Blog Post

What Is a Hygrothermal Building Assessment?

April 29, 2015

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Hygro refers to water, and thermal refers to heat. In buildings, you really can’t manage heat without also managing moisture. For example, if you increase how much insulation is in a wall, you may also be increasing the risk of moisture and mold problems.

There are four ways that buildings can get wet:

  • bulk water leaks (rain dripping through a hole in your roof)
  • wicking (groundwater being pulled up through a concrete foundation)
  • air leaks (condensation inside a wall assembly)
  • vapor diffusion (high interior relative humidity in the winter; high exterior relative humidity in the summer)

 And there are just three ways they can dry when they get wet:

  • drainage (intentional spaces between building components)
  • air flow (convective drying, like your hair dryer)
  • evaporation (low relative humidity and adding the sun for drying)

Frankly, four against three can add up to less than the greatest odds for drying.

When a building is examined from a hygrothermal perspective, both moisture and heat flows on, off, and through your building are systematically tracked and evaluated. We learn the balance between wetting and drying in your building: to correct the balance if you have a moisture problem or to keep the balance if you are doing a renovation or retrofit.


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moisture meterMany buildings have lasted a hundred years or more, often getting wet—and even repeatedly—but subsequently drying because of uncontrolled heat loss or heat gain. If you make a building more energy efficient, you can shift the energy-moisture balance and damage that same building or compromise the health of occupants.

A hygrothermal building assessment means managing energy and moisture with equal intensity; not because it is a good idea, but because “it’s the law.” The law of physics, that is.

Click for a PDF version of this post.

Read more

How Water Moves Through Buildings

EPA Primer on Moisture Control Full of Strategies, Checklists

The Hidden Science of High-Performance Building Assemblies

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May 29, 2015 - 1:09 pm

As all water transport mechanisms and driving forces other than gravity are bi-directional (water is indifferent to which way it moves), there are exactly the same number of wetting mechanisms as drying mechanisms.

Yost is confusing moisture sources (atmospheric, interior, mechanical and ground) with moisture mechanisms (bulk water movement, vapor diffusion, air transport, capillary action), and moisture forces (kinetic energy, gravity, air pressure, vapor pressure, temperature gradient, surface tension, capillary action).

Oversimplifying a complex process, such as the the wetting and drying of building envelopes (and ignoring moisture buffering), is doing a disservice to readers by adding confusion rather than clarity.

For a more in-depth look at hygro-thermal issues, see:

July 21, 2015 - 7:36 am

Never knew that buildings are assessed for moisture and heat check as well. Informative post on managing energy and moisture with equal intensity. ..