What is included in the IECC Code?

Date Published: March 29, 2022

We are often asked by builders, contractors, and architects – what is included in the IECC Code?  Understanding code content is critical to building and designing homes.  And yet so many people don’t completely understand the content of the IECC Code.  Reading codebooks from cover to cover seems to be a daunting task.  Most contractors and architects would rather source out energy code compliance to a third-party specialist.  And while that is our business and we value the relationships we have built with many great designers and builders, we believe having at least a good overview of the IECC code is important to success.

In this article, we are going to attempt to summarize the most important contents of the IECC in a concise and easy to understand format.  For reference, you can read the entire code on the International Code Council ICC website.  And since we deal with residential homes at Scott Home Inspection, we are restricting this summary to the residential half of the code.

IECC 2021

What is the IECC?

The International Energy Conservation Code (IECC) is a set of guidelines and prescriptions for constructing homes to help conserve energy.  The code defines minimum levels and specifications for insulation, window specs, heating and cooling, lighting, and other energy use items.  The code is a design document used to help architects and construction specialists design a residence to meet the minimum energy performance guidelines.

The recommendations and guidance outlined in the IECC vary based on where the home will be built, using climate zone modeling.  In addition to new construction, there is guidance included on existing buildings and recommendations for improving energy performance.

What is included in the IECC?

The following are the key highlights and important things to know from within the IECC code.  This is not meant to be a fully inclusive breakdown but is instead a summary of the key items to take away from the IECC.

Construction Documents

All architectural plan sets must include an overview of how the IECC will be met and a summary of the plans to comply.  This includes a breakdown of the insulation plans and R-values, window U-values and SHGC values, mechanical design system details, equipment controls, duct sealing, and insulation details, and air sealing details.

From our experience reviewing drawings and plans, we often see architects detail this in the form of a table outlining the planned levels.  Many also include a drawing of the building’s thermal envelope or boundaries.  Others will add the details on cross-sectional views the insulation plans and mechanical system location.  When documenting, consider how a plans examiner will locate and review the energy code items and attempt to display things in an easy-to-follow manner.

Climate Zones

Within the IECC is a detailed breakdown of the entire United States by state and by county, to define which climate zone is applicable for where the home will be constructed.  The applicable climate zone will be used to determine the minimum levels of insulation, window specs, and other performance items for installed components that impact the energy performance of the home.

Building Thermal Envelope

Section R402 of the IECC outlines the minimum insulation and window requirements for each climate zone.  The term “thermal envelope” is a fancy way of saying the walls, ceilings, and floors of a home are the barrier between heated or cooled space and the outside.  With a simple rectangular one-story home built on a slab-on-grade, this is really easy to define.

In a simple structure like this, you have the walls, windows, attic, and any slab insulation.  But as we all know, today’s houses are more complex with combinations of attic and vaults, basement and crawlspace, dormers, knee walls, etc.  Defining the thermal envelope can get somewhat tricky in more complex homes.

The components described in Table R402.1.2 highlight the minimum requirements for;

Window and Skylight U-Factor, Glazing SHGC (Solar Heat Gain Coefficient), Ceiling R-value, Wall R-value, Framed Floor R-value (over unconditioned space), Basement Wall R-value, Slab R-value and Crawlspace Wall R-value levels.

These are the minimum values that need to be met.  There is also an alternative table to be able to calculate an assembly U-factor as a method of compliance to take into account the entire assembly.  And there is a separate section related to steel-frame walls, ceilings, and floor values.

Air Leakage

Section R402.4 addresses the air leakage of a home and discusses the need to seal and limit air leaks.  Recommended air barrier and insulation installation guidelines are presented to minimize air leakage.  To validate air leakage results, testing of a home for leakage is a mandatory requirement.  Testing is done using a device called a Blower Door.

Third party testing is needed by an energy compliance specialist to visit the home, set up the blower door in a doorway, and using a high speed fan, measure the air leakage results.  The results are quantified in a term called air-changes-per-hour (ACH).  The IECC prescribes maximum leakage rates for each climate zone.

If the home fails this test, the energy testing specialist can help to locate where the main leaks are occurring to allow sealing of these areas and a re-test to validate compliance.  For detailed information on this testing, view our blower door testing article.


Section R403 discusses all the requirements related to heating, cooling and water heating systems and their impact on the energy efficiency of a home.  The key items to understand that are related to systems include:

  1. Controls – all heating and cooling systems must have a programmable thermostat present
  2. Ducts – any ducts that are running outside the thermal envelope (heated/cooled space) must be sealed and insulated
  3. Duct Testing – a ducted system that has any portion of the ducting running outside the thermal envelope must be tested for air leakage.  This can be done at rough-in stage or at post-construction stage.  Similar to an air-leakage test, this is a specific test done with a pressurizing device to quantify the amount of leakage present.  For detailed information view our duct leakage testing video.
  4. Mechanical System Piping – any piping used to carry hot water for mechanical systems should be insulated to R-3 value
  5. Hot Water System Piping – all hot water piping should be insulated to R-3 value
  6. Mechanical Ventilation – all homes shall be provided with ventilation.  This can be done using an ERV or HRV, or other ventilation methods outlined in the IRC or Mechanical Code.  For more detailed information view our mechanical ventilation system article.
  7. Equipment Sizing and Efficiency – all heating and cooling equipment must be sized in accordance with ACCA Manual S based on building loads calculated according to ACCA Manual J methods.  And all duct systems must be designed according to ACCA Manual D requirements.  A third party mechanical system specialist will need to prepare a report and design based upon the building plans, to calculate the load for heating and cooling, select equipment to meet this load, and propose a basic layout of the ducting system to properly heat and cool the home.  To learn more visit our Manual J/S/D services page.

Lighting Equipment

To help conserve energy with lighting, the IECC requires that at least 90% of all permanently installed light fixtures contain only high-efficacy lamps.  This basically means installing LED or CFL bulbs in all of these fixtures.  Since LED bulb technology has improved significantly we see most builders and electricians installing exclusively LED bulbs in all fixtures.

Energy Rating Compliance Alternative

As an alternative to compliance by strictly following the exact requirements laid out in the IECC, an energy rating can be obtained on a home to validate compliance.  A third-party building performance specialist can calculate compliance using specialized software and generate a report referred to as an ‘Energy Rating Index’.

A Certified HERS Rater will perform these calculations using architectural plans and by verifying installation items during construction and at post-construction to validate compliance.  The Energy Rating Index or ERI is a score generated that is relative to the energy performance of the home, with the lower the score meaning the less energy the home consumes.

While there are certain mandatory provisions in the code, using a HERS Rater and obtaining an ERI report can provide a builder with more flexibility in design.  And the HERS Rater will then be responsible for validating compliance to the IECC requirements.  At Scott Home Inspection we have HERS Raters on staff and can help anyone building a home in Colorado.  For more information read our HERS Rating series of articles.

Existing Buildings

Chapter 5 of the IECC contains general recommendations on addition improvements, and additions to existing homes and ways that energy performance is impacted and can be improved upon.

When a home is renovated, repaired or added onto, there are opportunities to add to existing insulation, improve air sealing, reduce duct leakage, enhance or improve mechanical system efficiency and re-balance mechanical ducting delivery and performance.  This section of the IECC provides a framework when certain components should be improved or evaluated as part of renovation project.

This summary was meant to provide a brief overview of what is included in the IECC code.  While the full code is much more detailed and contains specific recommendations for different use cases and for different climate zones, it can often be overwhelming to read a code book from cover to cover.  Hopefully this summary provided a run down of the highlights and items to consider related to the energy performance of a residential home.

At Scott Home Inspection we believe strongly in helping our clients live in safe, healthy and comfortable homes.  We have a team of Energy Services specialists to help homeowners, builders, contractors and architects achieve compliance with the IECC code and to generally help homes achieve a level of comfort and efficient performance.

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About the Author: George Scott

George founded Scott Home Inspection in 2006, and has grown the business into a multi-inspector firm serving the Colorado Front Range, from Fort Collins down to Colorado Springs. As an ASHI Certified Home Inspector and Certified Energy Rater, George is an excellent resource to help with inspection and energy-related requirements.

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