Green Building Materials: A Guide to Natural Building Systems

Enlarge Image Image Gallery Rammed earth building uses slightly dampened subsoil or a sand-cement mix in between forms attached to a foundation. Photo by Robert Reck

With their thick walls, sensuous earthen plasters and flowing lines, homes built using natural materials offer beauty and comfort. And natural building also provides an opportunity to create homes that are healthier than their conventional counterparts. More than a dozen natural building methods are in use today, and many natural builders use combinations of these to create a wide array of beautiful homes.

The Basics: Natural Building Methods

Adobe: Adobe is a time-tested natural building material dating as far back as 6000 B.C. Builders create adobe homes using blocks made from clay-rich mud (subsoil) and straw, dried and hardened in the sun. The blocks are placed like bricks, using wet adobe mud as mortar.

Cast Earth: Cast earth is a modern invention and one of the most expedient natural building materials available today. Earth is mixed with water, a special type of gypsum and some proprietary chemicals to form a slurry that’s poured into forms. Unlike most other natural building methods, this one is reserved for professionals, as only certified contractors are licensed to build with the material.

Cob: Cob is an ancient building material used in Europe at least 500 years ago. In this method, a timber frame typically supports the roof. The builder then literally handsculpts the walls by mixing clay-rich mud and straw and applying them to the foundation in wet clumps (cobs) that are kneaded and massaged.

Cordwood: Cordwood's exact origins are unknown, but some of the earliest cordwood buildings were built in Siberia and Greece about 1,000 years ago. Split or unsplit firewood is stacked on a foundation (generally with insulation between the logs) and held in place on both sides by cement mortar. Visible round log ends form interesting patterns in finished walls.

Earthbags: A newcomer to the natural building scene, earthbag construction got its start in the United States. Polypropylene bags—typically 50- or 100-pound grain bags—are filled with dirt and packed into place, then arranged in an overlapping pattern. Rows are sometimes secured barbed wire. Plaster protects the bags from the elements.

Log: Log homes were popular with early America’s European settlers. Interlocking notched logs make up the walls, and the gaps between them are filled with a chinking material to seal the structure. Alternatively, logs can be notched lengthwise so they fit snugly together, creating a more airtight seal and making chinking unnecessary.

Papercrete: Papercrete, which evolved relatively recently in the American Southwest, is made from a slurry of shredded newspaper and water mixed with cement and sand. When it dries, it forms lightweight bricks that are stacked in a running-bond (overlapping) pattern like conventional bricks. Wet papercrete is applied as a mortar to hold them in place.