Roof Construction and Types: A Brief Overview

Purpose of Roof Trusses

Roof trusses are critical timberwork, often the most expensive component of a house.
They must fulfill several requirements:
- Support the roof covering safely.
- Withstand wind and other external forces.
- Provide adequate ceiling height.
- Prevent rainwater accumulation.
- Enhance the building's overall appearance.

Components must be accurately cut and tightly fitted.
Industrial grade timber (grades 4, 6, and 8) is used for trusses.
Purlins and battens (lowest grade timber) are fixed to the rafters.
The king post is centrally positioned, determining the truss height and connecting to rafters and tie beams.
Maximum purlin spacing is 1200 mm centre-to-centre.
Battens have a nominal breadth of 38 mm and a depth of 38 or 50 mm, depending on the roofing material.

Simplest and least expensive, categorized as flat roofs.
Commonly used for extensions, carports, or small sheds.
Conventional lean-to purlins are nailed on top of rafters; modern ones are fixed between rafters.

Similar to couple roofs but include a tie beam that secures the rafters, preventing outward movement.
Suitable for spans up to 4 metres.

Feature opposed rafters and a horizontal collar beam, positioned higher than the tie beam in closed couple roofs.
Provides more space between the floor and ceiling.
Collar beams should not exceed half the rise of the roof.
Suitable for spans up to 5 metres.

The roof covering defines the roof's profile and protects against rain, heat, and cold.
Common materials include:
- Sheet metal (zinc or corrugated sheets)
- Concrete roofing tiles
- Thatch

Regulations govern the installation and functionality of roof coverings.
Safety is paramount:
- No work on roofs in rainy conditions.
- Effective precautions against falls are mandatory.
Devices used for affixing roofing must be corrosion resistant.