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Ready Survival Kits

Off-grid living · US

Building with earth, straw and your own lumber

What the building codes say about strawbale, cob and earth block walls, so you can make shelter from materials on your land.

By The Ready TeamExpert review: pendingSources checked 29 October 2026

Quick card · Building with earth, straw and your own lumberSources checked 29 Oct 2026

Before

  • Ask your building department which codes and appendices it has adopted. The strawbale and cob appendices apply only where a jurisdiction adopts them. 1 2
  • Structural lumber you mill yourself generally needs a grade stamp, with some exceptions for farm buildings and cabins. 4

During

  • Strawbale: bales must be at or below 20% moisture when the first plaster coat goes on. 1
  • Strawbale: plaster at least 3/8 inch thick on all bale walls, and clay plaster at least 1 inch thick. 1
  • Earth block (New Mexico code): blocks need a compressive strength of at least 300 psi and can't be used for foundations. 3
  • Keep earth walls off the ground on a stem wall. New Mexico requires at least 8 inches for compressed earth block. 3

What to have

  • Moisture meter with a bale probe 1
  • Lab or manufacturer test results for earth blocks 3

Why build from your own land

Straw, earth and timber can come from your own land or close by. Turning them into walls is one of the biggest ways to cut the cost of a home and to stop depending on the lumber yard. Several of these methods have their own building code sections, which matters when you apply for a permit.

This guide covers what the codes require. It is not a construction manual. Have a qualified designer or engineer check your plans, especially in earthquake or high-wind areas.

Codes first

The International Residential Code (IRC) has optional appendices for natural building. They are not mandatory unless your jurisdiction’s adopting ordinance references them. 1 2 Call your building department before you design and ask which edition and appendices it has adopted.

Strawbale

The 2015 IRC’s strawbale appendix (Appendix S) sets out how to build with straw bales. Key requirements: 1

  • Dry bales. Bales must be at or below 20% moisture by weight when the first coat of plaster or other finish goes on. Check with a probe meter, testing at least 5% of bales and no fewer than 10.
  • Plaster. Every bale wall needs plaster at least 3/8 inch thick, and no more than 2 inches. Allowed plasters include clay, soil-cement, lime, cement-lime and cement. Clay plaster must be at least 1 inch thick in two or more coats, with a protective finish such as lime wash where rain can reach it.
  • Let walls breathe. Class I and II vapor retarders aren’t allowed on bale walls.
  • Load-bearing walls. Plastered bale walls can carry roof loads in one-story buildings, but they must be precompressed to at least 100 pounds per linear foot before plastering.
  • Fire. Bale walls are treated as unrated unless built to a listed assembly. For example, a one-hour rated, non-load-bearing wall needs clay-plastered bales at least 18 inches thick.

Cob

The 2021 IRC added Appendix AU, Cob Construction (Monolithic Adobe), along with Appendix AQ for tiny houses. Like the other appendices, they apply only where adopted. 2

Earth blocks, adobe and rammed earth

New Mexico has one of the most detailed earthen building codes in the U.S. It covers adobe, burned adobe, compressed earth block, rammed earth and terrón. 3 Even if you don’t live there, it shows what a safe earth wall needs:

  • Height. No more than two stories for adobe, rammed earth or compressed earth block.
  • Thickness. Exterior rammed earth walls at least 18 inches. Compressed earth block walls at least 14 inches on the bottom story of a two-story building, and 10 inches above.
  • Strength. Cured compressed earth blocks need a compressive strength of at least 300 psi, tested on five random blocks per project unless the maker certifies them. Average modulus of rupture must be at least 50 psi.
  • Keep it dry at the base. Compressed earth blocks can’t be used for foundations or basement walls. Stem walls supporting them must rise at least 8 inches, and unstabilized blocks can’t be used within 4 inches of finished floor level.
  • Footings. At least 10 inches thick and at least 33% wider than the wall.

Earth walls are heavy and store heat well, which makes them good thermal mass for a passive solar home. 5

Your own lumber

A portable sawmill can supply framing, siding and outbuildings. Penn State Extension notes that structural lumber generally needs a grade mark from an accredited grading agency, with exceptions in Pennsylvania for agricultural buildings and recreational cabins. 4 See our sawmill guide for costs and drying times.

Sources

  1. International Code Council, 2015 International Residential Code, Appendix S: Strawbale Construction
  2. International Code Council, Adoptable appendices in the International Residential Code for cob construction and tiny houses
  3. New Mexico Administrative Code 14.7.4, 2021 New Mexico Earthen Building Materials Code
  4. Penn State Extension, Using Your Own Lumber for Building Projects
  5. U.S. DOE Energy Saver, Passive Solar Home Design