What constitutes a disaster-resilient house? Let an architect show you.
In 2011, the Philippines had been declared the world's most disaster-hit country. And as typhoons, floods and earthquakes struck one after another, such a pronouncement is easily believable, we were not given any respite in between these catastrophes.
In a recent study by the Swiss Re, the world’s second-largest reinsurance company, Manila has been listed as one of the riskiest cities to live in, second only to Tokyo. But, while Tokyo and many other vibrant world cities have already been confronting these natural calamities for quite some time through disaster-preparedness programs, we Filipinos seem to have just started to face scientifically these cataclysmic occurrences only recently. In responding to the global climate change, many countries have gone from risk management to mitigation to adaptation. Our country has passed up its chance for envisioning and went straight to troubleshooting. Thankfully, through collaboration and shared values within and outside the global community, the Philippines still stands as much chance as every other nation to cope with drastic climate change and other natural events.
In the management of risks, the need to identify, assess and prioritize risks is an initial step. Then, we need to apply resources that will minimize, monitor and control the impact of adverse events. Effective mitigation requires that we all understand local risks, address the hard choices, and invest in long-term community well-being. Without mitigation actions, we jeopardize our safety, financial security, and self-reliance. This is what it means to take action right at this moment before the next disaster strikes based on a strategy. Lastly, our efforts in adaptation is important in order to respond to the effects of climate change that are already happening, while at the same time being ready for its impact in the future.
Being an archipelago of 7,100 islands has its wonders, but having human settlements developed along the sea or waterways brings about flood risks that threaten more people than any other natural catastrophe. Since we are situated along the Pacific Ring of Fire, an area of high seismic activity in the Pacific Ocean, this is closely followed by earthquakes. Then there are also risks from strong winds and storm surges. Often, we have to be prepared to cope with more than one hazard at a time. While the chance of a major earthquake taking place and a typhoon happening simultaneously is exceptionally low, disaster preparedness dictate that we prepare for the eventuality of any or all of these taking place at any given time. In the light of global climate change, creating a comprehensively consistent index for aggregated risks makes more sense. Preparing for more helps us to cope better.
This is undoubtedly a daunting task. We have started to question and explore the challenge of changing the way we build. As such, the Emergency Architects currently headed by Architect Rey Gabitan, under the United Architects of the Philippines with the leadership of its national president, Architect Rozanno Rosal, was formed in order to respond to this need of preparing ourselves for the coming catastrophes, in the most scientific way, by well-built and functional structures.Their strategies include confronting the disaster at the temporary shelter stage, then a reconstruction phase, followed by a capacity-building to prepare for future disasters.
Studies have shown that disaster planning is most urgent in densely populated areas. As we plan for highly resilient structures, it is imperative that we take into consideration creating strategies to promote city resiliency. Creating buffer zones such as the development of liner parks along riverbanks and waterways is a possible mitigation action. Housing and resettlement ought to be anchored on Disaster Risk Reduction management. As such, the poor, the informal settlers, in particular, have to be resettled away from the danger areas of accumulated silt along the rivers and canals. It is highly imperative to clear these waterways of obstructions, mainly garbage and illegal constructions.
The reduction of carbon footprint through lower energy consumption and sustainable building practices is also important. There are already local government units, such as Quezon City, which have a Primer on Green Building which makes the practices of rainwater catchment in all new school buildings mandatory, as well as the use of biodigesters with biogas collection tanks in public markets. In markets and hospitals, sewage treatment plants are also made a requisite. Energy efficiency must be maximized by natural ventilation and natural lighting, as well as the use of LED and photovoltaic cells. By turning our rooftops into gardens, our cities can produce significant amounts of green areas. We should also promote pedestrianization and develop balanced, mixed-use communities, vertical living and better drainage systems. By now, we must realize how paved surfaces impede the ground’s ability to absorb rainwater. Lastly, the conservation and management of sensitive and critical eco-systems within the city has to develop in the citizenry by way of the creation of more eco-parks and other activities that will promote this paradigm.
To have a typhoon-resilient home, here are some strategies recommended by the UAP emergency architects:
1. Design the building to withstand the expected lateral and uplift forces.
2. The best shape to resist high winds is a square. For structures with a rectangular shape, the length is not more than three times the width. Consider a cluster arrangement for groups of buildings.
3. Maintain the integrity of the building envelope, including roofs and windows. There is a difference between hip roofs and gable roofs. Hip roofs offer much less wind resistance than gable roofs. For gable roofs, make them highpitched. As much as possible, avoid a low-pitched roof and adopt an angle at 25-40 degrees since it has the best record of wind resistance.
Roof eaves can be limited to 18-20 inches (40-50 cm).
Avoid large overhangs, and brace your roofs by ties held to the main structure. Better yet, design them as a separate construction rather than extensions of the main roof of the building.
A gauge#24 (0.4mm thick) roofing sheet is recommended. At ridges, eaces and overhangs, provide fixings at every two corrugations, and at all other locations, at every three corrugations at maximum spacing, using proper drive screws, large washers under the screws and embedded to purlins at 50mm.
Roof trusses and gables must be braced, providing metal tie-down straps that tie the roof structure all the way down to the foundation. As much as possible, provide various structural connectors to reduce uplift.
Anchor your roof framing to masonry wall through anchor bolts embedded in concrete cores.
Mind your fenestration, or the arrangement of windows and doors, of the house. Doors and windows must be protected by covering as well as bracing. Hurricane shutters can protect windows from most wind-blown debris. Window openings and panel sizes should be reduced to smaller dimensions and strengthened by pasting thin film or paper strips.
4. Make the construction system more wind resilient and which could possibly withstand more than 250 mph (400 kph) winds.
Tips for a flood-resilient design:
1. Location. Avoid as mush as possible any high-density development in low-lying areas because they are more prone to flooding. Homes located in flood-prone areas should be designed with all living spaces located above the designated flood-plain elevation.
2. Foundation. Flooding causes the saturation of soil, thus significantly affecting its safe bearing capacity. In flood-prone areas, the safe-bearing capacity should be taken as half of that for the dry ground.
3. On-stilts. Stilts should be properly braced in both the principal directions, with the knee bracings, preferably to full diagonal bracing so as not to obstruct the passage of floating debris during a storm surge.
Design strategies vs earthquake:
1. Foundation. Soil for a good foundation that can carry the weight of a house must be well-drained, therefore dry and not waterlogged. In an earthquake, water-logged soil can become liquefied, or turned into almost like a liquid, and structures will sink into the ground.
2. Plan shape/building configuration. Maintain the symmetry of a structure by distributing the seismic force resisting component evenly in all directions. This is crucial in reducing the earthquake impact. Avoid soft stories and asymmetrical floor plans, which can induce torsion.
3. Structural framing. Opt for a more regular structure so that the capacity to resist lateral forces should be the same for each floor. Decide on vertical frames that continue to the foundation. Roof trusses are to be placed over columns and tied to them, with the truss joints and particularly the central ones, bolted, not nailed.
4. Wall and window openings. For the purpose of providing lateral support to cross walls, the openings in load-bearing walls should not be within a distance of H/6 from inner corner, where H is the story height up to the level of the eaves.
Following the onslaught of back-to-back disasters, many architects and professionals in the allied field of construction have generously shared possible and tested solutions in the hope of rebuilding lives and supporting local communities affected by these calamities. Their collaborative responses are timely, but as we all have surmised, all these solutions are truly put to the test until the next disaster strikes. The impact of a major natural catastrophe can be avoided only to a certain extent. The effort and costs for relief, recovery and rebuilding will constitute a burden to all, but saving lives should take the highest priority in risk mitigation efforts.
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