Know the Code



Following a thorough review by elected officials, County authorities and local design and construction professionals, adoption of the 2015 International Construction Codes became official on January 1, 2018. Routt County, along with Steamboat Springs, Oak Creek and Yampa, enacted ordinances adopting the 2015 code series, providing an update to the previously adopted 2009 code series. Typically completed every three years, code updates are essential for keeping pace with the evolution of building science and construction techniques. While most code updates refine previous versions, either for clarity or with a goal of providing further safety measures in the construction of buildings, the updates often react to new construction methods and techniques that have proven worthy of adopting. There are noteworthy changes to the International Residential Code (IRC) and the International Energy Conservation Code (IECC) that Steamboat’s design and construction community should be aware of.

Tiny Houses

Defined as having a size of 400 square feet or less, not including lofts, tiny houses are now recognized as a unique dwelling product requiring a different set of standards for spaces of a much smaller scale. For example, habitable spaces are normally required to have a minimum ceiling height of 7 feet. When following the new Tiny Home code section, a ceiling height of 6’8” is allowable. Stair width and minimum room size are other areas where reduced clearances are acceptable. With the costs for home construction as high as they are in the Yampa Valley, rules that support the construction of significantly smaller dwellings could make building a home more attainable. For the content of the code that covers Tiny Homes, visit Routt County’s website

Energy Efficiency

The most significant updates to the code concern energy efficiency, which is covered by the IECC. The energy code now requires new standards for the thermal envelope of the building, including testing how well it’s been sealed. Architects and builders need to be particularly aware of wall insulation requirements in the 2015 IECC, as the changes require a different assembly than traditionally constructed walls. A continuous layer of insulation (CI) is now required on the outside of the wall framing (following the prescriptive compliance path, see below). The primary benefit of using CI is to provide a thermal break at the wall framing. It eliminates the thermal bridging from a wall stud, a material with very little capacity to insulate. Rigid foam board insulation is a common form of CI. There are also insulated sheathing products, which include both the insulation and sheathing bonded together.  The updated version of the International Residential Code (IRC) recognizes this in Sec. R702.7.1, requiring R-15 for a 2×6 wall and R-10 for a 2×4 wall, when a Class III vapor retarder is used.

Code Compliance Paths

While not new to the code, various compliance paths exist to meet the energy code. These options are more relevant than ever considering the new wall insulation requirements. The most commonly referred to path is called the Prescriptive Path, which stipulates easily identifiable values for building assemblies and components. Specify the assembly values from the code table in the design, and the project has complied with code.

As an alternative to using the prescribed values, the Prescriptive Path can also be met by using a free computer program offered by the USDOE called ResCheck2, which calculates whether the building assembly as a whole (total UA) meet the standard for compliance. Using ResCheck provides some flexibility since the program allows for trade-offs in the components that make up the thermal envelope. For example, if the window specified doesn’t precisely meet the prescribed value, wall insulation values could make up the difference. ResCheck also provides information related to heating and cooling needed for permitting; however, it is not a building energy performance modeling tool.  It is used only for measuring the thermal values of the building envelope.

The Simulated Performance Path requires a third party energy rater to quantify the annual energy cost. If the annual energy costs are found to be equal to or better than a reference home, the design has complied with code.  In this case, the reference home is another version of the same design that meets code by the Prescriptive Path. Using a Residential Energy Services Network (ResNet) certified rater to conduct a Home Energy Rating System (HERS) rating is the most commonly accepted method for evaluating energy cost performance required by this path. As an added benefit, the HERS score serves as a nationally accepted metric for building efficiency. It should be noted a HERS score is not required for compliance with this path, only the comparison of the annual energy cost measured by the testing procedure. The performance modeling includes a “from plans” simulation submitted at construction permitting showing compliance. Choosing the Simulated Performance Path still requires similar assemblies and construction techniques to be employed, but it allows for greater flexibility in how the building components are assembled. It reflects a holistic approach to the performance of the building because the modeling measures all assemblies and components working together, including building systems such as lighting, HVAC and domestic hot water. 

Another performance path that is new to the energy code is called the Energy Rating Index Compliance Alternative. Like the Simulated Performance Path, this compliance alternative requires a HERS performance test to be completed by a third party RESNET rater; however, in this case compliance is based entirely on the HERS score. This path is the most challenging to achieve, requiring a score of 53 (representing an efficiency of 47% better than the Prescriptive Path) for this climate zone, but may serve as a goal for a project team looking to make significant gains in energy performance similar to above-code green building rating systems. It is likely that in order to meet a rating of 53, renewable energy would have to be employed on site as part of the design.

The importance of air sealing

Another notable update to the code is the requirement for a blower door test. Conducted at end of construction, when all trim and finishes are in place, this test is a measure of how well sealed the building is. By creating negative pressure with a large fan used to pull air out of the home, a measurement of air leakage can be produced.  It effectively measures how many air changes per hour (ACH) will occur as a result of natural air infiltration. The lower the ACH, the better sealed the building.  The updated code allows for no more than 3 air changes per hour, and the test must be conducted by a third party. There are at least four energy consultants in Steamboat that provide this service for approximately $250.  Incidentally, Routt County has made the test optional for projects occurring outside the City limits while projects within the limits of Steamboat Springs are required to follow the code as written. 

The importance of mechanical ventilation

As greater attention is paid to air sealing and more robust thermal envelopes, we benefit from homes that are increasingly efficient and more comfortable to live in. Ambient indoor air temperatures are more consistent, and less is required from the HVAC systems. With better sealed homes, whole house mechanical ventilation becomes critical to ensure stale air that potentially contains toxins is exhausted from the home. While the code update requires whole house mechanical ventilation, some of the options for compliance fail to achieve the same level of performance established by better sealed homes. For example, one option for compliance is an exhaust-only system. Because there is no requirement for make-up air in this option, the home is consistently in a state of slight negative pressure instead of being balanced by intentional make-up air.

Architects and contractors should be mindful of the approach used to achieve good indoor air quality so that the building performs as well in this area as it does in others. Providing a balanced mechanical ventilation system, accomplished with the installation of a heat recover ventilator (HRV) or energy recovery ventilator (ERV), is the appropriate method for meeting the ventilation requirements. In addition to providing a continuous circulation of air, removing stale indoor air for fresh outdoor air, it occurs in a controlled fashion. The system exchanges the latent temperature exhausting from the house to the incoming fresh air. In the case of the ERV, it also exchanges the humidity.

Updates to the building code are essential in the evolution of the built environment and ensuring health, safety and welfare are maintained for the structures in which we spend our days. The recent code adoption will guide Routt County with various updates in residential construction. Local professionals should be mindful of the changes represented in the code update, while embracing the natural evolution of the industry.

1See “BSI-026: They All Laughed….” by Joe Lstiburek about vapor retarders written for Steamboat design and construction industry:


Additional code changes to be aware of

1.       Duct Insulation: R8 when 3” diameter or greater and R6 when less than 3” diameter

2.       Duct Testing: Mandatory when ducts are run in unconditioned space

3.       Mechanical Controls on Boilers and Snow Melt Systems

4.       Mechanical Piping Insulation Mandatory: R3 for piping carrying fluids in excess of 105 or less than 55

5.      Hot Water Pipe Insulation: R3

6.   Lighting: 75% of permanently installed lighting fixtures shall be high-efficacy lamps

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