directly on the foundation. The foundation wall and rim joist transfer the load into the ground. Because a single post can carry tens of thousands of pounds, the joinery at the top of the post, often a mortise and tenon, must fit tightly so the load travels through wood fibers rather than through bolts alone.
- Roof loads collect in the rafters and purlins.
- Rafters deliver their load to the plates and tie beams.
- Plates and tie beams pass the load to the posts at the wall tops.
- Posts carry it through the post pockets to the rim joist and foundation wall.
Plates, Girts, and Tie Beams: The Horizontal Members
Horizontal members do two different jobs: they tie the vertical posts together into a stable grid, and they support the floor and roof systems above.
The Plate: The Top of the Wall
The plate runs along the top of the posts and picks up the rafters. Its top surface sets the reference for everything above, which is why drawings mark the top of plate as a level line that the rest of the frame is measured from.
The Tie Beam and the Connecting Girt
A tie beam spans the building at the level of the wall tops and ties opposite walls together, resisting the outward thrust of the roof. A connecting girt runs between posts at an intermediate height, bracing the wall and supporting floor or loft loads. The rim joist closes the floor edges, and the loft floor and subfloor sit on top of the joists.
| Member | Primary function | Location |
|---|---|---|
| Plate | Carries the rafters and ties the post tops | Top of the wall, under the roof |
| Connecting girt | Braces posts and supports floor or loft loads | Between posts at intermediate height |
| Tie beam | Resists roof thrust and ties opposite walls | Spans the building at wall-top level |
| Rim joist | Closes the floor edge and transfers load | Perimeter of the floor assembly |
| Subfloor and loft floor | Walking surface and floor diaphragm | Above the joists |
Reading these members on a drawing is easier once you know the convention: plates and girts run in the plane of the wall, while tie beams and purlins run across the building. Framers also use the top of plate, the top of joist, and the top of subfloor as reference elevations, so a single dimension on a section drawing ties the whole frame together.
The Roof System: Rafters, Purlins, and the Ridge
The roof is where timber framing shows its full vocabulary, with several layers of members working together to turn a wide span into a rigid triangle.
Rafter Types and Roof Geometry
Common rafters run from the plate up to the ridge beam at regular intervals. Main rafters are the larger, primary rafters in a purlin roof, and common purlins run horizontally between them, picking up the smaller rafters. A ridge beam runs along the peak and carries the top ends of the rafters. Where the roof frames a bay, a pendant drops from the ridge to support the roof framing over the opening.
- Common rafter: runs from the plate to the ridge at regular intervals.
- Main rafter: the primary rafter in a purlin roof, carries the purlins.
- Common purlin: horizontal member running between main rafters.
- Ridge beam: runs along the peak and carries the rafter tops.
- Collar tie: ties opposite rafters together below the ridge.
Pitch and Span
Roof geometry controls the loads. Steeper pitches shed snow faster and give the frame more depth for joinery, while wider spans call for bigger rafters or intermediate purlin supports. The struts that run diagonally from the tie beam up to the purlins shorten the purlin spans and keep member sizes reasonable.
King Post and Queen Post Trusses
Two classic truss forms appear in nearly every timber frame. A king post truss has a single central post running from the tie beam up to the ridge, with two struts bracing the rafters. A queen post truss uses two posts, creating a wider opening in the middle of the ceiling. Hammer posts and hammer braces extend this idea for very wide halls. Owners who want the look in a conventional house can build a timbered ceiling combining timber frame aesthetics with stick frame efficiency instead of a full structural frame.
Braces, Tenons, and the Joinery That Holds It Together
The joints are the soul of a timber frame. Most connections are mortise and tenon joints locked with wooden pegs, and the braces keep those joints from working loose under wind and seismic loads.
Braces Against Racking
Knee braces run diagonally from posts to beams and are the most common brace in the frame. Hammer braces do the same job at larger scale, sweeping up from a post or corbel to support a beam above. Together they convert the rectangular bays of the frame into triangles, which resist racking and keep the frame square.
Joinery Details That Define the Style
Beyond function, joinery shapes the look of the frame. A Dutch tenon is a tenon with a sloped shoulder cut into the side of a beam, used where a rafter or brace lands on a purlin. Pendants, the decorative drops hanging below a beam junction, and the curves in braces are where builders show their craft. Curved timber techniques let a builder sweep a brace or a beam along a radius, adding visual motion but requiring careful layout and steam bending or laminated stock.
The Dutch Tenon in Practice
In a Dutch tenon, the tenon passes into the side of the receiving member and the shoulder follows the slope of the roof member, so the joint reads cleanly from below. It is a small detail that appears constantly in purlin roofs, and it is one of the easiest joints to identify on a raised frame.
Enclosing the Frame: SIPs and Hybrid Systems
Once the frame is raised, the enclosure takes over. The labeled parts continue upward from the structure: the structural insulated panel, or SIP, covers the outside of the frame, and the bay, loft floor, and subfloor complete the building envelope.
Structural Insulated Panels as the Enclosure
SIPs sandwich rigid foam between two structural skins, typically oriented strand board. They enclose the frame, insulate the building, and brace the structure in one component. Panel edges are cut to match the frame’s geometry, and the seams are taped to form an air barrier.
Hybrid Timber Construction
Not every timber home is a pure frame. Hybrid timber construction mixes timber frame members with log siding or conventional stick framing where it saves money or solves a design problem, and the materials around the frame, siding, windows, and insulation, all have to be coordinated with the frame’s movement and tolerances.
The parts of a timber frame, from the post pocket in the foundation to the common rafter at the ridge, form a system where each member depends on the next. Reading the anatomy is the first step to appreciating how these buildings go together, and the journey from forest to frame shows how raw wood becomes the finished structure. Once you can name the members, every future conversation with a framer, an engineer, or a builder starts from shared ground.