Updated August 25, 2026. Quick answer: the engineer’s certification people are told they need for a manufactured home is the lender’s requirement, not the title office’s. We read ten state conversion statutes this session and searched every one of them: the word “engineer” appears in exactly one of the ten. What the state asks for is usually a local-government certification that the home is affixed. What FHA asks for is an engineer or architect licensed in your state — and California asks for one too, in the single circumstance that catches older homes.
What the state actually asks for
Washington runs the clearest version. Its application list names the certification it wants, and it comes from the local government, not from a private professional:
“A certification by the local government indicating that the manufactured home is affixed to the land”
— RCW 65.20.040(3)
One of five items in the application package; the others are the affidavit, the certificate of title, the taxes and fees, and whatever else the department requires.
California asks for a building permit from the enforcement agency before installation, which is the same idea routed through the permit counter:
“Prior to installation of a manufactured home, mobilehome, or commercial modular on a foundation system, the manufactured home, mobilehome, or commercial modular owner or a licensed contractor shall obtain a building permit from the appropriate enforcement agency.”
— Cal. Health & Safety Code § 18551(a)(1)
Missouri is the interesting one, because it defines “permanently affixed” by pointing at the federal installation standard by name:
“For the purposes of this section, a manufactured home is permanently affixed if it is anchored to real estate by attachment to a permanent foundation, constructed in accordance with applicable state and local building codes and manufacturer’s specifications as provided in 24 CFR Part 3285, and connected to residential utilities, such as water, gas, electricity, or sewer or septic service.”
— Mo. Rev. Stat. § 442.015.1
The one state in the set that does name an engineer
California, and only when something is missing. Its permit package asks for the manufacturer’s installation instructions — or, if those are gone, plans signed by a licensed architect or engineer:
“The manufactured home, mobilehome, or commercial modular manufacturer’s installation instructions, or plans and specifications signed by a California-licensed architect or engineer covering the installation of an individual manufactured home, mobilehome, or commercial modular in the absence of the manufactured home, mobilehome, or commercial modular manufacturer’s instructions.”
— Cal. Health & Safety Code § 18551(a)(1)(D)
Read the “or”. The engineer is the fallback, not the default. On a home whose paperwork survived, the manufacturer’s instructions satisfy the item outright. On a home from the 1980s whose file is long gone — which is most of the homes this question gets asked about — the fallback is the only limb left, and that is the honest answer to whether California makes you hire one.
Where the engineer requirement really comes from
FHA. The handbook that governs FHA single-family lending puts the duty on the mortgagee, not on you, and it is specific about who may sign:
“The Mortgagee must obtain a certification by an engineer or architect, who is licensed/registered in the state where the Manufactured Home is located, attesting to compliance with the PFGMH.”
— HUD Handbook 4000.1, II.A.1, Manufactured Housing — Required Documentation — PFGMH Certification
Source: HUD Handbook 4000.1 (PDF)
And it reaches the appraisal, which is where most buyers first hear about it:
“For Manufactured Housing, the appraisal must be conditioned upon the certification of an engineer or architect that the foundation is in compliance with the Permanent Foundations Guide for Manufactured Housing (PFGMH).”
— HUD Handbook 4000.1, Appraiser requirements for Manufactured Housing
The order matters more than the document. FHA also requires the home to “be classified as real estate” to be eligible at all. So the conversion is not something you do after financing — it is the gate to it. What your state calls the conversion, and whose land counts, comes first.
“be classified as real estate (but need not be treated as real estate for purposes of state taxation)”
— HUD Handbook 4000.1, II.A.1, Manufactured Housing eligibility
One item in the eligibility list for a Manufactured Home.
The federal standard does name an engineer, for the design
The model installation standards in 24 CFR part 3285 refer to a registered professional engineer or architect repeatedly — but read who is being addressed. It is the party designing the foundation system, which is normally the manufacturer through its approved design program, not the homeowner:
“All foundation details, plans, and test data must be designed and certified by a registered professional engineer or registered architect, and must not take the home out of compliance with the MHCSS.”
— 24 CFR § 3285.301(c)
Where a site condition falls outside the published tables, the standard does push the question to a professional:
“When the frost line depth is not available from the LAHJ, a registered professional engineer, registered architect, or registered geologist must be consulted to determine the required frost line depth for the manufactured home site.”
— 24 CFR § 3285.312(b)(1)
The order you will meet these in
- The installer follows the manufacturer’s instructions — or, where they do not fit the site, a design certified by an engineer or architect. This is the design-side certification, and it happens whether or not you ever convert.
- The state converts the title on the evidence its own statute names — typically an affidavit plus a local-government or permit-office certification that the home is affixed. Ten of those statutes, side by side.
- The lender orders the foundation certification if you are financing with an FHA-insured mortgage. This is the engineer letter people mean when they say a manufactured home “needs an engineer”.
What we did not read, and what this does not say. The count above is a search of the ten statutory spans named on this page, not a statement about your county: a recorder, assessor or building department can require an engineer letter by local rule, and many do. We did not retrieve the Permanent Foundations Guide itself — both HUD locations we tried returned a not-found this session — so we quote the handbook that requires compliance with it and not the guide’s contents. VA, USDA, Fannie Mae and Freddie Mac have their own foundation rules and we did not read them here. Ask your lender and your county before paying for an inspection.
Related: what conversion unlocks and the ten-state comparison.
General information drawn from the state statutes and federal regulations cited on this page, not legal advice. Statutes change and counties apply them differently; every citation here carries the section it came from so you can read it yourself. Your own deed, title and lease govern your case, and the county recorder or assessor where the home sits is the only source for local practice. We sell nothing.