Making Sense 
of the 
Model Energy Code

Stephen Turchen is a mechanical engineer in the Office of Codes and Standards at the U.S. Department of Energy, and Craig Conner is senior research scientist in the Building Energy and Standards Program at Pacific Northwest National Laboratories.

Figure 1. Locations using the model energy code.

Whether a state has adopted it or not, the MEC applies to houses financed through the Federal Housing Administration (FHA), the Department of Veterans Affairs (VA), and the Rural Economic and Community Development (RECD, formerly Farmers' Home Administration). Loans received from or guaranteed by these agencies require that the financed house comply with the MEC. In a speculative housing development, some builders may choose to build all homes to at least MEC levels to preserve the option of getting financing from any of these sources.

Since the energy crisis of the 1970s, many states have developed their own energy codes (examples include New York, Washington, Oregon, California, and Florida). Because the MEC was referenced in both the National Affordable Housing Act of 1990 and the Energy Policy Act of 1992, more and more states have begun using the code as a reference, or adopting it outright. Reasons vary:

• Some states and local jurisdictions have found maintenance and support of their own code burdensome.
• Some are attracted to the support materials and training available for the MEC (see MEC Compliance Materials).
• In some cases, the organizations that supported the existing code are being eliminated or downsized, which may lead to the use of a nationally supported code.
• The Energy Policy Act of 1992 requires states to consider updating their code if it does not meet or exceed the MEC.
• Many home builders like the idea of meeting the residential energy requirements for an FHA, VA, or RECD loan at the same time as they meet their state or local energy code. Most builders dislike having to meet two different energy codes to get these loans and their local building permit.

The MEC allows for insulation tradeoffs between walls, ceilings, and floors.

The good news for builders is that the MEC can also be used as an effective marketing tool. Energy efficiency is one of the desirable features on home buyers' want lists. To the extent that a new home competes with the resale market of existing homes, homes built to the MEC are usually more energy-efficient. Builders can market MEC homes by pointing out anticipated savings on utility bills and increased comfort, or by citing MEC compliance as an indicator of quality. If the new home is financed via an energy-efficient mortgage, the buyer can qualify for a larger loan. This can allow the builder to include amenities in the home, such as upgraded cabinets, that the buyer could not have afforded otherwise.
 
 

The MEC's major focus is on building envelope insulation, including the windows. The MEC requires insulation on ceilings, walls (including basement walls), and floors, and around slabs. The amount of insulation required varies with the climate-the more severe the climate, the more insulation is required. Window energy efficiency requirements also increase with severity of climate. A Climate-Specific Code shows some sample insulation and window levels that meet the MEC requirements.

A whole-building energy analysis can be used to show energy use equal to that of an MEC-compliant home; however, this approach is complex and is seldom used. Before trying such an approach, builders should check with their local building department to be sure that it will be accepted.

In addition to the MEC insulation and window requirements, there are basic criteria that must be met regardless of which envelope compliance approach is used (see Figure 2). These include:

• Sealing the building envelope to restrict air leakage (caulking, sealing, and weatherstripping at all penetrations and joints).
• Installing vapor retarders in most climates.
• Identifying materials used for compliance (such as insulation R-values) on plans, specifications, and/or directly on materials in the residence.
• Installing temperature controls (separate adjustable controls for each HVAC system in single-family homes and for each multifamily dwelling unit).
• Insulating and sealing ducts in unconditioned spaces.
• Insulating pipes for hydronic heating and circulating hot water systems.
• Installing separate electric meters for each unit in a multifamily dwelling.
• Installing heater switches, covers, and time clocks for swimming pools.

Figure 2. In addition to insulation levels and window types, the MEC requires the measures shown above.

Who needs to comply? The MEC requirements apply only to new construction and additions to existing buildings. In these cases, builders should demonstrate compliance with the MEC if it has been adopted by their state or local jurisdiction. Builders also need to comply with the MEC if they want their homes to qualify for mortgages from the FHA, the VA, or the RECD.

What's the easiest way to comply with the MEC? Some builders don't have the time or the desire to consider insulation and window trade-offs. Using the compliance materials, they can choose from a list of insulation and window levels (referred to as prescriptive packages or options). Some compliance materials offer a simple table of prescriptive packages for the climate zone (see Figure 3). Users can choose a package of insulation and window requirements from the table. Each package specifies insulation levels, glazing areas, glazing U-values, and sometimes heating and cooling equipment efficiency. The builder must meet or exceed all the requirements it lists to achieve compliance. Few calculations are required.

What about trade-offs? The prescriptive requirements may not be quite appropriate for a particular project, or it may be cheaper to do it another way. In this case, builders can demonstrate compliance by using the trade-off approach. Users can trade off insulation and window efficiency levels in different parts of the building. They can trade off ceiling, wall, floor, basement wall, slab-edge, and crawlspace wall insulation; glazing and door areas; and glazing and door U-values.

Figure 3. MECcheck prescriptive package approach.

The local building department may specify a methodology for demonstrating compliance using a trade-off method. Several organizations, such as the U.S. Department of Energy (DOE) and the North American Insulation Manufacturers Association (NAIMA), have developed compliance materials that can be used to do trade-off calculations.

Documentation. The MEC requires that materials used for compliance (such as insulation) be noted on the plans, specifications, or other attached compliance documentation. The local building official may have a required form for submission. The MECcheck materials and NAIMA's Thermal Compliance Guide both include forms for this use.

The building department may inspect to verify the energy-conserving features. While numbers and types of inspections vary widely from jurisdiction to jurisdiction, knowledgeable departments try to incorporate energy inspections into their normal regime. The following list gives a sampling of features for which the inspector may check:

• Wall, ceiling, floor, slab-edge, and basement wall insulation are properly installed and meet required R-values shown on plans.
• Glazing and door U-values meet requirements shown on plans.
• Glazing area is as shown on plans.
• Penetrations and joints are caulked, sealed, and weatherstripped.
• Duct insulation is installed and meets required R-values shown on plans.
• Ducts are sealed.
• Vapor retarder is installed (where applicable).
• HVAC and water heater equipment maintenance information is left with the home.

Ask the local building department for additional information about its inspections.

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