The Ultimate HERS Rating Guide Part 3: What Is A Trade-Off?
Date Published: July 15, 2019
As we talked about in the earlier parts of this HERS rating guide, a HERS rating is a calculated score that quantifies the energy efficiency of a home. When a HERS rating is performed before a home is built, it can be used as a method to comply with energy efficiency code requirements instead of following the standard IECC pathway.
This is commonly referred to as prescriptive vs performance energy compliance. When building a home, using the prescriptive pathway requires following the code requirements line by line for each section of the home. Currently, this is more common but as the codes tighten it is becoming increasingly more difficult to meet every line item in the energy code.
The other option is the performance pathway. This includes using secondary reports such as HERS ratings or RESchecks to validate that a home is energy efficient enough to meet the current code standards.
It is called the performance path because you are measuring the physical energy performance of the building as opposed to following a set of guidelines.
This option gives builders the flexibility to alter sections of the home to be lower than the minimum required energy standards and make up for that deficiency elsewhere. This nets an equally energy efficient home as one built on the prescriptive codes but allows builders and architects to be more creative with their techniques and designs.
The above process is called a Trade-Off, and it is what we will be going through in this article.
Common Trade-Off Scenarios
There are endless scenarios where using a trade-off can help the building process but there are ones that come up frequently. A common trade-off trigger is window efficiency.
Trade-Offs: Window Efficiency
Say you are building a home with very large windows covering an entire wall. This is great to maximize your view, but energy efficient windows of this size that meet the prescriptive path U-value can be very expensive and difficult to find.
Because of this, many builders will opt for slightly less efficient windows and make up for it with a more efficient heating/cooling systems, for example.
You may lose more heat through the less expensive windows but it is now more efficient and less expensive to heat your home. This results in an energy neutral trade-off, and through the HERS model, the performance of the home should remain the same.
Trade-Offs: 2×4 Framed Exterior Walls
Occasionally, a builder or architect will want to use 2x4s to frame the exterior walls instead of the standard 2x6s. This typically cannot be done while following the prescriptive tables because the required exterior wall insulation is more than what can fit in 4 inches of space, or would require the use of more expensive closed-cell spray foam insulation.
However, this can be accomplished with a trade-off. The decrease in exterior wall insulation will cause your HERS score to increase. This can be offset by adding higher efficiency HVAC equipment, adding more insulation in other areas, or adding solar or other power generation techniques.
Rewards For Going Above and Beyond
Aside from trade-offs alone, going further than minimum expectations will decrease your HERS score as well. This means you get rewarded for being a great builder. If you have a duct leakage test performed, and the results are better than what was projected on the original HERS report, the HERS score will decrease.
This gives you extra room to make changes in the future if needed. A buffer zone in case you need to make an unforeseen trade-off. When building on the prescriptive path, you cannot capitalize on areas where you are more energy efficient than what is required.
The Trend Towards Performance
Because of the benefit of trade-offs, consumer understanding, and the demand for EnergySTAR homes, HERS ratings are becoming more and more popular and relevant in the building community.
To gain the maximum benefit from a HERS rating and the trade-off component, it is important to work with an experienced HERS rating company. A professional HERS rater will be able to identify where using trade-offs can save money and building time to ensure your project moves forward smoothly.
If you are interested in our HERS rating services, learn more here. We would be happy to talk to you about your project and answer any questions you may have.
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