Timber Frame Construction

Timber frame barn structure under construction showing hand-hewn beams and mortise-and-tenon joinery against a mountain backdrop

Timber framing is one of humanity's oldest permanent construction methods. It uses large-section wood members — posts, beams, and braces — connected with interlocking wood joinery rather than metal fasteners or nails. The result is a structure that is extremely strong, dimensionally stable, and visually striking. A timber frame building properly maintained will last 300–500 years. Traditional barns still standing from the 1700s in New England are evidence of this.

For a preparedness-focused owner-builder, timber framing is attractive because it uses locally sourced, natural materials; produces structures that are highly resilient to wind and seismic loads; and can be built with hand tools when power is unavailable. A basic 16 × 24 ft (4.9 × 7.3 m) timber frame cabin shell — posts, beams, rafters, and rough sheathing — can be completed for $8,000–$20,000 in materials, depending on species, region, and degree of owner-milling.

This page walks through the full build sequence. It assumes you are comfortable with basic carpentry but have never cut traditional timber joinery before. See Carpentry for foundational skills.

Understanding Timber Frame Structural Logic

Before cutting wood, you need to understand how the loads flow through the frame.

Gravity load path: Roof → rafters → purlins → tie beams → posts → sill → foundation. Every member must be sized to carry the loads transferred to it from above.

Lateral load resistance: Wind and seismic forces are resisted by diagonal knee braces connecting posts to beams, by shear walls (structural sheathing panels), and by the rigidity of the joinery itself. A frame without adequate diagonal bracing will rack (lean sideways) under lateral load.

Bay spacing: A bay is the space between two adjacent bents (wall frames). Standard bay spacing for residential timber frames is 16–20 ft (4.9–6.1 m) in the long direction and 16–24 ft (4.9–7.3 m) in the width direction. Wider bays require larger beams — doubling bay width requires roughly four times the beam section for the same load.

Post spacing in width (bent spacing): Bents are typically spaced at 16 ft (4.9 m) centers for a modest house or barn. A two-bay structure has three bents. A three-bay structure has four bents.

Step 1 — Species Selection and Sizing

Choose your timber species based on what is available locally, your structural requirements, and your budget.

Species Bending Strength (Fb) Hardness Cost (per BF) Best Use
Douglas Fir (Pacific NW) 1,500–1,900 psi Hard $3–$5 Posts, beams, all-purpose framing
Eastern White Pine 900–1,100 psi Soft $2–$4 Rafters, purlins, secondary members
White Oak 1,100–1,500 psi Very hard $5–$9 Joinery-heavy frames, traditional New England
Southern Yellow Pine 1,400–1,800 psi Hard $2–$4 Southeast US; excellent for beams
Hemlock 1,000–1,200 psi Medium $2–$4 Northeast US; common and affordable
Black Locust 1,700–2,000 psi Very hard $4–$8 Sill plates (extremely rot resistant)

BF = board foot. One board foot = 1 ft × 1 ft × 1 in thick.

Minimum sizing guidelines for a single-story residential structure with a 30 lb/sq ft (1.44 kPa) live load roof:

Member Minimum Section Notes
Corner posts 6 × 6 in (140 × 140 mm) 8 × 8 in for two-story
Intermediate posts 6 × 6 in (140 × 140 mm)
Major beams (tie beam, summer beam) 6 × 10 in (140 × 235 mm) for 16 ft span Size up for wider bays
Rafters 4 × 6 in (89 × 140 mm) at 24 in (61 cm) OC For spans to 12 ft (3.7 m)
Sill plate 6 × 6 in (140 × 140 mm), rot-resistant species Elevate off concrete
Knee braces 4 × 4 in (89 × 89 mm), 45° angle 24 in (61 cm) minimum arm length

For spans beyond these guidelines or for second-story loads, hire a licensed structural engineer to size your members. Engineering fees are a moderate investment for a simple timber frame.

Step 2 — Foundation Preparation

Timber frames are typically placed on a sill plate — a horizontal timber member anchored to the foundation perimeter. The sill must be level, square, and anchored to resist uplift and sliding.

  1. Pour the concrete foundation — perimeter stem wall or continuous footing, extending 12 in (30 cm) minimum above grade. Width: 8 in (20 cm) minimum for a 6 × 6 in (140 × 140 mm) sill.
  2. Set anchor bolts (1/2 in / 13 mm diameter, 12 in / 30 cm long J-hooks) at 4 ft (1.2 m) centers. Position anchor bolts 6 in (15 cm) from each corner and 18 in (46 cm) from planned post locations — you do not want a bolt directly under a post mortise.
  3. Install a sill seal (closed-cell foam gasket tape) between the concrete and the sill to prevent capillary moisture wicking.
  4. Lay the sill plate — use rot-resistant black locust, white oak, or pressure-treated timber for the sill. Mark post locations on the sill with a marking gauge before drilling anchor bolt holes.
  5. Check diagonal: Measure diagonally corner to corner in both directions. The two diagonal measurements must match within 1/4 in (6 mm) — this is your squareness check. Adjust sill position before the bolt nuts are tightened.

Field Note

Get the sill perfectly level before doing anything else. A sill that is 1/4 in (6 mm) out of level becomes 1 in (25 mm) of out-of-plumb at the top of an 8 ft (2.4 m) post. Shim the sill with stainless steel plate shims before tightening anchor bolts. Galvanized or plain steel shims will rust and stain the sill.

Step 3 — Timber Layout and Joinery Marking

Traditional timber framing uses a mortise and tenon joint as its primary connection. The tenon (a projecting tongue cut on the end of a beam) fits into the mortise (a rectangular cavity cut into the post). Wooden pegs (trennels or treenails) lock the joint mechanically.

Tools required:

  • Timber framing square (24 in / 61 cm framing square)
  • Marking gauge (mortise gauge)
  • Timber scribe (for scribing joint marks)
  • Circular saw or chainsaw (rough cuts)
  • Timber frame chisels: 1 in (25 mm), 1.5 in (38 mm), 2 in (50 mm)
  • Slick (long-handled paring chisel, 2–3 in / 50–75 mm)
  • Brace and bit or electric drill with 1.25 in (32 mm) auger bit for peg holes
  • Mallet (2–3 lb / 0.9–1.4 kg wood or rubber)

Standard mortise and tenon dimensions:

Application Tenon Width Tenon Thickness Tenon Length Mortise
Beam-to-post 1/3 post width 1/3 post width 4–5 in (100–127 mm) Match tenon + 1/4 in (6 mm)
Tie beam shoulder Full beam width - 1.5 in (38 mm) 2 in (50 mm) 4 in (102 mm) Match tenon
Brace-to-post 3 in (76 mm) 1.5 in (38 mm) 3 in (76 mm) Match tenon

Layout sequence:

  1. Mark the reference face of every timber with a lumber crayon — all layout measurements come from this face.
  2. Use the mortise gauge to scribe all mortise outlines — the gauge maintains consistent dimension from the reference face.
  3. Mark tenon shoulders with a framing square at exact right angles to the timber length.
  4. Mark peg hole locations: a single 1.25 in (32 mm) peg centered through the mortise, positioned 2 in (50 mm) from the tenon shoulder.

Step 4 — Cutting Joinery

Cutting a mortise:

  1. Drill out the waste with a 1 in (25 mm) auger bit, making overlapping holes within the mortise outline.
  2. Pare the sides flat with the 1.5 in (38 mm) chisel, working from both faces toward the center.
  3. Pare the ends square with a 1 in (25 mm) chisel.
  4. Check with a small square — the mortise walls must be flat and perpendicular to the timber face.
  5. Depth: mortise depth should equal tenon length plus 1/4 in (6 mm) bottom clearance.

Cutting a tenon:

  1. Saw the tenon shoulders with a circular saw or hand crosscut saw to the layout lines.
  2. Saw the tenon cheeks with a bandsaw, frame saw, or circular saw with a guide.
  3. Pare the cheek surfaces with the slick until they are flat and fit the mortise snugly. The tenon should slide in with hand pressure — not pounded, not loose.

Pegging:

  1. Assemble the joint dry. Drill the peg hole through the mortise side walls and through the tenon, with the peg hole offset 1/16 in (1.5 mm) toward the shoulder — this is called "draw-boring" and it pulls the joint tight as the peg is driven.
  2. Drive a tapered hardwood peg (1.25 in / 32 mm diameter, 10–12 in / 25–30 cm long) through the hole with a mallet.
  3. The peg should protrude 1/2 in (13 mm) on each side when fully seated.

Step 5 — Assembling Bents

A bent is a complete wall frame — two posts, a tie beam connecting them, and knee braces. Bents are assembled flat on the deck or ground before being raised into position.

  1. Lay the posts and tie beam flat on a level surface (saw horses or timber blocks) in their assembled position.
  2. Drive tenons into mortises for all joints. All pegs are installed now, while the work is at ground level.
  3. Check the bent for square: measure diagonally corner to corner. Both diagonals must match within 1/8 in (3 mm).
  4. Install knee braces: the braces run at 45° from post to beam, with the brace tenon driven into mortises in both the post and the beam. Knee brace length (measured along the brace itself) is typically 28–34 in (71–86 cm) for a 20 in (51 cm) arm length.
  5. Mark each bent clearly — a permanent lumber crayon mark on a non-visible face. Bent 1 (end), Bent 2 (first interior), etc.

Step 6 — Raising Sequence

The raising is the most dramatic — and most dangerous — step. Plan carefully and have adequate crew. Raising a single bent for a 16 × 24 ft (4.9 × 7.3 m) structure requires 6–10 people and takes a full day for an experienced crew. First-timers should plan two days.

Safety rules:

  • Never stand under a rising bent
  • All crew members must know the hand signals before raising begins
  • Temporary bracing must be installed before any bent is released by the crew
  • Work shoes with ankle support only — no sandals, no loose clothing

Raising sequence:

  1. Position temporary staging (2 × 4 in / 38 × 89 mm braces anchored to the sill) on the exterior of each post position. These catch the post bottoms as the bent comes up.
  2. Place post bases: set the post tenons (or post bases) into the sill mortises. The posts pivot around this point as the bent rises.
  3. Raise the first end bent: using pike poles (12 ft / 3.7 m long pushing poles) or a crane, push the bent from horizontal to vertical. One crew member per post base to keep it from sliding; remaining crew push with pike poles.
  4. Plumb and brace the first bent: immediately after it is vertical, install two temporary diagonal braces from the bent to the sill on each side. Check plumb with a level before releasing the pike poles.
  5. Raise the second bent (opposite end).
  6. Install tie beams connecting the two end bents at the top. These are lifted into position and their tenons driven into the post mortises by a crew member on a ladder or scaffold.
  7. Raise interior bents in sequence. Each new bent is connected to the previous one by tie beams before being released.
  8. Install purlins (horizontal members connecting bents along the roof slope) once all bents are standing and permanently braced.

Warning

If you are raising a bent without a crane, pike poles must be long enough to keep crew members clear of the falling arc of the timber. For a 10 ft (3 m) post, use pike poles at least 12 ft (3.7 m) long. A falling bent can travel 25 ft (7.6 m) from its base.

Step 7 — Structural Sheathing and Hurricane Ties

The timber frame itself carries gravity loads. Lateral loads (wind, earthquake) are resisted by structural sheathing panels and by the frame joinery.

Structural sheathing:

  1. Install 7/16 in (11 mm) oriented strand board (OSB) or 1/2 in (13 mm) plywood on all exterior walls, nailed to secondary framing (2 × 4 in / 38 × 89 mm studs infilled between timber posts) at 6 in (15 cm) on center at panel edges and 12 in (30 cm) in the field.
  2. Alternatively, install structural insulated panels (SIPs) directly between timber posts. SIPs provide both sheathing and insulation in one operation.

Hurricane ties:

All rafter-to-plate connections and all post-to-sill connections must be reinforced with metal hurricane ties in areas with design wind speeds above 90 mph (145 km/h) — check your local building code for the design wind speed requirement. Use Simpson Strong-Tie H2.5 or equivalent.

Step 8 — Weatherproofing and Enclosure

With the frame up and sheathed, proceed with roofing, windows, and doors. See Weatherproofing for the full sequence.

Key timber-specific details:

  • All post bases must be elevated off concrete or masonry with a post base connector that provides a 3/4 in (19 mm) air gap. Post bases sitting in standing water will rot in 5–15 years even with treated wood.
  • All exposed timber end grain (particularly rafter tails and purlin ends) must be sealed with end grain sealer or two coats of boiled linseed oil. End grain absorbs water 10× faster than face grain.
  • Apply a penetrating oil finish (tung oil, danish oil, or exterior-rated timber oil) to exposed interior timbers once and re-apply every 5–10 years. This prevents surface checking (cracking during drying) and keeps the wood from dulling.

Cost Summary

Item Low End High End
Timbers (16 × 24 ft / 4.9 × 7.3 m structure) $4,000 $12,000
Foundation $1,500 $5,000
Fasteners, hardware, hurricane ties $400 $1,200
Sheathing (OSB or SIPs) $1,200 $6,000
Roofing (metal, basic) $2,000 $6,000
Windows and doors (rough frames) $1,500 $5,000
Total shell (16 × 24 ft / 4.9 × 7.3 m) $10,600 $35,200

Interior finishing (insulation, drywall, flooring, utilities) adds a significant investment depending on finish level.

Common Mistakes

Mistake Consequence Prevention
Green (unseasoned) timber Severe checking and twist as it dries Use air-dried or kiln-dried timber where possible; expect minor checking in green timber
Mortises too tight Joint cannot be assembled; wood splits Target a hand-pressure fit — slide with light mallet taps
No draw-bore Joint loosens as wood dries Always draw-bore peg holes before pegging
No temporary bracing Bent falls during raising Install bracing before releasing pike poles
Post base in standing water Rot in 5–15 years Always use elevated post base connectors
  • Weatherproofing — roofing, drainage, and moisture details for timber frames
  • Insulation — insulating between and around timber frame members
  • Carpentry — foundational woodworking skills for joinery
  • Hand Tools — chisels, mallets, saws, and layout tools for timber work
  • Cob Building — compatible natural infill material for timber frame walls