The roof is a fundamental part of any building, and its design and construction are critical for safety and durability. In Bali, traditional building methods have long favored the use of wood for roof structures. However, with the increasing cost of wood, lightweight steel roof frames are becoming a popular alternative. This shift requires a new understanding of engineering principles and construction standards to ensure quality and safety.
Traditional Roof Structures in Bali
Traditionally, Balinese roofs were constructed with a simple design using a horizontal ridge beam supported by rafters, which are sloping beams, that were placed with the upper ends against the ridge beam and the lower ends resting on the walls. These roofs did not have gables to support the ridge beam; instead, the rafters supported the ridge. The weight of the roof tiles would push down on the rafters, creating a force that could potentially push the walls outwards. To counter this, horizontal beams were added at the bottom of the rafters to form a triangle, thus creating a roof truss.
The Rise of Lightweight Steel Roofs
In many countries, roof trusses have evolved over time to use lighter and stronger materials. Early roof frames were made of a few large beams but modern methods use hundreds of small strips of wood. Today, lightweight steel frames are mass produced in factories, transported to the building site, erected onto the walls, and have battens and bracing strips added. This evolution of roof trusses has simplified the construction process, and reduced costs.
However, in Bali, the majority of roofs were still being built using the old methods of rafters and ridge beams supported on the tops of the walls. But that is changing due to the high cost of wood and availability of lightweight steel alternatives.
Challenges with Lightweight Steel
While lightweight steel roof frames offer many advantages, it is important to be aware of the potential pitfalls. To minimize costs, steel amounts are kept to a minimum, meaning that these structures are only just strong enough for the job. Unfortunately, some contractors might attempt to further cut costs by using thinner steel, fewer trusses, or fewer bolts, compromising the structure’s integrity. This can lead to disastrous consequences, such as roof collapses, especially when heavy roof tiles are used.
Key Considerations When Choosing a Lightweight Steel Roof
When opting for a lightweight steel roof frame, several factors should be taken into account:
- Steel Quality: The quality of steel used is of utmost importance. Steel should be high tensile, of the correct thickness and alloy, and heat-treated, with a galvanised or zincalume plating to prevent rust. It’s best to opt for a well-known brand of steel like Bluescope or Lysaght.
- Professional Design: A computer-generated design is essential to ensure the roof is properly engineered and will hold up against the weight of the roof and the forces of nature.
- Construction Quality: It’s important to check the construction work, ensuring that:
- The steel is in good condition and its shape is not damaged.
- Each joint has three bolts to hold it together.
- Drilled holes for the bolts are not too close to the edge of the steel.
- Dynabolts, not just screws, are used to fasten the roof frames to the concrete structure.
Conclusion
Lightweight steel roof framing is a modern and cost-effective solution for construction in Bali. However, it’s critical to prioritize quality materials, professional design, and skilled construction to ensure the roof is safe, durable, and capable of withstanding the challenges of the Balinese environment. By carefully considering these points, homeowners and builders can reap the benefits of lightweight steel framing while avoiding potential problems.
