Tiny Homes on Wheels

A Tiny Home on Wheels (THOW) is a manufactured and transportable structure that provides independent living. It has everything you need to live: a place to sleep, eat, cook, and use the bathroom. Since September 4, 2025, the County of San Diego considers a THOW a dwelling unit per the zoning ordinance and may be used as either a primary or an accessory dwelling when specific requirements are met. 

Basic Requirements

A THOW must be smaller than 430 square feet. It can only have one floor but can include an additional a small loft up to 150 square feet for a loft. The THOW can be no taller than 16 feet. It must be checked by an approved company to meet special standards. The outside walls must be noncombustible and the roof fire resistant. Some homes will need fire sprinklers. Complete requirements are found in the Planning & Development Services (PDS) Director’s Determination Letter.

Getting a Permit

You need a permit from PDS to install a THOW on your land. Plans must be prepared to show compliance with the requirements. Your project might also need checks for:

  • Fire sprinkler and fire site access
  • Legal lot status
  • Septic system
  • Flood
  • Grading
  • Stormwater
  • Off-Grid Electrical
  • Right of Way

What to Include in Your Plans

Plans need to be prepared on large, printed sheets (11x17 minimum). Sheets should all be the same size. Two printed sets of the plans are needed and must have:

  • Project Scope. What you plan to build and the size.

  • Plot Plan. A map showing where your THOW will go on your land. See Plot Plan Minimum Requirements (PDS 090) for more information.

  • THOW Requirements. Show a scan of the Director’s Determination Letter as part of your plans.

  • Certification. A letter from an approved agency saying your home meets safety standards. Approved agencies include, but are not limited to, Pacific West Associates, National Organization of Alternative Housing (NOAH), and the RV Industry Association. If you plan to build a THOW yourself, you’ll need to work with one of the approved companies. The statement of certification should include the following:

    • Name of Approved Agency
    • Property Owner Name
    • Property Address or APN
    • Name of Manufacturer
    • Compliance with ANSI A119.5 Park Model RV Standard
    • Compliance with County of San Diego requirements

    • Signature and Date of Approved Agency

  • Stormwater Forms and Plans.

    • Breakdown of pervious areas, impervious areas, and land disturbance areas to determine level of stormwater compliance.
    • Locations of stormwater Best Management Practices (BMPs) for the site work and setup of the THOW.
    • Stormwater Intake Form. Coordinate with impervious and disturbed areas shown on plans.
    • Stormwater Quality Management Plan (SWQMP) for Standard Projects. Coordinate with BMPs shown on plans.

Inspection Requirements

Once a permit is issued, you must pass all required county inspections as part of the THOW installation. The type of inspections depends on your project but typically include underground plumbing/electrical, yard gas, water service, building sewer, and final. You also need inspections and sign-off from the fire district. For construction of the THOW, the approved agency needs to provide a readily visible placard or sticker indicating the unit complies with:

  • ANSI A119.5 Park Model RV Standard
  • County of San Diego requirements

Approval from an approved agency is not a substitute for required county inspections. After final inspection is passed, you are given occupancy of your THOW.

Park Trailers

The County of San Diego requirements for a THOW do not apply to Park Trailers in mobile home parks or RV parks. Park Trailers are used for recreational or seasonal use only, and not as a year-round or permanent dwelling.