Blog Post

Mobile homes move toward efficiency

August 3, 2016

Do you know which government in the United States is the biggest laggard on energy codes for homes? The federal government. But that’s about to change.

Manufactured homes and the “HUD Code”

Although building codes are mostly set by states, the federal government sets codes for manufactured homes (sometimes called mobile homes) because the factory does not always know where a home will end up. Manufacturers shipped 70,519 homes in 2015, more than the number of single-family homes built in any state except Texas.

Texas and the other states that built the most houses (Florida, California, North Carolina, Georgia, and South Carolina) all have energy codes as good as or better than the 2009 International Energy Conservation Code (IECC), the model code for “stick-built” homes. Unfortunately, the energy provisions of the “HUD Code” (set by the Department of Housing and Urban Development) that governs manufactured housing have not been changed significantly since 1994. Since then the IECC was created and has been updated five times.

So even though manufactured homes are relatively small, the owners pay a lot in energy bills, a national average of $1,800 per year in 2009. Although this is a little less than the average bill for single-family homes, the average energy cost per square foot is more than twice as high. And most of the people who pay the bills are low-income residents. The median income of families in manufactured homes is about $30,000. Many of them spend more on their energy bills than on home loans.

The new standard is a big saver

In 2007, Congress got fed up and directed the Department of Energy to set energy standards for manufactured homes based on the most recent IECC. The 2011 deadline came and went without even a draft. In 2014 DOE convened stakeholders for a negotiated rulemaking, and in October 2014 we (I was on the committee) successfully came to agreement on the key terms. A year later DOE submitted the proposed standard for Office of Management and Budget Review, and in June, after more than eight years, DOE finally issued the draft. The draft is open for comment through August 16.

The standard will make a real difference for homeowners and rural electric grids. DOE estimates the typical manufactured home will save 27% of energy use compared to a home that meets the current HUD Code. Average lifetime savings for homeowners are estimated at almost $4,000 net present value. Cumulative national savings include 2.3 quadrillion Btu of energy (equivalent to the energy use in one year of all homes in New York and Florida), $3-11 billion customer benefits (depending on discount rate), and 160 million metric tons of carbon dioxide.

In developing the draft, we started from the 2015 IECC but made many changes. Here are a few. We reduced the number of climate regions from eight to four, divided mostly along state lines, to make implementation easier. We replaced the performance path with an overall building shell heat transfer (U-factor) requirement, the metric currently used in the HUD Code (and we left out the new Energy Rating Index, which the manufacturers did not plan to use). We replaced the air leakage standard with construction quality requirements because it is hard to test a two-section home until it is assembled in the field. We adjusted for the lack of room to add roof insulation and still be able to truck the homes. And we eased up on required efficiency levels in the Southeast because manufacturers were especially concerned about the impact of the first cost on their low-income buyers there. But the standard would still save 28% compared to the HUD Code in that region.

Moving forward

Perhaps most importantly, the committee’s scope did not include implementation or enforcement, and DOE still needs to work out how to ensure manufacturers meet the new code without undue burden or conflicts with HUD’s enforcement of health and safety requirements. There also are more energy savings we should achieve in manufactured homes through voluntary programs or future measures, in part because we did not touch on appliances or heating or cooling equipment.

But the proposed standard would greatly benefit homeowners who need the help. We hope DOE will complete the standard and set a better example for states adopting codes without further delay.

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