Montana codes and classification (layer 3)

Written 13 Sep 2026. Every web source in this file was fetched 13 Sep 2026; the URL and the date sit with each section and again in the source list at the end.

What this file is: which codes and standards actually apply to Ken's two products in Montana, and how each product gets classified. It does not cover the statute and the rules as a body (see docs/montana/01-statute-and-rules.md) or the permit and approval path (see docs/montana/02-approval-process.md). Where those two files carry the detail, this one points at them.

The two products, from the product docs, not from me:

• The house. docs/wall-spec-v1.md. 40' x 29'-11" outside, 34 cast wall panels 4' wide and 10' or 12'-6" tall, stood and screwed together on a slab, wired and plumbed in the open cavity, clad, then pumped full. Roof strips cast on the ground and craned on. Two bed, two bath.
• The shower house. docs/showerhouse.md. A 1 or 2 bathroom unit, 8' panels, 10 / 12 / 14 feet outside width, 8 to 24 feet long, built complete in the plant on a welded HSS steel skid with fork pockets and four corner lifting lugs, hauled as one piece, set by crane or forklift, connected to water, sewer and power on site. Reference unit 12 x 20, 2 bath, one accessible, flat roof, 33,366 lb.

Rule for reading this file: I have not invented a code edition, a section number, an amendment or an adoption date. Anything I could not put a source under is marked NOT CONFIRMED. A building official's answer beats this file.

1. What Montana has adopted, and what is in force right now#

1.1 The list#

Montana adopts its codes in the Administrative Rules of Montana (ARM), Title 24, chapter 301, administered by the Department of Labor and Industry Building Codes Bureau. The current editions:

Sources: Montana DLI Building Codes Bureau, "Current Codes", https://bsd.dli.mt.gov/building-codes-permits/current-codes, fetched 13 Sep 2026 (the table of editions and the 6/11/2022 date). ARM 24.301.131, https://www.law.cornell.edu/regulations/montana/ARM-24-301-131, fetched 13 Sep 2026 ("the International Building Code, 2021 edition, unless another edition is specifically stated, together with Appendix Chapter C"; "2022 MAR p. 911, Eff. 6/11/2022"). ARM 24.301.154, 24.301.161, 24.301.301, 24.301.401, 24.301.146, 24.301.903 on the same Cornell mirror, fetched 13 Sep 2026. Rule numbers for the mechanical, fuel gas, existing building, pool, WUI and elevator codes: UpCodes Montana index, https://up.codes/codes/montana, fetched 13 Sep 2026. ARM 24.301.1203, https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1203, fetched 13 Sep 2026.

Two notes on dates. The DLI page prints 6/11/2022 for the whole set. Several of the individual rules carry a later history line, "AMD, 2024 MAR p. 2223, Eff. 9/21/2024". Those 2024 amendments did not change the model-code editions; they changed Montana's own modifications and, in subchapter 24.301.12, rebuilt the factory-built buildings rules and brought in ICC/MBI 1200 and 1205. So the right way to say it is: 2021 editions, Montana modifications as amended 9/21/2024. Confirm the current history line before a submittal; docs/montana/01-statute-and-rules.md carries the statutory side.

The register in docs/engineering/standards-register.md says under "Editions I am not certain of" that the Montana adoption year is "2021 as far as I know". That is now confirmed for building, residential, plumbing, mechanical, fuel gas, existing building and energy. The electrical code is 2020 NEC, not 2021 anything, and the plumbing code is the Uniform Plumbing Code, not the IPC. The standards register says "IPC / IRC Part VII (P) for the house, IPC for the shower house"; that line is wrong for Montana and should be changed to UPC 2021.

1.2 The Montana amendments that actually touch this product#

These are the ones that change a number Ken's model uses.

Snow load, IBC route. ARM 24.301.146(26): "Snow loads shall be determined by the building official. In areas of the state outside of certified city, county, and town jurisdictions, the design snow load shall be calculated using the 2022 edition of the American Society of Civil Engineer's 'Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE/SEI 7-22.'" (Cornell, ARM 24.301.146, fetched 13 Sep 2026.)

This matters. docs/engineering/standards-register.md says "IBC 2021 Chapter 16 ... which references ASCE 7-16". That is the model code. Montana sends the snow load to ASCE 7-22 outside certified jurisdictions. The PE has to be told which hazard source to use, and it is not the one the 2021 IBC points at. Inside a certified jurisdiction the building official sets it.

Snow load, IRC route. ARM 24.301.154 replaces IRC R301.6: design snow load from ground snow loads calculated using ASCE/SEI 7-22, with the ASCE 7 Hazard Tool named, and a minimum 30 psf design roof snow load unless a lower value is justified. (Cornell, ARM 24.301.154, fetched 13 Sep 2026.) The 30 psf floor is a hard number the house roof strips have to carry even on a mild site.

Energy, residential. ARM 24.301.161 amends the 2021 IECC. Climate zone 6 numbers Montana inserts in Table R402.1.2: frame wall U 0.045, mass wall U 0.060, ceiling U 0.026, floor U 0.033. Table R402.1.3 wood-frame wall options: "R-21 or R-20 + R-5ci or R-13 + R-10ci or R15ci". Air leakage, amended R402.4.1.2: "The building or dwelling unit shall be tested and verified as having an air leakage rate of not exceeding four air changes per hour in Climate Zone 6. Testing shall be conducted with a blower door at a pressure of 0.2 inches w.g. (50 Pascals)." Montana also caps R402.2.2 ceiling insulation at R-30 over a limited area, and deletes several commercial sections (C405.11 automatic receptacle control, C405.12 energy monitoring) and the required-inspection sections C105.2 and R105.2 for state enforcement. (Cornell, ARM 24.301.161, fetched 13 Sep 2026.)

One correction for docs/engineering/thermal-evaluation.md section 6: it uses a ceiling U of 0.024 (the model-code 2021 IECC zone 6 value) for the house roof. Montana's amended table says 0.026. That eases the roof gap slightly. It does not change the conclusion that the roof needs real board. The thermal doc already marks every code number VERIFY; this is the verification for the residential ceiling row and the wall rows (frame 0.045 and mass 0.060 are confirmed as Montana's numbers). The thermal doc's third wall row, mass wall at U 0.057 where more than half the insulation is on the inside, is NOT CONFIRMED in the Montana amended table; the Montana text I could read gives one mass wall figure, 0.060.

Energy, IRC route. ARM 24.301.154 deletes IRC Chapters 11 through 14, sending mechanical work to the adopted IMC. Energy therefore runs through the IECC as adopted at 24.301.161, not through IRC Chapter 11. (Cornell, ARM 24.301.154, fetched 13 Sep 2026. The exact chapter range and its wording is worth a second read before it goes in a submittal: marked PARTIALLY CONFIRMED.)

Plumbing fixture counts. ARM 24.301.146(27) points the fixture count at ARM 24.301.351 instead of IBC Table 2902.1. ARM 24.301.351 then adopts IBC Table 2902.1 (2021) with Montana additions, including an exception allowing a single unisex toilet in certain nonassembly buildings and an exemption from drinking fountains for buildings with 30 or fewer occupants. (Cornell, ARM 24.301.146 and ARM 24.301.351, fetched 13 Sep 2026.) For the shower house this is the rule that says how many fixtures the building itself must have, and it is not the only one; see section 4.3.

Walls, IRC route. ARM 24.301.154 amends R602.10 (bracing, allowing APA System Report SR-102 as an alternate method) and R602.10.10, and rewrites R403.1.6 foundation anchorage. None of that reaches a cast cellular concrete panel on cold formed steel studs, because the panel is not an IRC prescriptive wall at all. It goes in under the alternative material route (see 3.4). There is no Montana amendment I found that speaks to a cellular concrete or a cold formed steel cast panel assembly.

Appendix Q, tiny houses. ARM 24.301.154 adopts IRC Appendix Q, but Montana limits it: factory-built buildings of 400 square feet or less excluding lofts, single-family dwellings on permanent foundations, and prohibited for commercial or business uses. (Cornell, ARM 24.301.154, fetched 13 Sep 2026.) That closes the "call the shower house a tiny house" idea before it starts.

Electrical. ARM 24.301.401 adopts NFPA 70, 2020 edition, and amends 210.8(A) and (B) (250-volt receptacles removed from the GFCI lists) and 210.12 (all "kitchen" references deleted from the AFCI rules). "AMD, 2024 MAR p. 2223, Eff. 9/21/2024." (Cornell, ARM 24.301.401, fetched 13 Sep 2026.)

Accessibility. ARM 24.301.903 amends IBC Section 1109 and states that "Required toilet rooms and bathing facilities shall be accessible", with narrow exceptions where compliance is structurally impracticable because of terrain or is not practicable in relation to the proposed usage; those are determinations for the building official. ARM 24.301.904 covers site accessibility (parking, loading zones, private sidewalks, the route from the public way). The referenced technical standard is ICC A117.1-2017. "NEW, 1997 MAR p. 2061, Eff. 11/18/97 ... AMD, 2024 MAR p. 2223, Eff. 9/21/2024." (Cornell, ARM 24.301.903 and 24.301.904, fetched 13 Sep 2026.) Note the statutory purpose behind those rules, MCA 50-60-201: statewide uniformity in enforcing accessibility of newly constructed public buildings including building sites. Accessibility is one of the things Montana enforces on a statewide basis, not only where a local program exists; treat it as applying wherever the unit lands.

1.3 Who enforces it where#

Montana runs a state program through the DLI Building Codes Bureau, and cities, towns and counties may run their own certified programs covering building, plumbing, electrical and mechanical, all or in part. DLI lists the certified local programs. As of the fetch, Belgrade, Billings, Bozeman, Columbia Falls, Darby, Great Falls, Hamilton, Kalispell, Manhattan, Missoula, Polson, Silver Bow, Stevensville and Whitefish are listed as enforcing building, plumbing, electrical, mechanical and pool; Colstrip, Hardin, Libby, Troy and West Yellowstone are listed as residential building only; Pondera County and Toole County as commercial building only; Conrad, Choteau, Cut Bank, Forsyth, Glasgow, Havre, Lewistown and Red Lodge as building only; Deer Lodge County, Missoula County, Richland County and Silver Bow as county programs. DLI puts the total at 54 certified jurisdictions. (https://bsd.dli.mt.gov/building-codes-permits/certified-government, fetched 13 Sep 2026. The list as fetched is a summary, not a complete row-by-row transcription: treat the individual entries as needing a check against the live page before you rely on one for a specific job.)

Why it matters to this product, twice over:

1. The snow load source changes at the jurisdiction line. Outside a certified jurisdiction, ASCE 7-22. Inside, "as determined by the building official".
2. The shower house is a travelling product. It can be built in one jurisdiction and set in another. ICC/MBI 1200 section 102.2 makes you identify the authority having jurisdiction at the manufacturing facility and at the project location, and 102.3.1 says that where a state-wide modular program exists the project complies with both the state and the local requirements. Montana has such a program. So the plant answers to the state, and the site answers to whoever holds the site.

2. The classification question, set up properly#

Classification is not one question, it is four, and they are answered by different bodies of law that do not line up with each other:

• A. Montana factory-built buildings law. Does the unit need a state insignia before it can be sold or delivered? Statute MCA Title 50 chapter 60 part 4; rules ARM subchapter 24.301.12.
• B. Off-site construction standard. Is this off-site construction under ICC/MBI 1200 and 1205 as adopted at ARM 24.301.1203, and if so is it a module, a modular component, or a panelized system?
• C. IBC occupancy. What use group is it, which drives accessibility, energy path, ventilation and fire.
• D. Health licensing. If it lands at an RV park, campground, work camp or youth camp, ARM Title 37 chapter 111 subchapter 12 applies on top of everything else, through DPHHS and the local sanitarian.

A unit can be "not a factory-built building" under A and still be "off-site construction" under B, still need an IBC permit under C, and still fail D. These are not alternatives. Work all four.

3. Classification of the two products#

3.1 The controlling definitions, quoted#

Factory-built building, MCA 50-60-101(9)(a) and ARM 24.301.1205: "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." (https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0010/0500-0600-0010-0010.html and https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1205, both fetched 13 Sep 2026.)

Building, MCA 50-60-101(2): "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." (Same source.) Note what that does: "mobile" and "portable" are inside the definition of a building. Being movable does not put you outside the building code. It may put you outside the factory-built building definition, which is a narrower thing.

Recreational vehicle, MCA 50-60-101(16): "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." (Same source.)

Unit, ARM 24.301.1205: "has the same meaning as 'module' as defined in chapter two of the ICC/MBI 1200 Standard and the ICC/MBI 1205 Standard." (Cornell, fetched 13 Sep 2026.) This is the hinge. Montana's insignia rules are written around "units", and a "unit" is now a module as ICC/MBI defines it.

From ICC/MBI 1200-2021, chapter 2 (text from the ICC-posted approved ballot copy of the standard, https://www.iccsafe.org/wp-content/uploads/is_osmc/ICC1200-draft-ballot-apprvd.pdf, fetched 13 Sep 2026; the published edition should be checked against this, marked PARTIALLY CONFIRMED):

• MODULE. "A three-dimensional, volumetric section of a modular building designed and approved to be transported as a single section independent of other sections, to a site for on-site construction."
• MODULAR COMPONENT. "A sub-assembly, subsystem, or combination of elements, including panelized systems, building shells or bathroom pods, for use as a part of a modular building that is not structurally independent, but is a part of structural, plumbing, mechanical, electrical, fire protection, or other systems affecting life safety."
• PANELIZED SYSTEM. "Wall, roof or floor components that are constructed at a location other than the building site in a manner that prevents the construction from being inspected at the building site without disassembly, damage or destruction thereof."
• OPEN CONSTRUCTION. "A modular building, modular component or panelized system manufactured in such a manner that all portions can be readily inspected at the building site without disassembly, damage or destruction thereof."
• OFF-SITE CONSTRUCTION. "A modular building, modular component or panelized system which is designed and constructed in compliance with this standard and is wholly or in substantial part fabricated or assembled in manufacturing plants for installation, or assembly and installation, on a separate building site and has been manufactured in such a manner that all parts or processes cannot be inspected at the installation site without disassembly, damage to, or destruction thereof."
• PERMANENT FOUNDATION SYSTEM. "A foundation system for modular buildings designed to meet the applicable building code. In a permanent foundation system, anchorage of the building to the foundation is provided to resist the uplift and sliding forces that result from the application of the prescribed loads. The use of ground anchors or earth augers to resist uplift or sliding forces is not considered a permanent foundation."

And one more, from the health side, because the campground rules have their own definition and it is stricter:

Permanent foundation, ARM 37.111.1201(16): "concrete, concrete block, or wood pier, resting on embedded concrete or concrete block footings. The term does not include mud sill, pier and post, wood blocks, concrete block, or other types of temporary support, resting on the ground." Permanent structure, (17): "a structure attached to a permanent foundation." (https://dphhs.mt.gov/assets/publichealth/FCS/TrailerCourtCampgroundRules2023.pdf, fetched 13 Sep 2026.)

3.2 The house: modular home, or site-built out of manufactured parts?#

The test, in order.

1. Is any part of the house a three-dimensional volumetric section transported as a single section? No. Nothing leaves the plant as a room or a box. Wall panels go out flat, 4 feet wide; roof strips go out flat. So no module, so no "unit" under ARM 24.301.1205, so the insignia machinery that hangs off "unit" does not obviously reach the house. That is the argument that the house needs no factory-built buildings approval.
2. Does the house meet the statutory factory-built building definition? Read the three tests in MCA 50-60-101(9)(a) together: factory assembled structure, equipped with the necessary service connections, not readily movable, designed for a permanent foundation. The house fails the first two. What leaves Ken's plant is a panel, not a structure, and it has no service connections in it; the wire and the plumbing go in on site, in the open cavity, after the panels stand (docs/wall-spec-v1.md section 1, "wire and plumb in the open stud cavity after the panels stand"). So on the statutory text the house is not a factory-built building, and the finished house is site-built construction assembled from manufactured components.
3. But is it off-site construction? This is where the 9/21/2024 change bites. A wall panel that is 4 feet wide with studs, channel, mesh and a lifting zone cast inside two inches of cellular concrete is a wall component constructed at a location other than the building site in a manner that prevents the construction from being inspected at the building site without disassembly, damage or destruction thereof. You cannot look at the stud-to-channel screws, the mesh position or the skin pour depth once the panel is cured; you would have to break it. That is the definition of a PANELIZED SYSTEM, which is expressly inside the definition of OFF-SITE CONSTRUCTION, and both standards are adopted in Montana at ARM 24.301.1203 effective 9/21/2024. The roof strips are the same, and the shower house floor panel is the same.

So the honest answer for the house is a split one:

• The building is site-built. It is not a modular home. It needs an ordinary building permit for the site, under the IRC (or IBC if the jurisdiction routes it that way), with the panel carried as an alternative material.
• The panels are a panelized system, which is off-site construction. ICC/MBI 1200 chapter 1 says its requirements are in addition to the adopted codes (301.1), and 103.3 lists what the construction documents for a panelized system must contain: systems and components requiring special inspections, a statement on the sequence of construction, details of connections of panels to the building structure, and details of panel-to-panel attachments. 104.2 requires in-plant inspections, and 104.3 requires on-site inspection of the connections between off-site components and between off-site components and site-built work.

What is open, and it is the biggest open question in this file: whether Montana's Building Codes Bureau reads ARM 24.301.1203 as reaching a panel maker who is not a "unit" manufacturer, and if it does, whether it expects plan review, a registered manufacturer, an in-plant quality assurance manual under ARM 24.301.1223 and third-party in-plant inspection under ARM 24.301.1213 for the panel line. The subchapter's own insignia rule, ARM 24.301.1241, is written around units: "All units manufactured or delivered prior to sale or sold or offered for sale in Montana shall bear an insignia of approval." The panel is not a unit. But ICC/MBI 1200's definitions repeatedly name "modular buildings, modular components or panelized systems" in the same breath, and 1200's own INSIGNIA definition is "the approved form of certification issued by the authority having jurisdiction to the manufacturer to be attached to the modular building, modular component or panelized system". Those two readings do not agree, and the Bureau decides. This is a question for the Bureau in writing, not a question for the PE. The path for asking is in docs/montana/02-approval-process.md.

Practical consequence either way: even on the narrow reading, the panel line needs the documents ICC/MBI 1200 asks for, because those are the documents the site building official will want anyway when they cannot inspect what is inside the panel. The PE package already produces most of them (design basis, stamped typical details, panel-to-panel joint detail, base detail, roof bearing detail). What it does not yet produce is a written sequence of construction and a special inspection list, which 103.3 names specifically. See the gap table.

3.3 The shower house: five ways it could be classified, and the tests that pick#

Candidate 1: factory-built building needing a Montana insignia. The test is MCA 50-60-101(9)(a) again, and now the answer is close.

Read literally, the shower house is not a factory-built building, because it is readily movable and is not designed for a permanent foundation. That is not a comfortable place to land, because it means the state insignia program does not cover it and there is no other state-level pigeonhole for a complete occupiable building that arrives on a truck. The likely practical outcome, and this is my read and not a sourced conclusion (NOT CONFIRMED), is that the Bureau treats it as a unit / module under ARM 24.301.1205 (it is a "three-dimensional, volumetric section ... designed and approved to be transported as a single section") and asks for an insignia, on the reasoning that the alternative is an occupied commercial building with no plan review and no in-plant inspection of concealed plumbing and wiring. This is the single question to put to the Bureau first, because everything downstream depends on the answer: whether Ken needs manufacturer registration, a model plan review, an in-plant quality assurance manual and a third-party agency, or only a site permit at every destination.

The lever Ken controls: designing the skid as a foundation, and saying so. If the design basis says the skid, with a named bearing condition and named anchorage, is the permanent foundation system, and the PE stamps it as resisting uplift and sliding under the prescribed loads, then the unit is "designed to be used with a permanent foundation" and the classification collapses to factory-built building cleanly, insignia and all. The "readily movable" leg still argues the other way, but the two legs are joined by "and", so a unit designed for a permanent foundation is much more likely to be treated as an FBB. Whether Ken wants that outcome is a business decision, not a code one: the insignia route costs plan review and in-plant inspection, and buys a unit that any Montana jurisdiction must accept "without further inspection or fees except for zoning, utility connections, and foundation permits" (ARM 24.301.1245, effect of insignia, per the search summary of that rule, NOT CONFIRMED verbatim). For a product Ken wants to sell repeatedly across the state, that acceptance is worth a lot.

Candidate 2: recreational vehicle or park model. Dead on arrival, for three reasons, and it is worth writing them down because customers will suggest it.

1. The MCA 50-60-101(16) definition requires a "vehicular type unit primarily designed as temporary living quarters". A toilet and shower building is not living quarters and has no beds.
2. ARM 24.301.1207 (transferred and effective 9/21/2024): "Mobile homes and recreational vehicles shall not be utilized for any occupancy other than as a single-family dwelling" for commercial or business purposes, with narrow exceptions for a mobile home retailer's sales-lot office and for units at a circus, fair or similar event for 14 days or less. A campground shower house is a commercial occupancy. The RV route is expressly closed.
3. Montana adopts ANSI/A119.2 for new recreational vehicles at MCA 50-60-402 and expressly says "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." So even if you could squeeze into the definition, there is no state approval to rely on. (MCA 50-60-402, https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0020/0500-0600-0040-0020.html, fetched 13 Sep 2026.) Note this section names A119.2, not A119.5 (park models): the park model standard is NOT CONFIRMED as adopted anywhere in Montana, and I found no reference to it.

Candidate 3: accessory structure, Group U, no big deal. Also weak. IBC 312.1 Group U is "buildings and structures of an accessory character and miscellaneous structures not classified in any specific occupancy", and the illustrative list runs agricultural buildings, aircraft hangars accessory to a dwelling, barns, carports, communication equipment structures under 1,500 sf, tall fences, grain silos accessory to residential, livestock shelters, private garages, retaining walls, sheds, stables, tanks, towers. (IBC 2021 as published on the Montana UpCodes viewer, https://up.codes/viewer/montana/ibc-2021/chapter/3/occupancy-classification-and-use, fetched 13 Sep 2026.) A public shower and toilet building is not on that list, it is occupied by the public, it is plumbed, heated and wired, and it is subject to the accessibility rules regardless. Some officials will call it U; see section 4. But a Group U call does not buy an exemption from accessibility or from the DPHHS rules, and Ken should not plan around it.

Candidate 4: an IBC building, occupancy to be classified. This is the realistic frame. See section 4.

Candidate 5: a temporary structure. IBC has provisions for temporary structures, and ARM 24.301.1207's exception uses a 14-day window for circuses and fairs; ARM 37.111.1216(1) also excuses the service building where "the campground limits occupancy of individuals to 14 days or less". For a job site that comes and goes, a temporary-structure permit may be the right vehicle. For an RV park where the unit sits every season, it is not. Duration is a real variable, and 14 days is the number that keeps appearing.

3.4 The variables, and what each one changes#

This is the table to hand a building official. Each row is one fact about how the unit is used; the columns say what it changes.

4. Occupancy and use of the shower house under the IBC, and what follows#

4.1 The classification#

A stand-alone public toilet and shower building is not a dwelling and is not an R occupancy. It has no sleeping, no cooking, no permanent provision for living. The IBC does not name it in any occupancy list. IBC 304.1 Business Group B does not list restrooms; IBC 312.1 Group U does not list them either. (Montana UpCodes viewer of IBC 2021 chapter 3, fetched 13 Sep 2026.) Code officials split between the two: a shower building serving a campground is most often called Group U because it is accessory to the campground, and Group B is the fallback where the official will not stretch U. There is no consensus in the trade. (Discussion in The Building Code Forum thread "Use Group Classification for Toilets in Park", https://www.thebuildingcodeforum.com/forum/threads/use-group-classification-for-toilets-in-park.16675/, fetched 13 Sep 2026. This is a professional forum, not a code source, and is cited as evidence that the question is genuinely unsettled, not as authority.)

Ask the official and write the answer on the drawings. It is a one-line question and it decides four things.

4.2 What the classification changes#

4.3 Fixture counts: two rules, and the health rule usually wins#

For a campground, ARM 37.111.1216(1)(g) and Table I: 1 to 15 dependent unit sites need 2 toilets and 2 handwashing sinks; 16 to 30 need 4 and 4; 31 to 45 need 6 and 6; 46 to 60 need 8 and 8; 61 to 80 need 10 and 10; 81 to 100 need 12 and 12; above 100, two additional toilets for every additional 75 sites. Unisex or split evenly by sex. (https://dphhs.mt.gov/assets/publichealth/FCS/TrailerCourtCampgroundRules2023.pdf, fetched 13 Sep 2026.)

This is a sales fact, not just a code fact. A 2-bath unit covers a campground up to 15 dependent sites. A park with 50 sites needs 8 toilets, which is four of Ken's 2-bath units or a different product. Put this table in the sales material.

The same rule also carries requirements the unit must meet as built:

• "(a) the service building must be of permanent construction and equipped with lighting, handwashing sinks, toilets, and a janitorial sink"
• "(b) interior service building surfaces in plumbed areas must be smooth, nonabsorbent, and easily cleanable"
• "(c) showers, if provided, must have non-slip surfaces sloped to drain, provide warm water, not to exceed 120 F, and provide adequate ventilation"
• "(d) all windows, doors, and other openings must be screened or closed"
• "(e) the service building must be conveniently located within a radius of 300 feet from all sites designated for use by dependent units"
• "(f) the service building must be connected to approved water and wastewater treatment systems"
• "(i) the service building must have hand cleaner, disposable towels or hot air dryers, and toilet tissue at all times of operation"

Against docs/showerhouse.md and docs/showerhouse-items.json:

• No janitorial sink anywhere in the fixture list or the plan generator. That is a flat miss against 37.111.1216(1)(a). It has to go somewhere, and the mechanical closet (3 x 4 feet, already holding the water heater, the panel and the shut-off) is the obvious place, or a wall-hung service sink in one bathroom. It changes the plan, the takeoff and the plumbing wall.
• No towel dispenser or hand dryer in the items file (there is a mirror, paper holder, robe hooks and soap dish). Arguably the operator's consumable, but the dryer is a fixture and a circuit if it is electric. Cheap to add, awkward to retrofit.
• "Permanent construction" is the hard one, and it is the same issue as section 3.4 row 1. A unit on a skid on blocks is not obviously permanent construction. Pin this with the sanitarian in the plan review before the first campground sale.
• 120 F cap: the items list has a 27 kW tankless electric heater and pressure-balance shower valves. A tempering or master mixing valve limiting the distribution temperature to 120 F should be named explicitly, not assumed from the valve.
• Non-slip sloped surfaces: the cast floor with cast slopes and cast drains is a good answer, but the finish schedule offers "grind, seal" or tile or a spray coating; the slip resistance of each option needs to be stated, not left to the finish choice.
• Screened openings: the window is "obscure glass, fixed / awning". If it opens, it needs a screen.

4.4 Energy path for the shower house: commercial#

IECC 2021 defines a residential building as "detached one- and two-family dwellings and townhouses as well as Group R-2, R-3 and R-4 buildings three stories or less in height above grade plane". A shower house is none of those, so it takes the commercial provisions. IECC C101.2: "This code applies to commercial buildings and the buildings' sites and associated systems and equipment." C101.4.1 handles the mixed case. (Definition per multiple jurisdictions publishing the 2021 IECC text, e.g. https://www.pprbd.org/File/ByAlias/2021ieccunamend, fetched 13 Sep 2026; scope sections from the Montana IECC viewer, https://up.codes/viewer/montana/iecc-2021/chapter/CE_1/ce-scope-and-administration, fetched 13 Sep 2026.)

docs/engineering/thermal-evaluation.md section 6 already reaches this conclusion and computes the commercial numbers. This file does not recompute them. Pointers:

• Shower house, commercial mass wall, floor and roof: thermal-evaluation section 6, "The shower house is not a dwelling" block, U 0.127 wall against 0.090, U 0.125 roof against 0.032, U 0.192 floor against 0.051, all marked VERIFY.
• Semi-heated: same section. A shower house heated only for freeze protection may fall in ASHRAE 90.1's semi-heated column. That is a code-official call and the exact figures come from the adopted edition.
• Roof insulation above the deck: thermal-evaluation section 7 item 1 and docs/roof-insulation.md. Now a priced option.
• Montana's amendments to the commercial chapter (ARM 24.301.161) delete C405.11 and C405.12 and modify C402.5.1.2 (air barrier). Those are the amendments that touch a commercial envelope and a commercial electrical system; none of them changes the envelope U-factors the thermal doc uses. The commercial zone 6 U-factors themselves are NOT CONFIRMED against the Montana-amended commercial tables; I confirmed the residential table only. Somebody should read the adopted commercial table before the first commercial submittal.

The house takes the residential path, IECC Chapter 4 [RE] as amended by ARM 24.301.161, with the Montana zone 6 numbers in 1.2 above and the 4 ACH50 blower door limit. Thermal-evaluation sections 5, 6 and 7 carry the analysis.

4.5 Ventilation and fire, shower house#

• Ventilation. IMC 2021 as adopted at ARM 24.301.172. Toilet rooms and shower rooms carry exhaust rates in the IMC's exhaust table; the items file has a humidity-sensing exhaust fan ducted through the roof cap per room, which is the right shape of answer. The actual required cfm per room is NOT CONFIRMED here; the mechanical designer sizes it against IMC Table 403.3.1.1 and 37.111.1216(1)(c) "adequate ventilation".
• Fire. At 250 sf, detached, one storey, in a campground, fire separation distance and construction type are not likely to bind, but they are site facts, not product facts, and the site plan decides them. The cellular concrete should be tested to ASTM E136 for noncombustibility (already in docs/engineering/standards-register.md) because it is cheap and it settles a lot of arguments. The spray-in-place shower coating and the roof membrane need ASTM E84 / UL 723 flame spread and smoke data from the product manufacturer, for the interior finish requirements of IBC Chapter 8. No fire-resistance rating appears to be required for a detached 250 sf building; NOT CONFIRMED, site dependent.

5. Accessibility#

5.1 Which standards apply#

Two, at the same time, and the stricter of the two governs each dimension.

1. The 2010 ADA Standards for Accessible Design. Federal civil rights law, not a building code, and no building official enforces it. A campground or RV park is a place of public accommodation. It applies whether or not Montana inspects the building.
2. ICC A117.1-2017, reached through IBC Chapter 11 and Montana's own accessibility rules ARM 24.301.903 (building) and 24.301.904 (site). This is what a Montana building official checks.

ARM 24.301.903 (as amended 9/21/2024) puts it plainly for this product: "Required toilet rooms and bathing facilities shall be accessible", with exceptions only where it is structurally impracticable due to unique terrain or not practicable in relation to the proposed usage. (Cornell, ARM 24.301.903, fetched 13 Sep 2026.)

ARM 24.301.904 site accessibility matters more than people expect for a shower house: the accessible route from the parking, the loading zone, the private sidewalk and the adjacent public way to the building. A unit set on a skid on a gravel pad in a campground has a step up to the door and a gravel approach, and neither is an accessible route. ADA 206.2.1 requires at least one accessible route within the site from accessible parking, passenger loading zones, public streets and sidewalks, and transit stops to the entrance served. (Access Board, ADA chapter 2, https://www.access-board.gov/ada/chapter/ch02/, fetched 13 Sep 2026.)

This is the second of the three big open questions: nothing in the product today provides the accessible route or the level landing at the accessible door. The items file has "Pad allowance: gravel base, levelled" and a set-on-the-pad crane line. It has no ramp, no landing, no walk. The unit is 113.5" from skid bottom to roof top and sits on the skid, so the floor is above grade by the skid depth plus whatever it is blocked up. Somebody has to own the ramp and the landing, and right now nobody does. Options: a shipped-loose steel landing and ramp priced with the unit, a specified site-built concrete approach in the installation instructions, or a skid detail that sets the floor at grade with a recessed pad. It is a design decision, and it is also a sales decision, because "accessible" in the brochure and a 30 inch step at the door is the kind of gap that ends in a complaint.

5.2 What a single-user accessible toilet and shower room must provide#

Numbers below are the 2010 ADA Standards unless noted. ICC A117.1-2017 is very close on these but not identical everywhere; check both. Sources: US Access Board, ADA chapter 3 (https://www.access-board.gov/ada/chapter/ch03/) and ADA chapter 6 (https://www.access-board.gov/ada/chapter/ch06/), both fetched 13 Sep 2026, plus the section quotes noted.

Scoping, which is the good news for the 2-bath reference unit. ADA 213.2 requires each toilet room to comply with 603, with an exception: "Where multiple single user toilet rooms are clustered at a single location, no more than 50 percent of the single user toilet rooms for each use at each cluster shall be required to comply with 603." (Access Board ADA chapter 2, fetched 13 Sep 2026.) So a 2-bath unit with one accessible room is defensible, which is exactly what docs/showerhouse.md's reference unit does. Two cautions: the exception is written for a cluster, so a 1-bath unit standing alone has no cluster and the one room must be accessible; and where the campground's whole provision of toilet rooms is the cluster, the 50 percent is counted across the campground, not across Ken's unit.

5.3 Compare to what the shower house provides#

From docs/showerhouse.md "Rooms" and src/plan/showerhouse.js, an accessible room is: 8' x 10' inside minimum, a 60 inch turning circle clear of fixtures, a 36 x 60 roll-in shower with grab bars on two walls, a 36 inch door, toilet centreline at least 18 inches from a wall or fixture with 21 inches clear in front, a 30 x 20 lavatory. From docs/showerhouse-items.json, the ACCESSIBILITY section prices: grab bars for the shower (2) and the toilet (rear plus side), a fold-down shower seat, a hand shower on a slide bar, a roll-in threshold strip, an ADA lavatory upcharge (knee clearance, insulated trap, lever faucet), lever hardware and a 36 inch door upcharge, signage, and a door closer with reduced opening force.

Item by item:

One more scoping item. ADA 213.3.6: "Where bathtubs or showers are provided, at least one bathtub complying with 607 or at least one shower complying with 608 shall be provided." A 1-bath standard unit provides a shower and no accessible shower, so a 1-bath unit sold as the only shower facility at a campground fails that. The preset list in docs/showerhouse.md includes "1 bath, standard 10 x 12". That preset should carry a warning in the configurator: it is only lawful where another accessible shower serves the same site.

6. Energy: which path each product takes#

Short, because docs/engineering/thermal-evaluation.md has the arithmetic and this file should not repeat it.

Two things this file adds to the thermal doc:

1. The ceiling U target is 0.026 in Montana, not the model code's 0.024. Fix that row.
2. The 4 ACH50 blower door test applies to the house. A cast concrete house with screwed panel joints, a pumped cavity and a cast roof ought to test very tight, but nobody has tested one, and the joints between panels and at the wall-to-roof line are the risk. Add a blower door test to the first house, and put an air-sealing detail at the panel joint and the top track into the PE's typical details. The shower house is commercial and takes the C402.5 air barrier requirements instead, which Montana amended at C402.5.1.2.

7. Structural: what a transportable unit needs that the PE package does not yet ask for#

docs/engineering/pe-package.md is a good package. Section (d) already covers stripping, the panel pick, the roof strip pick, the shower house unit pick at 35,034 lb with rigging, the transport dimensions, and the skid on the ground. Section (e) questions 11 to 15 already ask for skid members, lug design, fork pocket reinforcement, the floor panel and the tie-downs. What is missing or thin:

1. A named road-load case. Question 15 asks for "the road-load case for the tie-downs and the lugs" but does not propose one. The usual practice is to design securement to 49 CFR 393 Subpart I (0.8 g forward, 0.5 g rearward and lateral, 0.2 g vertical for the securement system), and to design the unit for the inertial loads of transport, which is a different and larger question: a 33,366 lb concrete box on a trailer over Montana roads sees vertical accelerations that no building load case covers. Give the PE a number to design to, or ask for one. ICC/MBI 1200 chapter 7 covers transportation permitting, route, weight and methods of transport, and 701.1 requires the manufacturer to provide "instructions that include, transport, lifting and placement procedures", but it does not set a g-load. NOT CONFIRMED that any adopted standard sets the transport design acceleration; that is the PE's call and it should be stated in the design basis.
2. Anchorage at the site, as a designed thing with a drawing. ICC/MBI 1200 section 804.1 requires the manufacturer to provide instructions covering, among other things, "Foundation loads, anchorage details and required capacity of anchorage devices" and "Maximum foundation support, spacings, and any additional information necessary for the proper support of the modular building". Section 802.2 requires the foundation to be designed for the building plus all live, dead and construction loads and the site's geotechnical limits. Today the product says the unit sits on "gravel pad, blocks, or piers", which is not an anchorage design and not a support spacing. The PE has to produce: a bearing diagram (where the skid may be supported and where it may not), a maximum allowable pier spacing, a minimum bearing pressure, and an anchorage detail with a device capacity, for the wind uplift and sliding of the worst site Ken will deliver into. That single sheet also solves the classification lever in 3.3.
3. The envelope question. pe-package section (c) already flags it: does the shower house get designed for one site's loads or for an envelope of snow and wind it can be delivered anywhere under? Answer it before the first sale. An envelope is what makes the product a product. It also interacts with ASCE 7-22 being the Montana hazard source outside certified jurisdictions, and with the 30 psf minimum roof snow load on the IRC route.
4. Skid as foundation, stated or disclaimed. Not in the package at all today. See 3.3 and 3.4.
5. Special inspections and a construction sequence for the panels. ICC/MBI 1200 section 103.3 requires the panelized-system construction documents to name the systems and components requiring special inspection and to carry a statement on the sequence of construction. Neither exists yet. The animation phases are the sequence in effect; they need to become a written statement in the design basis.
6. Installation tolerances. ICC/MBI 1200 section 803.1 requires the registered design professional to detail construction tolerances for fitting module to module and module to foundation. For the house, panel to panel and panel to slab. Not in the package.
7. Lifting hardware acceptance. The package already names PCI MNL-120 and OSHA 1926.704 through the standards register, and asks for the lug proof-load value. Add: the insignia or label question for the lugs, meaning whether the lugs are treated as below-the-hook lifting devices under ASME BTH-1 with the marking and proof test that implies. The standards register names B30.20 and BTH-1; the PE package does not ask for the proof test record.

8. Plumbing and electrical: the plant inspection line#

This is the practical heart of the shower house classification, and it deserves to be separated from the legal question.

The problem. In the shower house, the DWV, the supplies, the trap primers, the sleeves through the cast floor panel, the conduit and the branch circuits are installed in the plant, and much of it is buried in cast concrete or inside a panel cavity that is later pumped full. A local plumbing or electrical inspector at the destination site cannot inspect any of it. There is no rough-in to look at. That is exactly the condition ICC/MBI 1200's OFF-SITE CONSTRUCTION definition describes: parts and processes that "cannot be inspected at the installation site without disassembly, damage to, or destruction thereof."

How the system is meant to handle it. ICC/MBI 1200 section 104 splits inspections: 104.2 in-plant inspections verify that construction complies with the approved construction documents; 104.3 on-site inspections verify that installation complies with the approved manufacturer's installation instructions and that the connections made on site comply with the approved construction documents. 104.3 then lists what the on-site inspection covers: interconnections between off-site components installed at site, connections between off-site components and adjoining site-built work including the building structure, other connections the AHJ wants, and connections of shipped-loose items.

Montana's side of that is the factory-built buildings program: manufacturer registration (ARM 24.301.1217), model plan review (24.301.1221), an in-plant quality assurance manual (24.301.1223), an approved third-party inspection agency (24.301.1213), and the insignia (24.301.1241), whose effect (24.301.1245) is that a unit bearing the insignia is accepted throughout Montana "without further inspection or fees except for zoning, utility connections, and foundation permits". The DLI Factory-Built Buildings page describes separate approvals for electrical, mechanical and plumbing systems, designated E, M and P, and lists 16 approved third-party inspection agencies. (https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/, fetched 13 Sep 2026; rule numbers from the Cornell subchapter 24.301.12 index, fetched 13 Sep 2026. The exact text of 24.301.1245 is NOT CONFIRMED verbatim.)

So the line falls here, and it is clean:

The risk if the unit is classified as NOT a factory-built building: there is then no plant inspection anywhere in the system, and a local inspector at the site is asked to sign off on plumbing and wiring they cannot see. Some will refuse. That is a strong practical argument for pursuing the insignia even if the literal definition would let Ken out of it, and it is the third of the three big open questions.

For the house, this is easier and mostly solved by the build sequence. The panels leave the plant with no plumbing and no wiring; the trades work in the open stud cavity on site after the panels stand, and the cavity is pumped full afterwards. So the electrical and plumbing rough-in is inspectable on site in the normal way, by the normal inspector, before the fill goes in. The one thing that changes is the order: the fill pour is irreversible and it buries the rough-in, so the rough-in inspection has to be scheduled before the pump truck, not before drywall. That belongs in the written construction sequence (section 7 item 5) and in the installation instructions, because a builder who pours first has destroyed the inspection.

9. Gap table#

10. The three things I would put in front of Ken first#

1. One letter to the Montana Building Codes Bureau, asking two questions. (a) Is the shower house, built complete on a steel skid with service connections, a factory-built building requiring an insignia under MCA 50-60-101(9)(a) and ARM 24.301.1241, given that it is readily movable and, as currently designed, is not designed for a permanent foundation? (b) Does the adoption of ICC/MBI 1200 and 1205 at ARM 24.301.1203 reach a plant producing cast wall, roof and floor panels that are panelized systems but not modules, and if so what does the Bureau require of that plant? Everything else waits on these two answers. docs/montana/02-approval-process.md has the mechanics of asking.
2. The skid-as-foundation sheet from the PE. Bearing diagram, maximum support spacing, minimum bearing pressure, anchorage detail with a device capacity, for a stated wind and snow envelope. It is one drawing and it answers the classification question, the DPHHS "permanent construction" question and gap 3 at the same time.
3. The accessible route. The product today prices an accessible room and does not price a way to get into it. Decide who owns the landing and the ramp, and price it, before the first campground sale.

11. Sources#

All fetched 13 Sep 2026.

Montana codes and adoption:

• Montana DLI Building Codes Bureau, Current Codes: https://bsd.dli.mt.gov/building-codes-permits/current-codes
• Montana DLI Building Codes Program: https://bsd.dli.mt.gov/building-codes-permits/
• Certified city, county and town programs: https://bsd.dli.mt.gov/building-codes-permits/certified-government
• Factory-Built Buildings Permits: https://bsd.dli.mt.gov/building-codes-permits/permit-applications/factory-built-buildings/
• ARM 24.301.131, IBC: https://www.law.cornell.edu/regulations/montana/ARM-24-301-131
• ARM 24.301.146, IBC modifications: https://www.law.cornell.edu/regulations/montana/ARM-24-301-146
• ARM 24.301.154, IRC: https://www.law.cornell.edu/regulations/montana/ARM-24-301-154
• ARM 24.301.161, IECC: https://www.law.cornell.edu/regulations/montana/ARM-24-301-161
• ARM 24.301.301, UPC: https://www.law.cornell.edu/regulations/montana/ARM-24-301-301
• ARM 24.301.351, plumbing fixtures: https://www.law.cornell.edu/regulations/montana/ARM-24-301-351
• ARM 24.301.401, NEC: https://www.law.cornell.edu/regulations/montana/ARM-24-301-401
• ARM 24.301.903, building accessibility: https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.903
• ARM 24.301.904, site accessibility: https://www.law.cornell.edu/regulations/montana/Mont-Admin-R-24-301-904
• ARM 24.301.1203, ICC/MBI 1200 and 1205: https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1203
• ARM 24.301.1205, definitions: https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1205
• ARM 24.301.1207, mobile homes and RVs not for commercial occupancy: https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1207
• ARM 24.301.1241, insignia when required: https://www.law.cornell.edu/regulations/montana/Mont-Admin-r-24.301.1241
• ARM subchapter 24.301.12 rule index: https://www.law.cornell.edu/regulations/montana/department-24/chapter-24.301/subchapter-24.301.12
• ARM subchapter 24.301.5 rule index (mostly transferred or repealed): https://www.law.cornell.edu/regulations/montana/department-24/chapter-24.301/subchapter-24.301.5
• UpCodes Montana code index and ARM rule cross-reference: https://up.codes/codes/montana
• Montana IBC 2021 viewer, chapter 3 occupancy: https://up.codes/viewer/montana/ibc-2021/chapter/3/occupancy-classification-and-use
• Montana IECC 2021 viewer, commercial scope: https://up.codes/viewer/montana/iecc-2021/chapter/CE_1/ce-scope-and-administration

Montana statute:

• MCA 50-60-101, definitions: https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0010/section_0010/0500-0600-0010-0010.html
• MCA 50-60-402, factory-built buildings and recreational vehicles to comply with standards: https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/section_0020/0500-0600-0040-0020.html
• MCA Title 50 chapter 60 part 4 index: https://mca.legmt.gov/bills/mca/title_0500/chapter_0600/part_0040/sections_index.html

Health licensing:

• ARM Title 37 chapter 111 subchapter 12, Trailer Courts, Campgrounds, Youth Camps and Work Camps, 2022 rules (NEW, 2022 MAR p. 1748, Eff. 9/10/22): https://dphhs.mt.gov/assets/publichealth/FCS/TrailerCourts/TrailerCourtCampgroundRules2023.pdf
• Work camp rules PDF (older vintage on some subjects): https://dphhs.mt.gov/assets/publichealth/FCS/TrailerCourts/WorkcampARM.pdf
• DPHHS Trailer Courts and Campgrounds program page: https://dphhs.mt.gov/publichealth/EHFS/TrailerCourtsAndCampgrounds

Off-site construction standard:

• ICC/MBI 1200-2021, ICC-posted approved ballot copy: https://www.iccsafe.org/wp-content/uploads/is_osmc/ICC1200-draft-ballot-apprvd.pdf (used for the Chapter 1 and Chapter 2 text quoted in section 3.1 and 3.2; the purchased published edition should be checked against it)
• ICC Digital Codes listing for ICC/MBI 1200-2021: https://codes.iccsafe.org/content/ICC12002021P1 (returns 403 to an automated fetch; listed so the reader can open it in a browser)

Accessibility:

• US Access Board, ADA Standards chapter 2 (scoping): https://www.access-board.gov/ada/chapter/ch02/
• US Access Board, ADA Standards chapter 3 (building blocks): https://www.access-board.gov/ada/chapter/ch03/
• US Access Board, ADA Standards chapter 6 (plumbing elements): https://www.access-board.gov/ada/chapter/ch06/
• US Access Board, guide to toilet rooms: https://www.access-board.gov/ada/guides/chapter-6-toilet-rooms/
• ADA.gov, 2010 ADA Standards for Accessible Design: https://www.ada.gov/law-and-regs/design-standards/2010-stds/
• Corada reproduction of 2010 ADA 608.3.2 (used to confirm the seat / no-seat grab bar split): https://www.corada.com/documents/2010ADAStandards/608-3-2

Energy:

• 2021 IECC unamended residential certificate reproducing the "Residential building" definition: https://www.pprbd.org/File/ByAlias/2021ieccunamend
• Montana DEQ residential energy code program: https://deq.mt.gov/energy/Programs/code
• Montana Residential Energy Code Handbook (NCAT): https://www.ncat.org/wp-content/uploads/2025/07/MT-2021-Residential-Code-Handbook_CRB_20250303.pdf

Trade discussion, cited as evidence of an unsettled question and not as authority:

• The Building Code Forum, "Use Group Classification for Toilets in Park": https://www.thebuildingcodeforum.com/forum/threads/use-group-classification-for-toilets-in-park.16675/

Project files referenced:

• docs/wall-spec-v1.md, docs/showerhouse.md, docs/showerhouse-items.json, src/plan/showerhouse.js
• docs/engineering/pe-package.md, docs/engineering/standards-register.md, docs/engineering/thermal-evaluation.md
• docs/roof-insulation.md
• docs/montana/01-statute-and-rules.md, docs/montana/02-approval-process.md