By Robert Nani
The 2015 IECC offers three methods for building envelope and energy code compliance: The prescriptive requirements, the performance method, and the energy rating index method.
The prescriptive requirements are the code minimums that are documented in the building code. These are the specific requirements, broken down by climate zone. When you install a specific R-Value or U-Value, like putting R-20 in a wall in Climate Zone 5, you are simply meeting the prescriptive code requirement.
Essentially, you can meet code by following the black and white letter of the code and using the minimum values specified by the code. This is the prescriptive method.
The performance method allows you to use simulated energy performance to show that the proposed design, the actual design that you are building, has an annual energy cost that is less than or equal to the annual energy cost of the standard reference design, or the 2015 prescriptive minimum. The most common way to document performance-based compliance is with the use of energy analysis software.
Finally, the Energy Rating Index, or ERI, is a calculated number on an index scale of 0 to 100, which compares the proposed design to an ERI reference building built to the minimum requirements of the 2006 International Energy Conservation Code.
The Energy Rating Index requirement ranges from 51 to 55, which means that the proposed design must outperform the ERI reference building by 45 to 49 percent, depending on climate zone.
The first compliance method, the prescriptive path, is the method that is most commonly used as a default by builders —there is no calculation, no analysis, no computer software required, all they have to do is follow a checklist; it is easy.
The prescriptive path means following the specific written requirements of the code, such as installing insulation to meet the R-value requirements of IRC Table N1102.1.2 (IECC Table R402.1.2) or the U-factor requirements of Table N1102.1.4 (IECC Table 402.1.4) displayed respectively on the opposite page.
For example, if you are in Dallas, TX, that is Climate Zone 3, and your prescriptive insulation requirements are:
To meet the prescriptive requirements, the insulation values installed in these locations have to be equal to or better than these minimum R-values or these maximum U-Factors. In the case of R-value, that means an equal or greater value and in the case of U-factor, that means an equal or lesser value.
Now, the second building envelope compliance method, one that is often overlooked, is the performance path from the 2015 IRC Section 1105.
As mentioned before, the key requirement for the performance path is that your building, the proposed design, must be shown to have an annual energy cost that is less than or equal to the annual energy cost of the standard reference design building, which is a building that meets the minimum prescriptive code requirements
So, how is this determined, you ask?
This type of energy performance calculation is typically conducted using software, such as:
- Elite RHVAC
- Wrightsoft Right-J8
- Florida Solar Energy Center’s EnergyGauge
In accordance with the building code, these software systems must produce a compliance report showing the proposed design outperforms the standard reference design.
Think about it this way – when your building, the proposed design, let’t call it Building A, is analyzed for annual energy consumption, the compliance software must show that it will use less energy than Building B, the reference design, built to the minimum prescriptive code requirements.
Why would this matter? How does this benefit you?
Well, you probably know that spray foam works exceptionally well, right. And, you may have wondered why the traditional code does not give you “credit” for the benefits of spray foam. Well, the performance-based code compliance path will. Using energy code compliance software, you can get credit for air-tightness of the building envelope, moving ductwork into conditioned space, having zero duct losses to the exterior, and other benefits. All of this adds up to improved performance that can be documented and proven for code compliance by using energy performance analysis software.
And, the final compliance method, a new compliance method in the 2015 IRC, is the Energy Rating Index.
As mentioned earlier, ERI is a calculated number, on a linear index scale, constructed with the ERI reference design having a value of 100 and a residential building that uses no net purchased energy having an index value of 0.
A one percent change in the total energy use of the rated design relative to the total energy use of the ERI reference design shall be represented by a change of 1 on the index scale. So, an ERI of 55 means that the proposed design outperforms the ERI reference design by 45 percent.
For the purpose of the ERI, the code identifies that the ERI reference design shall meet the minimum requirements of the 2006 International Energy Conservation Code prescriptive requirements.
To qualify for ERI compliance, the maximum energy rating index, allowable by climate zone, is identified in table 1106.4:
For example, in Climate Zone 3, like Dallas, TX, to qualify for ERI compliance, the building would have an energy rating index of 51. This means that the building would use 49% less energy than the 2006 IECC code minimum for the same building.
The building can have any design, it can have any building envelope and it can have any insulation values, as long as the analysis shows that the building will outperform the 2006 code minimum for the same building by at least 49 percent.
Just like the performance method, ERI requires a report that shows the proposed design meets the requirements of the ERI using calculations from an energy modeling software tool. The most common analysis to meet ERI is a HERS rating by a HERS rater, using REM/Rate analysis software. However, any analysis software can be used including:
- Elite RHVAC
- Wrightsoft Right-J8
- Florida Solar Energy Center’s EnergyGauge
The ERI compliance method is new to the 2015 code and offers another way to provide compliance when building high performance systems.
So, to recap, from a building envelope standpoint, you have three options to make sure that you and your customers are energy code compliant:
– The prescriptive requirements
– The performance method
– The ERI method
This is what the authority having jurisdiction, AHJ, is looking for. And the verification that they are looking for is the energy analysis report and the corresponding energy code certificate, it is mandatory.
Overall, the energy code certificate is the responsibility of the builder or the registered design professional and should be posted on or in the electrical distribution panel. And it should list the following:
- R-Values of insulation installed in or on ceiling/roof, walls, foundation, (slab, basement wall, crawl space wall and/or floor) and ducts outside conditioned spaces
- U-Factors for fenestration and the solar heat gain coefficient (SHGC) of fenestration
- Results from any required duct system and building envelope air leakage testing done on the building
- Types and efficiencies of heating, cooling, and service water heating equipment, if applicable
- Where there is more than one value for a component, the certificate shall list the value covering the largest area.
As an insulation professional, your activities are only a portion of the overall energy code certificate, but you should supply this information. To provide the best service to your customers, in my opinion, it is your responsibility to make sure that you leave behind an insulation certificate on your jobs.
If, by chance, you are not actively using insulation certificates, you can get a sample certificate from SPFA technical documents, SPFA-148, or possibly even from your material supplier.
On all of your projects in the future, make sure you are involved in the energy code compliance conversation and that you leave behind an insulation certificate, after all you are the insulation expert. •
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