Home / The guide / House design

Check the code route for natural or alternative systems

Natural and alternative systems often need extra steps for approval. Know the route before you commit money.

How

1. Ask your building authority which standards apply to your system. Examples: US IRC Appendix S (straw bale), Appendix R (light straw clay) and Appendix U (cob), which only apply where a jurisdiction adopts them; New Zealand NZS 4298 for earth buildings.
2. If no appendix is adopted, ask about an alternative materials and methods approval (US) or the local equivalent.
3. For straw bale in the US appendix, note: bales at 20 percent moisture or less when plaster goes on, bales at least 8 inches above earth, no Class I or II vapour retarders on bale walls, and structural bale walls limited to one storey.
4. Collect test data, engineer letters or manufacturer approvals the authority may ask for and pass them to the legal module.
5. Check that your insurer and lender accept the system; a neutral question early saves surprises.

Do these first

• legal-1

Sources

1. 2015 IRC Appendix S: Strawbale Construction. International Code Council (copy hosted by Ecological Building Network), accessed 2026-11
2. Cob Code Appendix Approved for the 2021 IRC. International Code Council, Building Safety Journal, accessed 2026-11
3. Construction systems (Smarter Homes guides). Building Performance, New Zealand Government (MBIE), accessed 2026-11

Open in the interactive guide