Note: If you’re new to earthbag building, first read the introductory Step-by-Step Earthbag Building and How to Build an Earthbag Roundhouse .
This Instructable includes complete step-by-step instructions on how to make an insulated earthbag foundation. You can use the same process to make insulated foundations for any type of structure – straw bale, earthbag, cordwood, etc.
Yurts or gers are very efficient and practical in harsh, cold climates, as evidenced by centuries of use in Mongolia. Benefits of yurts include affordability, rapid construction, ease of construction, wind resistance, great looks and portability (ability to take your home with you if you ever move). You may even save on taxes since some jurisdictions do not consider yurts permanent homes.
Many people build their yurts on a raised wooden platform to reduce moisture problems. But wood is expensive and building a platform/deck requires a fair amount of tools and carpentry know-how. Wood is vulnerable to fires and prone to rot and insect damage. It also requires regular painting or sealing. And if the wind and snow can blow underneath like most designs, then you’ll lose a lot of heat.
In addition to the many other uses for earthbags (retaining walls, domes, rootcellars, houses, etc.), you can build insulated foundations by filling the bags with insulation such as scoria. The benefits of the insulated earthbag foundation system described here include:
- Very low cost, especially if you can locate recycled grain bags from farmers
- Very simple construction using just a few tools most people already have
- Save energy and enjoy a more comfortable home because the floor and foundation are superinsulated (with no wind blowing under the floor to suck heat away)
- No deep footings/excavation required (see Frost-protected Shallow Foundations design guide mentioned below)
- The finished floor can be raised above grade as high as necessary. Deep snow? Flooding? No problem.
- Building a rocket stove into the foundation for heating.
For those who live in Canada or similar climates, you might want to follow the Earth-Sheltered Solar Canadian blog , who’s planning to build an insulated earthbag foundation that’s suitable for extremely cold climates.
Building in extremely cold climates uses the same process as outlined in this Instructable, but you will need a deeper trench with additional insulated earthbags below grade to create a Frost-protected Shallow Foundation (FPSF) . Combine these two ideas – FPSF and insulated earthbag foundations as shown in this Instructable – and you’ll have everything you need to know for free.
The following instructions assume you have cleared and leveled the site, removed topsoil, and positioned scoria around the building site to minimize work.
3D AutoCAD drawings show each step of construction.
Step 1: Foundation trench
Dig a foundation trench slightly wider than your earthbags. Use string or twine attached to a center stake to define the radius of the foundation. Install a French drain to remove moisture if needed, and then add 6”-12” of gravel or rubble, depending on climate. The depth of the trench will also vary according to climate. Consult the FPSF guide mentioned above for more details. For instance, the drawing shows how earthbags can be started at ground level (‘on-grade’) in mild climates. But for cold climates you have to use additional courses of earthbags that start below grade.
Tip: Throw the soil from the trench to the outside. This saves moving the soil later when you berm earth against the sides of the foundation.