Roofing

One factor to consider with roofing is it’s weight as well as the support structure holding it in place. If a roof collapses it can flatten all that is below it. The weight includes not just the roof buy also any ceiling, floor, and assemblies.

Below is an image of a roof that has limited strength in its underlying support structure yet is handling a fair amount of weight from the corrugated metal roof:

Roofing-support1-400.jpg

Limited roofing support close up:

Roofing-support2-400.jpg

While metal roofing is generally very strong and lightweight compared to some other roofing materials, it still weighs about a pound per square foot. This means a single panel that is three feet wide and twelve feet long will weigh 36 pounds. Additionally, when a panel collapses, generally the full panel, at a minimum, falls. An example can be seen below.

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Image attribution: https://pixabay.com/photo-1665879/; CCO released image

In cases such as this it is not just the weight of the items falling from above which could harm individuals, but also pathways to exits which could be blocked.
Trusses can offer added underlying support structure as found in below pre-fabricated trusses:

Strong Roof Support Structure

Ample roof support structure is important because collapse from above could be catastrophic to all that lies below. Thus, use of joints, rafters, and corner support is essential. Below is a sample of a well made roofing structure:

strong-roof-400.jpg
Image attribution: https://commons.wikimedia.org/wiki/File:Wooden_roof_structure.jpg

If the roofing materials are lighter, the risk is less, such as in below sample from Bali:

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In other cases, particularly with heavy roofing materials, roofing could collapse in an earthquake based on limited structural support, such as in below
sample from Bali:

P1000579-400.jpg

This type of roof collapse could be catastrophic. The underlying support system will not be able to handle stress as well as the weight. If any individuals were to attempt to climb on the roof to remain clear of incoming water, the situation would only worsen in relation to stresses placed on the structure. Also relevant is the quality of the joints, particularly when supporting a heavy load, such as with clay tiles. An example of strong joint work can be seen in below king post truss:

king-post-truss-400.jpg
Image attribution: https://commons.wikimedia.org/wiki/File:Trad-king-post.png

However, as in this sample from Jakarta, it seems there may be cases when the joints are perhaps less than optimal:

IMG_0196-400.jpg

In this sample from Lombok, the connection points and joints are weak:

IMG_0136-400.jpg

All joints should be reinforced in some fashion such as with a flat corner iron, a t-plate, corner braces, a wooden gusset, or wooden blocks. Even in areas with very limited resources, we recommend additional support structure on roofing. The goal is to not have the roof collapse on persons who might be under it at the time of an earthquake nor become an obstacle to pathways to safety.

Multi Story Buildings

In the case of multi-story buildings, earthquake safety risk increases as the number of levels increases. The stability and strength of each upper level is dependent on the strength of those below it to carry the weight of all above it. In some cases the weight and sheer strength needs can be quite significant, as in this image from Lombok:

P1010111-400.jpg

Learn more

Below are some helpful resources to help you understand the many components of roofing assemblies and associated recommendations.

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