Owners, buyers and installers keep running into the same federal numbers: how wide a door has to be, how far the frame must sit above the ground, how hot the bath water may get. They are all in the HUD Code, but spread across two long federal regulations written for manufacturers, not homeowners.
This page puts the figures people actually ask about in one place. Every number links to the exact section of the regulation it comes from, so you can check it yourself, and to the guide on this site that explains what it means in practice.
Two parts of the federal rules are covered. 24 CFR 3280, the Manufactured Home Construction and Safety Standards, governs how the home is built at the factory. 24 CFR 3285, the Model Manufactured Home Installation Standards, governs how it is set up on site. The construction standard applies to homes built from June 15, 1976 onward. States can add their own rules, especially for installation, and many do.
Doors and exits
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Clear opening, every exterior swinging door | 28 × 74 in (seals or stops may take up to 1 in) | 3280.105(b)(2) | Exterior doors |
| Clear opening, at least one egress door (edition in force since Sept. 15, 2025) | 32 × 74 in, no reduction | 3280.105(b)(2) | Exterior doors |
| Clear opening, exterior sliding glass door | 28 × 72 in | 3280.105(b)(2) | — |
| Number of exterior doors | At least 2, remote from each other | 3280.105(a) | — |
| Distance between the two required doors | ≥ 12 ft (single-wide), ≥ 20 ft (double-wide), center to center | 3280.105(a)(2) | — |
| Travel from a bedroom door to an exit door | ≤ 35 ft | 3280.105(a)(2)(iv) | — |
| Interior privacy locks | Emergency release on the outside | 3280.108(b) | Interior doors |
Labels and paperwork
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| HUD certification label (tag) | 1 per transportable section, about 2 × 4 in | 3280.11(a)–(b) | HUD tag |
| Where the label goes | Taillight end, about 1 ft up and 1 ft in from the road side | 3280.11(d) | HUD tag |
| Data plate | Near the main electrical panel or another accessible, visible spot | 3280.5 | Data plate |
| What the data plate lists | Plant, serial, model, date, label numbers, appliances, roof and wind zones | 3280.5(a)–(i) | Data plate |
Fire safety: interior finishes
A flame spread rating measures how fast fire travels across a surface. Lower is safer.
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Walls and partitions | Flame spread ≤ 200 | 3280.203(b)(1) | Painting walls |
| Ceilings | Flame spread ≤ 75 | 3280.203(b)(2) | — |
| Walls and ceiling around a furnace or water heater | Flame spread ≤ 25 | 3280.203(b)(3) | Water heaters |
| Surfaces next to the cooking range | Flame spread ≤ 50 (backsplashes up to 6 in exempt) | 3280.203(b)(4) | — |
| Plastic tubs, shower units and doors | Flame spread ≤ 200 | 3280.203(b)(6) | Bathtubs |
Structure: floors, roofs and framing
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Floor live load | 40 lb/ft², plus 200 lb on a 1-in disc with ≤ ⅛ in deflection | 3280.305(g)(1) | Soft floors |
| Floor deflection under design live load | ≤ span / 240 | 3280.305(d)(1) | Tile |
| Roof and ceiling deflection | ≤ span / 180 | 3280.305(d)(1) | Roof types |
| Roof design live load | North 40 psf · Middle 30 psf · South 20 psf | 3280.305(c)(3) | Roof types |
| Notch at the end of a joist | ≤ ¼ of joist depth | 3280.305 | Soft floors |
| Notch in the top or bottom of a joist | ≤ ⅙ of depth, never in the middle third of the span | 3280.305 | Soft floors |
| Hole bored through a joist | ≤ ⅓ of depth, ≥ 2 in from top and bottom | 3280.305 | Soft floors |
Plumbing
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Toilet drain connection | ≥ 3 in inside diameter, flange fastened to the floor | 3280.610(d)(1) | Toilets |
| Drain outlet for the whole home | Only 1, ≥ 3 in inside diameter | 3280.610(c) | Disposals |
| Clearance around the drain outlet | ≥ 3 in all round, 18 in unobstructed in front | 3280.610(c)(2) | — |
| Fixture drain sizes | 1¼ in (one lavatory) · 1½ in (2–3 fixtures) · 2 in (4+ vented) · 3 in (toilets) | 3280.610(e) | Disposals |
| Slope of horizontal drain pipe | ≥ ¼ in per ft (⅛ in with a full-size cleanout) | 3280.610(h) | — |
| Shower wall height (non-absorbent finish) | ≥ 6 ft above the bathroom floor | 3280.607(b)(3) | Shower surrounds |
| Shower receptor | Sides ≥ 1 in above threshold · depth 2–9 in · floor slope ¼–½ in per ft | 3280.607(b)(3) | Shower surrounds |
| Hot water to bathtubs | ≤ 120 °F (ASSE 1070 limiting device) | 3280.607 | Bathtubs |
| Shower and tub-shower valves | Pressure-balance or thermostatic (ASSE 1016), stops ≤ 120 °F | 3280.607 | Faucets |
| Plumbing vents through the roof | ≥ 2 in above the roof, ≥ 3 ft from air intakes | 3280.611 | — |
Gas, heating and water heaters
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Gas shutoff valve at an appliance | Within 6 ft of a cooking appliance, 3 ft of any other | 3280.705 | Furnace not igniting |
| Fuel-burning appliances (except ranges, ovens, dryers and a few others) | Combustion fully separated from the air inside the home | 3280.709 | HUD-approved water heaters |
| Tank water heaters | Corrosion-resistant drip pan draining outside or to a drain | 3280.709(h) | Water heaters |
| Supply air ducts | Insulation ≥ R-4 (unless inside R-4 floor or R-6 ceiling insulation) | 3280.715(a)(6) | — |
| Crossover ducts exposed to outside air | Insulation ≥ R-8, vapor retarder ≤ 1 perm | 3280.715(a)(7) | Crossover ducts |
| Attic or roof cavity ventilation | ≥ 1/300 of the cavity floor area (≥ 50% high, ≥ 40% low) | 3280.504(d)(1) | — |
Installation on site (24 CFR 3285)
| Requirement | The number | 24 CFR | Guide |
|---|---|---|---|
| Clearance under the frame | ≥ 12 in from the lowest main frame member to the grade | 3285.305 | Releveling |
| Shims on a pier | In pairs, driven tight, ≤ 1 in of height | 3285.304 | Releveling |
| Pier lean, top to bottom | ≤ ½ in (pier under 36 in) · ≤ 1 in (36–67 in) · over 67 in engineer-designed | 3285.306 | Releveling |
| Grade away from the home | ≥ ½ in per ft for the first 10 ft | 3285.203(c) | Gutters |
| Ground vapor retarder (skirted homes) | 6-mil polyethylene over the whole area, 12-in overlaps | 3285.204 | Vapor barriers |
| Crawlspace vents | 1 ft² per 150 ft² of floor · 1 per 1,500 ft² with a vapor retarder | 3285.505(a) | Vapor barriers |
| Ground anchor rating | Working load ≥ 3,150 lb, ultimate ≥ 4,725 lb | 3285.402 | Tie-downs |
What this page does not cover
State rules. Installation, titling, taxes and park tenancy are largely state law, and several states set stricter installation requirements than 24 CFR 3285. Your state agency is listed in HUD’s directory of state administrative agencies.
Homes built before June 15, 1976. They predate the HUD Code, and none of these numbers is guaranteed to apply.
Your home’s own manual. The installation instructions for your specific home can be stricter than the federal minimum, and where they are, they govern.
Checked against the eCFR edition current through October 20, 2026. Last updated: October 22, 2026. If you find a figure that has changed, tell us and we will correct it.
About the author
I’m Sergio Cobos Juan, and I research and write every guide on Mobile Home Handbook. Each one is built from primary sources — the federal HUD Code (24 CFR 3280 and 3285), state agency documents and manufacturer manuals — and lists them at the end. I’m not a contractor or installer: for gas, electrical, structural or anchoring work, hire a licensed professional.