Nevada - Overview of the Model Energy Code

Overview of the Model Energy Code

What are the major requirements of the Model Energy Code?

Ducts
Leakage from ducts is the biggest source of energy loss in homes and has been specifically targeted in the 1995 version of MEC. Mastic (with fiberglass mesh) is now required as a sealant. Duct tape is not permitted by the standard as a sealant on any ducts. All supply and return ducts in unconditioned spaces must be sealed and insulated.

Air-sealing
Air infiltration through cracks in the envelope is a significant source of energy loss. The MEC has specific provisions for caulking, gasketing, and sealing penetration in the home’s envelope.

Insulation
The MEC sets minimum insulation levels for insulation in the ceilings, walls and floors. Trade-offs are allowed between insulation, windows, and the heating and cooling system.

Windows
The MEC sets U-values for windows and encourages that builders use the tested values assigned by the National Fenestration Ratings Council. MEC includes, however, default tables for windows that are not tested.

Load calculations
The MEC requires that heating and cooling designs loads be calculated using ACCA’s Manual J method or equivalent.

How does a builder show compliance?

The MEC provides for four alternative paths to demonstrate that a home’s design meets the minimum energy efficiency requirements:

Prescriptive Method
The prescriptive method offers set efficiency levels for the various components of the home. The component energy values are based on the climate zone where the home is being built. Some envelope trade-offs are permitted but require calculations on the worksheets provided in the MEC.

Component Performance
Similar to the prescriptive method but allows more trade-offs between components and requires more calculations.

System Analysis
Where builders want additional component trade off credit for use of alternative building materials, such as thermal mass systems or use of renewable energy sources, they can perform an annual energy use analysis to verify that a home designed to comply under this method will not exceed the energy consumption of a home designed in accordance with component performance method.

MECcheck
MECcheck is a software program designed by staff of the Pacific Northwest Laboratories’ Building Standards and Guidelines Program under contract to the U.S. Department of Energy. This program is used to determine whether a home’s design meets the MEC. A builder enters the design elements such as the home area and insulation levels. The software then calculates the energy loss for each component and automatically indicates whether the design package meets the MEC. MECcheck prints out forms showing the assumptions made, other requirements such as duct and air sealing the builder must complete, and the proposed R-values for each component.

REM/Rate
Is a national home energy rating software program designed to meet the national home energy rating technical specifications developed by the U.S. Department of Energy. The software program is used by nationally accredited home energy rating systems such as Energy Rated Homes of Nevada. The program performs the same design analysis and MEC verification process as MECcheck but also produces a home energy rating which allows the builder to receive market value for meeting or exceeding MEC and the buyer of the home to receive preferred mortgage financing.