How to Build Cob Homes
Cob homes are one of the most environmentally-friendly houses to build. They are built using a clay and straw mixture that is placed by hand. While some methods mix the material using a backhoe, doing so alters the final composition, and cobber experts insist that hand mixing is the only way to maximize the potential. If a cob home sounds like an interesting way to build, here are a few tips to keep in mind before and during the construction.
Step 1: House on the Hill
Cob homes are built of unfired clay and straw. For this reason, a cob home should always be built on the highest point in the home area, so that water can flow away from the home instead of standing near the wall surfaces. When the foundation area is being laid out, save any displaced soil to use in the cob mixture later.
Step 2: Mixing the Material
The material for a cob house is mixed approximately 3 parts straw for each 1 part of clay. The clay is used to coat the straw and help it bind in the formula—not, as you might expect, as the main ingredient. Some builders pack cob into a form and then build with the dried blocks, but true cobbers are quick to point out such methods are not cobbing. The term itself is derived from the method of passing gobs of material from person to person during the home construction. Literally, a "cob" is one handful of the building mixture.
Step 3: Building the Walls
Cob building is a slow process. Only a small buildup of cob is used at a time, and the mixture needs to be allowed to dry thoroughly before more is applied. Experts recommend laying no more than 1 foot of cob per day and allowing a minimum of 24 hours drying time between each new cobbing.
The mixture should be damp, but should not be wet. It is a good idea to keep the construction area covered during the cobbing process, and many cobbers begin construction by building the roof before the cob procedure is begun.
Step 4: Eco-Friendly Roofing Options
A cob home is inexpensive to build, and many cob homes built more than a century ago are still standing today. If you want to make the home even more eco-friendly, consider installing a sod roof, which provides excellent insulation.
An even better idea is to roof your cob home with ultra-modern solar panels. The result is increased heat interception by the panels and decreased dependency on the local power company. Both method will require additional reinforcements over a traditional roof, as sod is extremely heavy and solar panels require a solid support base.
Step 5: Notes for Modern Cobbers
Use metal conduits for your electrical wiring to run through. This allows you to install all the conduits and electrical boxes before cobbing, which means that you can build your electrical directly into the walls.
Where plumbing is concerned, building the pipes into a cobbed wall means better insulation and less pipe stress, reducing the need for costly plumbing repairs.