Is it safe to build houses from straw, tires, or plastic bottles?

Sure, if they’re designed and built to be safe in earthquakes

At Build Change we mostly teach people to build masonry houses or timber houses. We do not use plastic bottles, tires, straw bales, earth bags, or any number of other approaches which have been touted as environmentally-friendly, cost-effective methods to rebuild devastated areas.

Why? What’s wrong with homes made from waste materials? Or plastic bottle houses? Or straw bale houses?

Well, nothing, really.

A lot of argument goes on over whether one building system is better than another, particularly in the seismically active zones where we work. There are really only two things that matter:
1. Can the house be built so that it is safe?
2. Will people want to live in it?

All the other questions and issues can be rolled into these two. If the necessary design expertise, or trained builders, or required fasteners are not locally available, then the building cannot be built so that it is safe. If the building is too small, or has no windows, or is too expensive, or is shaped like an igloo, then no one will want to live in it.

If one spends any time on Haiti it is obvious that right after food on the table, safe drinking water, and cholera, dealing with trash is a top priority. At the top of the J/P HRO refugee camp in Port-au-Prince there is a nice little green women’s health clinic built out of plastered plastic drink bottles. Turning Haiti’s trash into houses is a good idea. Straw is a byproduct of grain production and is so over abundant in most places that it is simply burned, gaining only pollution. Discarded tires take 100 years to decompose. We don’t want our trash to last for 100 years; we want our houses to last for 100 years. Diverting a low-grade waste stream to a high-grade reuse is a recycling coup. This kind of environmentally-friendly behavior should be encouraged.

But it is also tricky. Piles of tires or straw bales or plastic bottles are not houses. Houses are systems of materials and connections that shelter and protect people. They must be carefully designed to resist the forces they are expected to encounter. Most builders have a strong intuitive grasp of how to support gravity’s downward forces, of the weight of the house and the things in it. It’s the lateral systems, the ones that support the sideways forces, whether from earthquakes or wind, that are more complicated.

A force is a mass and something that accelerates it (F=ma, remember?). In an earthquake it’s the ground that is accelerating and the mass is the weight of the roof or second story. So the force isn’t in the ground, it’s in the roof. The roof moves sideways because it is trying to catch up with the ground. A lateral system is the series of connections from the roof to the foundation that safely transfers this sideways force to the ground while the structure stays intact. Any building can have a competent lateral system, it’s just difficult to understand, design, and build, and it often gets forgotten.

We can pile up straw bales, tires filled with earth, plastic bottles, or discarded Mutant Ninja Turtles action figures, make them into walls and cover them with enough steel-reinforced concrete plaster to create a system that will transfer those sideways forces during a natural disaster. But as with any system, it must be designed, tested, and built properly by people who know what they are doing, to ensure that innovative home-building solutions are also safe ones for families to live inside.