---
title: "King post, queen post, mansard trusses; thatch"
subject: "Building Technology"
chapter: 4
key: "semester_6/building_technology:king-queen-mansard-thatch"
source: https://www.bctengineer.com/q/semester_6/building_technology/king-queen-mansard-thatch
site: BCT Engineering
---

# King post, queen post, mansard trusses; thatch

Building Technology · Chapter 4: Roofs

- Asked in: 2080 Chaitra, 4+2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/king-queen-mansard-thatch
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-4

## Question

Compare king post, queen post and mansard roof truss with suitable sketch. What are the advantages and disadvantages of thatch roof covering?

## Short answer

King post truss has one vertical member for 5-8m spans; queen post has two posts for 8-12m; mansard has double slopes (lower 60-70°, upper 15-30°) for attic space. Thatch is cheapest, insulates well, light, and quick to repair but has high fire risk, short life (3-5 years), harbours pests, needs steep slope, and poor rain protection.

## Answer

#### Comparison of king post, queen post and mansard trusses
| Point | King post truss | Queen post truss | Mansard truss |
|---|---|---|---|
| Vertical members | One king post | Two queen posts | King and/or queen posts |
| Span | 5-8 m | 8-12 m | Large spans with attic |
| Top member | Single slope principal rafters | Straining beam between posts | Two slopes each side |
| Slope | Single, 30-45 degrees | Single | Lower 60-70, upper 15-30 degrees |
| Use | Houses, small halls | Halls, godowns | Attic rooms, public buildings |
| Complexity | Simple | More joints | Most complex |

```text
 King post        Queen post        Mansard
    /\               /\             ____
   /|\              /--\           /    \
  / | \            /|  |\         /      \
 /__|__\          /_|__|_\       |________|
```
#### Thatch roof covering
**Advantages:** cheapest and locally available (straw, khar, reed); good thermal insulation (cool in summer, warm in winter); light weight, so light supporting structure; quick to lay and repair.
**Disadvantages:** high fire risk; short life (3-5 years) and frequent replacement; harbours rats, insects and moulds; needs steep slope (45-60 degrees) and is not easily rain-proof; poor appearance and not suitable for urban areas.

## Check yourself

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

1. How many vertical posts does a king post truss and a queen post truss have respectively?
   A. One and two
   B. Two and one
   C. One and one
   D. Two and two
   Answer: A. King post truss has one central post; queen post truss has two. (Key point: Vertical members)

2. Which pairing of truss and span is correct?
   A. King post: 8-12 m
   B. Queen post: 8-12 m
   C. Queen post: 5-8 m
   D. King post: above 15 m
   Answer: B. King post 5-8 m, queen post 8-12 m. (Key point: Span ranges)

3. What distinguishes the mansard truss?
   A. A single slope of 30-45 degrees
   B. No tie beam
   C. Two slopes each side, lower 60-70 degrees and upper 15-30 degrees
   D. A straining beam between two posts only
   Answer: C. The double slope gives attic space; it is the most complex. (Key point: Mansard slope)

4. Which is a disadvantage of thatch covering?
   A. Heavy weight
   B. Poor thermal insulation
   C. Very high initial cost
   D. High fire risk and short life of 3-5 years
   Answer: D. Thatch is cheap and insulating but burns easily, decays quickly and harbours pests. (Key point: Thatch drawbacks)

## Related in Building Technology

- [Queen post truss and its elements](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aqueen-post-truss) — Building Technology, chapter 4, asked 2×
- [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 and mansard roof truss](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acouple-closed-mansard) — Building Technology, chapter 4
- [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
- [Roof covering materials for pitched roof](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-covering-types) — Building Technology, chapter 4, asked 3×
- [Factors for selecting roof covering](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-covering-factors) — Building Technology, chapter 4, asked 2×

## Related in other subjects

- [Use of trusses; cantilever truss member forces](https://www.bctengineer.com/question.md?key=semester_1%2Fapplied_mechanics%3Acantilever-truss-bc-be-ef-ab-af-bf) — Applied Mechanics, chapter 7
- [Roof truss member forces (1-11, 1-10 etc.)](https://www.bctengineer.com/question.md?key=semester_1%2Fapplied_mechanics%3Aroof-truss-members-1-11-1-10-1-2-2-10-10-11) — Applied Mechanics, chapter 7
- [Max wind force on roof truss, 50 yr, hill crest](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Awind-max-force-roof-truss-kathmandu) — Design of Steel and Timber Structure, chapter 8
- [Wind pressure on roof truss, 20 m span, 30 deg](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Awind-roof-truss-20m-span-30deg) — Design of Steel and Timber Structure, chapter 8