Build a Cob House A Step-By-Step Guide Copyright © 2013 by Alex Sumerall Page 1 www.thiscobhouse.com Table of Contents Introduction......................................................................................................................... 5 How, and By Whom, Should My Cob Building Be Built?............................................. 5 Characteristics of Cob Homes ........................................................................................ 8 Cob Home Concepts ................................................................................................... 8 Cob Home Advantages ............................................................................................... 9 Common Questions About Cob.................................................................................... 10 Site Selection .................................................................................................................... 12 Design ............................................................................................................................... 14 Materials and Tools........................................................................................................... 21 Selecting and Testing Soils........................................................................................... 21 Sand........................................................................................................................... 23 Clay........................................................................................................................... 24 Straw ......................................................................................................................... 25 Other Building Materials .......................................................................................... 26 Tools ............................................................................................................................. 27 Preparing Your Site for Building...................................................................................... 28 Foundations....................................................................................................................... 29 Rubble Trench Foundations.......................................................................................... 30 How to Build a Rubble Trench Foundation.............................................................. 31 Basic Stone Laying ................................................................................................... 33 Alternative Stem Wall Materials .............................................................................. 35 How to Make Cob............................................................................................................. 38 Tarp Method.................................................................................................................. 38 Making Test Bricks....................................................................................................... 42 Alternative Mixing Methods......................................................................................... 42 Cob Mixing – Problem and Solution ............................................................................ 43 How to Build Cob Walls................................................................................................... 44 Cob Loaves ................................................................................................................... 44 Monolithic Building...................................................................................................... 45 Windows and Doors.......................................................................................................... 50 Arches and Lintels ........................................................................................................ 50 Wall Anchors ................................................................................................................ 53 Non-Opening Fixed Windows ...................................................................................... 54 Roofs................................................................................................................................. 55 Gable Roofs .................................................................................................................. 56 Ceilings ......................................................................................................................... 58 Sheathing Your Roof .................................................................................................... 59 Thatch Roofs................................................................................................................. 59 Strong Thatch and Maintenance ............................................................................... 60 Living Roofs ................................................................................................................. 61 Insulating Your Roof .................................................................................................... 63 Smart Insulation Options .......................................................................................... 64 Roofing FAQ ................................................................................................................ 65 Earthen Floors................................................................................................................... 65 Page 2 www.thiscobhouse.com Materials ....................................................................................................................... 67 Tools ............................................................................................................................. 67 How to Install an Earthen Floor.................................................................................... 68 Earthen Floor Maintenance........................................................................................... 71 Natural Plasters and Finishes............................................................................................ 71 Materials for Plastering................................................................................................. 72 Tools for Plastering....................................................................................................... 73 Earthen Plasters............................................................................................................. 74 How to Mix Earthen Plaster...................................................................................... 74 Lime Plasters................................................................................................................. 75 Natural Plaster Suppliers............................................................................................... 77 Additional Information ................................................................................................. 77 Electrical and Plumbing.................................................................................................... 78 Building Codes and Permits.............................................................................................. 79 Cob Building Codes and How to Get a Permit to Build............................................... 79 Our Uncertain Future: Cob Offers Sustainable Solutions................................................. 81 Beginner Cob Projects ...................................................................................................... 82 Cob Oven ...................................................................................................................... 83 Cob Bench..................................................................................................................... 83 Cob Garden Wall .......................................................................................................... 84 Cob Dog House or Play House ..................................................................................... 85 Bibliography ..................................................................................................................... 86 Page 3 www.thiscobhouse.com Page 4 www.thiscobhouse.com Introduction Cob is a building material made out of earth, clay, sand, straw, and water that is pliable and can be hand-sculpted into buildings. Many people are familiar with adobe, which has similarities, but cob does not use bricks or forms. Cob has been used and tested for thousands of years all over the world and has proven to be a very viable building material. About thirty percent of the world’s population live in homes built out of earth, and about fifty percent of the population of developing countries live in earth buildings. Earth is the most common and accessible building material on the planet. There are many misconceptions today about earthen homes. They are not all mud huts in Africa with poor living conditions. Earthen homes can be very lavish, beautiful, and clean. Cob has until very recently been virtually unknown. About twenty years ago, there were no cob builders in North America. However, since the 1980’s, there has been a revival in cob building. People all over the world are now learning and reviving this ancient building technique. This revival is coming at a very opportune time as well. As materials and resources become scarcer, prices