healthy homes, at lower cost

Timber frame glossary

The name of each piece, where it is, and what it does. Both sketches are drawn by the designer.

The Biobâtir model — plain truss, purlins

P1A P1B P2A P2B P3A P3B S-A S-B E1 E2 E3 P1I1 P3I1 C1A+ C1B+ C3A- C3B- CG1A CG1B CG3A CG3B RP1A RP1B RP2A RP2B RP3A RP3B K1 K3 PA1A1 PA1A2 PA1B1 PA1B2 PA2A1 PA2A2 PA2B1 PA2B2 FT1 LF1+ LF3- STRUCTURE SUJETTE À L’APPROBATION D’UN INGÉNIEUR EN STRUCTURE (P.Eng. au Canada, Professional Engineer aux États-Unis). Ce document ne remplace ni un calcul ni un sceau. STRUCTURE SUBJECT TO APPROVAL BY A STRUCTURAL ENGINEER (P.Eng. in Canada, licensed Professional Engineer in the United States). This document replaces neither an analysis nor a seal. 123456
  1. Post — Vertical member. It takes down to the ground, in compression, what the roof and plates give it.
  2. Brace — The short diagonal between a post and a horizontal. It keeps the frame from racking: without diagonals, a pegged frame has no sideways stiffness.
  3. Wall plate — The horizontal at the top of the wall, post to post. Rafters sit on it; it carries the roof between bents.
  4. Tie beam — The bottom member of the bent, wall to wall. It TIES the spread: under snow the rafters push the walls out, and the tie beam, in tension, holds them.
  5. Principal rafter — Heavy rafter at the bents only. It carries the purlins.
  6. Purlin — Roof horizontal from bent to bent, on the principal rafters. The decking is nailed to it.

The Biobâtir model at a wide span — king post and central beam

P1A P1B P2A P2B P3A P3B S-A S-B E1 E2 E3 PB P1I1 P2I1 P3I1 C1A+ C1B+ C3A- C3B- CG1A CG1B CG3A CG3B RP1A RP1B RP2A RP2B RP3A RP3B K1 Q1A Q1B K2 Q2A Q2B K3 Q3A Q3B PA1A1 PA1A2 PA1A3 PA1A4 PA1A5 PA1B1 PA1B2 PA1B3 PA1B4 PA1B5 PA2A1 PA2A2 PA2A3 PA2A4 PA2A5 PA2B1 PA2B2 PA2B3 PA2B4 PA2B5 FT1 LF1+ LF3- STRUCTURE SUJETTE À L’APPROBATION D’UN INGÉNIEUR EN STRUCTURE (P.Eng. au Canada, Professional Engineer aux États-Unis). Ce document ne remplace ni un calcul ni un sceau. STRUCTURE SUBJECT TO APPROVAL BY A STRUCTURAL ENGINEER (P.Eng. in Canada, licensed Professional Engineer in the United States). This document replaces neither an analysis nor a seal. 1234567
  1. Interior post — Post in the middle of the building. It cuts the tie-beam span and takes the load down to the slab.
  2. Central beam — Beam along the building, under the middle of the tie beams, on posts.
  3. Tie beam — The bottom member of the bent, wall to wall. It TIES the spread: under snow the rafters push the walls out, and the tie beam, in tension, holds them.
  4. King post — Vertical at the middle of the bent, standing on the tie beam. In the model it carries the ridge and takes its load down into a post under the tie beam: it is in compression.
  5. Principal rafter — Heavy rafter at the bents only. It carries the purlins.
  6. Purlin — Roof horizontal from bent to bent, on the principal rafters. The decking is nailed to it.
  7. Ridge beam — The horizontal at the peak, gable to gable, set on the king posts; the rafters rest on it.

Words that are not pieces

Closed truss
A complete triangle: the two principal rafters and, at their feet, the tie beam that joins them. Under snow the rafters push outward; the tie beam, in tension, keeps that thrust inside the truss, so it does not push the walls apart. A collar tie set high does not close a truss.
Eave wall
One of the walls under the low edge of the roof slopes, where water drips off. Its top is level and the rafters bear on it: it carries the roof. A gable roof has two; on a shed roof, both the low and the high wall are eave walls.
Gable wall
One of the two walls of a gable roof that rise in a triangle to the ridge. It closes the end of the roof; the attic window often goes there.

Open the designer