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Building Envelope

The building envelope is a term often used by building scientists and home performance contractors. Insulation defines your thermal boundary, the air pressure zone makes up the other part of your building envelope.  These two boundaries must be in complete alignment in order to achieve energy efficiency. Our adviser will inspect the thermal boundary to determine the quality of installation (Often poor) and quantity of insulation.  The two together determine the R-Value (Resistivity to Heat Transfer).

Determining the pressure boundary is a bit more work.  We use the Blower door and zonal testing along with the infrared camera to map out your pressure boundary.  Shell improvements such as air sealing, insulation, caulking, weather stripping, windows, siding and roofing will bring your building envelope up to the standards needed for an energy efficient home.

One of North America’s premier building scientists talks very practically and understandably about building enclosures.   Read more of Joe’s articles at

A blower door test is used to conduct zonal pressure boundaries.  This tests the air flow between rooms as well as between the house and the garage or attic or crawlspace.  These areas want to be isolated from the main house.

Between rooms … this is important since air will move from a high pressure area to a low pressure area.  If a room has a higher pressure than the surrounding areas the heating or cooling will not be as effective.  Drafts will occur when these imbalances persist.

The house should be completely isolated from the crawlspace, garage and attic.  A blower door zonal test will test this and our auditors will inform you of the proper solution.

Insulation Quality

  • Insulation deteriorates over time.
  • Installation of the insulation effects the quality.
  • Air flow through the insulation greatly effects the quality


  • R-Value is a relative measurement of the insulation’s resistivity to heat transfer
  • R-Value is normally specified as a per inch value of the insulation installed
  • Air temperature effects the R-Value
  • Air flow through an insulation reduces its R-Value

Blower Door – A large fan with a cover on a frame to seal off an exterior door. A manometer measures the air pressure and air flow through the fan. We depressurize the house to -50 pascals of pressure and measure the amount of air leakage in CFMs. Cubic Foot per Minute.

Zonal Testing – Zonal testing is done by measuring the air pressure between rooms. (zones) We often use this to determine the air pressure boundary between the house and the attic and the house and the garage.

Alignment of pressure and thermal boundaries – The pressure boundary and the thermal boundaries must be tight together and in the same location to maximize energy efficiency.

Energy Efficiency – A process where wasted energy use is eliminated.

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Home Doctor of America

Home Doctor of America

Home Doctor of America is about creating a better home by using building science and a great attention to details. We conduct house energy audits designed to improve the...

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