“Raising the Roof: A Step-by-Step Guide to Building a Traditional Wooden King Post Truss”

By: Timber Craft Weekly | August 5, 2025

Good carpentry starts with solid joinery, and nowhere is that more evident than in a king post truss—one of the simplest yet strongest roof truss designs. The beautifully hand-drawn diagram above names each member in Italian: the monaio (king post), puntone (principal rafter), travicello (straining beam), arcareccio (collar tie), saetta (strut), catenaria (tie beam), and dormiente (wall plate). In this 1,000-word deep dive, we’ll show you, step by step, how to lay out, cut, assemble, and raise your very own king post truss—whether you’re framing a small pavilion, barn, or cottage.

Why the King Post Truss?

• Simplicity: Only seven members, all straight timbers.
• Strength: Central post (monaio) transfers roof loads down to the tie beam (catenaria).
• Versatility: Spans anywhere from 12 to 20 feet without intermediate support.
• Historic Charm: A time-tested form seen in medieval halls and rural buildings worldwide.

Materials & Tools Checklist

• Lumber
  • 2 × 8″ or 2 × 10″ for the puntone (principal rafters)
  • 2 × 6″ for the catenaria (tie beam) and travicello (collar tie)
  • 4 × 4″ timbers for the monaio (king post) and saetta (struts)
• Iron Straps & Bolts (staffe) for gusset connections
• Framing Square, Sliding Bevel, Tape Measure, Chalk Line
• Circular Saw or Hand Saw with Carpenter’s Pencil
• Auger Bit or Drill & Spade Bit for bolt holes
• Gusset Plates (plywood or metal) if preferred over straps
• Lifting Gear (block & tackle or gin pole) for raising the truss

Step 1: Set Out the Geometry

1. Determine Span & Pitch
   • Decide on your clear span—for example, 16 feet between wall plates (dormienti).
   • Choose a roof pitch (commonly 30°–45°).
2. Draw Full-Scale Layout
   • On the shop floor or layout table, snap a chalk line for the tie-beam length (catenaria).
   • At the center, mark the king-post location.
   • Using a bevel set at half the pitch angle (α/2), strike lines from each tie-beam end inward. This intersection marks the rafter heel cuts.
   • From the heel intersection, extend the same bevel line upward to locate the rafter-ridge points, establishing the full rafter length.

Step 2: Prepare the Tie Beam (Catenaria)

1. Cut to Length
   • Crosscut your 2 × 6″ tie beam to the span length, plus allowances for bearing tenons if using mortise-and-tenon seats on your wall plates.
2. Mark the King-Post Seat
   • At the tie’s midpoint, mark a vertical mortise or simply a bearing notch for the monaio (king post). Typical depth: 2″.
3. Notch the Strut Seats
   • Measure out from center along the tie beam—distance equal to where your saetta (strut) meets the travicello (collar tie).
   • Mark and cut angled seats at α/4 (a quarter of the roof pitch angle) to receive the bottom end of each strut.

Step 3: Craft the King Post (Monaio)

1. Cut to Height
   • From your layout, you know the ridge height above the tie beam. Cut the 4×4 post to that length plus your chosen joint depth.
2. Add Gusset Bearing
   • At the top, mark a half-lap seat (depth ≈ timber thickness) for the collar tie (arcareccio).
   • Drill bolt holes through the post to align with gusset plates, or lay out mortise and tenon for a wooden pin.

Step 4: Fashion the Principal Rafters (Puntone)

1. Rafter Heel Cuts
   • Using the heel lines from your layout, mark the plumb cut at the foot of each rafter.
   • Angle the bird’s-mouth seat: level cut sits on the wall plate (dormiente), and plumb cheek fits flush against the stud face.
2. Ridge Cuts
   • At the opposite end, mark the ridge cuts so both rafters meet neatly over the king post. Include a ½″–1″ overhang (look-out) if desired.
3. Gusset Plate Preparation
   • Where rafters meet the monaio and arcareccio, drill matching bolt-hole patterns in each member. Ensure all holes register precisely.

Step 5: Cut the Collar Tie (Arcareccio) & Collar Beam (Travicello)

1. Determine Collar Placement
   • Typical height: ⅓ down from the ridge. From your full-scale layout, transfer this distance onto each rafter.
2. Cut Notches
   • At each end of the collar beam (2 × 6″), cut shoulders matching the rafter face angle so it seats tightly.
3. Drill or Mortise
   • Prepare bolt holes for iron straps (gattelli) or mortise-and-tenon joinery if you prefer an all-timber connection.

Step 6: Struts (Saetta) and Bracing

1. Length & Angles
   • Struts run from near the collar beam to the tie-beam, meeting your α/4 seats marked in Step 2.
   • Cut both ends at the correct bevels so they bear fully in their notches.
2. Check Fit
   • Dry-fit each strut between its seat on the tie beam and its bearing under the collar, ensuring a snug, gap-free contact.

Step 7: Ironwork & Gusset Installation

1. Position Iron Straps (Staffe)
   • At each juncture—rafter to monaio (detail “a”), rafter to strut/travicello (detail “b”), and rafter to tie beam (detail “c”)—place flat steel straps on both faces.
2. Bolt Up
   • Use carriage bolts with washers and nuts, tightening to draw members together but not crushing timber. Typical bolt diameter: ½″ or ⅝″.
3. Optional Plywood Gussets
   • If you prefer, glue and screw plywood gussets over each face—just ensure moisture-resistant adhesive and stainless or zinc-coated screws.

Step 8: Dry Assembly & Inspection

1. Lay Out on Saddles
   • On two stable sawhorses or temporary saddles, assemble the entire truss, tapping into final alignment.
2. Check All Angles & Plumb
   • Use a level and square to confirm that the king post is perfectly vertical, rafters symmetrical, and collar tie horizontal.
3. Mark Member IDs
   • Before disassembly, chalk-mark each joint for re-erection order and orientation.

Step 9: Erecting the Truss

1. Rigging Up
   • Under the ridge intersection, install a gin pole or block-and-tackle anchored to a stable point.
2. Lift Carefully
   • Slowly hoist the truss upright, guiding rafter ends onto the wall plates (dormienti).
3. Seat and Secure
   • Once rafter heels seat fully in the wall-plate notches, nail or bolt through the wall plate into the rafter bird’s-mouth.

Step 10: Final Checks & Tying In

1. Tie Beam Anchors
   • Through-bolt the tie beam down into the masonry or timber sleeper below, preventing outward thrust.
2. Rafter Plumb Lines
   • Drop a plumb line from each rafter tip to ensure your ridge runs perfectly straight.
3. Gusset Retorque
   • After a day of settlement, re-check all bolt torque and add additional shims or packing if any joint has loosened.

Maintenance Tips

• Periodic Bolt Check: Every season, inspect and re-tighten iron fittings.
• Wood Treatment: Coat all end grains and cut surfaces with a quality exterior wood preservative.
• Moisture Management: Ensure good attic ventilation above the collar tie to prevent condensation in the heart of the truss.

Conclusion

Building a king post truss marries geometry, joinery, and muscle—yet yields a remarkably elegant structure that has stood for centuries. By following these ten steps—meticulous layout, precise cutting, robust ironwork, and careful erection—you’ll create a roof crowning your building with time-honored grace and enduring strength. Whether for a rustic barn or a modern timber frame pavilion, this truss will carry not just your roof load, but a legacy of craftsmanship into the next generation.