To make housing more affordable, and to capitalize on a growing trend, many US cities and towns have recently adopted zoning provisions for tiny houses. Walsenburg, Colorado, the island of Nantucket, and Portland, Oregon are just a few places that enable accessory dwelling units or (in the case of Walsenburg) primary homes without minimum size restrictions. But these rules almost always require a foundation, which means you still can’t permanently park a tiny house on wheels anywhere… except in Fresno, California.

Last year, Fresno changed its zoning code to allow a homeowner to place one permanent accessory dwelling of any kind on a property. The code explicitly allows a “Tiny House” and includes a definition: a Tiny House must satisfy six conditions, including licensure with the California DMV, towability, and basic functional areas for cooking and toiletry. The homeowner may keep the smaller house for personal use or rent it out. Any homeowner with a lot size 6200 square feet or larger can take advantage, adding a smaller house up to 440 square feet. There must be all-weather pedestrian access to the smaller house, but no additional parking space is required.

The nearby city of Clovis is encouraging tiny houses in its own way with the Old Town Cottage Home Program. It’s an initiative to beautify the city’s alleys and make them pedestrian-friendly with alley-facing tiny houses. Any property owner with alley access and an extra parking space can qualify. It’s an imaginative method of urban infill.

Houses in the US (and many other countries) are built to the standards of the International Residential Code, or IRC. Most jurisdictions have adopted this code as their standard, with states and sometimes cities adding appendices to meet local needs. But no version of the IRC has ever addressed the needs of tiny houses. Until now.

Thanks to tiny house builder Andrew Morrison, code guru Martin Hammer, and a team of advocates, last month the International Code Council (ICC) approved a new appendix to the IRC for tiny houses. You can read it here. The appendix will be included in the next edition of the IRC, due out in 2018. Although this edition of the code carries no legal weight until jurisdictions adopt it (many US locations are 2 or 3 editions behind), the very existence of a code gives tiny houses legitimacy. Now anybody who wants to own a tiny house can show this appendix to their local building department and demonstrate that their house will meet code.

For the first time, a “tiny house” has an official maximum size: 400 square feet. The appendix covers topics like ceiling height (6’-8”, lower than in a conventional house), loft access (dimensional requirements for stairs or ladders), and fire safety (egress skylights permitted up to 44” above the loft floor). The appendix includes a comment from the ICC explaining why the council believes a code for tiny houses is important. Here’s one statistic they provide about environmental impact: “The average house in the U.S. uses approximately 17,300 board feet of lumber and 16,000 square feet of other wood products. A 200 square foot tiny house uses only 1,400 board feet of lumber and 1,275 square feet of additional wood products. The lifetime conditioning costs can be as low as 7% of a conventionally sized home.”

Today’s action: Provide the IRC tiny house appendix to your local building department. Write an email or letter, or deliver it by hand.

Sample text: Dear Waitsfield Development Review Board, My name is Scott Silverstein and I own a structural engineering business in the Mad River Valley. I am a longtime advocate for building smaller and more efficient structures, and I am writing to share the official tiny house building code, which was approved by the ICC and which will be included in the 2018 IRC. Please consider using this code as a guideline when you review proposals for houses under 400 square feet. Thank you for your time.