NOAH Dwelling Standard for Tiny Houses on Wheels

1.1 Introduction

Unlike site-built homes, modular buildings, manufactured housing, or recreational vehicles, THOWs are designed to function as lawful highway-capable structures while serving as residential living spaces. Because THOWs travel public highways, they shall comply with applicable federal and state transportation requirements administered by the NHTSA, the U.S. DOT, Federal Motor Carrier Safety Regulations where applicable, and all applicable state transportation laws.

The wheeled chassis, towing, braking, lighting, dimensions, weights, and transport-safety requirements are foundational elements of THOW design — not secondary considerations. Standards such as ANSI A119.5 were developed for recreational occupancy and permit construction methods and thermal performance that may be inadequate for long-term residential use.

The purposes of this standard are to:

• establish residential-level life-safety criteria;
• preserve lawful highway transportability;
• recognize THOWs as a distinct housing type and distinguish them from recreational vehicles;
• provide a uniform framework for manufacturers, builders, insurers, lenders, and jurisdictions;
• support lawful placement as ADUs, primary residences, workforce housing, and emergency housing;
• and encourage innovation in attainable housing while protecting occupant safety and public welfare.

1.2 Transportation Compliance

THOWs shall comply with all applicable federal and state transportation laws governing trailers and transportable highway vehicles, including where applicable axle ratings, GVWR, braking systems, lighting and reflectors, tire and wheel ratings, hitch and coupler systems, safety chains, breakaway braking, width/height/length limitations, load securement, and roadway operational safety. The chassis and transportation systems shall safely withstand highway transport loads, vibration, dynamic loading, torsional and braking forces, and environmental exposure. Nothing in this standard exempts a THOW from applicable federal or state motor vehicle regulations.

1.3 Intent & Order of Precedence

The intent is to establish residential-level safety and performance criteria while preserving the mobility unique to THOWs. Where referenced standards conflict, precedence applies in the order: (1) this NOAH Dwelling Standard; (2) applicable federal transportation regulations; (3) applicable state or local law; (4) engineering requirements; (5) referenced standards.

Where electrical requirements are not specifically addressed, the NEC applies — first Article 552, then Chapters 1–4 for items not addressed by 552. Where plumbing is not addressed, the plumbing code adopted by the jurisdiction of initial installation governs (IPC, UPC, or other adopted standard). This standard takes precedence over recreational vehicle standards, ANSI A119.5, and NFPA 1192 where conflicts occur.

1.4 Occupancy Classification

A THOW constructed to this standard shall be considered a Tiny House on Wheels Dwelling Unit (THOWDU).

1.5 HUD Manufactured Housing

This standard is not intended to classify THOWs as HUD Manufactured Homes.

1.6 Compliance

Compliance shall be demonstrated through third-party inspection, approved engineering documentation, manufacturer certification, or AHJ approval.

1.7 Alternate Materials and Methods

Alternative materials, equipment, systems, or methods not specifically prescribed shall be permitted where the alternative meets the intent of this standard and provides equivalent or greater safety, durability, structural integrity, fire resistance, and energy performance.

2.2 Definitions

• Accessory Dwelling Unit (ADU) — a secondary residential dwelling unit on the same lot as a primary dwelling.
• Authority Having Jurisdiction (AHJ) — the organization, office, or individual responsible for approving installations and enforcing this standard.
• Chassis — the structural wheeled frame forming the transportation base of a THOW.
• Design Life — the anticipated service life of the structure under normal residential occupancy.
• Emergency Egress and Rescue Opening — an operable window or exterior opening intended for emergency escape and rescue.
• Habitable Space — a space used for living, sleeping, eating, or cooking.
• Loft — a floor level above the main living floor and open to the room below on at least one side.
• Park Model RV — a recreational vehicle certified to ANSI A119.5, intended primarily for seasonal or temporary recreational use.
• Permanent Residential Occupancy — occupancy as a primary residence for more than 180 days within a calendar year; the chassis remains integral even during permanent installation, and installation does not alter classification.
• Tiny House on Wheels (THOW) — a transportable residential dwelling unit on a wheeled chassis, designed for highway transport and residential occupancy, containing independent living facilities (living, sleeping, cooking, sanitation, storage), certified by the manufacturer to this standard, with a maximum habitable footprint of 400 sq ft or less (excluding lofts).
• Tiny House on Wheels Dwelling Unit — a THOW built to this standard, recognized as a residential structure movable without disassembly and capable of repeated or one-time transport on public roadways.
• Wheeled Chassis — a structural steel or engineered frame equipped with axles, wheels, and towing components intended to support and transport a THOW.

3.2 Authority

The AHJ may adopt, amend, or supplement this standard to address climate, wind exposure, snow loads, seismic conditions, flood hazards, wildfire exposure, and local utility requirements.

3.3 Existing THOWs

Existing THOWs legally constructed before adoption may continue occupancy where deemed safe by the AHJ.

3.4 Data Plate, Decal & Certification Label

Each compliant THOW shall have a data plate near or on the electric panel (or inside the sink base door) identifying manufacturer, serial number/VIN, date of manufacture, climate zone, design loads, and certification agency. A Transportation Compliance Decal shall show GVWR, and a permanent certification label/seal from an accredited third-party inspection agency shall be located on the hinge side of the main entry door.

3.5 Inspections

• Chassis, framing, electrical, plumbing, mechanical, and energy inspections
• Final life-safety inspection
• Transport compliance verification

3.6–3.9 Engineering, Climate Zones, Conflicts & Severability

Structural systems outside prescriptive requirements shall be engineered by a licensed PE. Climate zones generally follow the IECC climate zone map (see Chapter 13). Where referenced standards conflict, the more restrictive provision affecting occupant safety governs. If any word or section is found invalid, the remainder remains in effect.

4.2 Minimum Design Loads

4.3–4.4 Lumber & Wall Framing

Structural framing shall be minimum No. 2 SPF, Douglas Fir-Larch No. 2, or equivalent; No. 3 lumber is not permitted in load-bearing framing. Exterior load-bearing walls: min 2x4 studs at ≤16" o.c. unless engineered. 2x3 framing is prohibited in load-bearing walls (permitted non-load-bearing). Load-bearing walls use a single continuous 2x4 bottom plate (bolted min ½" dia. with 2"×2" plate washers, max 1' from ends/joints then every 4') and double continuous 2x4 top plates lapped ≥4' at splices and interlocked at corners.

4.4.3 Header Requirements

Headers exceeding 10 ft require engineered design. Headers consist of doubled members separated by a min ½" structural filler (plywood, OSB, or steel), fastened to act as one assembly, bearing fully on jack studs.

4.5 Roof Framing

Roof systems shall resist dead, live, snow, and uplift loads plus transport vibration and dynamic forces. Rafters and ceiling joists follow the 2024 AWC Span Tables (or successor); trusses shall be engineered, and field modification is prohibited without a PE. Sheathing shall be plywood/OSB sized for framing spacing, roof loads, and transport vibration. Connections shall use hurricane ties, structural screws, framing anchors, or engineered connectors. Overhangs shall be braced for highway wind and uplift; roof slopes shall provide positive drainage per roofing manufacturer minimums.

4.6 Engineering Thresholds

Engineered structural calculations are required for THOWs exceeding 13'6" transport height (some states allow 14'6", but such units must remain in that state), 12' width, or 26,000 lb GVWR.

Use APA-rated Exposure 1 or exterior panels, strength axis perpendicular to supports, staggered joints, 1/8" edge gap, no overdriven nails. Provide continuous load path roof→framing→walls→floor→foundation→ground. At 170 mph use WFCM or site-specific engineering — not generic tables.

5.2–5.5 Weight & Transport Setup

Tongue weight shall generally be 10–15% of gross trailer weight unless engineered. Loads shall be distributed as evenly as practical among axles without exceeding any rated capacity. Center of gravity should generally be ~60% forward / 40% rearward of the axle-assembly centerline, with heavy components positioned to minimize sway. Before transport: secure propane cylinders, restrain loose components, secure doors, latch windows, and verify transport systems.

5.1.1–5.1.2 Materials & Main Frame Rails

Chassis members shall be structural steel meeting ASTM standards — min ASTM A36 steel or A500 tubing (aluminum requires engineering). Provide a minimum of two continuous longitudinal main frame rails running the full structural length, min 6" steel channel, 6" rectangular tube, or engineered equivalent.

5.1.3–5.1.11 Members, Tongue, Axles & Welds

Cross members (support floor framing, resist twisting) at ≤24" o.c., min 2x3 steel tube / 3" channel, welded or mechanically fastened to rails. Outriggers support cantilevered floor loads (max 24" projection unless engineered). The integrated tongue (A-frame, boxed, or engineered) includes coupler, safety-chain points, breakaway-brake attachment, and jack mounting. Axles attach via engineered hangers, torsion, or spring systems with reinforced attachment points. All steel shall be corrosion-protected (galvanizing, coatings, powder, epoxy); field welds recoated. Structural welding per AWS D1.1; critical welds visually inspected. Max vertical deflection L/360 for occupied conditions unless engineered.

5.1.10–5.1.13 Attachment & Alternates

The floor framing shall be positively connected to the chassis (bolting, welding, structural screws, or engineered brackets) to resist uplift, sliding, vibration, and torsion. Identified jacking/support points shall transfer loads directly into the primary frame. Alternate chassis systems (monocoque, integrated subframes, hybrid steel/composite) are permitted with engineering demonstrating equivalent structural integrity, durability, transport safety, fatigue resistance, and load capacity.

6.3–6.4 Prescriptive Foundations & CMU Piers

Permitted supports include concrete pads, CMU pier systems, steel piers, helical piles, or approved equivalents. CMU piers bear on solid concrete footing pads.

Pads bear on undisturbed soil, compacted fill, or engineered base (organic/uncompacted fill prohibited). Piers: solid grouted CMU, dry-stacked with caps, or equivalent; min 8"×16" nominal; max unsupported height 36" unless engineered/braced.

6.4.4 Pier Spacing

• Beneath main chassis rails, major load points, axle areas, and concentrated loads
• Max spacing 8' o.c.; 2' from a corner; either side of all door openings
• Additional piers at point loads, large openings, heavy appliances, and loft-bearing walls

6.5 Anchoring Requirements

Anchors resist wind uplift, lateral movement, transport shifting, and seismic displacement. Ground anchors (auger/helical/driven) min 4' length, corrosion resistant, installed ≤8' o.c. along both sides with additional anchors at corners, tongue, and high-uplift zones. Galvanized/stainless straps connect directly to the primary steel chassis or engineered attachment points.

6.6–6.11 Wind, Frost, Drainage & Alternates

Anchoring designed for min 130 mph ultimate wind (more in coastal/hurricane regions). In frost areas, prevent frost heave or extend below frost depth. Grade to direct water away — standing water beneath the THOW is prohibited. Provide access to plumbing, electrical, gas, and chassis inspection points. Skirting is not structural unless engineered; ventilate enclosed underfloor spaces. Alternate engineered foundation/anchoring systems (helical piles, perimeter foundations, slab interfaces, adjustable pedestals) are permitted where equivalent or greater performance is shown.

7.2–7.3 Weather Protection & Cladding

Exterior assemblies shall prevent bulk water penetration, uncontrolled air leakage, and moisture accumulation using flashing, weather barriers, sealants, drip edges, and drainage. Approved cladding: wood siding, fiber cement, metal panels, engineered wood, stucco, composite, or equivalent — resisting wind, transport vibration, moisture, UV, and freeze-thaw.

7.4 Windows

Windows shall resist water intrusion, air leakage, vibration, and structural movement, installed per manufacturer specs. Minimum double-pane insulated glazing (single-pane prohibited). Safety glazing at hazardous locations (doors, adjacent to doors, shower/tub enclosures, stairways, low glazing). Emergency egress windows comply with Chapter 9.6.

7.5 Exterior Doors

Doors shall provide weather resistance, structural stability, air sealing, security, and safe operation, securely fastened to framing that resists transport vibration and wind pressures. Permitted types: hinged swing, sliding glass, accordion/folding glass wall systems, insulated metal, fiberglass, or equivalent (all listed for exterior use). Swing doors include thresholds, perimeter weather stripping, and flashing; sliding and accordion systems add interlocking seals, drainage, and structural support framing engineered for roof/wind/transport loads. Doors that could open during transport require positive locking or restraint.

7.6–7.10 Roof, Flashing, Air Sealing & Alternates

Roof assemblies resist water intrusion and provide positive drainage. Flashing (corrosion resistant) at windows, doors, penetrations, intersections, and material transitions. Seal the envelope at framing joints, penetrations, and utility openings. Minimize thermal bridging via continuous insulation, insulated framing, or thermal breaks. Alternate envelope systems (SIPs, composite/curtain walls, insulated steel, rainscreens) permitted where equivalent or greater performance is shown.

8.2 Smoke Alarms

Listed, permanently installed smoke alarms shall be located in each sleeping area, outside each sleeping area, within loft sleeping spaces, and on each floor level, powered by building wiring with battery backup or sealed long-life batteries.

8.3 Carbon Monoxide Alarms

Required in all THOWs regardless of fuel type — outside sleeping areas, within loft sleeping areas, and on each level containing habitable space. Combination smoke/CO alarms are permitted.

8.5–8.11 Escape, Finishes, Clearances & Systems

Provide safe means of escape (per Chapter 9); occupants shall not pass through another sleeping area to reach an exit. Interior finishes meet flame-spread requirements. Heat-producing appliances maintain listed clearances. Electrical fire protection includes overcurrent, GFCI, AFCI, grounding, and bonding (Chapter 14). Fuel-gas systems comply with Chapter 12, including CO alarms, LP leak detection, and combustion air.

8.12–8.15 Egress Lighting, Fireblocking, Transport & Alternates

Egress remains reasonably illuminated (battery emergency lighting encouraged). Fireblocking and draft stopping at floor penetrations, concealed cavities, loft framing intersections, and chases. Mounted safety equipment resists roadway vibration and remains functional after transport. Alternate systems (residential sprinklers, monitored/wireless interconnected alarms, engineered fire protection) permitted where equivalent or greater performance is shown.

9.2–9.3 Area & Ceiling Height

Sleeping/living lofts: min 35 sq ft floor area; no horizontal dimension less than 5 ft (except sloped-ceiling conditions). Minimum ceiling height 3 ft measured at the lowest portion of the required area. Where sloped, ≥50% of the required loft floor area shall have ≥3 ft ceiling height; areas below 3 ft don't count toward required area.

9.4–9.5 Access & Guards

Access via stairways, alternating tread devices, ladders, ships ladders, or equivalent (per Chapter 11), permanently installed; portable ladders must be securely attached in use. Lofts more than 30" above the floor below require guards min 36" high; guards shall not pass a 4" sphere (except at stair/ladder openings). Catwalks between lofts: min 20" clear width, slip-resistant, guarded where >30" high, and shall not obstruct escape openings, egress paths, ventilation, or alarm coverage.

9.6 Emergency Escape & Rescue Openings

THOWs shall have a primary escape/rescue opening no less than 32" wide × 78" high. All sleeping areas require a primary and secondary emergency escape and rescue opening.

Openings shall be operable from inside without keys, tools, or special knowledge, and remain accessible during occupancy.

9.9–9.14 Structure, Head Protection & Alternates

Loft floors: min 30 psf (sleeping) / 40 psf (habitable), resisting transport vibration, dynamic loading, and torsion, positively connected to primary wall framing. Reduced-headroom areas near walking paths shall be clearly identifiable. Lofts shall not be the sole required means of egress. Alternate loft configurations permitted where equivalent safety, accessibility, structural integrity, and egress are demonstrated.

10.2 Potable Water

Approved piping: PEX, copper, CPVC, stainless, or equivalent (interior pressurized PVC prohibited). Flexible connections at water heaters, fixtures, pumps, tanks, and service connections accommodate vibration and chassis movement. Design for min 40 psi, max 80 psi without regulation (regulators required above 80 psi). Exterior connections include shutoffs, freeze protection, approved hose bibbs, and backflow prevention.

10.3–10.5 Tanks & Wastewater

Freshwater and holding tanks (freshwater, black, gray) shall be potable-safe/leakproof as applicable, securely mounted to resist transport vibration and full-tank loading, with access for service, venting, and freeze protection. DWV systems include traps, venting, and cleanouts using ABS, PVC DWV, copper, or equivalent, supported against vibration and sagging.

AAVs permitted where approved by the AHJ; at least one vent terminates to the exterior atmosphere unless engineered. Holding tanks vent to exterior, above roofline where practical.

10.6–10.7 Fixtures & Water Heating

Permanent-occupancy THOWs include toilet, lavatory, kitchen sink, bathing fixture, and hot water. Where a separate bathroom lavatory won't fit, the kitchen sink may serve as lavatory where the kitchen adjoins the bathroom. Composting toilets permitted where AHJ-approved. Water heaters (tank, tankless, or heat-pump) include T&P relief valves with discharge piping and are secured against transport movement/overturning.

10.10–10.12 Testing & Alternates

Potable systems pressure-tested at ≥80 psi; DWV tested with a min 10-ft water column or equivalent. Protect plumbing from road debris, vibration, freezing, UV, and chassis movement. Alternate systems (composting/incinerating toilets, vacuum drainage, graywater recycling, rainwater harvesting, engineered off-grid) permitted where AHJ-approved.

11.3–11.4 Heating/Cooling & Mini-Splits

Permanently installed heating and cooling shall maintain thermal comfort (min 70°F, 2' above the main floor), humidity control, and acceptable air quality; portable devices shall not be the sole primary heat source. Ductless mini-split heat pumps are a preferred system (compact, efficient, variable-speed, humidity-capable). Condensate discharges to approved drainage/pumps/exterior points, protected from freezing, blockage, and transport damage.

11.5–11.8 Humidity, Ventilation & Exhaust

Provide humidity control (dehumidifiers, HVAC dehumidification, dry-mode, whole-house units, ERV/HRV) maintaining ~30–60% RH. Provide continuous/intermittent fresh-air exchange (exhaust-only, balanced, HRV/ERV).

Bath and kitchen exhaust terminate directly to the exterior (not into attics, cavities, or crawl spaces). Recirculating range hoods only where AHJ-approved.

11.9–11.14 Radiant, Combustion, Condensation & Alternates

Radiant floor systems (electric/hydronic) include vapor control and moisture-resistant materials. Combustion appliances vent to exterior with adequate combustion air; unvented heaters shall not be the primary source. Manage condensation via insulation, thermal breaks, air circulation, and vapor control (attention to toilet tanks, cold lines, metal framing, window frames). Equipment secured for transport and reviewed before occupancy. Alternate systems (solar-assisted, geothermal, desiccant, passive ventilation, smart controls) permitted where equivalent or greater performance is shown.

12.3 Piping Materials

Listed/approved gas piping: black steel, galvanized where approved, LP-approved copper, stainless, CSST, listed flexible connectors, or approved manifolds. Plastic gas piping is prohibited inside occupied portions. Protect piping from abrasion, puncture, vibration, corrosion, road debris, heat, and transport movement; use grommets/sleeves/plates through framing.

12.4–12.6 Cylinders, Regulators & Shutoffs

Cylinders locate outside habitable space in vented compartments (vent near bottom, no ignition sources), mounted for highway transport, upright unless listed horizontal, with pressure-relief discharge away from interior/enclosed spaces. Two-stage regulation required for multiple appliances/residential use (~11" w.c. output), located outside habitable space, protected, with vents unobstructed (commonly downward/"6 o'clock"). A labeled, tool-free main manual shutoff at the supply; each appliance has a shutoff within 6 ft upstream of the connector; excess-flow/emergency shutoff encouraged.

12.7–12.10 Appliances, Venting & Detection

Appliances shall be listed, secured for transport, and maintain listed clearances to combustibles. Direct-vent/sealed-combustion units are preferred; combustion products vent directly to exterior without re-entry through windows, doors, or intakes. Install listed CO alarms and LP gas detectors (near floor level, since propane is heavier than air). Compartments vent to exterior and stay unblocked by skirting/storage/insulation.

12.11 Pressure & Leak Testing

Piping shall pass a pressure test at 1.5× working pressure with no measurable loss for a minimum 15 minutes, performed before concealment. After connection, verify operating pressure (~11" w.c. after second-stage regulation). Leak detection via calibrated gauges, manometers, approved solution, or electronic detectors — open-flame testing prohibited. A pressure-drop test is a recognized method.

12.12–12.14 Transport, Checklist & Alternates

Before transport: close cylinder valves, turn off appliances, secure cylinders, protect regulators/pigtails, restrain loose components, latch compartments — systems shall remain leak-free after transport. Fuel-gas inspection verifies materials, support, protection, shutoff/regulator details, cylinder mounting, ventilation, clearances, vent terminations, relief discharge, CO/LP detectors, the 1.5× test, operating pressure, and final leak test. Alternate systems permitted with AHJ/agency approval and supporting documentation.

13.2 Climate Zone Insulation

Alternate assemblies permitted where equivalent or greater thermal performance is demonstrated via engineering, testing, or energy modeling.

13.3–13.5 Thermal Envelope, Air Sealing & Barriers

Minimize conductive loss, infiltration, thermal bridging, and condensation using insulation, air/weather barriers, thermal breaks, and vapor control. Reduce bridging via continuous insulation, insulated sheathing, staggered framing, or thermal-break materials. Seal windows, doors, and all penetrations. Exterior walls include an approved weather-resistant barrier (house wrap, integrated/taped sheathing, fluid-applied) lapped, taped, flashed, and sealed per manufacturer.

13.6 Windows

Minimum double-pane insulated glazing (single-pane prohibited).

Lower U-values are permitted and encouraged. Install per manufacturer with flashing, sealing, drainage, and air-barrier integration.

13.8–13.12 Assemblies, Moisture & Alternates

Roof/ceiling assemblies provide continuous thermal protection and moisture control with ventilation or approved unvented design. Floors are insulated and secured against vibration/sagging. Energy measures shall not trap moisture — balance insulation, vapor control, ventilation, and drying potential. Mechanical moisture control includes bath/kitchen exhaust, dehumidification, ERV/HRV, and mini-split dry mode. Alternate systems (SIPs, composite panels, double-wall, VIPs, advanced framing) permitted where equivalent or greater performance is shown.

14.2 Electrical Service

Full-time THOWs shall be sized for residential loads — minimum 50 A, 120/240 V, single phase, unless approved load calculations show a smaller service is adequate. Permitted connections: RV-style pedestal, listed cord-and-plug, direct hardwired, transfer switches, or equivalent. RV-style shore-power uses listed connectors, outdoor-rated cords, weather-resistant inlets, and NEC-compliant 120/240 V grounding, conductor sizing, and overcurrent protection. Direct wiring includes disconnect, grounding, overcurrent protection, and approved feeders with flexible connections for chassis movement.

14.3–14.4 Panels & Branch Circuits

A listed distribution panel remains accessible, moisture-protected, and securely mounted — not in bathrooms, kitchens, or closets. As a subpanel fed from exterior service/pedestal, neutrals are isolated from grounds; neutral-to-ground bonding occurs only at the service disconnect. Kitchens: min two 20 A small-appliance circuits (no lighting on them). Dedicated circuits for mini-splits, water heaters, microwaves, induction cooktops, refrigerators, laundry, and EV charging.

14.5 Receptacles — GFCI & AFCI

GFCI protection in kitchens, bathrooms, exterior, laundry, within 6' of sinks, underfloor storage, and rooftop decks. AFCI protection for habitable spaces, sleeping areas, lofts, living rooms, and kitchens (combination-type permitted). Extension cords shall not serve as permanent wiring.

14.6–14.12 Wiring, Grounding, Renewables & Testing

Approved methods (NM where permitted, MC, conduit, flexible metallic conduit, raceway) protected from vibration, abrasion, and puncture, with bushings/grommets/nail plates through framing and protection for exterior/underfloor runs. The steel chassis is bonded to the equipment grounding system; metal roofing/siding bonded where required. Renewable systems (PV, battery storage, inverters, hybrid off-grid) comply with the NEC; lithium batteries include a BMS and protection from heat/vibration/off-gassing. Equipment is secured for transport and tested before occupancy for grounding continuity, polarity, AFCI/GFCI function, and overcurrent protection.

15.1.1 Manufacturer Responsibility

Compliance remains the responsibility of the manufacturer/builder, who certifies compliance with this standard, approved documents, engineering, and quality control. Third-party agencies independently verify compliance, document conditions, review QC systems, and provide impartial oversight — they do not certify construction on the manufacturer's behalf or relieve responsibility for code compliance, quality, materials, structural adequacy, or life safety.

15.2 Approved Inspection Agencies

Agencies shall demonstrate competence with THOWs, transportable/factory-built and site-built construction, and meet ASTM E541, ANAB accreditation, ISO/IEC 17020, or equivalent — maintaining impartiality, consistency, record retention, inspector qualification, and quality assurance. Inspectors possess demonstrable knowledge of residential construction, transportable structures, electrical/plumbing/fuel-gas/mechanical systems, structural framing, and transport safety.

15.3 Inspection Philosophy & Plan Review

Because many elements become concealed, inspections occur across multiple phases before concealment, emphasizing transparency, traceability, and permanent documentation. Construction shall not begin until documents undergo plan review and approval by the agency, a design professional where required, or the AHJ. Minimum documents: floor plan, sectional drawings, electrical layout, plumbing fixture layout, and elevation drawings — plus engineering, truss, chassis, energy, and anchoring details as required.

15.4–15.5 Methods & Required Stages

Inspections may be in-person, remote, or hybrid; remote inspections use live video, photography, cloud software, geolocation, and timestamped media allowing real-time direction and verification before concealment. Records are securely stored, tamper-protected, and retained ≥5 years. Minimum stages: (1) chassis/foundation, (2) framing/structural, (3) rough electrical, (4) rough plumbing, (5) rough mechanical, (6) insulation/envelope, (7) final. Alternate sequencing (interior-first, panelized, modular) is accommodated so long as systems are inspected before concealment.

15.13–15.16 Certification Paths & Labels

Path A — Certified Facility: approved written QC program with unannounced audits at least quarterly; non-compliance can lead to increased inspections, probation, suspension, or revocation. Path B — Individual Unit: each THOW inspected at all stages (owner-builders are the manufacturer), documented and traceable via serial/VIN/seal numbers. Certified units receive a permanent label/seal identifying manufacturer, agency, certification number, serial/VIN, date, and standard, plus a signed manufacturer certification statement (name, address, VIN/identifier).

15.17–15.20 Corrections, Impartiality & Agency Role

Deficiencies are documented and corrected, with reinspection before proceeding. Agencies and inspectors remain independent and shall not approve work in which they have a financial interest. Alternate inspection systems (automated platforms, AI-assisted review, enhanced engineering verification) are permitted where equivalent transparency, traceability, accountability, and life-safety verification are shown. The agency is an independent compliance verifier — not the manufacturer, designer, engineer, contractor, or guarantor — and does not assume responsibility for design adequacy, concealed defects, workmanship, material failure, or ongoing maintenance.

THOWs transported on public highways shall comply with all DOT and state transport regulations. Oversize THOWs shall obtain required permits. Before transport: secure appliances, disconnect utilities, restrain loose items, and verify tire pressures. Consider weight distribution, route planning, and transport-safety checklists.

Jurisdictions may permit THOWs as ADUs, primary residences, workforce housing, or infill housing. Permanent installations may include sewer, water, and electrical connections plus anchoring. Foundations may be piers, slabs, perimeter supports, or engineered systems. THOWs installed for permanent occupancy shall comply with local zoning and land-use regulations, and permanent utility installation, frost protection, and site drainage provisions apply.

C2 Model Codes & Consensus Standards

• ICC — IRC, IBC, IPC, IMC, IFGC, IECC
• NFPA — 70 (NEC), 54 (Fuel Gas), 58 (LP Gas), 1192 (Recreational Vehicles)
• AWC — 2024 Span Tables for Joists and Rafters; NDS for Wood Construction
• ASTM — E541 (agencies for manufactured building components)
• ISO/IEC — 17020 (inspection body requirements)

C3–C9 Supplemental References

Referenced sources include RVIA (ANSI A119.5, park model standards), Tiny House Alliance USA and NOAH Certified Inc. materials, DOT and NHTSA transport references, RV propane/fuel-gas technical publications, building-science and moisture-management guidance (Building Science Corporation, U.S. DOE, ENERGY STAR), NEC electrical safety references, and residential HVAC/indoor-air-quality guidance.

C10 Disclaimer

Inclusion of a publication or organization does not imply endorsement, adoption of the entire publication, or mandatory compliance beyond the requirements stated within this standard. Users remain responsible for determining applicable laws, adopted codes, manufacturer instructions, engineering requirements, and jurisdictional regulations for individual projects.

D2–D5 Propane, Moisture, Transport & High-Wind

Propane vapor is heavier than air and may accumulate near floor level; two-stage regulators reduce cylinder pressure to ~11" w.c.; regulator vents commonly face downward. CO detectors (not CO₂) should be replaced per expiration, often 5–7 years. THOWs experience rapid humidity accumulation; ventilation, dehumidification, and air circulation reduce condensation. Transport loading differs from stationary loading — consider sway, axle loading, center of gravity, braking, torsion, and vibration. Roof corners, edges, ridges, hips, valleys, and gable ends see elevated uplift; ring-shank fasteners and continuous load paths help; the AWC WFCM provides recognized high-wind guidance.

D6 Fire Extinguishers

Each THOW should contain at least one listed, accessible portable fire extinguisher mounted within 2 ft of the primary exterior exit door, minimum rating 2A:10BC or equivalent, securely mounted to resist transport vibration and accidental discharge.

D7 Energy Efficiency Commentary

Because THOWs contain small conditioned volumes, excessive insulation thicknesses may yield diminishing returns while reducing valuable interior living space.