Montana factory-built buildings: statute and rules (Layer 1)

Research date: every source below was fetched September 13, 2026 unless noted. Nothing here is legal advice. Everything is cited. Where I could not confirm something it says NOT CONFIRMED and names who can answer.

Companion document: docs/montana/02-approval-process.md walks the same rules as a step-by-step process. This document is the law itself. Where the two touch the same rule they agree; the one place they differ on a fact is flagged in section 9.

How to read this#

Two things you are building:

• Product A: the house. 40x28, panels cast in the plant, assembled on site on a permanent foundation.
• Product B: the shower house. 1 to 2 bathrooms, built complete in the plant on a steel skid, hauled to site as a finished unit.

Montana has one program that probably covers both, and a federal program that probably covers neither. Section 7 frames the likely classification of each as a question to put to the bureau, not as a conclusion.

Where the rule text came from#

The live Administrative Rules of Montana site, https://rules.mt.gov, serves rule text from JavaScript and cannot be fetched directly. Cornell LII mirrors the live rule text at https://www.law.cornell.edu/regulations/montana/ARM-24-301-XXXX, including the official history note with NEW / TRANS / REPEALED markers and effective dates. Every rule quoted in this document was pulled from LII on 2026-09-13 and checked for a repeal marker before quoting. Rules I could not retrieve are listed per rule, not glossed over.

0. What changed on 21 September 2024#

This is not pending. It happened. Montana rewrote and renumbered its entire factory-built building rule set, and adopted two national off-site construction standards by reference.

The adopting rule, in full:

24.301.1203 INCORPORATION BY REFERENCE OF INTERNATIONAL CODE COUNCIL AND MODULAR BUILDING INSTITUTE STANDARDS (1) The department adopts and incorporates by reference the International Code Council and Modular Building Institute 1200 Standard for Off-site Construction: Planning, Design, Fabrication and Assembly, 2021 edition (ICC/MBI 1200 Standard). (2) The department adopts and incorporates by reference the International Code Council and Modular Building Institute 1205 Standard for Off-site Construction: Inspection and Regulatory Compliance, 2021 edition, (ICC/MBI 1205 Standard). (3) A copy of the off-site standards may be obtained from the International Code Council at www.ICCsafe.org.

NEW, 2024 MAR p. 2223, Eff. 9/21/2024. AUTH: 50-60-203, 50-60-401, MCA; IMP: 50-60-201, 50-60-203, 50-60-401, 50-60-402, MCA

What this means for Ken, in one sentence: you have to buy ICC/MBI 1200-2021 and 1205-2021 from ICC, because the state adopted them by reference and does not republish them, and your quality assurance manual has to be written to chapter 5 of ICC/MBI 1205, not to the eleven-item list that DLI's own web page still shows.

Old rule number to new rule number#

Use this if you are holding an older document, or reading DLI's own web page and forms, which still cite repealed rules.

Every status above was read off the LII page for that old rule number, which carries the official history note. "Transferred" rules show TRANS, to 24.301.12xx, 2024 MAR p. 2223, Eff. 9/21/2024. "Repealed" rules show REP, 2024 MAR p. 2223, Eff. 9/21/2024.

One rule outside subchapter 5 was not touched and is still live: 24.301.204 (subchapter 2, Local Government Enforcement), last amended eff. 6/11/2022. See section 3.

There is a separate, newer rulemaking in progress#

Do not confuse it with the above. DLI's Building Codes Program home page carries this notice:

There will be a public hearing on the upcoming code adoption on Friday, August 28, 2026 at 9:00 AM ... An electronic version of the rule proposal can be found at dli.mt.gov/rules. The deadline to submit written comments is Friday, September 4, 2026 at 5:00 PM.

As of the fetch date, dli.mt.gov/rules says "There are no active rules notices at this time," so that comment window has closed. NOT CONFIRMED: what that 2026 rulemaking contains (it is described only as "the upcoming code adoption," most likely moving Montana from the 2021 to the 2024 I-code editions), and whether it has been adopted. This matters to you directly, because ARM 24.301.1233(2)(a) revokes a plan review when the department adopts a different code version, and ARM 24.301.1231(3) bars renewing plans reviewed under the old codes. That is question 2 in section 8.

A caution on one DLI document: the PDF at https://bsd.dli.mt.gov/_docs/building-codes-permits/ProposedRuleAmendments.pdf is still posted and still reads as a proposal, with placeholder fields for the notice number and hearing date. Its NEW RULE I, II and III match adopted rules 24.301.1203, .1217 and .1213 nearly word for word, its repeal list matches what was actually repealed, and its 115 MPH / seismic D / 30 psf design load floor matches adopted 24.301.1221(3). It is the 2024 proposal, left on the server. It is not a live proposal. Do not cite it as pending.

Sources for section 0

• Montana adopts ICC/MBI off-site construction standards, Modular Building Institute. https://www.modular.org/2024/10/04/montana-adopts-icc-mbi-off-site-construction-standards/ (fetched 2026-09-13; gives the 20 September 2024 approval date)
• ARM 24.301.1203, Incorporation by reference of ICC and MBI standards. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1203 (fetched 2026-09-13)
• Old-to-new status for each rule, from the history note on each old rule page: https://www.law.cornell.edu/regulations/montana/ARM-24-301-501 , -511, -513, -515, -516, -517, -518, -519, -520, -521, -522, -523, -525, -535, -536, -540, -542, -543, -544, -545, -546, -547, -549, -550, -557, -558, -559, -560, -561, -562, -563, -564, -565, -566, -567, -576, -577 (all fetched 2026-09-13)
• ARM 24.301.204 (still live). https://www.law.cornell.edu/regulations/montana/ARM-24-301-204 (fetched 2026-09-13)
• Montana Building Codes Program home page (2026 hearing notice). https://bsd.dli.mt.gov/building-codes-permits/ (fetched 2026-09-13)
• DLI rules page. https://dli.mt.gov/rules (fetched 2026-09-13)
• Proposed Rule Amendments PDF (the 2024 proposal, still posted). https://bsd.dli.mt.gov/_docs/building-codes-permits/ProposedRuleAmendments.pdf (fetched 2026-09-13)

1. Who regulates this in Montana#

The agency is the Montana Department of Labor and Industry (DLI). The statute defines it:

"Department" means the department of labor and industry provided for in Title 2, chapter 15, part 17. (50-60-101(7), MCA)

ARM 24.301.1205(1) is the rule that names the bureau: "'Bureau' means the Building and Commercial Measurements Bureau of the Department of Labor and Industry."

Note that the old rule assigning enforcement in one sentence, ARM 24.301.514 ("The Building and Commercial Measurements Bureau shall administer and enforce all the provisions of Title 50, chapter 60, MCA"), was repealed effective 9/21/2024 and has no direct successor. The authority now rests on the statute, MCA 50-60-103 ("The department shall administer parts 1 through 7"), plus the bureau's role written through the individual new rules.

Division name, NOT CONFIRMED. DLI's building codes pages carry the header "Employment Standards Division" and sit on the host bsd.dli.mt.gov, which reads as Business Standards Division; the sibling document 02-approval-process.md says Business Standards Division. It does not change any obligation, but ask before you put a division name in a manual.

Contact route#

Ask for the Factory-Built Building program by name. DLI does not publish staff names on that page and I am not going to invent one.

Sources for section 1

• 50-60-101, MCA. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0010/0500-0600-0010-0010.html (fetched 2026-09-13)
• 50-60-103, MCA. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0030/0500-0600-0010-0030.html (fetched 2026-09-13)
• ARM 24.301.1205, Definitions. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1205 (fetched 2026-09-13)
• ARM 24.301.514 (repealed 9/21/2024). https://www.law.cornell.edu/regulations/montana/ARM-24-301-514 (status read from the LII history note, fetched 2026-09-13)
• Factory-Built Buildings Permits. https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/ (fetched 2026-09-13)
• Montana Building Codes Program home. https://bsd.dli.mt.gov/building-codes-permits/ (fetched 2026-09-13)

2. The statute: MCA Title 50, Chapter 60#

All MCA text below was pulled on 2026-09-13 from the Montana Legislature's own site, which serves the Montana Code Annotated 2025. That is the current official text. Each section's history line is given so you can see when it was last touched. Chapter 60 was not part of the September 2024 rulemaking; rulemaking changes rules, not statutes.

Chapter 60 is "Building Construction Standards," nine parts:

Part 4 is your part. Four sections. The heavy lifting is in the rules.

2.1 Part 4, section by section#

50-60-401. Department to adopt rules for factory-built buildings. Last amended 1997 (amd. Sec. 2, Ch. 240, L. 1997). Full text:

The department may adopt by reference nationally recognized construction standards, in whole or in part, for the construction of factory-built buildings, but this does not prevent the department from adopting rules more stringent than those contained in the national standards.

This is the authority the department used in September 2024 to adopt ICC/MBI 1200 and 1205. It appears as an AUTH citation on every rule in subchapter 12.

50-60-402. Factory-built buildings and recreational vehicles to comply with standards. Last amended 1997 (amd. Sec. 3, Ch. 240, L. 1997). The operative prohibition and the operative benefit. Full text:

(1) A person, firm, or corporation may not manufacture, sell, or offer for sale any new factory-built building unless the factory-built building and its components, systems, and appliances have been constructed and assembled in accordance with the standards defined in this part.

(2) A factory-built building that has been approved by the department is considered to be in full compliance with the standards and rules prescribed in parts 1 through 4.

(3) All factory-built buildings approved by the department are acceptable as meeting the requirements of parts 1 through 4 throughout the state of Montana without further inspection or fees except for zoning, utility connections, and foundation permits required by local ordinance.

(4) A person, firm, or corporation may not manufacture, sell, or offer for sale a new recreational vehicle unless the vehicle has been constructed and assembled in accordance with the American national standards institute ANSI/A119.2 standard for recreational vehicles. The department is not responsible for enforcing the compliance of recreational vehicles with the ANSI/A119.2 standard as part of the state building code.

Read subsection (3) twice. That is the business case: one state approval, good statewide, and the local jurisdiction can charge you only for zoning, utility hookups, and the foundation permit. Subsection (1) is the other edge: you cannot even offer for sale an unapproved new factory-built building.

50-60-403. Use of independent testing laboratories authorized. Last amended 1997. Full text:

The department may use independent testing laboratories or the agencies of other states to determine if approved models of factory-built buildings are being constructed in accordance with the approved plans and specifications for those models.

This is the "independent contracted third party" hook. The statute says the department may use them. In practice it is mandatory for you: ARM 24.301.1221(2)(c) requires the model plan review application to name "the approved third-party inspection agency responsible for on-site inspections," and both DLI forms mark the third-party inspector field ***required***. 50-60-403 now appears as an IMP citation on ARM 24.301.1213, .1235, .1241, .1245 and .1261.

50-60-404. Enforcement of building construction standards for modular homes. Last amended 2003 (amd. Sec. 18, Ch. 443, L. 2003). The local-factory carve-out. Full text:

(1) The provisions of this chapter apply to factory-built modular or prebuilt homes or buildings.

(2) A county, city, or town may regulate the construction of factory-built modular or prebuilt homes or buildings as provided in 50-60-106 if: (a) the homes or buildings are constructed inside the jurisdiction of the county, city, or town; (b) the homes or buildings are sold primarily to persons in the county in which the factory is located; (c) the factory does not manufacture more than 100 homes or buildings a year; and (d) the county, city, or town has an agency or officer assigned to inspect and enforce building construction standards.

(3) Inspection and enforcement approval given by a county, city, or town under this section may be recognized and accepted by any other county, city, or town of the state to which the factory-built home or building is transported for final installation. Additional inspections need not be conducted.

For a Montana plant selling mostly locally under 100 units a year this is a real alternative. All four conditions in (2) must hold at once, and (d) requires the local jurisdiction to actually run a certified program. NOT CONFIRMED: whether the bureau reads 50-60-404 as an alternative to state FBB approval or as an extra layer on top. Question 4 in section 8.

2.2 Part 1 sections you will touch#

All confirmed current on the live MCA site, 2026-09-13.

2.3 Part 2, the state building code itself#

50-60-203. Department to adopt state building code by rule. DLI adopts construction, equipment and materials rules by rule; "may adopt by reference nationally recognized building codes in whole or in part" and "may adopt rules more stringent than those contained in national codes." Those adopted rules are the state building code. Legislative limits are baked in: no residential fire sprinkler mandate for one- and two-unit dwellings, no mandated solar or EV wiring, no banning an energy source, no banning EPA-listed refrigerants. Amended in 2021, four times in 2023, and again in 2025 (amd. Sec. 1, Ch. 368, L. 2025), so treat any older summary as stale. 50-60-203 is the lead AUTH citation on every rule in ARM 24.301 subchapter 12.

2.4 Penalties and enforcement in the statute#

• Misdemeanor, 50-60-110.
• Injunction, 50-60-109.
• Prohibited sales notice and insignia confiscation, which live in the rules: ARM 24.301.1241(1), .1271.
• Hearing rights, ARM 24.301.1273, under the Montana Administrative Procedure Act.

2.5 Exemptions#

The one that matters most is 50-60-102(1)(a): the state building code does not apply to residential buildings with fewer than five dwelling units, or to farm or ranch buildings of any size, unless the local legislative body adopts it. That is an exemption from the state building code in Part 2. It is not on its face an exemption from 50-60-402(1), the "may not manufacture, sell, or offer for sale any new factory-built building" rule in Part 4. Different sentences, different parts.

NOT CONFIRMED: whether a factory-built single-family house, being under five dwelling units, still needs a Montana FBB insignia. My reading is that it does, because 50-60-402(1) is not conditioned on the state building code applying, because ARM 24.301.1201(2)(a) expressly contemplates review to the IRC as well as the IBC, and because DLI's FBB application form has a "Residential" model type checkbox. Get it in writing. Question 1 in section 8.

Sources for section 2

• Chapter 60 parts index. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/parts_index.html (fetched 2026-09-13)
• Part 4 sections index. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/sections_index.html (fetched 2026-09-13)
• 50-60-401. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0010/0500-0600-0040-0010.html (fetched 2026-09-13)
• 50-60-402. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0020/0500-0600-0040-0020.html (fetched 2026-09-13)
• 50-60-403. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0030/0500-0600-0040-0030.html (fetched 2026-09-13)
• 50-60-404. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0040/0500-0600-0040-0040.html (fetched 2026-09-13)
• Part 1 sections index. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/sections_index.html (fetched 2026-09-13)
• 50-60-102, -103, -104, -106, -108, -109, -110, all at https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_00XX/... (each fetched 2026-09-13)
• 50-60-203. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0020/section_0030/0500-0600-0020-0030.html (fetched 2026-09-13)
• NOT CONFIRMED by direct fetch: the full text of 50-60-105, 50-60-107, 50-60-115, 50-60-117 and 50-60-118. Their section numbers and titles come from the Part 1 index page above; I did not open them individually. Their substance as described here comes from the index title plus the AUTH/IMP citations in the ARM rules.

3. The administrative rules: ARM Title 24, chapter 301, subchapter 12#

Chapter 24.301 is "BUILDING CODES." Department 24 is Labor and Industry. The subchapter you live in is 24.301.12, "Requirements for Recreational Vehicles and Factory-Built Buildings," rules 24.301.1201 through 24.301.1273. The subchapter uses odd numbers; the gaps (1209, 1219, 1229, 1239, 1251 through 1259, 1267, 1269) are reserved and hold no rule, which I confirmed by probing each one.

One rule outside the subchapter matters and is still live:

24.301.204 FACTORY-BUILT BUILDINGS (1) Once factory-built buildings are approved by the department as meeting the codes, the units shall be subject only to city, county, or town inspection and fees for zoning, utility connections and foundations. As part of the city, county or town's submittals to the department, provisions must be included stating how factory-built buildings will be handled with respect to permits and inspections to include the charges for permits covering these types of units. (AUTH 50-60-302, IMP 50-60-302, MCA; AMD, 2022 MAR p. 911, Eff. 6/11/2022)

That rule sits in subchapter 2, Local Government Enforcement, and binds certified local programs to honor your state approval. Print it and carry it.

3.1 What the rules adopt by reference#

Two layers. ARM 24.301.1201(2) points at the model codes and now at the off-site standards:

24.301.1201 APPLICABILITY OF STATE STATUTES AND ADOPTED ADMINISTRATIVE RULES (1) These rules and standards are based on the provisions of Title 50, Chapter 60, MCA, to carry out the statutory provisions relating to the manufacture and sale of factory-built buildings and components thereof. (2) Factory-built buildings shall meet the requirements of the following nationally recognized construction standards: (a) the International Building Code as adopted and amended by ARM 24.301.131 or, as applicable, the International Residential Code as adopted and amended by ARM 24.301.154; (b) the National Electrical Code as adopted and amended by ARM 24.301.401; (c) the International Mechanical Code as adopted and amended by ARM 24.301.172; (d) the Uniform Plumbing Code as adopted and amended by ARM 24.301.301; (e) the International Energy Conservation Code as adopted and amended by ARM 24.301.161; (f) the International Wildland-Urban Interface Code as adopted and amended by ARM 24.301.181; (g) the International Code Council and Modular Building Institute 1200 Standard for Off-Site Construction: Planning, Design, Fabrication and Assembly as adopted and amended by ARM 24.301.1203; and (h) the International Code Council and Modular Building Institute 1205 Standard for Off-Site Construction: Inspection and Regulatory Compliance as adopted and amended by ARM 24.301.1203. (3) The requirement listed in 50-60-402, MCA, for new factory-built buildings applies to all new units, whether offered for sale, lease or rent, which are first utilized in the state of Montana, regardless of the unit's point of origin or route of delivery. A person cannot arrange to accept delivery of a new unit at an out-of-state location to avoid the need for a state of Montana insignia of approval on the unit.

TRANS, from 24.301.501, 2024 MAR p. 2223, Eff. 9/21/2024. AUTH: 50-60-203, 50-60-401, MCA; IMP: 50-60-201, 50-60-203, 50-60-401, 50-60-402, MCA

Two changes from the old .501 worth noting: the International Swimming Pool and Spa Code was dropped from the list, and the two ICC/MBI standards were added. Note (2)(a) again: IBC "or, as applicable" the IRC. That phrase decides whether your 40x28 house is reviewed to the residential or the commercial code.

Which editions are currently adopted, from DLI's Current Codes page:

Plus, since 21 September 2024, ICC/MBI 1200-2021 and ICC/MBI 1205-2021. DLI's Current Codes page does not list the two off-site standards; they are in ARM 24.301.1203. NOT CONFIRMED: whether DLI intends to add them to that page. Either way the rule controls.

DLI's own note on that page: all of these are amended by ARM Title 24, chapter 301. You cannot design to a clean ICC book. You design to the ICC book as amended by Montana rule. Get the amendment list.

3.2 Subchapter 12 rule map, all 26 live rules#

Every rule below was fetched from LII on 2026-09-13 and carries its own history note. "NEW" means the rule did not exist before 9/21/2024. "TRANS" means it moved from subchapter 5.

3.3 The three rules you will work from#

24.301.1217 MANUFACTURER REGISTRATION, full text:

(1) Each manufacturer shall obtain approval from the department and be subject to Section 601 of the ICC/MBI 1205 Standard as adopted by the department. (2) Manufacturers applying for model plan review per ARM 24.301.1221, once approved, will be listed as an approved manufacturer in the state of Montana.

NEW, 2024 MAR p. 2223, Eff. 9/21/2024

There is no separate manufacturer licence or registration fee. You become an approved manufacturer by getting a model plan approved. But note (1): you are "subject to Section 601 of the ICC/MBI 1205 Standard," and you will not know what Section 601 requires until you buy the standard.

24.301.1221 APPLICATION FOR MODEL PLAN REVIEW, full text:

(1) Any manufacturer of modular buildings or modular building components shall apply to the bureau for plan review of a model or model group before construction. (2) The application for model plan review shall include the following: (a) the applicable plan, quality assurance manual, and system inspection fees required by ARM 24.301.1261; (b) the quality assurance manual as defined in ARM 24.301.1223; (c) the approved third-party inspection agency responsible for on-site inspections; (d) all applicable plan approval items provided for in chapter 3 of the ICC/MBI 1205 Standard; and (e) the first page of the construction document shall include the wind load (Vult), construction type, seismic design category, and ground snow load. (3) If the permanent site location of the building is unknown (nonsite-specific), the building must meet the following structural design loads: (a) Wind load of 115 MPH. (b) Seismic design category of D. (c) Snow load of 30 psf.

NEW, 2024 MAR p. 2223, Eff. 9/21/2024

This is a much shorter rule than the old .535, and that is the point: the detailed submittal list moved into chapter 3 of ICC/MBI 1205. The old rule spelled out floor plans, cross sections, connections, live and dead loads, electrical feeder sizes, BTUH ratings, trap arm lengths and so on. Those items are no longer in Montana rule. Note also that (1) says "manufacturer of modular buildings or modular building components," which explicitly reaches components, not just whole modules.

24.301.1223 IN-PLANT QUALITY ASSURANCE MANUAL, full text:

(1) The manufacturer shall submit a quality assurance manual outlining a program of quality assurance prior to or with the manufacturer's first request for plan review, including the quality assurance manual review fee required by ARM 24.301.1261. (2) The quality assurance manual must include all applicable items as listed in chapter 5 of the ICC/MBI 1205 Standard and be reviewed and approved by the bureau prior to the approval of plan review. (3) When the quality assurance manual is revised, one copy of the revised manual shall be submitted to the bureau for review, and the manufacturer shall include the quality assurance manual review fee required by ARM 24.301.1261.

NEW, 2024 MAR p. 2223, Eff. 9/21/2024

Two things bite here. First, the manual must be approved before the plan review is approved, so it is on the critical path and you cannot do it last. Second, the content spec is chapter 5 of ICC/MBI 1205, not the eleven-item list DLI's web page still displays. Write to the standard.

3.4 Rules I could not confirm#

None in subchapter 12. All 26 live rules listed in 3.2 were fetched individually from Cornell LII on 2026-09-13, and each returned its own rule text plus the official history note. The reserved gaps (1209, 1219, 1229, 1239, 1251, 1253, 1255, 1257, 1259, 1267, 1269) and a range check at 1202, 1210, 1275 and 1281 all returned a generic index page, meaning no rule exists at those numbers.

What I did not fetch, and am therefore not summarizing: the text of ICC/MBI 1200-2021 and ICC/MBI 1205-2021. They are copyrighted ICC publications sold by ICC, not published in the ARM and not free. Sections 401 (third-party agencies), 601 (manufacturers), chapter 2 (definitions, including "module"), chapter 3 (plan approval items) and chapter 5 (quality assurance manual) are all cited by Montana rule and all live inside those two books. You have to buy them. Until you do, nobody can tell you what your submittal or your manual must actually contain.

Sources for section 3

• ARM 24.301.204. https://www.law.cornell.edu/regulations/montana/ARM-24-301-204 (fetched 2026-09-13)
• ARM 24.301.1201. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1201 (fetched 2026-09-13)
• ARM 24.301.1203. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1203 (fetched 2026-09-13)
• ARM 24.301.1205. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1205 (fetched 2026-09-13)
• ARM 24.301.1207, .1211, .1213, .1215, .1217, .1221, .1223, .1225, .1227, .1231, .1233, .1235, .1237, .1241, .1243, .1245, .1247, .1249, .1261, .1263, .1265, .1271, .1273, each at https://www.law.cornell.edu/regulations/montana/ARM-24-301-XXXX (all fetched 2026-09-13)
• Subchapter title, "Subchapter 24.301.12 - Requirements for Recreational Vehicles and Factory-Built Buildings," from the LII breadcrumb metadata on the rule pages above (fetched 2026-09-13)
• Current Codes, Montana Building Codes Program. https://bsd.dli.mt.gov/building-codes-permits/current-codes (fetched 2026-09-13)
• Live rule site for verification: https://rules.mt.gov

4. The definitions that decide which regime you are in#

4.1 Montana definitions, quoted#

"Factory-built building" appears in two places and they say the same thing.

MCA 50-60-101(9), the controlling one:

(9) (a) "Factory-built building" means a factory-assembled structure or structures equipped with the necessary service connections but not made so as to be readily movable as a unit or units and designed to be used with a permanent foundation. (b) The term does not include manufactured housing constructed after June 15, 1976, under the National Mobile Home Construction and Safety Standards Act of 1974, 42 U.S.C. 5401, et seq.

ARM 24.301.1205(4), the live rule:

(4) "Factory-built building" means a factory assembled structure or structures equipped with the necessary service connections, but not made so as to be readily movable as a unit or units and designed to be used with a permanent foundation.

DLI's web page shortens it in a way that drops a clause. The page says a factory-built building is "a factory assembled structure(s) equipped with the necessary service connections and designed to be used with a permanent foundation," leaving out "but not made so as to be readily movable as a unit or units." If anyone argues from the website version, go to the statute.

The rest of ARM 24.301.1205, in full, because there are only six definitions left and the shrinkage is itself the news:

(1) "Bureau" means the Building and Commercial Measurements Bureau of the Department of Labor and Industry. (2) "Components" means the prefabricated wall, floor, ceiling, or roof panels or pre-cut building kits or similar units of construction or any combination of such units. (3) "Engineer" means a professional engineer who, by reason of special knowledge of the mathematical and physical sciences and the principles and methods of engineering analysis and design, acquired the right to practice engineering as attested by his registration as a professional engineer. (4) "Factory-built building" [as above] (5) "Prohibited sales notice" means a printed notification issued by the bureau that the unit may not be offered for sale because of violations of these rules. (6) "Unit" has the same meaning as "module" as defined in chapter two of the ICC/MBI 1200 Standard and the ICC/MBI 1205 Standard.

Subsection (6) is a big deal for you. The old rule said "Unit" means "a factory-built building and components thereof." It now means module, as defined in a book you have to buy. That changes what a "unit" is for insignia purposes, and it interacts directly with the panel-count question in section 7.

Also note what disappeared from the definitions when .511 became .1205: insignia, listing agency, local enforcement agency, alteration or conversion, model, model group, recreational vehicles, system, testing agency, and third party certification and inspection agency. That last one used to be defined in Montana rule as an agency that "inspects and certifies, in lieu of state inspectors" and "is not under the control or jurisdiction of any supplier, manufacturer, or dealer." That definition is gone from the ARM. It now lives in Section 401 of ICC/MBI 1205, via ARM 24.301.1213(1).

"Recreational vehicle" (MCA 50-60-101(16)):

(16) "Recreational vehicle" means a vehicular type unit primarily designed as temporary living quarters for recreational, camping, or travel use that either has its own mode of power or is mounted on or towed by another vehicle, including but not limited to a: (a) travel trailer; (b) camping trailer; (c) truck camper; or (d) motor home.

"Building" (MCA 50-60-101(2)):

(2) "Building" means a combination of any materials, whether mobile, portable, or fixed, to form a structure and the related facilities for the use or occupancy by persons or property. The term must be construed as though followed by the words "or part or parts of a building".

Note "whether mobile, portable, or fixed." A skid-mounted building is still a building.

"Manufactured home" (MCA 15-24-201(3), and identically at 15-1-101(1)(n)(i)):

(3) "Manufactured home" means a residential dwelling built in a factory in accordance with the United States department of housing and urban development code and the federal Manufactured Home Construction and Safety Standards. A manufactured home does not include a mobile home or a housetrailer.

"Mobile home" (MCA 15-24-201(4)):

(4) "Mobile home" means forms of housing known as "trailers", "housetrailers", or "trailer coaches" exceeding 8 feet in width or 45 feet in length, designed to be moved from one place to another by an independent power connected to the mobile home or any trailer, housetrailer, or trailer coach up to 8 feet in width or 45 feet in length used as a principal residence.

15-1-101(1)(n)(ii) adds that a manufactured home "does not include a mobile home ... or a mobile home or housetrailer constructed before the federal Manufactured Home Construction and Safety Standards went into effect on June 15, 1976."

"Modular home." There is no defined term "modular home" in MCA 50-60-101. The word appears only in the title and body of 50-60-404, which says "The provisions of this chapter apply to factory-built modular or prebuilt homes or buildings." In Montana a modular home is a species of factory-built building, not a separate regime. Note that ARM 24.301.1221(1) now uses "modular buildings or modular building components" as the operative phrase for who must apply.

"Commercial modular" and "residential modular" are not Montana statutory or rule terms. The closest thing is the FBB application form's Model Type field: Commercial, Residential, or Other. That is an administrative sorting field, not a legal category. "Commercial modular" as a defined term is California language, not Montana.

"Park trailer" and "park model." MCA 50-60-101(16) lists travel trailer, camping trailer, truck camper and motor home, "including but not limited to," so the list is open. 50-60-402(4) names only ANSI/A119.2 and says the department "is not responsible for enforcing" it as part of the state building code. NOT CONFIRMED: whether Montana treats a park model unit (the ANSI A119.5 family) as a recreational vehicle, a factory-built building, or neither. I found no Montana statute or rule naming A119.5. Bureau question.

4.2 What actually separates the categories#

The two tests that do the real work for your products are permanent chassis and designed for a permanent foundation and not readily movable as a unit. Everything else follows.

One live rule constrains use rather than construction:

24.301.1207 ... (2) These units do not meet code requirements for commercial or business occupancy and are therefore prohibited for these types of uses. Except as provided in (4), manufactured homes, mobile homes, and recreational vehicles shall not be utilized for any occupancy other than as a single-family dwelling, whether for transient stay or longer periods.

Note the wording changed when .513 became .1207: it now says "manufactured homes, mobile homes, and recreational vehicles," where the old rule said "manufactured (mobile) homes and recreational vehicles." Either way it is the reason you cannot solve the shower house problem by buying a park model and calling it a bathhouse.

Sources for section 4

• 50-60-101, MCA. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0010/0500-0600-0010-0010.html (fetched 2026-09-13)
• 50-60-402 and 50-60-404, MCA. URLs as in section 2 (fetched 2026-09-13)
• 15-24-201, MCA. https://mca.legmt.gov/bills/mca/title_0150/chapter_0240/part_0020/section_0010/0150-0240-0020-0010.html (fetched 2026-09-13)
• 15-1-101, MCA. https://mca.legmt.gov/bills/mca/title_0150/chapter_0010/part_0010/section_0010/0150-0010-0010-0010.html (fetched 2026-09-13)
• ARM 24.301.1205. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1205 (fetched 2026-09-13)
• ARM 24.301.1207. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1207 (fetched 2026-09-13)
• ARM 24.301.1221. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1221 (fetched 2026-09-13)
• ARM 24.301.511 (old definitions, transferred, for the comparison of what was dropped). https://www.law.cornell.edu/regulations/montana/ARM-24-301-511 (fetched 2026-09-13)
• 24 CFR 3280.2 Definitions. https://www.law.cornell.edu/cfr/text/24/3280.2 (fetched 2026-09-13)
• Factory-Built Buildings Permits (DLI page wording, Model Type field). https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/ (fetched 2026-09-13)

5. What the program costs, on paper#

Rechecked against the live fee rules, not the archived ones. The dollar figures did not change on 21 September 2024. What changed is the rule numbers, one added fee line, and the insignia unit of measure.

Plan and system review, ARM 24.301.1261 (transferred from .565)#

ARM 24.301.1261(1)(h)(i) and (ii) add that any approved units to be used in the next plan period must be renewed, and units not renewed by the 31 December deadline expire and need a new application.

Note the internal inconsistency in the live rule: the heading of (1)(a) still says "Quality control manual review," while ARM 24.301.1221 and .1223 both call it the quality assurance manual. Same fee, same document. Worth one line of clarification from the bureau.

Insignia, ARM 24.301.1263 (NEW; old .566 was repealed)#

(1) The fee for an insignia of approval for a factory-built building is $40 per section. This fee covers the building construction, plumbing, electrical, and mechanical.

The old .566 said "$40 per part." The live rule says "per section." Same money, different word. Combined with ARM 24.301.1205(6), where "unit" now means "module," the vocabulary has shifted toward the ICC/MBI standard's terms while ARM 24.301.1261 still prices plan review by "parts." NOT CONFIRMED: whether "part," "section," "unit" and "module" are meant to be the same thing here. For a panelized house the answer decides your cost model. Question 3 in section 8.

Miscellaneous, ARM 24.301.1265 (transferred from .567)#

Since you would be an in-state manufacturer, ARM 24.301.1265(2) does not bite you. That is a real advantage over the Indiana and Utah plants on Montana's approved manufacturer list.

What the forms say#

The DLI forms still print the same dollar figures, so form and rule agree on the money even where they disagree on rule numbers:

• Application for Approval of Factory Built Building (Rev. 4/23): the same $325/$450/$650 structural tiers, $35/$55/$75 trades, $125/$20 resubmission, $100 plan renewal, $20 quality control manual. Also: "Plans must be sent by cd, thumb drive, drop box, email, or paper (no larger than 11x17)" and "ALL INCOMPLETE APPLICATIONS WILL BE RETURNED UNPROCESSED." The 3rd Party Inspector block is marked ***required***.
• Application for Factory Built Building Insignias (Rev. 7/24): $40.00 per insignia, and "INSIGNIAS WILL ONLY BE ISSUED IF THE MANUFACTURER IS ABLE TO PROVIDE THE NAME OF MODEL, MODEL NUMBER, SERIAL NUMBER, AND DESTINATION IN MONTANA WHERE THE UNIT IS BEING SHIPPED, NO EXCEPTIONS." This form still cites ARM 24.301.558, which was repealed 9/21/2024. The live rule is ARM 24.301.1243, which says the same 12-month void period.
• Montana Certification Application for Third Party Inspection Agencies: $20 application review fee, matching the new line in ARM 24.301.1261(1)(b).
• HUD 309 installation inspection: $225. NOT CONFIRMED by direct fetch; see section 8A.

You cannot stockpile insignia. Every label is tied to a known unit going to a known Montana address, and goes void 12 months after issue (ARM 24.301.1243(3)), with no replacement for a void one (ARM 24.301.1247(2)).

Sources for section 5

• ARM 24.301.1261. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1261 (fetched 2026-09-13)
• ARM 24.301.1263. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1263 (fetched 2026-09-13)
• ARM 24.301.1265. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1265 (fetched 2026-09-13)
• ARM 24.301.566 (repealed), for the "per part" wording it used. https://www.law.cornell.edu/regulations/montana/ARM-24-301-566 (fetched 2026-09-13)
• Application for Approval of Factory Built Building (Rev. 4/23). https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/FBBP_APPLICATION_ADOBE_F.pdf (fetched 2026-09-13)
• Application for Factory Built Building Insignias (Rev. 7/24). https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/FBBP_INSIGNIA_APP_ADOBE_F.pdf (fetched 2026-09-13)
• Montana Certification Application for Third Party Inspection Agencies. https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/3rdPartyInspCertApp.pdf (fetched 2026-09-13)
• Approved FBB manufacturers list, dated 9/02/2026. https://bsd.dli.mt.gov/_docs/building-codes-permits/FBBManufacturersWeb-2026.pdf (fetched 2026-09-13)

6. Reciprocity and third-party agencies#

6.1 The reciprocity rule, quoted in full#

24.301.1235 RECIPROCITY (1) Any unit manufactured in a reciprocal state which has been reviewed as meeting the standards of that state shall be deemed to meet the standards of the state of Montana. Reciprocal status shall be granted to other states at the discretion of the bureau. In addition to the insignia of the reciprocal state, a Montana insignia of approval is necessary on all units manufactured or offered for sale within the state of Montana. (2) The bureau chief shall have the authority to enter into reciprocal agreements with other states. (3) Reciprocal status for factory-built buildings may be granted to HUD-approved Category III states.

TRANS, from 24.301.523, 2024 MAR p. 2223, Eff. 9/21/2024. AUTH: 50-60-203, 50-60-401, MCA; IMP: 50-60-203, 50-60-401, 50-60-403, MCA

Emphasis mine. Reciprocity gets your plan review accepted. It does not get you out of the Montana insignia. Every unit still needs the Montana label and the label fee. ARM 24.301.1245(1) says the same from the other direction.

24.301.1237 is the mechanism for pushing a Montana review out to a reciprocal state:

(1) Plan review, panelized system reviews, and/or quality assurance manual reviews may be transmitted to a reciprocal state for approval in the following manner: (a) A manufacturer shall make a written request to the bureau for transmittal ... to a specific reciprocal state. (b) The request shall designate the models and/or system review numbers to be transmitted. (c) Once the request is complete, the bureau shall transmit the review to the reciprocal state electronically. (2) The reciprocal state shall follow that state's procedure for processing and approving the review materials, including notifying the manufacturer of approval or rejection ...

This is a genuine improvement over the repealed .544, which required "two reproductions" on paper showing the reviewing state's stamp. It is now electronic and the receiving state runs its own process.

NOT CONFIRMED: which states Montana currently has reciprocal agreements with, and what "HUD-approved Category III states" means operationally in 2026. That phrase survives from an older HUD categorization and I found no current authoritative list. The bureau chief holds the agreements per ARM 24.301.1235(2). Question 7 in section 8.

6.2 Interstate compacts#

NOT CONFIRMED, and probably no. I found no Montana statute or rule joining an interstate compact for factory-built buildings. MCA 50-60-403 only authorizes the department to "use independent testing laboratories or the agencies of other states," which is contracting authority, not a compact. Nothing in subchapter 12 references a compact. Question 8.

What Montana did do in September 2024 is adopt the same two national standards Virginia, Utah and the U.S. General Services Administration have adopted, per the Modular Building Institute. That is not reciprocity, but it is convergence, and it is worth asking whether the bureau expects it to ease multi-state approval.

6.3 Third-party agencies Montana has already certified#

From DLI's FBB page, stamped "Last Updated 1/28/26":

Five state agencies sit on that list (MN, CO, ID, NE, WA). That is the practical shape of reciprocity in this program: another state's agency does the plant inspection under contract.

Phone numbers are on DLI's page. I am not reproducing them so you always pull the live list.

6.4 What Montana requires of a third-party agency#

The rule is now one sentence pointing at the standard:

24.301.1213 APPROVAL OF THIRD-PARTY INSPECTION AGENCY (1) Third-party inspection agencies shall meet the requirements of Section 401 of the ICC/MBI 1205 Standard as adopted by the department. (2) Third-party inspection agencies shall apply on an application form supplied by the department and include the third-party inspection agency fee required by ARM 24.301.1261. (3) Once approved by the department, the third-party inspection agency will be listed as an approved third-party agency in the state of Montana.

DLI's certification form fills in what that looks like in practice:

• Disciplines sought: structural, electrical, plumbing, mechanical.
• Years actively engaged in inspection services; list of manufacturers served in Montana.
• Required documents: accreditation certificate from an ISO/IEC 17011-compliant accreditation body for inspection services (or a box to check if not accredited); list of key personnel with primary functions; professional licenses or plan review and inspector certifications for personnel doing in-plant inspections. The form notes: "The inspector shall only inspect in areas in which they are licensed or certified."
• Fee: $20 application review fee.
• Independence certification: no actual or potential conflict of interest, no affiliation with or control by a client manufacturer.
• Initial plant certification: written certification report to the manufacturer and the AHJ, requiring "100 percent inspection of the aspects of construction on not fewer than one module or modular component" plus verification that the manufacturer has a functioning quality assurance process. If the first module fails, more get inspected.
• Ongoing inspections: inspect each module in a phase of construction against the plant certification; for modular components or panelized systems the agency sets the frequency.
• Written or electronic inspection report after each inspection identifying every deficiency. "The third-party agency shall only issue labels after all deficiencies have been corrected."
• A procedure for controlling the agency's labels; errors and omissions insurance.

Read that block as a description of what your plant will experience.

One change worth noting: the repealed .516 required state inspectors to "monitor the third party inspection agencies regarding the accuracy and quality of their inspections and reports" and to "inspect and monitor all manufacturers, dealers, and installers." That rule is gone. What replaced it is narrower on its face: ARM 24.301.1211 (inspector independence) and ARM 24.301.1215 (inspection of retailers). NOT CONFIRMED: where bureau oversight of third-party agencies and of manufacturers now lives, whether in ICC/MBI 1205 or in the department's general authority under MCA 50-60-103. Question 11.

Sources for section 6

• ARM 24.301.1235. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1235 (fetched 2026-09-13)
• ARM 24.301.1237. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1237 (fetched 2026-09-13)
• ARM 24.301.1213. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1213 (fetched 2026-09-13)
• ARM 24.301.1211, .1215, .1245. https://www.law.cornell.edu/regulations/montana/ARM-24-301-1211 , -1215, -1245 (all fetched 2026-09-13)
• ARM 24.301.516 and .544 (repealed), for what was removed. https://www.law.cornell.edu/regulations/montana/ARM-24-301-516 and -544 (fetched 2026-09-13)
• 50-60-403, MCA. URL as in section 2 (fetched 2026-09-13)
• Factory-Built Buildings Permits, third party agency list, page stamp "Last Updated 1/28/26". https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/ (fetched 2026-09-13)
• Montana Certification Application for Third Party Inspection Agencies. https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/3rdPartyInspCertApp.pdf (fetched 2026-09-13)
• Montana adopts ICC/MBI off-site construction standards, MBI. https://www.modular.org/2024/10/04/montana-adopts-icc-mbi-off-site-construction-standards/ (fetched 2026-09-13)

7. Federal overlay: where HUD takes over#

7.1 The federal definition, quoted#

24 CFR 3280.2:

Manufactured home means a structure, transportable in one or more sections, which in the traveling mode is 8 body feet or more in width or 40 body feet or more in length or which when erected on-site is 320 or more square feet, and which is built on a permanent chassis and designed to be used as a dwelling with or without a permanent foundation when connected to the required utilities, and includes the plumbing, heating, air-conditioning, and electrical systems contained in the structure. ... The term does not include any self-propelled recreational vehicle.

(Emphasis mine.) Two federal parts do the work:

• 24 CFR Part 3280, Manufactured Home Construction and Safety Standards. The "HUD code."
• 24 CFR Part 3282, Manufactured Home Procedural and Enforcement Regulations. Who inspects, who approves designs, how states participate.

7.2 DAPIA, IPIA, PIA, SAA, quoted from 24 CFR 3282.7#

(aa) Primary Inspection Agency (PIA) means a State /or private organization that has been accepted by the Secretary in accordance with the requirement of subpart H of this part. There are two types of PIA: (1) Design Approval PIA (DAPIA), which evaluates and approves or disapproves manufactured home designs and quality control procedures, and (2) Production Inspection PIA (IPIA), which evaluates the ability of manufactured home manufacturing plants to follow approved quality control procedures and provides ongoing surveillance of the manufacturing process. Organizations may act as one or both of these types.

(jj) State Administrative Agency (SAA) means an agency of a State which has been approved or conditionally approved to carry out the State plan for enforcement of the standards pursuant to section 623 of the Act, 42 U.S.C. 5422, and subpart G of this part.

(u) Manufacturer means any person engaged in manufacturing or assembling manufactured homes, including any person engaged in importing manufactured homes for resale.

The federal Quality Assurance Manual (3282.7(cc)) is "prepared by each manufacturer for its manufacturing plants and approved by a DAPIA," containing the quality assurance program statement, an org chart by position, a list of tests and test equipment, a station-by-station description of the manufacturing process, a list of inspections at each station, and the titles of people responsible for each inspection. Useful as a shape even though your Montana manual must follow chapter 5 of ICC/MBI 1205.

7.3 The dividing line: 24 CFR 3282.12#

This lets a structure that would otherwise meet the federal manufactured home definition be excluded as a modular home, if the manufacturer certifies that:

(1) The structure is designed only for erection or installation on a site-built permanent foundation; ... (2) The structure is not designed to be moved once erected or installed on a site-built permanent foundation; ... and (3) The structure is designed and manufactured to comply with the currently effective version of one of the following [nationally recognized building codes].

And on criterion (2):

A structure meets this criterion if all written materials and communications relating to erection or installation of the structure, including but not limited to designs, drawings, calculations, and installation or erection instructions, indicate that the structure is not intended to be moved after it is erected or installed and if the towing hitch or running gear, which includes axles, brakes, wheels and other parts of the chassis that operate only during transportation, are removable and designed to be removed prior to erection or installation on a site-built permanent foundation.

Read that last clause against the shower house on a steel skid. It says the hitch and running gear must be removable and designed to be removed. It does not say the structure can have no steel frame. A structural steel skid that is part of the permanent structure and carries loads into the foundation is a different animal from axles, brakes and wheels. But whether your skid reads as a "permanent chassis" under 3280.2 is a real question, and it is a federal question the Montana bureau cannot settle for you.

Also note 3282.12 applies only to structures designed to be used as a dwelling. A standalone public shower and restroom building is not a dwelling, so the federal manufactured home definition arguably never reaches it and 3282.12 is unnecessary. That is a cleaner argument than the chassis argument. Make both.

7.4 Montana's role as a State Administrative Agency#

Montana is not an SAA. HUD's State Administrative Agencies page lists the 33 states that partner with HUD as SAAs, then lists the states "handled by HUD's Office of Manufactured Housing Programs." Montana (MT) is in the second list. For HUD-code manufactured housing, HUD itself is the administrative agency for Montana, not DLI.

What Montana does do in the manufactured housing space is installation inspection: DLI runs a HUD 309 Inspection program for setting HUD homes in the state. That is a set-and-install program, not a manufacturing approval program, and it does not touch your factory.

7.5 The practical summary#

Sources for section 7

• 24 CFR 3280.2. https://www.law.cornell.edu/cfr/text/24/3280.2 (fetched 2026-09-13)
• 24 CFR 3282.7. https://www.law.cornell.edu/cfr/text/24/3282.7 (fetched 2026-09-13)
• 24 CFR 3282.12. https://www.law.cornell.edu/cfr/text/24/3282.12 (fetched 2026-09-13)
• 24 CFR Part 3280. https://www.ecfr.gov/current/title-24/subtitle-B/chapter-XX/part-3280 (URL recorded; eCFR blocked my fetch on 2026-09-13, text above from the Cornell LII mirror)
• 24 CFR Part 3282 Subpart G. https://www.ecfr.gov/current/title-24/subtitle-B/chapter-XX/part-3282/subpart-G (URL recorded, not fetched)
• State Administrative Agencies, HUD. https://www.hud.gov/hud-partners/state-administrative-agencies (fetched 2026-09-13; MT appears in the list of states handled by HUD's Office of Manufactured Housing Programs)
• HUD's Office of Manufactured Housing Programs. https://www.hud.gov/hud-partners/manufactured-home (fetched 2026-09-13)
• ARM 24.301.1213, .1221, .1223, .1243, .1263. URLs as in section 3 (fetched 2026-09-13)

8. What this probably means for your two products#

Everything here is a question to confirm with the bureau, not a conclusion. Send them section 9, not this.

8.1 Product A, the 40x28 site-assembled house#

Likely classification: factory-built building, residential model type.

Why it probably lands there:

• Panels are cast in a factory and the finished structure is designed for a permanent foundation, which is the affirmative half of MCA 50-60-101(9)(a) and ARM 24.301.1205(4).
• It is not "readily movable as a unit" once assembled, which is the negative half.
• It is not built on a permanent chassis, so it is not a HUD manufactured home under 24 CFR 3280.2, and the 50-60-101(9)(b) carve-out does not apply.
• MCA 50-60-404(1) says the chapter applies to "factory-built modular or prebuilt homes or buildings," a direct hit, and ARM 24.301.1221(1) reaches "modular buildings or modular building components."

The open questions, and the September 2024 rewrite made two of them sharper:

1. Panels versus modules. Your house ships as panels. ARM 24.301.1205(2) still defines "Components" as "the prefabricated wall, floor, ceiling, or roof panels or pre-cut building kits," and ARM 24.301.1221(1) expressly covers modular building components. But ARM 24.301.1205(6) now says "Unit" has the same meaning as "module" per chapter 2 of the ICC/MBI standards, and the insignia fee in ARM 24.301.1263 is "$40 per section," while plan review in ARM 24.301.1261 is priced by "parts." How does a panelized house get counted? Per panel would be ruinous; per building would be $325 plus $105 plus $40. This is the single biggest unknown in your cost model, and the vocabulary shift makes it more urgent, not less.
2. IBC or IRC. ARM 24.301.1201(2)(a) says IBC "or, as applicable" IRC. A single-family house normally falls to the IRC, but the IRC has no chapter for cellular concrete panels, so you may end up in IBC alternative-materials territory anyway.
3. The state building code exemption. MCA 50-60-102(1)(a) removes residential buildings with fewer than five dwelling units from the state building code. Does that change the FBB insignia requirement in 50-60-402(1)? I do not think so. Do not spend a dollar on the assumption.
4. Cellular concrete as a material. MCA 50-60-103(4) lets the department require testing and approval of materials, devices and methods of construction and issue certification of acceptability. Note that ARM 24.301.519 (Product standards, the listed-products rule) and 24.301.520 (Alternatives) were both repealed in 2024 with no direct successor, so the route for an unlisted material is less obvious than it was. ARM 24.301.1233(2)(c) still revokes a plan review for "materials not listed and reviewed by a listing agency, or reviewed as an alternate or equivalent by the bureau," so the concept survives even though the rule describing it is gone. DLI also runs an "Approved Alternative Methods and Materials" page.

8.2 Product B, the shower house on a steel skid#

Likely classification: factory-built building, commercial model type. Possibly a hard case.

Why it probably lands there:

• It is a "building" under MCA 50-60-101(2), which covers structures "whether mobile, portable, or fixed."
• It is factory-assembled with service connections, the front half of the definition.
• It is not a dwelling, so the HUD program almost certainly never reaches it.
• It is not a recreational vehicle under MCA 50-60-101(16).
• ARM 24.301.1207 bars using manufactured homes, mobile homes and RVs for commercial or business occupancy, closing the door on classifying it as any of those.

The hard part:

5. "Not made so as to be readily movable as a unit" versus a steel skid. This is the crux and the September 2024 rewrite did not change the definition, so the question is exactly as open as it was. Your shower house is built complete and hauled whole. The definition requires the thing to be designed to be used with a permanent foundation and not readily movable as a unit. A skid-mounted building you can pick up and set down again may fail one or both halves as the bureau reads it. If it fails it is not an RV, not a mobile home, not a manufactured home. It may simply be a building that must be permitted and inspected conventionally at every site, which destroys the point of building it in a plant.
6. Does the skid become the foundation, or sit on one? Give the bureau specifics: how the unit is anchored, whether the skid transfers loads to a site-built permanent foundation, whether the unit is designed to be relocated. If your sales pitch is "movable," say so up front rather than let the bureau find it in your marketing later.
7. Design loads when the site is unknown. ARM 24.301.1221(3) now sets an explicit non-site-specific floor: 115 MPH wind, seismic design category D, 30 psf ground snow. That floor is probably too low for much of Montana. ARM 24.301.1221(2)(e) also requires the first page of the construction document to carry the wind load (Vult), construction type, seismic design category and ground snow load. Ask whether designing above the floor is expected, and how a site-specific unit differs at plan review.
8. Accessibility. ICC A117.1 2017 is adopted. A public restroom building has unforgiving accessibility requirements and getting them wrong after tooling up is expensive.

8.3 A note on MCA 50-60-404, the local option#

If your plant sits inside a city or county with a certified building code enforcement program, you sell mostly into that county, and you stay under 100 units a year, 50-60-404 lets the local jurisdiction do the inspecting and enforcing, and 50-60-404(3) says other Montana jurisdictions may recognize that approval and need not re-inspect. Note "may" in (3) versus the much stronger "are acceptable ... without further inspection or fees" in 50-60-402(3) for a state-approved building. The state path is the stronger product. The local path could be a faster way to get a first unit built while state approval is in process. Ask before assuming.

8A. One thing I could not verify directly#

The HUD 309 installation inspection fee of $225 and the 10-day inspection window appear in search-engine summaries of DLI's HUD 309 page, but my direct fetch of https://bsd.dli.mt.gov/building-codes-permits/hud-309-inspections returned no content. Treat both figures as NOT CONFIRMED. They only matter if you ever set HUD homes, which is not your business.

Sources for section 8

• MCA 50-60-101, 50-60-102, 50-60-103, 50-60-402, 50-60-404. URLs as in sections 2 and 4 (fetched 2026-09-13)
• ARM 24.301.1201, .1205, .1207, .1221, .1233, .1261, .1263. URLs as in sections 3 and 5 (fetched 2026-09-13)
• ARM 24.301.519 and .520 (repealed 9/21/2024). https://www.law.cornell.edu/regulations/montana/ARM-24-301-519 and -520 (fetched 2026-09-13)
• 24 CFR 3280.2 and 3282.12. URLs as in section 7 (fetched 2026-09-13)
• Current Codes (A117.1 2017). https://bsd.dli.mt.gov/building-codes-permits/current-codes (fetched 2026-09-13)
• HUD 309 Inspections page. https://bsd.dli.mt.gov/building-codes-permits/hud-309-inspections (fetch returned no content 2026-09-13; figures NOT CONFIRMED)

9. Questions for the bureau#

Contact: Factory-Built Building Program, Building Codes Program, Building and Commercial Measurements Bureau, Montana Department of Labor and Industry. Email buildingcodes@mt.gov, phone (406) 841-2056, program page https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/. Ask for the Factory-Built Building program by name. Do not ask for a person by name.

Ask for answers in writing. For anything touching code application, MCA 50-60-117 provides a central registry of formal building code interpretations, so you can ask whether an issue warrants a registered interpretation rather than an email.

1. Does a factory-built single-family house need a Montana insignia of approval even though MCA 50-60-102(1)(a) exempts residential buildings with fewer than five dwelling units from the state building code? If yes, which code does the bureau review it to, IBC or IRC, under ARM 24.301.1201(2)(a)?

2. What is the status of the rulemaking heard on 28 August 2026? What does it change, has it been adopted, and what is the effective date? Given ARM 24.301.1233(2)(a) and ARM 24.301.1231(3), what is the transition for a manufacturer whose plans are approved under the 2021 code editions, beyond the 90-day insignia window in ARM 24.301.1233(3)?

3. How does the bureau count "parts" for plan review fees under ARM 24.301.1261 and "sections" for insignia fees under ARM 24.301.1263, for a panelized building that ships as individual wall, floor and roof panels and is assembled on site? Given that ARM 24.301.1205(6) now defines "unit" as "module" per the ICC/MBI standards, are "part," "section," "unit" and "module" the same thing in this program?

4. Is MCA 50-60-404 an alternative to state FBB approval or an additional layer? If a Montana plant meets all four conditions in 50-60-404(2), can it sell without a state insignia, or does 50-60-402(1) still require one?

5. How does the bureau classify a complete bathroom or shower building built in the plant on a structural steel skid and hauled to site as one piece? Specifically, does a steel skid that transfers loads to a site-built permanent foundation defeat the "not made so as to be readily movable as a unit or units" element of ARM 24.301.1205(4) and MCA 50-60-101(9)(a)? If it does, what regime does such a building fall under?

6. For a model whose permanent site is unknown, is the ARM 24.301.1221(3) floor of 115 MPH wind, seismic design category D and 30 psf ground snow sufficient for sale anywhere in Montana, or will the authority having jurisdiction reject a unit at a higher-load site? How does a site-specific submittal differ at plan review?

7. Which states does Montana currently have reciprocal agreements with under ARM 24.301.1235, and what does "HUD-approved Category III states" mean in current practice? Which states will accept a Montana review transmitted under ARM 24.301.1237?

8. Is Montana a member of any interstate compact or multistate reciprocal program for factory-built or industrialized buildings? Now that Montana, Virginia, Utah and GSA have all adopted ICC/MBI 1200 and 1205, does a Montana approval travel any more easily?

9. What is the approval sequence and typical timeline for a brand-new Montana manufacturer? ARM 24.301.1223(2) says the quality assurance manual must be approved before plan review approval. Can the manual and the plan application be submitted together, or must the manual clear first? What else does the bureau want to see before listing a manufacturer as approved under ARM 24.301.1217(2)?

10. What does Section 601 of ICC/MBI 1205 require of a manufacturer, in the bureau's reading? ARM 24.301.1217(1) makes us "subject to" it but the standard is not published in the ARM. Is there a checklist or guidance document?

11. Where does bureau oversight of third-party inspection agencies and of manufacturers now live? ARM 24.301.516 (third party inspections to be monitored) and .517 (inspection of manufacturer) were repealed on 21 September 2024. Is that oversight now inside ICC/MBI 1205, or does it rest on the department's general authority under MCA 50-60-103?

12. Two rules were repealed with no visible successor and I want to know what replaced them. ARM 24.301.525 required a data plate with model, serial number, date of completion and design load maximums. ARM 24.301.549 required a manufacturer's serial number and placement of the insignia on the exterior wall adjacent to the rear or side exit. Are data plates and unit identification still required, and if so under what authority, ICC/MBI 1200 or 1205?

13. What is the path for approval of a construction material and assembly the model codes do not cover, in our case a cellular concrete structural panel? ARM 24.301.519 (product standards) and .520 (alternatives) were repealed. Is the route now an "Approved Alternative Methods and Materials" submission, a code interpretation under MCA 50-60-117, a testing-and-approval action under MCA 50-60-103(4), or something the third-party agency and a Montana-licensed professional engineer handle inside the plan review?

14. Does the bureau require a Montana-licensed professional engineer's seal on the model plan submittal, and if so on which documents? ARM 24.301.1205(3) defines "Engineer" but no live rule I found states when a seal is required.

15. The DLI forms and web page still cite repealed rules. The insignia application cites ARM 24.301.558, repealed 9/21/2024. The FBB web page cites ARM 24.301.565 through .567 and still shows the old eleven-item quality control manual list. Are the forms current in substance, and should our quality assurance manual follow chapter 5 of ICC/MBI 1205 rather than the web page list?

16. ARM 24.301.1261(1)(a) says "quality control manual review" while ARM 24.301.1221 and .1223 say "quality assurance manual." Same document, same $20 fee?

17. Are there Montana licensing or registration requirements for the manufacturing entity itself beyond the FBB program, for example construction contractor registration, that the bureau expects before listing us as an approved manufacturer?

Sources for section 9

• Factory-Built Buildings Permits (contact route, forms, third party requirement). https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/ (fetched 2026-09-13)
• Montana Building Codes Program home (hearing notice, office address, portal). https://bsd.dli.mt.gov/building-codes-permits/ (fetched 2026-09-13)
• MCA 50-60-117 (section title from the Part 1 index). https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/sections_index.html (fetched 2026-09-13)
• MCA 50-60-103. https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0030/0500-0600-0010-0030.html (fetched 2026-09-13)
• ARM 24.301.1205, .1217, .1221, .1223, .1231, .1233, .1235, .1237, .1261, .1263. URLs as in sections 3 and 5 (fetched 2026-09-13)
• ARM 24.301.516, .517, .519, .520, .525, .549, .558 (all repealed 9/21/2024). https://www.law.cornell.edu/regulations/montana/ARM-24-301-XXX (each fetched 2026-09-13)

Appendix A: where this document and 02-approval-process.md differ#

The two documents were researched separately. They agree on every rule citation, every fee figure, every deadline, and the old-to-new mapping. Three differences, none of them a conflict about the law:

1. Bureau division name. 02-approval-process.md says Business Standards Division. This document says the DLI building codes pages carry the header Employment Standards Division, and flags it NOT CONFIRMED. Both readings come from DLI's own site. Ask the bureau.
2. Physical address. 02-approval-process.md gives 301 South Park Ave., Floors 4 and 5, Helena, MT 59620, which is the DLI division contact block in the page footer. This document gives 2705 Skyway Drive, Helena MT, which is what the Building Codes Program home page says when it tells you where to visit "our office." Both are on DLI pages. The mailing address (PO Box 200517) is the same in both. Confirm before driving anywhere.
3. Scope. 02-approval-process.md treats ARM 24.301.1263 as the insignia fee rule and quotes "$40 per section"; this document agrees and adds that the repealed .566 said "per part," which is where the older DLI form language comes from.

No place was found where the live rules contradict what 02-approval-process.md says.

Appendix B: what I could not confirm#