Week 7: The Scientific Vernacular (progress)

To what degree can bamboo technology control the environmental conditions of interiors and semi-interiors compared to industrial building materials?

Introduction

From the external perspective, as objects for the eye of a distanced beholder, bamboo buildings appear first as works of art, as arrangements of volume and void and colour, as sculpture. The eye is pulled by the building’s appearance into its plan into its use; emphasizing the most important dimensions of buildings lie inside. The experience of the interior makes the provision of internal spaces to shelter people and help them order social occasions.  None of these developed in extreme climates.

We humans have desire a certain minimum level of comfort inspite of the weather or location. The major elements of climatic environment which affect human comfort are air temperature, air movement and humidity through our bodily heat transfer of heat gains and heat loss and noise level. Therefore, shelter is the main instrument for fulfilling the requirements of comfort. It modifies the natural environment to approach optimum conditions of livability.

The building envelope is the physical separator between the interiors and exterior of the building. Components of the envelope are typically walls, fenestrations, roofs and floors. In this paper, a brick-concrete building is selected as a baseline with the same floor area and window ratio as the bamboo-structure building; is compared to distinguish intrinsic differences of the technical potentials of the environmental conditions of interiors and semi-interiors.

Thermal Insulation

Envelope insulation being assessed through energy use and carbon emission is identified within the boundary of the functional requirements of the building.

 According to Dongwei Yu et. al., they indicate the bamboo-structured building has an embodied energy or carbon of 3003.4Mj/m² and a thermal resistance of 168.9kg CO₂/m²; in contrast to having a brick-concrete building of 3532.90Mj/m² of embodied energy used and 326.1kg CO₂/m² of thermal resistance.

The embodied energy and carbon parameters the envelope in the two types of buildings with regard to main envelope materials, bricks used in brick-concrete building have Pe.k = 2409.8  and Pc.s = 192.8 in contrast to Pe.k = 53.6 and Pc.s = 3.13 for the bamboo-structure building. Therefore, the walls of the bamboo-structure building have lower embodied energy and carbon and higher performance thermal insulation than those of the brick-concrete building. It implies that the bamboo-structure building has a promising perspective to be one of the sustainable buildings. In general, the embodied energy or carbon on a volumetric basis increases with the increasing density; while the thermal conductivity decreases with the increasing density.

Wind Pressure

Roof with walls that pass breeze but not rain is the most ideal for building by maximising natural ventilation. Both positive and negative pressures occur simultaneously when wind interacts with a building. The differences between a bamboo-structure building and a brick-concrete building are the open eaves and porous bamboo slats for walls and floor that maximize natural ventilation. The most extensive use of bamboo in construction is for the walls and partitions. They are the major elements that carry the dead load and live load of the building. An infill between framing members is required to complete the wall to protect against rain, wind, animals; and to provide in plane bracing to ensure the overall stability of the overall structure when subjected to horizontal forces.

 Wind can cause an increase or decrease in pressure within the building. Internal pressure changes occur because of the porosity of the building envelope (eg, openings of doors and windows, air infiltration through walls that are not absolutely airtight).

When a building is pressurized, the internal pressure pushes up on the roof. This push from below the roof is combined with the suction above the roof, resulting in an increased wind load on the roof. The internal pressure also pushes on the side of the rear walls. This causes the roof cover damage (eg. Metal edge flashing lifted) and window damage (eg. Outer panes of windows broken) occur due to the pressure of the aerodynamic forces. The monitored wall section was subjected to air pressure differentials, outdoor-to-indoor, within ±18 Pa, which is typical for most brick-concrete buildings.

When a building is depressurized, the internal pressure pulls the roof down, reduces the amount of uplift exerted on the roof and pulls in the windward wall, which increases the wind load on external wall. Therefore, the air pressure differential outdoor-to-indoor reduces to the range in between -9 to +2Pa.

Solar Shading

Tropical climates are hot and humid. Therefore keeping the heat of the sun off is the top priority. Bamboo-structure building provides a unique screen that protects the building from intense sun and provides a veranda. The windows and prefabricated walls are so well insulated that the home’s primary sources of heat are the occupants and the sun and a heat recovery ventilator provides fresh air. The temperature difference between the exterior and the interior of a bamboo-structure building averages 4-5 degrees on a hot summer day.

Acoustic

Bamboo-structure building is also a sound barrier that drowns out noise. But, the screen must be dense and at least 3 to 8 feet wide; thus depending on the cause of the noise. According to forestry experts, bamboo has a reflection, absorption and blocking effect to sound wave. It can greatly reduce noise level by 10-15 dB. Therefore, bamboo-structure building creates a unique sound environment and soundscape. But brick-concrete building has a higher noise transmission loss of 32-36 dB. It is already known for its specified for noise barriers. According to Anderson (1984), Effects of vegetation on human response to sound, a 10 dB reduction makes a sound appear to be half as loud as our human ear does not perceive sound in a linear way. Therefore, bamboo-structure building is sufficient to reduce noise at the surroundings.

Conclusion

This vernacular architecture has grown out of simpler forms of indigenous building as done by more primitive cultures, and usually includes the same set of climate responsive parameters and similar materials but using somewhat higher technology in the construction. It has been built to reduce the range of local climatic variations; to avoid some of the heat of the sun in hot climates, to welcome the breezes when they can provide desired cooling and to admit light in sufficient amounts for task lighting and to keep out excessive or unnecessary light. Bamboo, as an alternative building material, helps in decentralizing the construction process which has both economic and ecological advantages; to control environment conditions for human comfort.