High Performance Home – Glossary of Terms

ACH 50

Air Changes per Hour at 50 Pascal’s, commonly referred to as ACH and is the main unit of measurement for a blower door test.


Advanced Framing

Framing in such a way where insulation is allowed at corners, interior / exterior wall intersections, and headers without compromising any structural integrity.


Air Barrier

An air barrier is usually a solid material, such as plywood, thermo ply, or foam board that stops the flow of air through the homes envelope. House wrap is only considered an air barrier if it is sealed at the perimeter and seams.


Air Sealant

An air sealant is a flexible material such as caulk or foam that fill gaps or seams in air barrier materials to stop the flow of air through the homes envelope.



Typically framing members are added to the structure in specific locations to create proper air barriers.


Blower Door Test

A blower door test is the industry standard tool to quantify a home’s air leakage rate and is a measure of leakage at a specified pressure of 50 Pascal’s compared to the home’s volume.


CFM 50

Cubic Feet per Minute at 50 Pascal’s.


Duct Blast Test

The HVAC and duct system test is performed through the use of a “Duct Blaster”. This tool quantifies duct leakage volume in CFM at 25 Pascal’s. This is the test method used to demonstrate compliance with the duct leakage requirements of High Performance Home Program and North Carolina energy code and HERO code.


EnergySmart Builder

Builders who commit to 100% HERS Ratings for all of their homes are licensed to use the EnergySmart Builder logo and other marketing resources offered by RESNET.



Sometimes called a home’s Shell or Thermal Envelope, we are referring to the boundary of the home that follows the conditioned space as it abuts unconditioned space. is usually comprised of the floors, walls, and ceilings. Ideally the homes insulation (thermal barrier) and Air Barriers are working together to create an effective envelope. Unfortunately many homes built today will have significant failures in the homes envelope and is often the reason for high energy bills, uncomfortable rooms, moisture issues, and air quality issues. We believe getting the home’s Envelope right is essential! To get the home’s envelope right, it must be done before drywall is hung.


HERS Rating

Home Energy Rating System (HERS) rating is the standardized process for evaluating and estimating a home’s energy consumption.



North Carolina’s optional HERO code stands for High Efficiency Residential Option code. This is a more stringent optional code that some utilities and builders can choose to follow.


HERS Index

Home Energy Rating System (HERS) Index is a number given to a home after a “Confirmed” rating has been performed by a HERS Rater. The HERS Index indicates how much more or less efficient a home is as compared to the 2006 International Energy Codes (IECC). A home with a HERS Index of 70 means it uses 30% less energy than a Standard Home built to the 2006 IECC which would score a 100.


Home Energy Monitoring System

A home energy monitoring system provides instant feedback to occupants about energy use and costs of home operation. When appliances are shut off, occupants can see how much money they are saving.


Knee Walls

Vertical walls of homes envelope with conditioned space on one side and attic space on the other. Like other exterior walls, we want effective air barriers on all six sides of these walls.



Solar Heat Gain Coefficient is a rating for windows which expresses the amount of solar thermal radiation that is rejected and not allowed to pass through the window. A SHGC of .30 means that 70% of the radiant heat coming through sunlight is blocked and not allowed to enter the home.



A rating of the thermal performance of material, typically for windows and doors. Expressed as a fraction, the U-Factor is the inverse of R-Value and the lower U-Factor, the better thermal performance of the window.


Manual J

This is the manual that specifies the process to determine how to produce a load calculation for a home, which in turn, determines the size of the HVAC equipment for the home.


Mechanical Fresh Air

A mechanical fresh air system provides clean, dehumidified, filtered fresh air for the occupants. We don’t want a home to leak just enough, we want to build it tight and ventilate it right.


Right Sized

Right Sized is the process for ensuring accuracy in determining the load for the home, which determines the equipment size. Particularly in Hot Humid climates, we want the HVAC system to run long enough to dehumidify the air in the home. Too often, homes have over-sized HVAC systems and they get to set-point temperature quickly, but don’t run long enough to reduce humidity. When the occupant isn’t comfortable due to high humidity, they drive the thermostat down and the cycle continues until dew point is met and moisture issues take their toll on the home in the form of condensation, mold and mildew, nail pops, and on. In this climate it is critical that the HVAC system is Right Sized!



Residential Energy Services Network or RESNET is the governing body for our industry and HERS Ratings.


Standard Home

A home built to the minimum energy code.