Building a typhoon resistant house. Observations from Typhoon Yolanda/Haiyan. Like just about everyone else we’ve been horrified by the reports, photos and videos of typhoon Yolanda/Haiyan damage coming out of Tacloban, Leyte and elsewhere.
We have looked at the photos of the destruction to see if there is any pattern to the destruction, any lessons could be learned about building in the Philippines. In other disasters, especially earthquakes, teams of engineers have gone to the disaster areas, studied buildings and made recommendations for improved designs. Given that this type of storm may become more and more common, one hopes that engineers can make practical and affordable building construction recommendations to reduce loss of life.
Each type of natural disaster imposes its own challenges to buildings. In an earthquake, as we have seen in the recent Bohol earthquake, a flexible wood or bamboo building can be safer than a massive Spanish church. In Tacloban, buildings faced a storm surge similar to a tsunami and extremely high winds. The flexible bamboo and wood buildings were almost entirely destroyed.
We have looked at all the photos we could find of buildings in Tacloban which survived, which were damaged and which were destroyed and drawn a few very tentative conclusions.
The first conclusion is, of course, is that building a house in the Philippines close to the ocean is an inherent risk. Areas facing into east, into the normal typhoon track, are especially risky. Carol and I made an offer on a pretty oceanfront property, but were unable to come to terms with the seller and so bought property about one kilometer from the ocean and about forty feet above sea level. Everyone has to make their own calculation of risk and reward regarding the property they buy. Especially after Yolanda, we might not sleep so well in an oceanfront house, especially when a typhoon is forecast.
Google Earth is a great tool to use in evaluating property. It can tell you the elevation above sea level, proximity and elevation of nearby rivers and so forth. The property we bought, while at forty feet above sea level, is one of the lowest elevations in the general neighborhood. That was not immediately apparent from visiting the property.
This is a typical news photo of Tacloban destruction. It shows a devastated area on low-lying land near the ocean. The informal houses were of wood, bamboo and other weak materials.
The destruction in Tacloban was not complete. Many strongly built buildings did stand up to the truly unimaginable forces of Typhoon Yolanda. Certainly, the first priority is protecting life and not buildings. Nonetheless, a building which survives is more likely to protect its occupants, both before and after disaster, than one which is swept away.
Here is a photo of the Tacloban Convention Center which is located immediately on the waterfront. It seems to have survived all that Yolanda gave it with relatively minor damage to its roof.
Here is a photo of downtown Tacloban, showing that commercial buildings seemed also to have survived.
Here is an aerial view of Tacloban. On the lower right, one can see concrete residential buildings directly on the ocean which seem to have survived intact, even their roofs.
Here are a couple of photos of two story houses where it appears that the storm surge knocked down the first floor hollow block walls but where the second floor and the reinforced concrete frame survives. In the one case the second floor seems to be occupied.
I have always been appalled at how weak walls of 4” hollow block seem. The conclusion I draw is that using higher quality 6” hollow block with adequate reinforcing bar and well-filled concrete (not mortar) cores might help the survival of the building and its occupants. Since commercial buildings almost always use 6″ block and they seem to have survived, this may further buttress this idea.
Below one sees a residential area with concrete buildings which retain their roofs and those which did not. Keep in mind that some buildings retained their entire roof structure – rafters, purlins and sheet metal roofing. This suggests that a good roof and withstand the highest winds.
Some buildings lost their entire roof structure suggesting that the ties of the roof to the columns and roof beams were inadequate. Here’s a photo of how the rebar protruding out of the tops of our columns were wrapped around the roof girders and welded.
This is a photo of the roof structure of our house. While the rafters (girders) are securely attached to exterior walls, there are additional attachment possibilities presented by rebar protruding from the interior column ends. Steel straps could be welded to the rebar ends, connecting them to girders.
Some buildings retained their roof structure but lost their roofing. This suggests a close look at the attachment of the roofing panels to the purlins. Even before Yolanda, we observed that our roofing panels were not screwed at every intersection of roof panel and purlin – that the number attachment points exceeded the number of actual attachment. If you have a fixed bid for your roofing, the contractor may want to minimize the number of expensive “Tek” screws used. We’ll be studying roofing standards and see if the attachment of our roofing is optimal.
Some buildings lost their roofing and had torn and twisted purlins. I have seen may houses going up which use very light angle bar for the roof structure. Perhaps adding a bit of strength here is called for.
Finally, we used a somewhat complicated roof design in an attempt to emulate the look of the Philippine native house. In retrospect, we feel this was a bad decision. It was more complex and more expensive than the very practical, wind-shedding hip roof found on most Philippine roofs. The ventilators in our roof are vulnerable to wind driven rain and make the roof less streamlined to resist strong winds.
These are just a few preliminary comments. We are not engineers. These are the thoughts from a couple who built their own home in the Philippines, so take them for what they are worth. Your comments are very welcome. Also see how we designed and built the roof of our Philippine house at: http://myphilippinelife.com/our-philippine-house-project-roof-and-roofing/
Revised Nov 17, 2013