Editor’s note: This post is one in an occasional series on Vijay Govindarajan’s and Christian Sarkar’s idea to create a scalable housing solution for the world’s poor. Each post will examine the challenge from a different perspective, including design, technology, urban planning and more. Today, David Sands explores how to make affordable housing scale sustainably.
I was pleased to discover the $300 House challenge and I applaud the efforts of Vijay Govindarajan and Christian Sarkar. My passion for a sustainable future led me to quickly say yes when asked to collaborate on this important project.
It’s easy to say a $300 House for the poor should be designed a sustainable solution, but it’s no easy feat. To be sustainable, all the elements must be good for the user, good for the environment and good for those who made them. Where do the materials come from? Of what are they composed? Are they nontoxic? Or better yet, are they biophilic: Is life on earth improved for everyone and all creatures because this product is being made? Also, if it is not affordable, it is not sustainable! With their reduced economic means, fewer choices are available to the poor and cost precludes many otherwise sustainable options.
The Case for Bamboo
I was first drawn to bamboo as a construction material seventeen years ago for many reasons:
Hardiness: Bamboo can be annually cropped for many decades without replanting. It’s a pioneering plant that will grow on marginal land not good for food production (such as steep hillsides or eroded land) and it shows promise for watershed regeneration.
Strength: One square inch of bamboo can hold up to 7 tons of weight before failure. In 1992, 95% of all homes were built with softwoods like Douglas fir. University studies show softwoods can’t match bamboo’s compression and tensile strength.
Hurricane-resistant: Properly constructed bamboo homes surpass the toughest hurricane codes in the U.S. In 1995, bamboo homes withstood three back-to-back hurricanes in which winds maxed out at 173 mph. Recent tests show that conventionally built wood homes can’t stand up 100 mph winds. (Watch the video.)
Earthquake-resilient: In April 1991, twenty bamboo houses built for the National Bamboo Foundation in Costa Rica suffered no structural damage from an earthquake that measured 7.5 on the Richter scale. These homes were located in the epicenter. The same earthquake leveled scores of conventionally built homes, hotels and resorts. (Read the article in Washington’s Observer Reporter)
Bamboo is only one of a number of promising materials for the $300 House. But whatever materials are used, they must share certain qualities. First, they will need to be less expensive than current building materials. The source material will need to be readily available locally and cheap to obtain and process.
Ideally, the source material also solves some other environmental problem such as providing long term storage of carbon from the atmosphere, as in the case of bamboo. Large scale sustainable bamboo projects, like homes and eco-developments, serve as carbon sinks, and have a zero or less than zero carbon footprint.
To be a sustainable solution the material must be highly durable itself or have a highly durable finish, otherwise the structures will need to be replaced regularly. One very promising option with which I am involved is a bamboo-silica composite panel. Through a process of molecular surface modification the silica material develops high strength and fire resistance properties and the durability of glass without the brittleness. The durability of this material and the high strength of the bamboo have proven to be an excellent combination for creating structural panels. These panels also provide a high level of thermal comfort in a thin cross section.
Considerations for a $300 House
Given my experience with bamboo, I’ve also started to envision how a $300 House might work using it as a base material. I envision a cube structure 2.2 meters on a side as the basic unit made up of 12 panels all the same size: two panels for the floor, two for each wall and two for the roof. Wall panels have a door, a window or are solid. Each 1.1m x 2.2m panel is light enough for one person to carry by hand and is easily connected with other panels to form a weather tight structure.
The size of the structure is dictated by the length required for two people to sleep comfortably side-by-side. Sleeping mats can be rolled up and put away during the day and all other activities such as food preparation and cooking can be adapted to the size of the space available. In tropical areas, a covered porch is needed for outside cooking. The flat roof is designed to support rainwater collection. The essential module can be added onto over time by installing adjoining modules or adapted by attaching site built structures.
Due to issues with land ownership in most slums, the buildings are permanent temporary structures, that is, built to last but designed to be disassembled quickly and then easily reassembled elsewhere. The foundation system needs to be moved as quickly as the structure itself. I envisioned long pegs with auger tips that anchor each corner of the building and resist the uplift of hurricane winds keeping the building firmly planted in the unstable soil of slopes where slums are often built. The pegs are installed and removed by hand and attached to the building through a clip at each corner that allows for leveling of the floor.
The technology we have developed can be used to create local production facilities that process bamboo harvested from nearby farms. With some initial investment into the panel production facility and bamboo farms, inexpensive and sustainable bamboo housing becomes an enduring and versatile option for a community in need. The carbon offset credits also become an asset in that emerging market, providing additional streams of revenue for the local production facility and farmers.
Finally, this system not only addresses the housing issues of the impoverished, but creates local jobs and stimulates the economy. We have first-hand evidence of this with our work in Vietnam. We think this idea could scale, and that it could scale sustainably.
David Sands is the co-founder and architect of Bamboo Living, which makes bamboo prefab homes meeting U.S. building code standards. He served on the INBAR (International Network for Bamboo and Rattan) committee to develop the International Standards Organization (ISO) standard for structural bamboo.