Tuesday 11 December 2018 18:50:51 PHT

Rebuilding Bohol: Houses

IJsselstein, Monday, 25 November 2013

Now that the first needs are being addressed, the number of aftershocks start to reduce, and a huge storm has blown over, it is high time to start thinking about rebuilding.

Actually, since our family's home was also heavily damaged, I've been studying several methods for building houses, since the day of the earthquake. Unfortunately, most will be very hard to apply locally, and we will probably have to fall back to time-tested traditional methods, augmented where possible and needed with modern insights to make them more durable. I would like to share these ideas and insights on this site.

I noticed that a lot of houses collapsed due to various design errors or shortcuts that could have been avoided. Although I am not an construction engineer, it is my intention to collect useful information on this site, and make it available otherwise, to make people aware of potentially live-threatening problems.

Constraints

Lets start by looking at the constraints. A house in the Philippines needs to withstand a some environmental extremes:

  • Earthquakes effects up to intensity VII (on the PHIVOLCS Earthquake Intensity Scale (PEIS))
  • Typhoon winds with gusts up to 350 km/h (97m/s) for coastal areas (This is Yolanda's lesson: all building codes I've seen use lower values: in the US the highest norm is for its dependency Guam, at 195 mph (87 m/s); standards for design loads are available from the ASCE/SEI 7-10 Standard; an on-line calculator is at the Engineers Edge website.)
  • Torrential rains. Yolanda dropped about 180 mm of water in a few hours time. I've personally witnessed large trees collapsing during such tropical downpours.
  • In coastal areas: salt water blown by storms that cause corrosion to exposed metal.
  • Aggressive pests, such as termites, that can eat through exposed wood and bamboo.

Flooding, land-slide and sink-hole danger need to be avoided by proper site selection. The name Bohol comes from buho, which means hole. The name is proper, as 80% of the island is made out of limestone, with countless caves, some as large cathedrals--not just tourist attractions, but also terrific hiding places from typhoons and in times of war (foreign invaders found out the hard way: neither the Spanish nor the Japanese could get a grip on the inland population). However, such caves may collapse due to earthquakes or continued erosion beyond a certain point.

Another important constraint is the availability of skilled labor. Although sometimes a local panday can be found who delivers excellent workmanship, such skilled people are rare and often hired to work abroad.

The biggest constraint, however, is the extremely limited budget available to build a house to most people in the Philippines. As a corollary to the well known joke that the three most important price-factors in real estate are location, location, and location, the three biggest hurdles for every house buyer are budget, budget, and budget.

Traditional Building Methods

Bahay Kubo

Bahay kubo is the Tagalog name for the nipa hut, and is known in Cebuano as payag, hut. This type of house is an icon of rural Philippine living. They are easy to build out of locally available materials: coco-lumber frame, woven bamboo (amakan) walls, and a nipa (palm leave) roof. Improved variants can be augmented with hollow-blocks, concrete poles, and corrugated iron roofs.

A very basic nipa hut can cost as little as 11000 pesos (EUR 185, USD 250). A design has been started by Project Kamalig (kamalig = "shed") to provide these to people who have lost their home to the earthquake.

A more up-scale amakan house with concrete posts and better roofs will cost about 60k pesos (1000 EUR, 1366 USD) to construct. They are pretty safe during earthquakes, but will be blown away with every storm, and lasts about 3-5 years. The practice has simply been to rebuild them every time needed, but that puts up a continuous strain on scarce resources.

Wooden House

Traditionally, most of the better houses in Bohol where made of wood. The wonderful ancestral houses still standing in a few places are very nice monuments of that past. With their excellent carpentry (wood-pin construction without nails), polished floors, and their wonderful sliding capiz windows and overhanging nipa roof they provide a great living environment, of which a few can still be seen in Tagbilaran and Baclayon. Some old houses been build from huge teak planks, and the wood alone is now worth a fortune, which actually may gives rise to the danger that they will be demolished for their wood.

Rebuilding in wood has become near impossible, as most good quality trees have gone, with hardly any teak or other tropical hard-wood remaining, and even the lesser quality woods becoming scarce. Further more, we do not want to relentlessly cut these remaining trees, if only because that would increase the danger of land-slides.

A wooden house is much safer than hollow-block ones during an earthquakes. A common sight is to see a core of the house (with the bedrooms) being build in wood, and the surrounding areas in hollow block.

Hollow Blocks

Most current houses in the Philippines are made of concrete hollow blocks, the quality of which can differ considerably. Building a house in hollow blocks requires about the same amount of concrete and iron as a cast concrete house, but has the benefit that most laborers know how to work with them, and that the house can be constructed in parts, as budget is available. However, their strength depends very much on the proper use of materials: using substandard mixes (too much sand and stone, mixing in a hole in the ground or on "gut feeling", without measuring), too few re-bars, or too thin, or using steel wire without ribs, etc. all help to deteriorate the build quality. Similar with roof constructions: use of thin plates, not enough connections to the frame, a frame of low-grade wood that will quickly be eaten by termites...

An excellent description of building an good quality house (costing about 3M pesos, 70k USD, 50k EUR) from hollow-blocks is on this blog, which gives a lot of details and important considerations when building a house from hollow-blocks.

Alternative Building Methods

Several architects have prepared quite fancy looking designs as alternative homes for developing countries, but I think most of these won't work out in practice. Even if we skip "cultural acceptability", which is not a small issue... We need to cope with earthquake danger and storm resistant design (which often leads to conflicting requirements: earthquakes call for light and flexible: storms for strong and heavy), in a climate where the sun can be scorching hot and rains heavy (from which you need to protect walls, suing an overhanging roof, which again makes it less storm resistant.) Cost of materials is a big consideration, but also cost of operation. You can build a house from a shipping container, but you'll need air-con or some other way of making the inside climate bearable. Air-con is no option for most, with the current cost of electricity (PHP 11 or EUR 0.20 or USD 0.27/kWh, almost double the US rates in real money, not to talk about purchasing power parity).

Prefab Waffle Concrete

I've been investigating prefab waffle concrete panels as building materials. These panels are bolted together on location. Waffle concrete panels saves about 60% of the amount of concrete being used, and results in lighter, and thus potentially saver houses. Another benefit is these panels are produced in better controlled environments, leading to better quality products.

The technology is available in the Philippines, but the company doing this apparently isn't interested in small projects like building a single house. Of course, for a one-off designed house, there is hardly any gain from this process, but when there is a need for 100.000 new houses now (next to the actually 3.5 million houses the Philippines urgently needed before these disasters), it would be great to have a bunch of standard designs ready. (Open Source House, anybody?), and have such panels mass-produced, such that with a single or double truck-load all required materials for a house can be transported.

A variant on this idea are prefab waffle concrete boxes. In stead of panels, complete integrated boxes are build. Some building companies are starting to introduce them in the Philippines.

Stucco Concrete

One of the problems of concrete is that it is heavy, and thus is potentially deadly when it collapse. There are two ways to counter this: make it so strong that it will not collapse, increasing the expense, or, make it much lighter.

You can actually make sailing yachts and canoes from concrete, and I've seen sites describing how to build houses from concrete on chicken-wire-mesh or bamboo frames. The latter can result in very thin walls that are still strong, but requires some skills and care with mixing the concrete. I have my doubts about using bamboo as re-bar, as bamboo will (just as wood) expand when wet, and thus crack the concrete, allowing termites to destroy the bamboo) -- an ancient technique of breaking rocks and enemy walls was to put very dry wood in tightly drilled holes, and then wet the wood.

When using stucco concrete and chicken-mesh, you can be very flexible in the shapes you make. You could actually inflate a balloon and cover it with concrete to build a strong, dome-shaped home.

Shipping Containers

Shipping containers are constructed by the millions in standardized formats. They offer about 30 square meters of area a piece and can be stacked up to 7 levels (fully loaded). About 90% of these containers are produced in China, and when new cost about 130k pesos (EUR 2216, USD 3000) a piece for a 40 ft standard container (and about PHP 88k, EUR 1477, USD 2000 for a 20 ft unit) This excludes transport to the Philippines. Due to China's huge positive trade balance, far more containers are being send abroad than back, and as a result, empty used containers are far cheaper in Europe and the US than in Asia. Don't be surprised to double in the Philippines as compared to in the US or Europe for a used container (and shipping them empty often doesn't make economic sense).

Some companies have utilized the Chinese container manufacturing capacity to build complete container sized apartments. These can be as cheap as 265k pesos (EUR 4430, USD 6000), again excluding the price of transport. Two or three such fully furnished containers can be taken together to form a decent-size home.

In-place cast concrete

In-place cast concrete houses are, if done right, much stronger than hollow block homes can be, however, they require skilled labor, the availability of sufficient quantities of good quality concrete, and the use of casing, preferably reusable casing.

The cost of building a cast concrete house would boil down to about 20-25k pesos per square meter (300-400 euros/m2; 38-50 USD/sq ft), not much more than a completely finished hollow-block based house would cost.

Concrete can be used to prepare double walling, in which the gap is filled with styrofoam, which will improve the insulation, and thus will make the house much cooler (or save energy when using air-conditioning). Houses in cold countries always use double walling with stone or glass wool insulation between them.

Jeroen Hellingman

What readers think...

Wayne mercer wrote:
Sunday, 5 July 2015 08:27:58 PHT
hello, great article, however your missing two very important structure types that are slowly being implemented in philippines. Earths hips and earth bag houses. Using soil and tyres or soil and bags, tightly compact earth can create a very low cost and very durable structure.

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