Post and Beam Construction

Part of Woodworking

Post-and-beam (timber framing) is the oldest method of building large structures from wood. Every joint is cut by hand, every connection is locked with wooden pegs, and the frame can stand for centuries without a single nail or metal bracket. This is how you build a house, a barn, or a workshop when all you have is timber, hand tools, and community effort.

Post-and-Beam vs. Stick Framing

Modern construction uses “stick framing” — many small pieces (2x4s, 2x6s) nailed together, relying on thousands of fasteners and sheathing for strength. Post-and-beam uses fewer, much larger timbers connected by joinery.

Feature	Post and Beam	Stick Framing
Timber size	150x150 mm minimum (6x6 inches)	38x89 mm (2x4 inches)
Number of pieces	Few (dozens)	Many (hundreds)
Fasteners	Wooden pegs only	Thousands of nails/screws
Metal hardware	None required	Joist hangers, hurricane clips, etc.
Structural dependence	Frame self-supporting	Sheathing provides racking resistance
Skill required	High (joinery knowledge)	Moderate (nailing)
Strength	Enormous	Adequate for light loads
Lifespan	200-500+ years	50-100 years
Buildable without industry	Yes	No (requires factory-milled lumber and nails)

Tip

Post-and-beam is the only structural framing system that works with zero manufactured materials. Timbers can be hewn from logs with an axe, joints cut with a chisel and mallet, and the entire frame pegged together with hand-carved wooden pins.

Choosing Timber

Species Selection

Species	Suitability	Notes
Oak	Excellent	Strong, durable, traditional. Heavy.
Douglas fir	Excellent	Strong, straight, lighter than oak
Eastern white pine	Good	Light, easy to work, but softer
Hemlock	Good	Affordable, moderately strong
Cedar	Fair	Rot-resistant but soft — use for sills and plates only
Spruce	Fair	Light, straight, but lower strength

Minimum Sizes

Member	Minimum Size	Typical Size
Posts	150x150 mm (6x6)	200x200 mm (8x8)
Beams (connecting posts)	150x200 mm (6x8)	200x250 mm (8x10)
Plates (top horizontal)	150x200 mm (6x8)	200x200 mm (8x8)
Girts (mid-wall horizontal)	100x150 mm (4x6)	150x200 mm (6x8)
Rafters	100x150 mm (4x6)	150x200 mm (6x8)
Knee braces	100x100 mm (4x4)	100x150 mm (4x6)

Timber Preparation

1. Fell trees in late autumn or winter — sap is down, moisture lower, fewer insects
2. Hew or mill to approximate dimension. Hewn timbers (shaped with a broadaxe) are traditional and functional. Mill-sawn faces are easier for joinery layout.
3. Allow some drying: Green timber is easier to cut but will check (crack) as it dries. Air-dry under cover for 3-6 months if possible, or work green and accept checking.
4. Inspect every timber: Reject pieces with large knots at joint locations, severe twist, rot, or insect damage.

Warning

Never place a knot inside a mortise or tenon. Knots are where branches grew — the grain swirls and weakens. A knot in a mortise wall causes splitting; a knot in a tenon causes the tenon to snap. Position timbers so knots fall in the middle of clear spans, away from joint locations.

Frame Anatomy

A post-and-beam frame consists of:

Bents

A bent is a single cross-section of the building — typically two posts connected by a beam across the top. Think of it as one slice of the building. A small building might have 3 bents (two ends plus one middle); a large barn might have 6 or more.

Plates

Plates run the length of the building along the top of the posts, connecting the bents to each other. They carry the roof load.

Girts

Girts are horizontal members connecting posts at mid-height. They stiffen the frame and provide attachment points for wall sheathing.

Sills

Sills are the bottom horizontal members that sit on the foundation. All posts stand on the sills.

Braces

Knee braces are short diagonal members connecting posts to beams (or posts to girts). They prevent the frame from racking (leaning sideways). Without braces, the frame is a series of rectangles that can parallelogram and collapse.

Rafters

Rafters lean from the plates to the ridge (or to each other if paired). They support the roof.

Layout on the Ground

All joinery is cut with the timber lying flat on the ground or on sawhorses. Never try to cut joints on a standing frame.

The Process

1. Create a layout floor: Clear a flat area at least as long as your longest timber. Level the ground or lay down a few parallel logs as a platform.
2. Lay out the sill frame first: All four sills arranged in a rectangle. Check for square using 3-4-5 triangles at the corners.
3. Mark post positions on the sills. Transfer these marks to the posts.
4. Lay each bent flat: Both posts and the connecting beam arranged on the ground exactly as they will stand. Mark all joint locations from a single reference line.
5. Cut joints on the ground: Mortises, tenons, lap joints — everything is cut while the timber is accessible at waist height on supports.

Tip

Use a chalk line snapped along the timber face as your reference line. All joint measurements come from this line, ensuring everything aligns even if the timber is not perfectly straight.

Cutting Joints

Common Timber Frame Joints

Joint	Where Used	Description
Mortise and tenon	Posts to beams, girts, braces	Standard pegged M&T — tenon is 1/3 of timber width
Housed mortise and tenon	Posts to beams (heavy loads)	Tenon sits in a shallow housing for bearing surface
Lap joint	Sills meeting at corners, plates crossing	Half the thickness removed from each member; they overlap
Half-lap splice	Extending sills or plates beyond one timber length	Overlapping half-laps with pegs, extending the run
Birdsmouth	Rafters sitting on plates	V-shaped notch in the rafter bottom fits over the plate corner
Scarf joint	Joining two timbers end-to-end	Interlocking angled cuts that resist tension and compression

Cutting a Timber Mortise

1. Lay out the mortise with a chalk line, square, and marking gauge
2. Drill a series of holes with a large auger to remove bulk waste
3. Chop the remaining waste with a heavy framing chisel (called a “slick” when very large) and a mallet
4. Pare the walls flat and check for square
5. Size: the mortise width is 1/3 of the post width; depth is typically 75-100 mm

Cutting a Timber Tenon

1. Mark tenon cheeks using a gauge set to the mortise width
2. Mark the shoulder line all around with a square
3. Saw the cheeks with a large handsaw or two-person crosscut
4. Chisel or saw the shoulders
5. The tenon should slide into the mortise with firm hand pressure

Birdsmouth for Rafters

1. Set the rafter on the plate at the desired roof pitch
2. Mark where the bottom of the rafter crosses the inner corner of the plate
3. Cut a notch (the birdsmouth) — a horizontal seat cut and a vertical plumb cut
4. The seat cut rests on top of the plate; the plumb cut bears against the inside face
5. Depth of the birdsmouth should not exceed 1/3 of the rafter depth — deeper cuts weaken the rafter

Warning

A birdsmouth that is too deep turns the rafter into two weak halves connected by a thin section at the cut. Keep it to 1/3 of rafter depth maximum. The remaining 2/3 provides the bending strength that holds the roof up.

Numbering and Marking Pieces

Every joint must be cut to its specific mate — no two mortises are identical after hand-cutting. Traditional marking ensures you never mix up pieces.

The System

1. Number each bent: I, II, III, IV (Roman numerals, by tradition — they are easier to chisel than Arabic numbers)
2. Mark each joint within the bent: Add tick marks — one tick for the left post, two for the right
3. Chisel the marks into the timber face near each joint — they survive handling, weather, and centuries
4. Match marks on mating pieces: The mortise gets the same mark as its tenon

Orientation Marks

• Mark which face of each timber faces outward (exterior)
• Mark which end is up (for posts) or which end is which (for beams)
• These marks prevent the disastrous error of installing a timber backwards or upside-down

Raising a Bent

This is the dramatic moment — lifting the assembled bent from horizontal to vertical.

Preparation

1. Pre-assemble each bent flat on the ground: Posts, beam, and braces all pegged together
2. Position the bent at its final location, lying on its back (beam at the top, posts at the bottom, base of posts at the sill line)
3. Attach temporary bracing ropes to the top of the bent — these will be held by people or staked to the ground to prevent the bent from falling past vertical

The Raise

1. Crew positions: Several people at the base of each post to prevent sliding. The rest spread out along the beam.
2. Pike poles: Long poles (3-5 meters) with a forked or pointed end. Workers place the pike poles against the beam and push upward.
3. Start the lift: Crew pushes the beam upward while base crew holds the post bottoms on the sill
4. Walk it up: As the bent rises, pike poles reach higher. Workers walk toward the bent as it goes vertical.
5. Past 45 degrees: Gravity starts helping. Slow the rise with ropes from the far side.
6. Vertical: The bent is guided into position on the sill. Post tenons drop into sill mortises.
7. Brace immediately: Nail or lash long temporary braces from the bent to stakes in the ground. The bent must not fall before the next bent and connecting members stiffen the frame.

Warning

Raising a bent is dangerous. The timber is heavy, the forces are large, and a bent that tips past vertical will fall the other way. Always have ropes on the far side controlled by strong crew members. A bent should never free-stand without temporary bracing. Children and bystanders must be well clear of the raising area.

Crew Size

Bent Weight	Minimum Crew	Comfortable Crew
Under 500 kg	6-8 people	10-12
500-1000 kg	10-15 people	15-20
Over 1000 kg	15-20+ people	20-30

Connecting Bents

Once two or more bents are standing, connect them with horizontal members:

1. Plates: Lift into position on top of the posts. Insert tenons into post mortises. Peg.
2. Girts: Fit between posts at mid-height. Tenon into post mortises. Peg.
3. Sills: Already in position on the foundation — posts were set into sill mortises during the raise.
4. As each connection is made, the frame becomes more rigid. Remove temporary bracing only after enough members are in place to provide permanent stability.

Bracing

Bracing is what prevents a post-and-beam frame from collapsing sideways. Without braces, the frame is a series of hinged rectangles.

Knee Braces

• Short diagonals (typically 100x100 mm or 100x150 mm, 600-900 mm long)
• Connect post to beam at each joint, forming a triangle
• The triangle cannot change shape — this is what provides rigidity
• Install in pairs — one brace on each side of the post, or one in each direction

Diagonal Bracing

• Full-length diagonal members from one corner of a wall panel to the opposite corner
• Provides the strongest racking resistance
• Typically let into the face of the posts and girts (housed in a shallow groove)
• Used where knee braces alone are insufficient — tall walls, heavy wind or snow loads

Rules of Bracing

1. Every post-to-beam connection should have at least one knee brace
2. Each wall should have at least two knee braces
3. Braces work in compression — they push the post and beam apart to prevent them from folding together
4. Longer braces at shallower angles provide better resistance than short steep braces
5. 45-degree angle is optimal; 60 degrees is the minimum effective angle

Roof Structures

Common Rafter Roof

Every rafter pair forms an A-shape (or inverted V). Rafters are spaced 400-600 mm apart and connect at the ridge.

• Ridge board or ridge beam: A horizontal member at the peak that rafters attach to
• Collar ties: Horizontal members connecting opposing rafters partway up, preventing them from spreading
• Simple and material-efficient but requires many rafters

Purlin Roof

A few large rafters (principal rafters) carry horizontal purlins. The purlins support common rafters or roof boards directly.

• Fewer joints — principal rafters are part of the bent structure
• Purlins span between bents — typically 100x150 mm or larger
• Common in traditional timber framing because it uses less total timber
• Purlins are let into or set on top of the principal rafters

Roof Pitch

Pitch	Angle	Best For
4:12	18 degrees	Minimum for shingles; sheds water but barely
6:12	27 degrees	Standard — good balance of headroom and runoff
8:12	34 degrees	Steep — excellent water/snow shedding
12:12	45 degrees	Very steep — maximizes loft space, sheds snow

Infill Options

The timber frame provides the skeleton. You still need walls. The frame allows many infill options because it carries all structural loads — the walls are just weatherproofing.

Infill Method	Description	Difficulty
Wattle and daub	Woven sticks plastered with clay/straw mix	Easy
Cob	Thick clay/straw walls packed between posts	Easy
Straw bale	Bales stacked between posts, plastered	Easy
Board siding	Sawn or riven boards nailed to girts	Moderate
Brick nogging	Bricks laid between timbers	Moderate
Stone	Dry-stacked or mortared stone between posts	Hard

Tip

The beauty of post-and-beam is that infill can be replaced without touching the frame. A wattle-and-daub wall that deteriorates after 30 years is simply knocked out and rebuilt. The frame behind it stands indefinitely. Choose the easiest infill you can manage now — you can always upgrade later.

Post and Beam Construction — At a Glance

Post-and-beam framing uses large timbers joined by hand-cut mortise-and-tenon joints and locked with wooden pegs — no nails or metal required. Use minimum 150x150 mm posts and 150x200 mm beams from durable species like oak or Douglas fir. Cut all joints with timbers flat on the ground, number every piece with chiseled Roman numerals, and assemble bents (cross-frames) before raising them with pike poles and community labor. Connect bents with plates and girts, brace every joint with knee braces for rigidity, and choose your roof structure based on available timber. The frame carries all loads — infill the walls with whatever material is available, from wattle-and-daub to boards. A well-built timber frame will outlast every other part of the building.