Bamboo Architecture and Construction with Oscar Hidalgo
Notes by CASSANDRA ADAMS

Architect Oscar Hidalgo has dedicated his life to bamboo research, and teaching the world about the limitless possibilities of this remarkable plant. Born in a bamboo house in Chinchina, Colombia, bamboo construction was common in his state, where many residential and public buildings were constructed using this cheap and widely available material. Like most homes, in his house the bamboo was hidden beneath plaster, and indeed, it looked like it was made of brick.

After he left the university, Oscar was intrigued by the possibilities of using bamboo in construction, and embarked on a project to construct a country club kiosk 23 meters in diameter using this material. Five days before the opening ceremony, there was a hurricane which distorted the building extremely, moving the kingpost 90 cm off-center. After only two hours of working with a winch, however, the structure was successfully moved back into place without collapsing. He was sold on bamboo. Amazed at its structural integrity and aesthetic possibilities, he embarked on a program of research which has taken him to Asia, Costa Rica, Brazil, and elsewhere to study this plant and to create experimental structures.

The Bamboo Plant

The largest of the grasses, there are over 1600 species of bamboo, 64 percent of which are native to Southeast Asia. Thirty-three percent grows in Latin America, and the rest in Africa and Oceania. In North America there are only three native species of bamboo as opposed to the 440 species native to Latin America.

Of the two types of bamboo, the "running" type occurs only in temperate climates or in the high mountains of the tropics. Running bamboo produces both a culm (the above-ground vertical shoot) and long horizontal underground shoots called rhizomes. Tropical bamboo is almost always a "clumping" type, which tends to produce larger-diameter and thicker-walled culms. But its rhizomes are very short, so the bamboo plant stays more contained in a "clump."

Bamboo reproduces almost exclusively from its rhizomes, and is extremely fast growing. Under ideal conditions, for instance, a culm of the Guadua angustifolia species with a diameter of 22- 24 cm (9-10 inches) will grow to its full height in 3-4 months. It can produce an incredible number of culms per hectare (2.2 acres): native to Colombia, Guadua ang. produces 7-10,000 culms per hectare, while some Guadua species from Brazil can produce 60,000 culms per hectare.

Bamboo flowers in three different ways. Some bamboos bloom and produce seeds annually. Sporadic flowering occurs when a few plants will bloom. The type of flowering peculiar to many bamboos is gregarious flowering, when most of the plants of a species flower at about the same time around the world. This blossoming occurs at 10-145 year cycles, depending on the species. Bamboo is particularly fragile at this time, as after the flowering occurs, all the existing culms die off, and the bamboo seed is only viable for six months. This can cause great problems for people or businesses dependent on a constant supply of culms.

Different species of bamboo have different wall thickness, with a couple species being entirely solid. Bamboo is a natural composite. The walls are composed of "vascular bundles" of which there are five types. The outside portion of the culm wall is dense, containing about 5% silica. It has an exterior waterproof film which occurs on the softer interior portion as well. Bamboo is particularly strong at the node, where there is an inner disc called the septum which connects the outside walls, strengthening the stalk and separating in into compartments. Bamboo is widest at ground level, but is quite consistent in diameter throughout its length.

Using Bamboo

Bamboo is useful for different things at different ages:

<30 days it is good for eating
6-9 months for baskets
2-3 years for bamboo boards or laminations
3-6 years for construction
>6 years bamboo gradually loses strength up to 12 years old

Bamboo for construction is best cut right after new shoots have started to grow, as the plant will have given all its starch to the new culm. It is important to cut bamboo just above the node at the base.

The age of the culm is very important to know in order to select culms with the greatest strength for bamboo construction. One-year-old bamboo is an emerald color with the sheaths just beginning to fall off. Bamboo 2-3 years old has white spots on the culm, indicating the beginning of lichens. At 5-6 years these lichens can be clearly seen. Branches also tell the age of a bamboo plant. Every year each culm of bamboo loses its branches which are replaced with new branches. Old bamboo is attacked by insects from the interior of the plant, which can be difficult to detect.

Height can be determined in species over 5cm in diameter by multiplying the base circumference by 58.2. If culms are found to have a ratio of less than 58.2 the bamboo is of lesser quality. In Colombia, the best examples of Guadua angustifolia grow at elevations between 900-1,800m. In Ecuador, the same species has much lower strength characteristics.

For longer lasting structures it is important to treat bamboo against rot and insects. One method is to cure the bamboo by standing cut culms on a stone for a month amongst the living culms. The leaves are left on as they continue to remove starch from culm. When air curing bamboo it is best to keep it vertical, as it takes half the time to dry as horizontal storage. Once the bamboo is cured it is soaked in water for approximately four weeks. It is then soaked in the fumes of a .3 solution of caustic soda.

Perhaps the best way of treating bamboo is to force a solution of 3-10% of half borax and half boric acid through bamboo using an air compressor to create 20-30 lb of pressure. The bamboo is left on a slight incline with the base closest to the tank (though it is also possible to do it in the other direction) and the chemicals gradually move through the vascular system.

To protect bamboo from fire use plaster. For structural bamboo it is important not to penetrate the septum as it is the crucial part of the bamboo for strength. Small diameter holes can be put in the sides of bamboo, however. To avoid problems it is important that the bamboo is dry before used in construction.

History of Bamboo Construction

The ancient Chinese created "fire arrows," which were made of bamboo filled with gunpowder, to get more distance to their arrows. These arrows eventually evolved to become the rockets and firecrackers we are familiar with today. More recently, Thomas Edison used carbonized bamboo for the first successful light filaments. It has been used to make paper, cloth, and even Rayon.

Bamboo's tensile strength has been essential in the development of bridges. The Chinese invented suspension bridges using bamboo to cross rivers. Using only the exterior part of the bamboo, which is four times as strong as the interior, they created tension cables up to 120 meters long. Bamboo bridges were also constructed in India, and by the Incas in South America. In both cases, the structural cable was strung above the walking surface, which hung from it. And in Colombia, tension bridges were created using this amazingly strong material, with tensile strengths of up to 3,200 kg/cm2 for the species Guadua. Similar building techniques have also been used to create gabions to dam rivers and streams, where a long basket of bamboo is filled with stones with each end secured to the banks.

It has been crucial to the development of many inventions. Bamboo has been used to build boats and zeppelins. In aeronautical research, structural members of kites and early planes were constructed using the material as it is light and extremely strong. A plane made completely of bamboo was built in the Philippines, while the Chinese commonly used it in their planes during World War II. Plans for bamboo planes were even available in "Popular Mechanics" magazine.

Bamboo also has a long history of use in buildings, being common to the vernacular architecture of China, Southeast Asia and Central and South America. The Chinese could span up to ten meters with their corbelling technology, and bamboo has been used extensively all over Indonesia, especially in the Celebes Islands. In Hong Kong, all scaffolding for highways construction is built of bamboo, and tied with bamboo strips only 1 mm thick. Although they have a great history of building with bamboo, today the Japanese use it only for their traditional tea houses.

Structural Characteristics of Bamboo

Bamboo is unique in that it is strong in both tension and compression. While tensile strength remains the same throughout the age of the bamboo plant, compressive strength increases as it gets older. There is some controversy in determining proper testing protocols, as it is important to test bamboo which is at least three years old, and that the test should occur on a piece of bamboo with an entire internode and two intact nodes. Some testing research has not used these criteria, and thus the results are not as useful.

To utilize bamboo to its best capabilities, several conditions are important to consider. One consideration is that bamboo grown on slopes is stronger than bamboo grown in valleys, and that bamboos that grow in poor dry soils are usually more solid than those grown in rich soils. Bamboo will shrink diametrically, so Oscar does not recommend tied connections. Bamboo takes at least four months to dry, and should not be kiln dried, as the moisture inside leaves mostly through the ends.

There are certain limitations of the use of bamboo in construction. The starchy interior is attractive to insects. In addition, because bamboo has a slick waterproof coating, it cannot be painted. However, this coating allows bamboo to be used as water pipes.

As bamboo is extremely flexible from 6-12 months of age, it can be used to create a number of curving forms. In India, curving roofs called Chocals were developed, and bamboo domes have been built in New Guinea. A parisian architect named Friedman built some beautiful ringed buildings in India, but they were unfortunately destroyed by insects within a few years, as they were not treated. Indeed, the type of bamboo construction used can greatly affect the longevity of buildings. Architect Gernot Minke of Germany has developed a catenary arch using laminated strips of bamboo.

Bamboo Joints

In standard bamboo construction, joints are difficult to make. In bamboo geodesic structures, joints are formed by creating "flaps" at the end of a culm by incising the bamboo radially. The soft inside of each "flap" is cut away, allowing them to bend easily. These flaps are then bent over a cone with a threaded rod sticking out of the tip. An additional cone is place on the outside of the bent flap area and secured with a bolt. Besides increasing structural strength, this external cone protects against insect entry. This results in an end which can easily be attached to a central hub.

Bamboo Roofing

A number of cultures have used bamboo for roofing materials. The Chinese used bamboo for roofs with the ends covered with round tiles. In the Philippines, roofs of interlocking split bamboo are created with the part receiving the water being the soft inner surface of the bamboo. Unfortunately, this technique encourages mold, fungus and splits from ultraviolet exposure, and roofs made in this fashion rarely last more than a year. These roofs can be made to last longer if the upper pieces, where the denser exterior of the bamboo is exposed, are laid close together, protecting the more vulnerable pieces underneath. These roofs are perhaps most appropriate as temporary roofing solutions.

It is imperative that bamboo roofs are treated to extend their longevity. A boric acid/ borax solution is used to preclude fungus and insect infestation. Roofs can also be treated with lime to protect them. Long lasting tiles made with bamboo utilize a bamboo strip reinforced fiber-cement laminate where the bamboo strips are weaved into a web for additional strength.

A variety of techniques have been developed to create roof support systems. These include a prefabricated triangular truss system comprising of units eight meters long. These trusses can be carried by only four people, and only deflect 2 1/2 centimeters along their entire length. These frames are then covered with bamboo boards, lath and plaster to create a waterproof roof. Additional systems include A-frame and space-frame roof structures.

An excellent system utilizes bamboo rafters with bamboo boards. This is plastered on both sides, and fired clay tiles are used to waterproof. Besides structures built of whole bamboo, truss systems have been developed using flat bamboo strips which are connected with bolts.

A roof for a kiosk made by "uneducated" Ecuadorian Indians is an umbrella-like system with a tension ring surrounding it at the level of the eaves. A different radial roof concept with numerous peaks and valleys is held up by tension cables which connect across the structure where the valleys end. Geodesic domes can easily be made with bamboo, as can emergency temporary housing for homeless in the case of earthquake, flood, etc. These roofs are simple bamboo framing with bamboo strips between the main structural members. The roofs described above can last up to 15 years with periodic maintenance.

Bamboo as Concrete Reinforcement

Many studies have been done to determine the feasibility of using bamboo to reinforce concrete. The problem is, however, that bamboo soaks up the water in the concrete, causing the bamboo to swell then shrink, the process of which can break the concrete. In addition, adhesion between the bamboo and the concrete is poor. Oscar has experimented with braided bamboo as reinforcement, but it takes an excessively long time to braid.

Feasible uses of bamboo with concrete include making stirrups with 9 month old bamboo. Also tanks can be made by applying cement plaster to bamboo baskets. These can be used for toilets, water storage or boats. Waffle slabs of concrete can be formed utilizing bamboo baskets to create the void spaces. Woven bamboo mesh at 6" on center can be used to reinforce a 5" concrete slab. All-in-all, Oscar does not recommend the use of bamboo with concrete in house construction, with the exception of it being used as reinforcing for slabs on grade.

Laminated Bamboo

Many of the problems associated with bamboo can be alleviated by creating laminates of bamboo strips. These are formed by simply dividing the length of the culm into individual strips which are then laminated together to create a number of products. In 1942 a study was commissioned by the US government regarding the use of bamboo laminates in ski poles.

Currently, bamboo laminate products include floor tiles with one type being particularly good for heavy floor traffic as only the end grain is exposed. The softer strips of bamboo from the interior of the culm can be safely used in the interior portion of very large glu-lam beams.

There is really no limit to the uses of laminated bamboo. It can be used for chairs and other furniture, plates and utensils. In fact it can be used just like laminated wood, with the advantage that bamboo laminates are much lighter in weight. To create the strips used for lamination, the interior soft part of the bamboo is removed with a plane, leaving the hard exterior for the lamination strip.

Architectural Design Considerations

There are many ways to design using bamboo. Commonly in Colombia, structural bamboo is used as studs in walls, covered with bamboo "boards" or lath, then plastered on both sides. The bamboo boards are created by smashing a culm with a hammer, then splitting it open and flattening it. Lath is made from bamboo strips, 2-3cm wide.

With proper joinery, bamboo can be used to create incredible spans, most dramatically evidenced in the work of Colombian architect Simon Velez. Spans of 3.5 meters (11 ft.) are easily possible in simple structures use 12cm (4-5 in) diameter bamboo.

In Latin America, Guadua angustifolia bicor is the most prized species for construction. Guadua de castilla and Onion Guadua (G. cebolla) are also a good construction species. To create special effects, bamboo can be bent or straightened by heating and clamping until cool. Square bamboo is a unique product used for decorative purposes that is created by training the culms into forms.

Bamboo Construction in Latin America Marizales, a coffee growing region in Colombia, used to have many bamboo buildings. As recently as the 1930s, all houses in Caldas State (of which Marizales is capital) were made of bamboo. Many public buildings and apartments were made of bamboo as well. Although now bamboo is limited to residential construction, there continue to be many beautiful bamboo houses in rural areas. The most common construction method is to use platform frames with reinforcing diagonals in the walls. Some houses built with this technique on steep hillsides have five-story understructures. Because of the difficulty of leveling the varying dimensions of bamboo, lumber is often used for beams and joists.

A typical wall section is created with bamboo studs where spacing is determined by the thickness of the bamboo boards applied to the studs. For example, when a 1 cm board is used, stud spacing is 40cm. The bamboo boards are attached, and two layers of plaster are applied. The first layer of plaster is 1:3 cement to sand mix and the second layer is a 4:5 cement to sand mix. The plaster is aesthetically essential as visible bamboo is not acceptable to Colombians.

Another wall system uses bamboo studs as described above with smaller pieces of bamboo attached with 1 1/2-2" nails. This is then plastered with a clay/straw mixture on the outside. This system is much heavier than the previous example. Bamboo was often used as scaffolding in Colombia, but is now largely replaced by rented metal systems. In Ecuador the bamboo is smaller and the bamboo boards are applied vertically.

A prefabricated bamboo house system utilizes wall panels built on the floor, resulting in better construction. This system allows for homeowners to build their own houses through sweat equity. An additional feature is to locate the kitchen and bathroom directly over water tanks, which allows water to be easily hand-pumped to where it is needed. Oscar established a prefab house building program in Costa Rica, the Costa Rican "roof-floor" program was one in which the government provided a floor, roof and sink. Oscar then built pre-fabricated bamboo panels for these dwellings.

Practitioners

Besides Oscar, there are a number of other important bamboo architects in South America. These include recently deceased architect Carlos Vergara from Cali, who made houses entirely of bamboo. He created a multi-column system where the loads are carried by the septum of the bamboo. He also used bolts through concrete nodes to create joints. He was able to achieve spans up to 24 meters with his techniques. Jorge Arcila of Marizales did a series of "stacked houses" and is currently writing a history of bamboo in America.

Simon Velez, an architect who mostly practices in Colombia, has built a number of extraordinary bamboo structures. These projects have ranged from a horse stable, residences, a observation tower and a country club. His structures feature massive cantilevers and he was the first to use multi-culm beams. He uses a unique bolt and concrete system in the internodes to create extremely strong joints, which has allowed him to create cantilevers as large as 7 meters (37 feet).

American efforts include those of Doug La Barre, who is setting up a manufacturing facility for creating laminated lumber from imported Guadua. The Trus-Joist corporation is also doing work to create nontoxic adhesives for laminated bamboo.

Issues in Bamboo Construction

As bamboo architecture has reemerged in Colombia, many new architects are making avoidable mistakes. It is important that the ends of joints not be cut too short and that all connections use the concrete-filled internode/bolt system. Additionally, columns must be raised above grade or floor level. Multi-culm beams should be made of culms of the same diameter, and bolted vertically at least every meter on center. In temperate climates it is better to use the smaller, stronger bamboos, and if the structure is protected it will last longer. The strongest of the temperate bamboos are Phyll. bambusoides and Phyll. mequinods.

Neither Oscar or Simon Velez use engineers in their building, having developed an intuition about the capabilities of bamboo. Oscar knows, however, that many architects do not have the years of experience he has, and so wants to establish the norms for the mechanical characteristics of bamboo. Much work in this regard has been done by Jules Jannson, and research and testing continues in his native Netherlands.

Another major problem is that in many places bamboo is disappearing, just like our world forest resources. In Brazil there were 85,000 sq km of bamboo in 1976, while in 1983 there were only 32,000 sq km. It is feared that within a decade all bamboo in Brazil will be gone. Guadua is among the threatened species because it only grows at tropical latitudes. But this dire situation is common all over the world.

The biggest problem affecting the adoption of bamboo architecture in those areas which have a vernacular history of building with this material, is the perception that it is considered "poor people's" housing. In India, the highest castes use stone to build, the middle castes, wood, and only the lowest castes use bamboo. Thanks to Simone Velez, however, bamboo is becoming a building material of choice for the wealthy. Oscar believes that if those needing shelter see rich people using bamboo, so will they.

Cassandra Adams is an architect and professor of architecture at UC Berkeley specializing in construction methods and materials with a focus on environmental issues and traditional Japanese construction.

Also about Oscar Hidalgo
From DESIGNER/Builder, September 1997

...the most exciting technology Hidalgo has developed is to deform the bamboo plant as it grows to create incredibly strong pre-stressed arches. A form of wood and plywood with a predetermined arc is placed over a bamboo shoot. As the bamboo grows, it assumes the shape of the arc, permanently.

"You can make any type of construction member when you deform the bamboo," Hidalgo says. "To make one curved laminated beam could cost $25,000. But to grow the equivalent in bamboo would cost only $100."

A cross and longitudinal section of a bamboo plant reveals its amazing properties and the strength and resilience the mature plant gains from its vertical fibers and horizontally reinforced chambers. A bamboo plant is fully formed as it starts up from the ground, its future chambers compressed against one another like an accordion. As the plant matures, the shoot expands and these chambers spread out, beginning from the lowest internode. And if the shoot is deformed on the way up, it assumes its new shape permanently.

"The most expensive thing is the form," Hidalgo says. "But once you have a form you can grow many of the same arches for a very low price. You tell me what kind of a structure you want and I will deform the arcs for you."

Excerpted with permission from DESIGNER/builder magazine, copyright 1998. DESIGNER/builder is published monthly at 2405 Maclovia Lane, Santa Fe, New Mexico, 87505; (505) 471-4549. Annual subscription: $28.

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