Tuesday, April 30, 2019

Building Science for Dummies

When it comes to building a custom home, the fun part is choosing the building site, designing the home, and selecting colors.

What most home buyers don’t think about is how the construction of their home will impact their comfort and affect their health. That’s where building science comes in. A house is much more than four walls and a roof. It is an interactive system made up of many parts (e.g. the structure itself, ventilation systems, heating, and cooling systems, etc.). Each component influences the performance of the entire system.

Home building materials and home building techniques have improved substantially over the years. While this is good overall, for builders and home buyers that haven’t kept up, it can be bad. When homes were leaky, moisture that was created in the home could escape. That doesn’t happen in today’s homes. Let’s learn more about how building science impacts your home.


Your home is a collection of systems that work together (usually) to support your comfort, protect you from the elements, and to promote your health. It’s called building science, not building art. Buildings perform in a very predictable fashion. The process is governed by the second law of thermodynamics:

The second law of thermodynamics says that when energy changes from one form to another form, or matter moves freely, entropy (disorder) in a closed system increases. Differences in temperature, pressure, and density tend to even out horizontally after a while.

The performance characteristics of a home are based on four basic principles of physics. While solid design is the starting point for a healthy home it is important to remember that proper maintenance is required to keep all systems working properly.

Here are three basic concepts to remember as you review the four principles:
Moisture moves from wet to dry. Heat moves from hot to cold. Air moves from high pressure to low pressure.


Moisture Movement – The moisture level in a home depends on a number of different factors such as lifestyle (showering and cooking), the number of occupants, leaks, and air or ground moisture. Moisture always wants to move from areas of high vapor pressure to areas of low vapor pressure. Vapor pressure is the pressure exerted by water molecules in a mixture of air. For example: when a home is being heated, moisture wants to move to the outside, and when the home is being air conditioned, moisture wants to move from the outside to the inside of your home.

One of the most common terms we use to discuss moisture in homes is known as relative humidity (RH). RH is a percentage that indicates the amount of moisture in the air relative to the maximum amount the air can hold at that temperature. Warm air can hold more moisture than cool air, so the RH of a sample of air will change as the temperature changes, even though the actual amount of moisture in the sample does not. If we raise the temperatures, we lower the RH and if we lower the temperature, we raise the RH.

Click Here to read the rest of this article by Ken Semler, founder of Express Modular and Chair of the NAHB’s Building Systems Council

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