Major Provisions of the HUD Code

HUD Wind Zones and Thermal Zones

A HUD home is designed and built to be wind resistant and energy efficient. Wind resistance is provided by metal hurricane straps that connect the roof, walls, and floor together and to the foundation or ground. Homes that will be located in zones with higher winds will have stronger and more robust systems to tie the home to its foundation. For instance, a home located in coastal Louisiana must be more wind-resistant than one in Kentucky.

Similarly, the colder the climate the more insulation and thermal resistance is required for the home envelope. Homes located in Michigan will require higher envelope thermal resistance than homes located in Florida.

The HUD Code specifies wind and thermal resistance requirements based on dividing the U.S. into zones. There are three wind zones and three thermal resistance zones and the division of the country is different for the wind zones compared to the thermal zones. The wind and thermal requirements and their corresponding zones are described in the following sections.

HUD Wind Zones
Each manufactured home must be designed according to the federal HUD Code. The HUD Code stipulate that the home shall be designed and constructed to conform to one of three wind load zones. The higher the number of the Wind Zone, the more stringent are the requirements fo wind-resistant construction. The appropriate Wind Zone used in design is dependent on where the home will be initially installed. Homes designed and constructed to a higher Wind Zone can be installed in a lower Wind Zone (a Wind Zone III home can be installed in a Wind Zone I or II location). However, a Wind Zone I home cannot be installed in either a Wind Zone II or III area.

Wind loads are lateral loads that must be resisted by the home. The home must be capable of transferring these imposed lateral loads to the home’s stabilizing devices without exceeding the allowable stresses and other deflection requirements. Wind Zone I, Wind Zone II and Wind Zone III are identified on the basic Wind Zone Map below. The manufactured home producer designs the home to resist the wind load, which is measured in pounds per square foot. Wind Zone I equates to a 70-mph fastest-mile wind speed; Wind Zone II to a 100-mph fastest-mile wind speed; and Wind Zone III to a 110-mph fastest-mile wind speed. Most of the US is in Wind Zone I except for Gulf and Atlantic coastal areas. Wind Zone III is a small area in south Florida that includes Miami and the Florida Keys plus portions of Louisiana.

HUD Thermal Zones
In addition to the Wind Zones, HUD specifies three Thermal Zones that designate varying levels of thermal resistance for the home envelope. The higher the Thermal Zone number, the more thermal resistance or insulation is required. The Thermal Zones are shown below together with the minimum required Uo value. Uo indicates how much resistance the wall, window, or roof must have to energy flows between the outside and home interior. The lower the Uo value the more thermal resistance the envelope must have. The further north the home will be installed, the lower the Uo value must be to provide adequate thermal resistance for the purpose or reducing energy consumption and cost. In simple terms, a lower Uo value indicates the home envelope has more insulation. Note that a higher number Wind Zone has a lower Uo value.

The Uo value is the overall coefficient of heat transmission of the manufactured home based on the respective thermal zone location and an indoor design temperature of 70 ^oF, and is defined in units of BTU/(hour)(square foot)(^oF). The overall Uo value for the home thermal envelope design must not exceed the values as shown on the above map. The design Uo value for Thermal Zone 1 is 0.116 BTU/hr·ft²·^oF, for Thermal Zone 2 is 0.096 BTU/ hr·ft²·^oF, and for Thermal Zone 3 is 0.079 BTU/ hr·ft²·^oF. Again, the lower the Uo value, the greater the thickness of insulation that is required.

Major HUD Code Requirements

Lighting and Ventilation

Lighting. Each habitable room shall be provided with exterior windows and/or doors having a total glazed area of not less than 8 percent of the gross floor area.

1. Kitchens, bathrooms, toilet compartments, laundry areas, and utility rooms may be providedwith artificial light in place of windows.
2. Rooms and areas may be combined for the purpose of providing the required naturallighting provided that at least one half of the common wall area is open and unobstructed, andthe open area is at least equal to 10 percent of the combined floor area or 25 square feetwhichever is greater.

Whole-house ventilation. Each manufactured home must be provided with whole-house ventilation having a minimum capacity of 0.035 cubic feet per minute (cfm)/ft² of interior floor space or its hourly average equivalent. This ventilation capacity must be in addition to any openable window area. In no case shall the installed ventilation capacity of the system be less than 50 cfm nor more than 90 cfm.

1. The ventilation capacity must be provided by a mechanical system or a combination passive and mechanical system. Mechanical means fan powered and passive refers to ventilation cbyair flow that is caused by natural forces such as the chimney effect in which air rises due to warming. Passive implies a fan is not being used. A combination passive and mechanical system can operate in either mode.
2. The ventilation system or provisions must exchange air directly with the exterior of the home, except that the ventilation system must not draw or expel air from or to the space underneath the home. The ventilation system must not draw or expel air into the floor, wall, or ceiling/roof systems, even if those systems are vented. The ventilation system must be designed to ensure that outside air is distributed to all bedrooms and main living areas. The combined use of undercut doors or transom grills connecting those areas to the room where the mechanical system is located meets this requirement.
3. The ventilation system or a portion of the system is permitted to be integral with the home’s heating or cooling system. The system must be capable of operating independently of the heating or cooling modes. A ventilation system that is integral with the heating or cooling system is to be listed as part of the heating and cooling system or listed as suitable for use with that system.
4. A mechanical ventilation system, or mechanical portion thereof, must be provided with a manual control, and must be permitted to be provided with automatic timers or humidi stats.
5. A whole-house ventilation label must be attached to the whole-house ventilation control,must be permanent, and must state: ‘‘WHOLE-HOUSE VENTILATION.’’

Additional ventilation.

1. At least half of the minimum required glazed area in paragraph (a) above shall be openable directly to the outside of the manufactured home for unobstructed ventilation.
2. Kitchens shall be provided with a mechanical ventilation system that is capable of exhausting 100 cfm to the outside of the home. The exhaust fan shall be located as close as possible to the range or cook top, but in no case farther than 10 feet horizontally from the range or cook top.
3. Each bathroom and separate toilet compartment shall be provided with a mechanical ventilation system capable of exhausting 50 cfm to the outside of the home. A separate toilet compartment may be provided with 1.5 square feet of openable glazed area in place of mechanical ventilation, except in Uo value Zone 3.

Exit Facilities and Exterior Doors.

Number and location of exterior doors. Manufactured homes shall have a minimum of two exterior doors located remote from each other.

1. Required egress doors shall not be located in rooms where a lockable interior door must be used in order to exit.
2. In order for exit doors to be considered remote from each other, they must comply with all of the following:
   1. Both of the required doors must not be in the same room or in group of rooms which are not defined by fixed walls.
   2. Single wide units: Doors may not be less than 12 ft. from each other as measured in any straight line direction regardless of the length of path of travel between doors.
   3. Double wide units: Doors may not be less than 20 ft. from each other as measured in any straight line direction regardless of the length of path of travel between doors.
   4. One of the required exit doors must be accessible from the doorway of each bedroom without traveling more than 35 ft.

Egress Windows and Devices.

1. Every room designed expressly for sleeping purposes, unless it has an exit door, shall have at least one outside window or approved exit device.
2. The bottom of the window opening shall not be more than 36 inches above the floor.
3. Locks, latches, operating handles, tabs, and any other window screen or storm window devices which need to be operated in order to permit exiting, shall not be located in excess of 54 inches from the finished floor.
   (4)Integral rolled-in screens shall not be permitted in an egress window unless the window is of the hinged type.

Room Requirements.

1. Every manufactured home shall have at least one living area with not less than 150 sq. ft. of gross floor area.
2. Rooms designed for sleeping purposes shall have a minimum gross square foot floor area as follows:
   
   1. All bedrooms shall have at least 50 sq. ft. of floor area.
   2. Bedrooms designed for two or more people shall have 70 sq. ft. of floor area plus 50sq. ft. for each person in excess of two.
3. Every room designed for sleeping purposes shall have accessible clothes hanging space witha minimum inside depth of 22 inches and shall be equipped with a rod and shelf.

Toilet Compartments.

Each toilet compartment shall be a minimum of 30 inches in width, except, when the toilet is located adjacent to the short dimension of the tub, the distance from the tub to the center line of the toilet shall not be less than 12 inches. At least 21 inches of clear space shall be provided in front of each toilet.

Hallways.

Hallways shall have a minimum horizontal dimension of 28 inches measured from the interior finished surface to the interior finished surface of the opposite wall. When appliances are installed in a laundry area, the measurement shall be from the front of the appliance to the opposite finished interior surface. When appliances are not installed and a laundry area is provided, the area shall have a minimum clear depth of 27 inches in addition to the 28 inches required for passage. In addition, a notice of the available clearance for washer/dryer units shall be posted in the laundry area. Minor protrusions into the minimum hallway width by doorknobs, trim, smoke alarms or light fixtures are permitted.

Glass and glazed openings.

Windows and sliding glass doors. All windows and sliding glass doors shall meet the requirements of the ‘‘Standard for Windows and Sliding Glass Doors Used in Manufactured Homes’’.

Safety glazing. Glazing in all entrance or exit doors, sliding glass doors, units (fixed or moving sections), unframed glass doors, unbacked mirrored wardrobe doors (i.e., mirrors not secured to a backing capable of being the door itself), shower and bathtub enclosures and surrounds to a height of 6 feet above the bathroom floor level, storm doors or combination doors, and in panels located within 12 inches on either side of exit or entrance doors shall be of a safety glazing material. Safety glazing material is considered to be any glazing material capable of passing the requirements of the governing standards.

Fire Safety and Flame Spread Requirements

Materials are rated with respect to their fire safety by the Flame Spread Index. The Flame Spread Rating is a ranking derived by laboratory standard test methodology of a material’s propensity to burn rapidly and spread flames. The higher the Flame Spread Index the more rapidly that flames will burn across the material surface. In general, the National Fire Protection Association defines three classes of materials depending on their Flame Spread Index:

Smoke alarm requirements.

1. Labeling. Each smoke alarm required must bear a label with evidence of conformance with HUD requirements
2. Required smoke alarm locations. At least one smoke alarm must be installed in each of the following locations:
   1. To protect both the living area and kitchen space. Manufacturers are encouraged to locate the alarm in the living area remote from the kitchen and cooking appliances. A smoke alarm located within 20 feet horizontally of a cooking appliance must incorporate a temporary silencing feature or be of a photoelectric type.
   2. In each room designed for sleeping.
   3. On the ceiling of the upper level near the top or above each stairway, other than abasement stairway in any multistory home. The alarm must be located so that smoke rising in the stairway cannot be prevented from reaching the alarm by an intervening door or obstruction.

Structural design requirements.

General. Each manufactured home shall be designed and constructed as a completely integrated structure capable of sustaining the design load requirements of this standard, and shall be capable of transmitting these loads to stabilizing devices without exceeding the allowable stresses or deflections. Roof framing shall be securely fastened to wall framing, walls to floor, and the floor to the chassis.

Fastening of structural systems.
Roof framing must be securely fastened to wall framing, walls to floor structure, and floor structure to chassis, to secure and maintain continuity between the floor and chassis in order to resist wind overturning, uplift, and sliding, and to provide continuous load paths for these forces to the foundation or anchorage system. The number and type of fasteners used must be capable of transferring all forces between elements being joined.

Walls.
The walls shall be of sufficient strength to withstand the load requirements. The connections between the bearing walls, floor, and roof framework members shall be fabricated in such a manner as to provide support for the material used to enclose the manufactured home and to provide for transfer of all lateral and vertical loads to the floor and chassis.

Floors.

1. Floor assemblies shall be designed in accordance with accepted engineering practice standards to support a minimum uniform live load of 40 lb/ft² plus the dead load of the materials. In addition (but not simultaneously), floors shall be able to support a 200–pound concentrated load on a one-inch diameter disc at the most critical location with a maximum deflection not to exceed one-eighth inch relative to floor framing.
2. Wood, wood fiber or plywood floors or sub floors in kitchens, bathrooms (including toilet compartments), laundry areas, water heater compartments, and any other areas subject to excessive moisture shall be moisture resistant or shall be made moisture resistant by sealingor by an overlay of nonabsorbent material applied with water-resistant adhesive.

Roofs.

1. Roofs shall be of sufficient strength to withstand the load requirements. The connections between roof framework members and bearing walls shall be fabricated in such a manner to provide for the transfer of design vertical and horizontal loads to the bearing walls and to resist uplift forces.
2. Roofing membranes shall be of sufficient rigidity to prevent deflection which would permit ponding of water or separation of seams due to wind, snow, ice, erection or transportation forces.
3. Cutting of roof framework members for passage of electrical, plumbing or mechanical systems shall not be allowed except where substantiated by engineering analysis.
4. All roof penetrations for electrical, plumbing or mechanical systems shall be properly flashed and sealed. In addition, where a metal roof membrane is penetrated, a wood backer shall be installed. The backer plate shall be not less than 5⁄16 inch plywood, with exterior glues, secured to the roof framing system beneath the metal roof.

Windstorm protection.
Each manufactured home shall have provisions for support/anchoring or foundation systems that, when properly designed and installed, will resist overturning and lateral movement (sliding) of the manufactured home as imposed by the respective design loads.

Anchoring Systems.

1. The provisions of this section shall be followed and the support and anchoring systems shall be designed by a Registered Professional Engineer or Architect.
2. The manufacturer of each manufactured home is required to make provision for the support and anchoring systems but is not required to provide the anchoring equipment or stabilizing devices.
3. For anchoring systems, the instructions provided by the Engineer or Architect shall indicate:
   
   1. The minimum anchor capacity required;
   2. That anchors should be certified by a professional engineer, architect, or a nationally recognized testing laboratory as to their resistance;
   3. That ground anchors should be embedded below the frost line and be at least 12 inches above the water table; and
   4. That ground anchors should be installed to their full depth, and stabilizer plates should be installed to provide added resistance to overturning or sliding forces.
4. Anchoring equipment should be certified by a registered professional engineer or architect to resist these specified forces in accordance with testing procedures in ASTM Standard

Thermal Protection

Ceiling vapor retarders.

1. In Thermal Zones 2 and 3, ceilings must have a vapor retarder installed on the living space side of the roof cavity.
2. For manufactured homes designed for Thermal Value Zone 1, the vapor retarder may be omitted.

Exterior wall vapor retarders.

1. Exterior walls must have a vapor retarder installed on the living space side of the wall; or
2. Unventilated wall cavities must have an external covering and/or sheathing that forms the pressure envelope. Formed exterior siding applied in sections with joints not caulked or sealed,are not considered to restrict water vapor transmission; or

Air infiltration.
The opaque envelope shall be designed and constructed to limit air infiltration to the living area of the home. Any design, material, method or combination that accomplishes this goal may be used. The goal of the infiltration control criteria is to reduce heat loss/heat gain due to infiltration as much as possible without impinging on health and comfort and within the limits of reasonable economics.

1. Envelope penetrations. Plumbing, mechanical and electrical penetrations of the pressure envelope, and installations of window and door frames shall be constructed or treated to limit air infiltration. Penetrations of the pressure envelope made by electrical equipment, other than distribution panel boards and cable and conduit penetrations, are exempt from this requirement. Cable penetrations through outlet boxes are considered exempt.
2. Joints between major envelope elements. Joints not designed to limit air infiltration between wall-to-wall, wall-to- ceiling and wall-to-floor connections shall be caulked or otherwise sealed. When walls are constructed to form a pressure envelope on the outside of the wall cavity, they are deemed to meet this requirement.

Plumbing Systems

General requirements.

Any plumbing system installed in a manufactured home shall conform, at least, with the provisions of this subpart.

1. General. The plumbing system shall be of durable material, free from defective workmanship, and so designed and constructed as to give satisfactory service for a reasonable life expectancy.
2. Conservation. Water closets shall be selected and adjusted to use the minimum quantity of water consistent with proper performance and cleaning.
3. Connection to drainage system. All plumbing, fixtures, drains, appurtenances, and appliances designed or used to receive or discharge liquid waste or sewage shall be connected to the manufactured home drainage system in a manner provided by this standard.
4. Workmanship. All design, construction, and workmanship shall be in conformance with accepted engineering practices and shall be of such character as to secure the results sought to be obtained by this standard.
5. Components. Plumbing materials, devices, fixtures, fittings, equipment, appliances,appurtenance, and accessories intended for use in or attached to a manufactured home shall conform to applicable standards.

Water distribution systems.

1. Supply piping. Piping systems shall be sized to provide an adequate quantity of water to each plumbing fixture at a flow rate sufficient to keep the fixture in a clean and sanitary condition without any danger of back flow or siphonage. The manufacturer shall include in his written installation instructions that the manufactured home has been designed for an inlet water pressure of 80 psi, and a statement that when the manufactured home is to be installed in areas where the water pressure exceeds 80 psi, a pressure reducing valve should be installed.
2. Hot water supply. Each manufactured home equipped with a kitchen sink, and bathtub and/or shower shall be provided with a hot water supply system including a listed water heater.

Drainage systems.

1. Each fixture directly connected to the drainage system shall be installed with a water seal trap.
2. The drainage system shall be designed to provide an adequate circulation of air in all piping with no danger of siphonage, aspiration, or forcing of trap seals under conditions of ordinary use.
3. Materials
   
   1. Pipe. Drainage piping shall be standard weight steel, wrought iron, brass, copper tube DWV, listed plastic, cast iron, or other listed or approved materials.
   2. Fittings. Drainage fittings shall be recessed drainage pattern with smooth interior waterways of the same diameter as the piping and shall be of a material conforming to the type of piping used. Drainage fittings shall be designed to provide for a 1⁄4 inch perfoot grade in horizontal piping.

Heating, Cooling, and Fuel Burning Systems

Heating, cooling and fuel burning appliances and systems in manufactured homes shall be free of defects, and shall conform to applicable standards in the following table unless otherwise specified in this standard.

Gas piping systems.

General. The requirements of this section shall govern the installation of all fuel gas piping attached to any manufactured home. The gas piping supply system shall be designed for a pressure not exceeding 14 inch water column (1⁄2 psi) and not less than 7 inch water column (1⁄4 psi). The manufacturer shall indicate in his written installation instructions the design pressure limitations for safe and effective operation of the gas piping system. None of the requirements listed in this section shall apply to the piping supplied as a part of an appliance. All exterior openings around piping, ducts, plenums or vents shall be sealed to resist the entrance of rodents.

Materials. All materials used for the installation, extension, alteration, or repair of any gas piping system shall be new and free from defects or internal obstructions. It shall not be permissible to repair defects in gas piping or fittings. Inferior or defective materials shall be removed and replaced with acceptable material. The system shall be made of materials having a melting point of not less than 1,450 F.

Heat producing appliances.

1. Heat-producing appliances and vents, roof jacks and chimneys necessary for their installation in manufactured homes shall be listed or certified by a nationally recognized testing agency for use in manufactured homes.
2. A manufactured home shall be provided with a comfort heating system.
   
   1. When a manufactured home is manufactured to contain a heating appliance, the heating appliance shall be installed by the manufacturer of the manufactured home in compliance with applicable sections of this subpart.
   2. When a manufactured home is manufactured for field application of an external heating or combination heating/cooling appliance, preparation of the manufactured home for this external application shall comply

Exhaust duct system and provisions for the future installation of a clothes dryer.

All gas and electric clothes dryers shall be exhausted to the outside by a moisture-lint exhaust duct and termination fitting. When the clothes dryer is supplied by the manufacturer, the exhaust duct and termination fittings shall be completely installed by the manufacturer. However, if the exhaust duct system is subject to damage during transportation, it need not be completely installed at the factory when:

1. 1. The exhaust duct system is connected to the clothes dryer, and
   2. A moisture lint exhaust duct system is roughed in and installation instructions are provided.

 

1. A clothes dryer moisture-lint exhaust duct shall not be connected to any other duct, vent or chimney.
2. The exhaust duct shall not terminate beneath the manufactured home.
3. Moisture-lint exhaust ducts shall not be connected with sheet metal screws or other fastening devices which extend into the interior of the duct.
4. Moisture-lint exhaust duct and termination fittings shall be installed in accordance with the appliance manufacturer’s printed instructions.

Appliances, cooling.

Every air conditioning unit or a combination air conditioning and heating unit shall be listed or certified by a nationally recognized testing agency for the application for which the unit is intended and installed in accordance with the terms of its listing.

Circulating air systems.

Supply ducts and any dampers contained therein shall be made from galvanized steel, tin-plated steel, or aluminum. A duct system integral with the structure shall be of durable construction that can be demonstrated to be equally resistant to fire and deterioration.

Electrical Systems

1. The National Electrical Code, and specifically Article 550 of the National Electrical Code(NFPA No. 70–2005), plus the HUD Code address the electrical conductors and equipment installed within or on manufactured homes and the conductors that connect manufactured homes to a supply of electricity.
2. The provisions of the HUD Code apply to manufactured homes intended for connection to a wiring system nominally rated 120/240 volts, 3-wire AC, with grounded neutral.
3. All electrical materials, devices, appliances, fittings and other equipment shall be listed or labeled by a nationally recognized testing agency and shall be connected in an approved manner when in service.
4. Aluminum conductors, aluminum alloy conductors, and aluminum core conductors such as copper clad aluminum; are not acceptable for use in branch circuit wiring in manufactured homes.

Power supply.

1. The power supply to the manufactured home shall be a feeder assembly consisting of not more than one listed 50 ampere manufactured home power supply cords, or a permanently installed circuit. A manufactured home that is factory-equipped with gas or oil-fired central heating equipment and cooking appliances shall be permitted to be provided with a listed manufactured home power-supply cord rated 40 amperes.

Disconnecting means and branch-circuit protective equipment

1. The branch-circuit equipment is permitted to be combined with the disconnecting means as a single assembly. Such a combination is permitted to be designated as a distribution panelboard. If a fused distribution panel board is used, the maximum fuse size of the mains must be plainly marked with lettering at least 1⁄4-inch high and that is visible when fuses are changed.
2. Plug fuses and fuse holders shall be tamper-resistant, Type ‘‘S,’’ enclosed in dead-front fuse panelboards. Electrical distribution panels containing circuit breakers shall also be dead-front type.
3. A single disconnecting means shall be provided in each manufactured home consisting of a circuit breaker, or a switch and fuses and their accessories installed in a readily accessible location near the point of entrance of the supply cord or conductors into the manufactured home. The main circuit breakers or fuses shall be plainly marked ‘‘Main.’’ This equipment shall contain a solder less type of grounding connector or bar for the purposes of grounding with sufficient terminals for all grounding conductors. The neutral bar termination of the grounded circuit conductors shall be insulated.

Grounding.

1. General. Grounding of both electrical and nonelectrical metal parts in a manufactured home shall be through connection to a grounding bus in the manufactured home distribution panelboard. The grounding bus shall be grounded through the green-colored conductor in the supply cord or the feeder wiring to the service ground in the service-entrance equipment located adjacent to the manufactured home location. Neither the frame of the manufactured home nor the frame of any appliance shall be connected to the neutral conductor in the manufactured home.
2. Insulated neutral. The grounded circuit conductor (neutral) shall be insulated from the grounding conductors and from equipment enclosures and other grounded parts. The grounded (neutral) circuit terminals in the distribution panelboard and in ranges, clothes dryers, counter-mounted cooking units, and wall-mounted ovens shall be insulated from the equipment enclosure.