HCD MH 415 Application for Alteration: Filing, Fees, and Inspection

To alter, add to, or convert a manufactured home or mobilehome in California, you complete the HCD MH 415 application for alteration, addition, or conversion, attach the plans and other supporting documents your project requires, and submit the package with the correct fee to the California Department of Housing and Community Development (HCD) area office that covers your unit’s location. Approval must be in your hands before any work begins.

When the Form Is Required

California Health and Safety Code Section 18029 makes it unlawful to alter or convert the structural, fire safety, plumbing, heat-producing, or electrical systems of a manufactured home or mobilehome without HCD authorization, and Title 25 of the California Code of Regulations extends that rule to any unit bearing (or required to bear) an HCD insignia of approval or a federal HUD label.¹²

“Alteration” is defined broadly to cover the conversion, replacement, addition, reconstruction, modification, or removal of anything that affects those systems.³ In practice, that means work such as:

Electrical: adding or rerouting circuits, upgrading the panel, installing new outlets
Plumbing: replacing or relocating water or drain lines
Gas: adding or modifying gas supply lines or appliances
Structural: building an addition, removing or moving a wall, or altering the roof or chassis
Fire safety: modifying smoke-detection systems, altering ignition-resistant construction, or changing egress windows

Conversions are separate. A conversion changes the use, building type, or occupancy classification of a unit, such as converting a commercial modular from one occupancy group to another, or converting a commercial modular into a mobilehome.⁴ If how the unit is used is changing, that counts as a conversion even if no wall is touched.

Work That Does Not Trigger the Form

Routine maintenance and like-for-like repairs generally do not require MH 415. Replacing a faucet with the same model, swapping a light fixture on an existing circuit, or repainting interior walls are upkeep, not alteration. The line is whether the work changes the original design, capacity, or routing of a system. Put back what was already there with equivalent materials and no design change, and you are in maintenance territory. Upgrade, relocate, add capacity, or change materials in a way that affects how a system functions, and HCD treats it as an alteration.

One exception catches people off guard. If your home has an ignition-resistant exterior system and you want to alter those materials, even with something you consider equivalent, HCD requires MH 415 and an inspection of the completed work.⁵ When in doubt, call HCD’s area office before starting.

Completing the Form Section by Section

The form has five numbered sections plus three declarations. Download the current version from HCD’s Manufactured Housing forms page.⁶ For a standard alteration, addition, or conversion, you complete all five sections and the declaration that fits your situation.

Section 1: Unit Information

Identify the unit. Check the box for the type (manufactured home, mobilehome, commercial coach, or multifamily manufactured home). For a commercial coach, add the occupancy group code. Then enter:

Serial number or VIN, found on the Manufacturer’s Certificate of Origin, the Certificate of Title, registration documents, or stamped on the front cross member of the unit
Year manufactured and manufacturer name
Decal or license number from the DMV plate or the HCD-issued decal
Insignia or HUD Label number, if known

These identifiers let HCD pull the unit’s original design specifications and verify what was approved at manufacture.⁷

Section 2: Owner and Applicant Information

Enter the registered owner’s name and the address where the unit is located. If the owner’s mailing address differs from the site, fill in both. When someone other than the owner is handling the application, such as a property manager or contractor, that person’s name, address, and phone go in the applicant fields. HCD corresponds with whoever is listed as the applicant, so use the person who will answer questions and schedule inspections. If the owner is the applicant, the applicant fields can be left blank.⁷

Section 3: Contractor, Architect, or Engineer Information

If a licensed contractor is doing the work, enter the contractor’s name, address, license number, license class, and expiration date. If an architect or engineer prepared the plans, add their information as well.

Section 4: Description of Work

Describe every modification you plan to make. Be specific. “Add 12×14 bedroom on north side, tie into existing electrical panel and plumbing” is far more useful to a reviewer than “room addition.” Include materials, dimensions, and which systems the work affects. Vague descriptions slow review because HCD comes back asking for clarification.

Section 5: Certification

The applicant, or the owner if handling the application personally, signs and dates the certification affirming that the information on the form is accurate.

Which Declaration to Sign

The form includes three declarations. You complete only the one that applies.

The Licensed Contractor Declaration is signed by the contractor under penalty of perjury, stating that their California contractor’s license is current and in full force, and listing the license number, class, and expiration date.⁷

The Owner-Builder Declaration applies if you are doing the work yourself, or through your own employees paid only in wages. You check the box stating you are exempt from contractor licensing because you own the property and the structure is not intended or offered for sale. If you sell the home within one year of completing the work, the burden shifts to you to prove you did not make the improvements for the purpose of sale. A second option under this declaration lets you state you are exclusively hiring licensed contractors for the project. Either way, you sign under penalty of perjury; misrepresenting your status carries a civil penalty of up to $500.⁷

The Workers’ Compensation Declaration requires a contractor to provide the workers’ compensation insurance carrier’s name and policy number. A contractor with no employees who is exempt can check the box for that instead.

Supporting Documents to Include

The application alone is rarely enough. Depending on scope, add:

Engineered plans or blueprints. Alterations that change structural loads, modify the roof, add weight, or attach new construction to the chassis usually need drawings prepared or stamped by a licensed engineer or architect. Lenders may require a professional engineer’s certification for additions like carports, porches, and room extensions to confirm the work does not compromise the original unit’s structural integrity.
Manufacturer’s installation instructions for components that were not part of the original design, showing how they should be installed and that they are compatible with the unit.
Local government approvals if the project changes the unit’s exterior footprint or triggers zoning or land-use requirements.

Bundle everything with the completed form before submitting. Missing paperwork is one of the most common reasons applications stall; HCD does not begin review until the submission is complete.

Where to Submit and What It Costs

For most alteration, addition, and conversion permits, submit the completed MH 415 and supporting documents to the HCD area office that covers the unit’s location:

Northern Area Office (NAO): 9342 Tech Center Drive, Suite 550, Sacramento, CA 95826
Southern Area Office (SAO): 3737 Main Street, Suite 400, Riverside, CA 92501

For alternate approval requests, the form’s printed instructions direct you to mail the application to the Department of Housing and Community Development, Manufactured Housing Section, P.O. Box 278180, Sacramento, CA 95827-8180.⁷

Fees are set by Title 25, Section 4044 of the California Code of Regulations. Plan-checking fees start at $223 for the first hour or any fraction of an hour of plan-check time.⁸ Additional hours, inspection fees, and other charges may apply depending on the complexity of the project. Make checks or money orders payable to the Department of Housing and Community Development. Call the area office to confirm the total before you submit; submitting the wrong amount will delay processing.

Approval and Inspection

Once HCD receives a complete application, it reviews the proposed work against Title 25 standards and may request additional information during that period. When the application is approved, HCD returns the processed white copy of the form to the applicant. Do not start work until that copy is in hand; it is your proof the permit has been issued.⁷

After the work is finished, contact the area office listed on your processed application to schedule an inspection. An HCD representative visits the site and checks that the completed alterations match the approved plans. Passing the inspection closes the permit. If the inspector finds deficiencies, correct them and schedule a follow-up inspection before the permit can be finalized.

What Happens If You Skip It

HCD has sole authority over permit issuance and inspections for alterations and conversions of manufactured homes and can require you to dismantle unpermitted modifications.⁴ Insurance carriers routinely deny claims tied to unpermitted work, and some cancel or decline to renew policies once they discover unpermitted modifications. Lenders require evidence the home meets applicable codes, so undocumented alterations raise problems during appraisals and underwriting on a sale or refinance. Retroactive permits, engineer’s reports, and redoing substandard work almost always cost more than getting the permit the first time.

1
California Legislative Information. California Health and Safety Code 18029
2
Legal Information Institute. California Code of Regulations Title 25 4040 – Alteration or Conversion
3
Legal Information Institute. California Code of Regulations Title 25 4004 – Definitions
4
Department of Housing and Community Development. Information Bulletin 2024-04 Manufactured Housing Permit Requirements – Alterations or Conversions
5
Legal Information Institute. California Code of Regulations Title 25 4216 – Maintenance and Repair or Alteration
6
California Department of Housing and Community Development. Forms
7
Department of Housing and Community Development. HCD MH 415 Application for Alteration, Addition or Conversion
8
Legal Information Institute. California Code of Regulations Title 25 4044 – Fees