Building Science Glossary

***This post is designed to provide definitions to technical and industry specific terms throughout our blog posts and website.  It is in alphabetical order, so if you get directed to this page please scroll down to the word you are looking for***

Building Science Glossary

Building Science – Building science is the scientific understanding of how a home (or any building) will respond to the forces of nature.  These practices are used in the construction industry to utilize building materials and trades in a durable and safe way.

  • Builders should have a general knowledge of building science but, also consult regularly with a building science expert, such as GreenEdge.
  • Our Home Energy Audit & HERS Index Rating (RESNET) use building science at its core to either rate a home and/or identify areas of needed efficiency improvements.


Blower Door – This is an advanced tool used to measure a buildings air infiltration by pressurizing or depressurizing the structure.  Measuring the air infiltration can help determine if the home is performing with an ideal balance between efficiency and safety.  If the home is too leaky, there is room for air sealing and if the home is too air tight, then the home needs mechanical ventilation.  This device is used in our Home Energy Audit, HERS Index Rating (RESNET) and ENERGY STAR Certified Home ratings.


Combustion Appliances – These are any appliances within a home that use fuel as an energy source for combustion.  Most common examples would be furnace, water heater and range.  Many homes use natural gas to fuel these appliances.  They can be very dangerous if they are not working properly.  Carbon monoxide (CO) is a by product of incomplete combustion.  If the appliance is producing CO and not exhausting it properly, this can lead to poor indoor air quality.  For example; many homes still have naturally drafting water heaters.  If the water heater is not exhausting the gases safely, they could be spilling back into your home.  Most of the new high efficient furnaces and water heaters are closed combustion units or at least have an mechanically assisted fan helping to exhaust the gases.  Our Home Energy Audit not only looks at the efficiency of your home, it also tests the combustion appliances to see if they are working safely.  Here are the tests performed:

  • Spillage – This test will see if exhaust gases are spilling back into the home (CAZ) upon start up and steady state (start up is within 60 seconds & steady state is after at least 5 minutes of the unit running)
  • Draft pressure – This will determine if the flue has enough draft pressure based on the outdoor temperature, with the appliance running at steady state.
  • Undiluted CO – Meaning CO not mixed with ambient air and usually within the combustion chambers.  For example: we will insert the tip of our combustion analyzer into both sides of the turbulator, within the water heater.  If the appliance is producing too much undiluted CO, it means the unit is not working properly and needs to be either serviced or replaced.
  • We only test for undiluted CO on a gas range.
  • If the furnace and water heater are commonly vented, we test them individually and when they are both running at the same time.


Combustion Appliance Zone (CAZ) – This is the area of the home where the furnace and water heater are located (as long as they are fueled by natural gas).  Sometimes this zone is a utility closet and sometimes its the whole basement.  It can even be two separate rooms if the appliances are in separate places.  Basically, its the area of the home that can be closed off from the living space, which houses at least one drafting combustion appliance (not including the range).  Testing this area is a very critical part of our Home Energy Audit.  BPI Standards give us a limit to which this area can be depressurized (we will calculate a depressurization limit based on the set up of the appliances).  If a CAZ gets too depressurized, it can lead to back drafting.  If our tests show this area to fail the depressurization limit, then measures need to be taken to ensure good air quality.

Home Energy Audit – A home energy audit is a whole house approach to identifying areas of the home that need to be fixed or upgraded to allow for more energy efficiency, durability, sustainability and safety.  Our Home Energy Audit includes:

  • A interior and exterior evaluation of the water management or lack of water management systems, as well as lighting.
  • We test the accessible natural gas lines inside and outside the home to see if there are any leaks.
  • Combustion appliance testing on the furnace, water heater and range (if natural gas) to see if they are operating safely and efficiently.
  • Blower door test to see if the home is too air tight with a need for mechanical ventilation or if there are potential areas of needed air sealing for improved efficiency.
  • We can also (as an upgrade) test for duct leakage to see if the ducts need to be tightened for increased efficiency(almost always do).
  • This includes a full report with real life numbers, observations, pictures and recommendations.


Infrared Thermal Imaging (Thermography) – This type of camera can detect radiation in the infrared range of the electromagnetic spectrum and produce images called thermograms.  Basically, it will show temperature differences.  Objects within the image that have different temperatures will be well defined.  If the objects have similar temperatures, the image will be hard to make out.  Thermal imaging is used in all different kinds of industries.  GreenEdge is trained to use this technology in the building science industry.  Here are some common uses for this industry:

  • Will show air infiltration through wall assemblies, windows/door frames and other areas of the home (works best in the winter and summer, when there is a greater temperature difference between inside and outside the home).  Using the blower door in conjunction with this camera is really useful (we do this in our Infrared Thermal Scan and Home Energy Audit)).
  • It can show problems happening within the air conditioner condenser and electrical panel.
  • It can also show moisture within a wall cavity if the conditions are right.
  • This is a great tool for locating where duct work is running within the wall.


  1. Building Science | GreenEdge Michigan - January 22, 2013

    […] rooms.  This is just one of many examples of how a home interferes with the laws of science.  Building science is understanding how a property is going to react to the forces of […]

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