Will the tin roof roof fly away when a typhoon comes? Wind-resistant inspection of roof structures of old apartments and complete analysis of the causes of roof lifting in strong winds

Every year there are reports of iron roofs being blown off by typhoons

When a typhoon comes, one of the most common disasters on the news is that iron roofs are blown off and steel plates are scattered on the road. In the densely populated areas of old apartments in Taipei City and New Taipei City, there are a very large number of tin houses with roof tops. Most of these additions were built decades ago to increase usable space. The construction quality and material standards back then were far from what they are today. After years of exposure to wind, sun, and rain, the structural safety has long been compromised.

Why is the iron roof being "sucked" away?

Many people think that the iron roof is "pushed" away by the wind, but in fact, it is more accurate to say that it is "sucked" away. This is similar to the principle that aircraft wings can generate lift - the Bernoulli effect.

When strong winds blow across the roof surface, the wind speed above the roof is faster than below. According to Bernoulli's law, the faster the wind speed, the lower the pressure. There is low pressure above the roof and relatively high pressure below. This pressure difference is like an invisible big hand, "sucking" the roof up from the bottom up. If the upward suction force exceeds the weight of the roof plus the fixing force of the screws, the iron sheet will be lifted off.

What is even more dangerous is that if the doors and windows of the tin house are not closed or are blown open during a typhoon, strong winds pour into the house through the openings, which will instantly increase the internal pressure, which is equivalent to an extra "thrust" under the roof. Coupled with the suction from the outside, the chance of the roof being blown off will greatly increase under a double attack.

The three most common problems in tin houses

1. Loose screws due to corrosion: The corrugated boards of the tin house are fixed to the C-shaped steel or H-shaped steel frame below with self-tapping screws. The waterproof rubber gasket on the screw will harden and crack after more than ten years of UV exposure. After rainwater penetrates through the screw hole, the screw rod begins to rust, and the fixing force decreases year by year. When the typhoon comes, these screws that have long existed in name only become the weakest link.
2. The spacing between frames is too wide: In order to save costs, the spacing between frames (purlins) may exceed 120 cm or even wider in the early years of roofing. If the spacing is too wide, the middle section of the wave board lacks support. Under the action of wind pressure, it is easy to produce the "wind vibration effect" of bouncing up and down. Repeated vibrations will eventually cause the edges of the wave board to tear apart.
3. The connection between the wall and the roof is weak: Some iron roofs are placed on brick walls, and the brick walls themselves do not have a good ring beam (Ring Beam) structure. The force of strong winds or earthquakes can cause the tops of brick walls to crack and the entire roof to fall off, along with its anchors.

Safety inspection checklist for tin houses before typhoon

Legal responsibilities cannot be ignored

According to Taiwan's "Construction Law", adding roof tops without a construction license and usage license issued by the competent authority is an illegal construction. After being reported, according to the regulations of each county and city, new illegal buildings are usually reported and demolished immediately, while existing illegal buildings (mostly with the 1984 year of the Republic of China as the watershed) are listed and suspended.

However, regardless of whether it is a new illegal construction or an existing illegal construction, if the iron roof falls off during a typhoon due to improper fixation, injuring passers-by or damaging vehicles, the homeowner must bear civil liability or even criminal negligence injury. According to Article 191 of the Civil Code, the owner of a building or other work shall be liable for damages caused to others due to defective installation or maintenance. "Typhoon is a natural disaster" does not completely exempt the property from liability. The court will usually examine whether the owner has fulfilled the obligation of maintenance and management.

Conclusion: If you are not sure, seek professional advice

The safety of the iron roof on the roof cannot be judged 100% by the naked eye. If you live in an old apartment with a roof, especially one that has been roofed for more than fifteen years, it is recommended to have a professional ironworker or structural technician do a comprehensive inspection before the typhoon season. The fixed cost of repairs usually ranges from several thousand to tens of thousands of yuan, but if it is blown away by a typhoon and hits someone or a car, the subsequent compensation amount may start in the hundreds of thousands.