Lessons from Yolanda – Building Construction

Share the joy

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.

tacloban_house_3 tacloban_house_2

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

Comments (13) Write a comment

  1. Carol & Bob,
    Hi again. No, none of the roofing in this discussion is Industrial Strength, nor anything else in the ‘modern’ Philippines. That requires reinforced 8 inch Concrete skin. Where a roof is punctured in the extreme velocity winds, contents are sucked out at 384 miles per hour. While the struts provide style, they do not provide life support. In Darwin, of the 5% still standing houses, many of those had roof holes and no occupants. One roof hole survivor was found. His leg snagged under a toilet was almost torn off, the daughter in his arms when the ST hit was never found. Hate to sound dramatic, but think about your roofing lots more carefully. The traditional circle-style homes that I saw in 400 year old Spanish illustrations had log roofs and one had logs across the courtyard (must have been built in Tacloban). The concrete roof sloped to ground can really be very attractive. It’s not like a death sentence for appealing livability, to sport calimansi and orchids over dining room and bedroom skylights (see min glazing specs below. But myself? I wouldn’t live under roof glaze. Too risky. fenestration and egressing courtyard would be exciting and hi-tech. If you want a glimpse of really ridiculous modern colonial residential tropical oceanic construction, take a look at the Bimini Clueless cat 5 invitation.
    Will they rebuild. Yes. For now, visitors are providing income. But given post-storm chill (in New Orleans, some homes still submarine), and given inevtible increases in strength and frequency due to global warming, better enjoy it while you can, if you can. The ancient Filipinos were not fatally absent-minded, like the world we all share today. Modern materials, their floor plan will turn every ST into an indoor party excuse.


  2. George et al,

    In addition to my critique of your understatement, two more things about the F4 resistant industrial strength requirement, and a final mention for community capacity (the tariff and trade enslaved building environment). European and Japanese technology driving the best satellites accessed by the States (at least, before the NSA-induced technology slump initiated last week) is that do indicate a Sustained Wind Speed, and a ‘gusting to’ Maximum Wind Speed’. In the fine print how to read at the US agency, the internal Sub-Storm Turbulence is better explained. Though at the best of times MIT has difficulty to access that information in its most up-to-date content. Anyway, using those public MWS values, Yolanda flattened the burbs as a low end F4. Being prone to sailing and understanding real wind impact, in that sense, the turbulent microsecond structure shredding SST is really more relevant. That’s why, in fact, Yolanda was (and behaved like) a medium F4.

    Finally, in designing the industrial strength unit, you mention tradtition Philippine building practices. In my letter to the Minister, my argument was that we need to consider traditional architecture, that is now only an archived relic. So essentially, a concrete, steel-reinforced unit with double-plated 2@3/4 inch floor-to-ceiling glazing no more than 2 feet across and no less than one foot apart, standard 9 inch I-bem upgrights 3 feet on center with adjoining roof members, would slope to ground with a central !important circular court yard. Egress and garage etc would engage the concept… However, mention must also be made of tiles. In the super-T that hit Darwin, all those dreading years ago, the F4 winds happened to include boulders and so forth that dislodged some tiles. Then those dislodged other tiles, and so on. 2 miles in from town where the bank was the only structure left standing, forensic analysis showed that 20 pound tiles have no problem remaining airborne more than 8-10 miles. Essentially, excepting 5% of homes shielded behind a hill, tiles flattened the entire city. At which point the current wire strapping (thanks in np small part to a year of private investment and political wrangling from my father), is now a global standard in the wind belt (essentially, everywhere).

    Ninoy will never take his country to a forensic analysis. But on the bright side, two tiles were chipped on their edges on mother’s house. Again, miraculous. In fact, we know that flying tiles were contributing factors. See above, general design specs. Global community capacity housing does not presently afford Super Typhoon protection.


  3. It is good to see a public share about Yolanda impact at myphillippinelife.com. But your discussion seems to avoid community capacity and realistic consideration of the force of the storm. Much like Nino’s appointed minister in response to an email. Disconnected.

    Where you show us a photo of a roof intact, has nothing to do with good design, in the context of a super-typhoon. Check out your tornado wind scale. Yolanda was a medium F4, which at its ground contact, wipes flat any residential and light commercial/industrial structure. However, F4’s are a square mile contact point. Yolanda was over 450 miles across, meaning an inner-half area of F4 contact point in the hundreds of thousands of square miles. Now, inside of that vast area, consider a city block within a 10 second interval. During that brief period, the F4 wind direction will shift across portions of the block hundreds of time. Many shifts will initiate sub-storm wind accelerations, mini tornados inside the parent storm. This sub-storm acceleration is what shreds structure. That’s millions of violent accelerations per second in Yolanda. A lot of wiped structure. Miraculous that anything not bolted, concrete encased, and cemented to solid foundation can survive.

    Further, we need to consider the social landscape. Average annual income in the Philippines is just over a thousand. But that estimate includes scoping the globalized millionaire elite, beside $90 per month average household incomes. Which simply demonstrates enormous disparity of wealth. Only a few thousand people capable of constructing an industrial strength residence. You seem to understand that principle, though you failed to quantify with fact, so fact is offered here. At least “tens of thousands” reported victims. But according to satellite images, hundreds of thousands of bodies carpeting the ocean around each of the cities, and similarly collaring many towns, indicating a floating count over 1 million. Having provided shelter for only about 750,000 of 12 million residents, the sweet-hearted President froze when it came to what humanity suffered. There were tears in his eyes, but his face was in shock, expressionless, lost! The official death count still isolates only the tiny elite’s commercial minions. The rest is “agreeably” too much to deal with. “Let the fish eat.” Not a cynical or distasteful comment from the schizophrenic President, at a moment of immense stress even for the very best of us, but in context, he got it right. Perhaps this feast provided by nature has much more spiritual significance in the Philippines, an oceanic culture. Yes.

    Consider again the size of the storm’s F4 contact. My mother-in-law’s house was something like that proud intact red roof above (in your discussion). A dent to a new 4 wheel drive Toyota, from a swinging garage gate and a disappeared house shading tree the only damage. Her neighbors’ homes of equal stature faired not so well. For two, only foundations were left, and the rest not livable, in a flat waste land. The hardest part of storm preparation with Yolanda rolling in, was getting our loved ones to accept the shelter provided to them. They are accustomed to opening their doors to ‘swept clean’, not wiped flat. You know, your discussion seems unique. But very unreal. Perhaps it will take some time for the strength and significance of Yolanda to sink in, for you.


  4. Of all my travelling around the Philippines I took noticed that all the roofs which has lasted the longest in the Philippines during typhoons is the ones built by the Spanish which are made of tile. When I built my house I didn’t want to go looking for it every time there is a storm. And my wife said that she always liked the looks of tile roofs when she was growing up in the Philippines. So when we built are house we had tile installed instead of tin. I know this is a little over kill but I know it will be there for my kids and grand kids even though the only way they will be able to sell it if some local can afford it. So far after 10yrs and I don’t no how many typhoon in Samar which is in typhoon belt have not had to go looking for same. Here in states if you install tile on your roof and company is still in business you have life time warranty. In Philippines it is only ten years and they do not install underlayment like in states. I also installed 1/4 steel to hold roof up and 5/8 marine plywood according to invoice from hardware store???. During typhoon most relatives head for our house to ride out storms. Still have not found energy efficient windows for house which dose not cost more then what it cost here in states using slave wages.


    • George,

      I too love the look of tile roofs. Our house in New York had a slate roof which had been in place more than 100 years. However, any heavy roof increases danger from earthquakes. The weight, up high, can accentuate the stresses on the structure of the building during an earthquake’s lateral sway. The roof can act as a sort of pendulum. That’s part of the difficulty of designing buildings for the Philippines. There are so many risks; earthquakes, typhoons, surges/tsunamis, flooding, salt spray, insects and so forth. A bamboo house is great for earthquakes and terrible for typhoons. A hollow block house is good in floods but might be bad in earthquakes. I’m not sure what the right answer is!



  5. From Ted:

    I first found these almost two months ago on an Australian website.


    They are cyclone shutters (the US has hurricane shutters) and their purpose is to: protect the most vulnerable part of the house i.e. the windows and doors. When wind speeds reach those of a Cat 4 or 5 cyclone the wind pressure will bow a 2 metre window several centimetres. If it shatters, the glass breaks with explosive force doing extreme damage to internal walls and furnishings. Persons are in grave danger if they are exposed to this situation. Broken windows can increase the aerodynamic load on a roof thus increasing the chance of a roof separating from the house.

    I thought they were an interesting alternative to security grills – but now, I will definitely install these instead of the typical security grills.

    Reply from Bob:


    I agree, this is a very interesting alternative. Such “shutters” could be made here quite cheaply and could serve for storm protection, security and to keep direct sun off of windows. Actually these shutters look very much like the louvered shutters I have seen which are intended to keep a house cool. A concept with great potential!


    From Ted:

    I remember that you were concerned about ruining your view of the mountains – a window or screen issue. I also remember that you said there was a safety concern (Fire Department inspection) about security grills being hinged on the inside to allow egress.

    The cyclone shutter will resolve all of those issues. The steel shutters can be hinged at the top and remain open until needed for pending storm or security as can those shutters hinged on the sides or those that slide open/closed. All can be secured on the inside/outside.

    I remember the preparation before Hurricane Hugo in Goose Creek, SC – late ’80’s (a little north of Charleston). My son and I covered out windows/patio doors with sheets of plywood before I went to my ship and sent the family to NC.

    When I finally got home – three days after the storm – I discovered the roof on our duplex was severely damaged because the neighbor did not cover his windows. All his windows were blown out along with the roof.



  6. Atmospheric Pressure increases inside when your house is on the path of the Typhoon winds.

    Do you know back in the Caribbean is advisable to leave, One Small window open! preferably the window that is not been batter by the Winds. @dry side. That way you could equalized the Atmospheric pressure of the air trying to Siphon your roof and windows.

    I left all my bathroom windows open, including the doors for deflation effect.
    Correct me, If I’m wrong.



  7. Bob,
    Can you provide a reference for correct positioning of the Tekscrews. In the US the “general rule” is to start panels at the end of the building, opposite from the direction of prevailing wind. Use Tekscrew with a rubber or neoprene washer on one side 3/4″ from each rib in the flat and on both sides of the overlapping rib. A screw is also placed at the top of the overlapping rib. If purlins are more than 610mm apart, then stitching screws are recommended on the lapping rib between the purlins.
    I suppose, if rubber or neoprene washers are not available, then the “next best thing” is the way your roofing panels were installed to prevent a water-leakage problem.
    However, since the Tekscrew does not effect a tight mating of the steel roofing panel and the steel purlin, how does that affect the Tekscrew single shear strength, axial tensile strength and the torsional strength (shear load, tensile load and torque required to break the screw)?


    • From Ted:

      There appears to be differing opinions depending on world location.

      Union Corrugating Company is a major US roofing manufacturer and they insist that fasteners be placed in the “flat” using neoprene of rubber washers. This fastening technique has been approved by Florida, Texas, North Carolina, South Carolina, Georgia, Oklahoma, Virginia, Pennsylvania, Mississippi, and Ohio – ALL hurricane states.

      In our part of the world, BlueScopeSteel.com is the leading manufacturer and Lysaght.com is a distributor for that company.

      The method of fixing depends on the panel profile. You can place screws in the ribs or pans/valleys, but to maximize water-tightness place screws in the ribs WITHOUT over-tightening the screw which will deform the panel profile and cause the penetration to leak.

      Where a screw penetrates the rib of the sheeting, ‘the top thread section’ feature is recommended to maximize resistance to water penetration.

      There should be at least three threads protruding past the support you are fixing to. Where rib fixing is done then the ‘shank protection’
      must not reach the support.

      I have included “Fasteners” so you can review the illustrations to better understand what I typed.

      There is a maximum recommended spacing for the purlins depending on the panel profile and a minimum thickness of 1 mm (1/16″).

      Now, I am wondering if DN Steel provides any recommendations like the above?

      From Bob:


      Once again, thanks for this information. My screws are just like the illustration on page 10; self-drilling, hex head with rubber (neoprene? EPDM?) gasket. There is no “dwell section”, the entire screw is threaded. The overall length of the screw is 6 CM or about 2 1/2″

      I got out my house plans. There were no details for the attachment of the roofing to the purlins.

      I do see that the specs you provided shows ribbed roofing with attachment through the pans or ribs and that in some of the illustrations not every rib is screwed down. However, I don’t see any downside to adding screws so that each rib/purlin intersection is screwed down.

      One would think that the architect or engineer would spec these things, but the plans are really just needed to get the building permit and then the contractors can do whatever they like, using whatever materials they like, subject to supervision by an architect or pesky owner. That’s the great thing about being your own general contractor. You pay the workers and if you want something done better or done over, you are paying the bill and no one argues or complains

      What you are doing is very wise; researching all these issues before you build. We did not do that. As we built, we tried to use good materials and workmanship, but limited by our own knowledge of both materials and standards. So, it could be worse and it could be better. We did not cut any corners, at least ones we knew about. We really did not spare any expense.

      Regarding the roof, we did try to make it strong. We ordered and checked (calipers) the angle bar that went into the the girder and trusses. We paid quite a lot extra for the heaviest roofing. Now we’d just like to get it screwed down as well as possible plus do some additional ties between the trusses and the rebar coming out of the interior walls. Then mother nature can decide if we did well enough! We are starting our forth year in the house and we love it. The trees and shrubs and plants are growing and making our formerly barren lot a real tropical paradise.

      Best regards,


      From Ted;

      There is no downside to adding additional Tekscrews. Those were just minimum recommendations. Perhaps more screws will add ‘lifting strength’ to the panels. Those screws with the ‘top thread portion’ just ensure that the steel is drawn up tight against the washer to prevent leaks. When tightening screws with washers there are three possible outcomes – too tight, just right, and too loose. Too tight and too loose cause “leak’ problems. How do you ensure ‘just right’ ?

      Adding tie-downs/straps between truss and interior wall rebar will provide additional strength to the roof. The ‘collar ties’ that you added to the trusses also helped.



  8. Bob and Carrol

    I was contemplating the picture of the tech screws, the lapses of you roof with no tech screws Makes your roof week in that particular area. The rules is: The face down area of your GI sheet is not to be drilled, The Drilling is done in the Raise portion of the GI sheet, that is done because helps the rain run to run into the flat surface of the GI sheet.

    All raise areas of your GI sheet that touches your cross sections, should be bolted Vertically across firmly, straight down. To avoid burbling bouncing movement of the sheets Just think of your tech screws as the Razor sharp teeth of a shark biting and slashing through metal sheets and not letting go.

    Another consideration to be concern, is the type of roof Gage material you are using, the thicker. the strongest,the better.

    Most tech screw are Chinese made. I rather pay a little more money in buying tech screws made here in the Philippines, for some reason, they are forged to American code standards. The best tech screws are stainless steel not the galvanized kind, very expensive and sometimes are in short supply.

    ROOF rafters are a tricky one, How do you distinguished between Chinese made steel rafters from Filipino made?

    Is on the Gage and weight. Again that is when you pull your caliper tool and start Gage your soul away, the whole length and edge. You will see discriminatory differences.

    Filipino steel AKA rafters are more heavy and sturdy. the Chinese are light, even they are the same Gage and have a tendency to bend in the center. They don’t flex back and forth, they just flex one time and the loose their dimensional straightness.

    I did that test and kindly irritated, the merchant. Don’t care, is my money not theirs, they should spoke honestly and told me that metal was Chinese made and not Filipino.

    Eventually, I moved on and bought mines at other local hardware store This happen when I was building an extension roof in the back of my house for my wife’s laundry area.

    Again I’m no expert, but it is my experience that speaks out.


    • David,

      All good points. We are going to add tek screws where they should be but are missing. This was an issue which I never considered when our roof was installed but seeing all blown-away roofing in photos of Yolanda damage (and some roofs NOT blown away) has focused my mind on attachment; attachment of roof panels, attachment of purlins to rafters and attachment of rafters to the building itself. We did use .6mm roofing, the thickest and most expensive available from DN Steel. Your focus on the quality and gauge of C-purlins is also good. Spending a little more to get better quality could be the difference between having a roof and not having one. I have seen some shockingly weak looking roof structures going up. Thanks again for your comments.

      Bob and Carol


  9. Great site, information and resources…..

    A hip roof is by far the most storm resistant and I have also noticed – I rarely have seen hurricane shutters in the Philippines and doors more often then not open inward instead of the more storm worthy – outward (the force of the wind can not blow it in easily and it is also harder to kick in) If the typhoon/ storm winds get into the house – it is finished and the pressure could create a blow out …

    I still have 6 years until I retire to my property in Kalibo so all this research and sites like this – helps tremendously…

    I will be visiting Nov 2014 and try to get some fill onto the property, dig a well and plant lots of trees.


  10. Bob and Carol

    I’m glad that you guys survived, that is what counts First. Knowing this allow me to share some views.

    You know all those fancy windows and design in my sub division, for me, is like looking for troubled in the horizon, My steel casing windows do hold their own weight, just keep caulking some of windows and checking for minor damages. Nothing of the extraordinary we can’t be handle.

    My roof still intact, no visible damages yet!

    As you mention some of the design of the roofs varies, slope down roofs are better in deflecting the wind gust. My house is six “Aguas” but the design is a 45 angle slope all around, that helps deflect the wind gust. The less friction the better.

    Pretty much the anchorage of the roof is the same as yours, folded over and welded, then rust proof painted. There is no magic wand when using GI roofing, just the technique.

    Unless you want to pour a concrete roof, for which you could use steel decking with steel bars. and pour 3 inches of concrete and water proof with paint and rubberized products. That cost money. I’m from the Caribbean and that is how we build houses in cement to withstand Hurricane winds.

    I recently, before the storm, had the portals replaced with aluminum siding, double coat painted from the factory and re-bolted with new and more robust furling. Those upgrades paid off.

    Recently had my gutters clean from birds nest and debris, including the installation of a net barrier between the gutter opening and the roof, to keep those birds and their debris of my gutters. The flow of water was excellent.

    The worst offenders are the sparrows, that are migratory birds or semi- permanent, that are always feeding in the rice paddies causing havoc, I do curtail them, when they become a nuisance with my home made sling shot.

    Drainage of storm water is important. My house was built, around the house with a solid french drainage , so far so good. Nothing spectacular, low cost french drainage and walla! water runs off faster. Just keep it clean.

    Most important, in case of a worst case scenario, when disaster strikes, BUY YOURSELF A DECENT HOME OWNERS INSURANCE based and in accord TO THE VALUE OF YOUR HOUSE and belongings. Do your homework first!, my house with all our belongings is insured up to 13 millions pesos, My payment was 15 thousand pesos , CASA COMPLETA!
    and acts of GOD coverage. Trust me in this one, I sleep better……

    Take care and be blessed,
    So tell us How is your House?


Leave a Reply

Required fields are marked *.