Robert Naini, your Spray Foam Advisor, talks about control layers and the natural flow of water, air, vapor and heat around buildings.
To truly understand how spray foam affects buildings and be able to teach this to your employees and customers, it helps to think a little about the fundamentals of building physics – or how buildings work.
Taking this one step further, you should know the different control layers in a building envelope, the purpose of these control layers and the natural flow of liquid, air, moisture, and heat around a building.
The best synopsis I have ever read about control layers is from Dr. Joseph Lstiburek with Building Science Corporation in his post, BSI-001: The Perfect Wall.
As he explains, after providing structural support, a wall is intended “…to keep the outside out and the inside in.” This means managing rain, air, vapor, and heat in such a way as to create a comfortable interior environment and extend the useful life of the building.
Joe goes on further to explain that there is an order of importance for the control layers and protection of the structure:
“…if you can’t keep the rain out don’t waste your time on the air. If you can’t keep the air out don’t waste your time on the vapor.”
The reason for the order of importance is the magnitude of effect that each of these components has on the structure and the environment.
- Liquid water, like rain, is most damaging
- Then comes air, because it can carry a lot of moisture
- Then vapor, because when it accumulates, it can condense to liquid
- And lastly, there is temperature, heat transfer and UV exposure
The damage these components cause includes material decay and movement (expansion and contraction), none of which is favorable to building materials in the long run.
Not only is there an order of importance for these control layers, but Joe further explains that there is an ideal location, since “…most of the bad stuff comes from the outside…”, these control layers should be placed on the outside of the structure, to protect the structure and the interior environment, from all of the exterior contaminants – rain, air, vapor, heat, etc. And, combining all this together, here is the design that Mr. Lstiburek and Building Science Corporation describe as the 500-year wall:
He goes on to say, “A clever version of this first wall is where spray-applied closed-cell high-density foam is used to combine the four principal control layers in one material.” Here is the detail that he offers, titled “The Clever Wall”:
Understanding these control layers, and how spray foam insulation can play a role in these designs, will help you and your team explain how spray foam changes the way buildings work.
Now that you understand control layers in a building separation and their purpose, let’s discuss the natural flow of liquid, air, moisture and heat around buildings.
On a hot summer day, what happens when a breeze blows open your porch door?
On a relaxing day at the gym, what happens when you open the door to the sauna?
When you bake cookies for dessert, what happens when you open the oven door?
In all of these situations, there is a natural flow and movement, as all of the components – liquid, air, moisture and heat, try to reach equilibrium by moving from high to low. Air moves from high pressure to low pressure, moisture or water vapor moves from high concentration to low concentration and heat moves from high temperature to low temperature.
So, let’s look at those examples from earlier:
On a hot summer day, what happens when a breeze blows open your porch door?
Air comes rushing in – moving from high pressure to low pressure
On a relaxing day at the gym, what happens when you open the door to the sauna?
Moisture vapor comes rushing out – moving from high concentration to low concentration
And, when you bake cookies for dessert, what happens when you open the oven door?
Heat comes rushing out – from high temperature to low temperature
You know this intuitively, right. That is why you tell your kids to close the front door and not air condition the outside.
Liquid, air, moisture and heat all flow naturally to find equilibrium, therefore control layers are important for buildings to separate the exterior contaminants (liquid, air, moisture and heat) from the interior of the building.
This same dynamic movement occurs inside your building also.
Air moves due to exterior wind pressure and interior air pressure from the HVAC system.
Moisture moves based on the interior relative humidity and the amount of moisture created inside the building by eating, breathing, bathing, cooking, etc.
And heat moves through conduction, convection, and radiation.
All this movement affects the interior comfort of a building, and if you and your team understand how these comfort components work, you can provide more solutions for your customers.
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