Why R-Value Alone Doesn’t Matter: Spray Foam Kansas City
If you’re looking at insulation for your home or building, you have likely heard product comparisons in terms of R-value – the conductive heat flow resistance of the material. This measurement is made using the guarded hotbox apparatus (see photos), a test procedure that measures the thermal conductivity of insulation material. One side of the material is heated to a specific temperature and after steady state heat flow has been reached, the temperature on the other side is measured. This measurement solely defines the conductive heat flow resistance of the material. 
Once the R-value is determined, the heat flow through it can be calculated using Fourier’s Law, an equation that calculates the benefit of increasing the thickness of any type of insulation as long as there is no air movement through it.
This last part is of this is key. While R-value may be the conventional method for evaluating the performance of insulation, it doesn’t account for air sealing, which is the most important part. In a home or building, air sealing and insulation work together to make the space comfortable, and to improve durability and energy efficiency.
If you’re still wondering why you need air sealing instead of just adding more insulation, consider this example from the Department of Energy. Think of insulation like a fuzzy wool sweater on a winter day. It will certainly keep you warm if the air is calm. But, if the wind picks up, you are going to need a windbreaker to keep the breeze from carrying away the heat. Air sealing is like adding the wind breaker. It keeps the conditioned air where it belongs. 
As you might imagine based on the structure of fiberglass and cellulose, both lose insulating value when air is passed over or through them. This air leakage works against the energy efficiency of your home and can lead to issues, including mold and rot. The newest edition of the International Energy Conservation Code (IECC) (2012) sets the bar higher for energy efficiency, and new air sealing requirements are one of the key provisions.
Browse through these resources before you make an insulation decision, and give us a call if we can help explain how the benefits of spray foam insulation can support proper air sealing. Remember the saying, “Build them tight, insulate right!”
