Manufactured Home Design

Like the traditional site-built homes, new manufactured homes can be designed for energy efficiency and use renewable energy systems. You can also remodel or retrofit an older manufactured home to improve its energy efficiency and/or use renewable energy.

Manufactured homes are those built entirely in a factory. They are then transported to a building site and installed. Manufactured homes include:

  • Modular Homes

    Modules are transported to the site and installed.

  • Panelized Homes

    Panels—a whole wall with windows, doors, wiring and outside siding—are transported to the site and assembled.

  • Pre-Cut Homes

    Building materials are factory-cut to design specifications, transported to the site, and then assembled. Pre-cut homes include kit, dome, and log homes.

  • Mobile Homes

  • This is the term used for factory-built homes produced prior to when the HUD Code went into effect.

Here you can learn more about the following:

  • Manufactured Home Requirements (Dept. of Housing and Urban Development)

  • Requirements, including energy efficiency standards, new manufactured homes must meet.

  • Suggested energy efficiency improvements for manufactured homes, especially for those built prior to the 1976 HUD Code.

  • Energy-efficient retrofiting

  • Considerations for using renewable energy systems to provide heating, cooling, and electricity for manufactured homes.

  • Renewable Energy in manufactures Homes

Manufactured Home HUD Code Requirements

Unlike all other forms of factory-built housing, which must meet state and local codes, manufactured homes must conform to the U.S. Department of Housing and Urban Development (HUD) 1976 Federal Manufactured Home Construction and Safety Standards Acts, commonly known as the "HUD Code."

The Energy Policy Act of 1992 required HUD to revise its energy efficiency standards. New rules for manufacturers took effect in October 1994. Manufactured homes built after that date must have the following:

  • Higher insulation levels (see table below)
  • Double-Pane Windows in all zones
  • Ventilation fans in kitchens and bathrooms
  • A whole-house ventilation rate of 0.10 air changes per hour. When added to the average natural ventilation rate for new manufactured homes of 0.25 air changes per hour, this meets the 0.35 air changes per hour rate recommended by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) for residences.

In addition, the HUD climate zone maps were also changed. Previously, only homes manufactured for Alaska were required to meet the strict Zone 3 standards. The new map places most of the Northern United States into Zone 3 as well. Only the states bordering the Gulf of Mexico and South Carolina remain in Zone 1.

Old versus New Insulation Standards
  1976 Standards 1994 Standards
  Single-Wide Double-Wide Single-Wide Double-Wide
Zone # 1 2 3 1 2 3 1 2 3 1 2 3
Ceiling R-11 R-11 R-19 R-11 R-11 R-19 R-14 R-19 R-19 R-14 R-22 R-22
Walls R-7 R-7 R-13 R-7 R-11 R-11 R-11 R-13 R-19 R-11 R-13 R-19
Floor R-7 R-11 R-14 R-7 R-11 R-19 R-11 R-19 R-19 R-14 R-19 R-22

While the HUD minimum standards are helping to reduce energy costs for manufactured home buyers, still there is room for improvement. Several manufacturers are building homes that exceed the minimum HUD insulation standards, and that have advanced, energy-efficient ventilation systems to maintain healthy indoor air quality even with very tight construction. Such homes use 30–50% less energy for space heating than homes built to the minimum HUD standards. Several manufacturers are partners in the ENERGY STAR and Building America Programs.

Manufactured Home Energy-Efficient Retrofit Measures

There are many differences between manufactured (mobile) homes built before the HUD Code took effect in 1976 and those built afterward. Many manufactured homes made before 1976 are likely to have the following:

  • Air leakage through walls
  • Little or no insulation
  • No vapor retarder in the roof cavity
  • Uninsulated heating system ducts
  • Uninsulated doors.

If you have a pre-1976 manufactured (mobile) home, you may want to make the following energy efficiency improvements to reduce heat loss:

  • Install energy-efficient windows and doors
  • Add insulation to the belly
  • Make general repairs (caulking, ducts, etc.)
  • Add insulation to your walls
  • Install insulated skirting
  • Install a belly wrap
  • Add insulation to your roof or install a roof cap.

Instead of rolling back the roof, many installers prefer to use roof caps for insulating, in spite of their inferior performance. Roof caps come in kit form and consist of insulation boards, usually of dense fiberglass, with a synthetic rubber or metal covering. Roof caps can insulate the roof to R-19 without disturbing the existing roof. If all leaks in the old roof covering are sealed, the old roof acts as a vapor retarder, eliminating moisture problems and the need for ventilations.

Also, blowing loose-fill insulation into an existing manufactured home is difficult because of the narrowness of the wall and roof cavities. Pre-1976 homes often had only 2" × 2" studs (5.08 cm × 5.08 cm) (new manufactured houses are required to have at least 2" × 4" [5.08 cm × 10.16 cm]). Trusses also hinder adding more roof insulation. Rolling back the roof to add insulation can lead to realignment problems and leaks. Furthermore, if the rollback method is used, adding some type of mechanical ventilation system to alleviate moisture condensation problems in the roof cavity may be necessary.

The above energy efficiency measures are based on experiments conducted on pre-1976 manufactured homes by the National Renewable Energy Laboratory (NREL) from 1988–1991. A survey of 36 mobile homes by the Colorado Division of Housing found that using these NREL-developed retrofit measures resulted in a 31% reduction in heating fuel usage.

To improve your home's energy efficiency, you should also consider the following:

  • Caulking and weather-stripping windows and doors, especially if you can't replace them with more energy-efficient ones

  • Air Sealing any openings around plumbing fixtures and ducts

  • Using energy-efficient lighting and appliances

Renewable Energy Use in Manufactured Homes

You can use renewable energy to provide electricity, heating, and cooling for your manufactured home. Renewable energy systems not only reduce energy costs, but they also help the environment.

You might consider the following:

    *Geothermal heat pump

      A geothermal heat pump (GHP) can provide a manufactured home with both space heating and cooling. GHPs are most cost effective to install at the same time a manufactured home is installed. The systems can’t be moved, so GHPs only work for permanently sited manufactured homes.

*Passive solar design

      Adding a sunspace can help heat your manufactured home. Site orientation, landscaping, and shading devices are other important elements to consider for reducing energy consumption.

*Solar water heating system

      Solar water heating for manufactured homes is much more limited than for site-built houses. The lightweight construction of some manufactured homes limits roof support for heavy solar collectors. However, you can use lightweight roof-mounted air collectors for water heating, or you can install the heavier liquid-type solar collectors on the ground. Consequently, these systems are best suited for manufactured homes that are seldom moved.

*Small solar electric system

      Unlike solar water heating systems, solar electric or photovoltaic (PV) systems are light and can be installed on the roof of a manufactured home. Actually, in 1994, one manufacturer began to build PV-integrated modular homes.

*Small wind electric system

      If your manufactured home is or will be located in a rural area on at least one acre of land, you can use a small wind turbine to generate electricity.

*Microhydropower system

      If your manufactured home is or will be located where you have access to flowing water, you might be able to use a microhydropower system to generate electricity. While you can move a microhydropower system, you can't take the hydropower resource with you. Therefore, a microhydropower system is best suited for permanently sited manufactured homes.