---
title: "Collar timber roof"
subject: "Building Technology"
chapter: 4
key: "semester_6/building_technology:collar-roof"
source: https://www.bctengineer.com/q/semester_6/building_technology/collar-roof
site: BCT Engineering
---

# Collar timber roof

Building Technology · Chapter 4: Roofs

- Asked in: 2073 Magh
- Video: [Rafter Ties vs Collar Ties | What Every Builder Must Know](https://www.youtube.com/watch?v=1JS0pH4PPv4) — Conventional Framing
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/collar-roof
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-4

## Question

Describe collar timber roofs with necessary sketches.

## Short answer

A collar roof has a horizontal collar beam joining rafters at one-third to one-half the rise, reducing sag and allowing slightly larger spans (~5 m) while maintaining more headroom than a couple-close roof; walls still resist some thrust.

## Answer

A **collar roof** is a couple (or couple-close) roof in which a **collar beam** (horizontal tie) joins each pair of rafters at about one-third to one-half of the rise above the wall plate. The collar stops the rafters sagging and spreading, and allows slightly larger span (about 5 m) than couple-close roofs.

```text
            ridge
             /\
            /  \
     collar/----\ collar beam
          /      \
         /        \
      __/__________\__
     wall plate   wall plate
```
Members: wall plate (75 x 100 mm), common rafters (50 x 100 mm at 450 mm c/c), collar beam (40 x 100 mm, bolted), ridge board (40 mm thick), battens and covering.

The collar beam does not take the full thrust like a tie beam; hence walls should still be strong enough to resist some outward thrust. It is used for small residential spans and cottages.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Where is the collar beam placed in a collar roof?
   A. At the feet of the rafters on the wall plate
   B. At about one-third to one-half of the rise above the wall plate
   C. At the ridge
   D. Below the wall plate
   Answer: B. The collar joins rafter pairs at one-third to one-half of the rise above the wall plate. (Key point: Collar position)

2. What does the collar beam mainly prevent?
   A. Rain leakage at the ridge
   B. Termite attack on the wall plate
   C. Rafters sagging and spreading
   D. Uplift of the covering by wind
   Answer: C. The collar stops the rafters sagging and spreading, allowing a slightly larger span (about 5 m). (Key point: Collar function)

3. How does a collar beam differ from a tie beam in thrust resistance?
   A. It takes the full thrust like a tie beam
   B. It removes all horizontal thrust
   C. It transfers thrust to the ridge board
   D. It does not take the full thrust, so walls must still resist some outward thrust
   Answer: D. The collar is higher up and cannot take the full thrust, so walls must be strong enough. (Key point: Collar vs tie)

## Related in Building Technology

- [Timber collar beam roof and roof coverings](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acollar-beam-roof-coverings) — Building Technology, chapter 4
- [Roof types, functional requirements, timber roofs](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-types-requirements-timber) — Building Technology, chapter 4, asked 5×
- [Roof covering; double and triple roofs](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-covering-double-triple) — Building Technology, chapter 4
- [Single, double, multiple timber roofs; king post truss](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Atimber-roofs-king-post) — Building Technology, chapter 4, asked 2×
- [Couple closed roof versus collar roof](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acouple-vs-collar) — Building Technology, chapter 4, asked 2×
- [Steel trusses versus timber; triple timber roof](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asteel-truss-triple-roof) — Building Technology, chapter 4