- What is Z-Value?
Z-Value is an Efficiency Rating
R-Value is only 25% of the efficiency rating.
The Z-Value is a new rating system used to determine the overall energy efficiency of an insulation product.
The value is determined by using test results from all three of the main physics principals that affect the energy efficiency of the building envelope (see chart to the right).
As seen in the chart, there are two other major factors that affect efficiency:
- Air Loss / Air Gain - being the most important
- Vapor Drive – being equally as important as the R-Value
The Z-Value is a better alternative for rating overall energy efficiency than the currently used "R-Value".
The Whole Picture
- Failings of the R-Value
Failings of the R-Value
1948, WWII ends and Truman is President. R-Value is established as a measure of rating the efficiency of the thermal envelope of a building at the University of Pennsylvania. The only two insulators are Fiberglass (Rock Wool) and Cellulose.
2013, R-Value still the preeminent means of rating the Efficiency Rating of a building.
Since 1948 we have used the "R-Value" to quantify the worthiness of a specific thickness or amount of thermal insulation. Like all things, technology rolls on, passing along not only products, but the valuation system used to show their worthiness. With the advent of Closed Cell Polyurethane Foam, the entire thermal envelope equation has changed. No longer are we able to use such an ambiguous term.
What is "R-Value"? Technically it is the reciprocal of K-Factor. In reality, it is the rate of heat transfer through a given material. The problem with a single point of reference to an insulation material, is that it completely ignore all other physics principles that govern the worthiness of the total building assembly. These are principles such as its ability to stop vapor drive, and air movement, into and out of the envelope of a building. We are now in need of a new valuation system.
1930's, WWII has not started yet. BASF and Bayer chemical of Germany have created the bases for Polyurethane. Used in Rommel's tanks and aircraft in WWII military.
1959, NASA chooses to use closed cell polyurethane foam (CCPF) to insulate space capsules.
1960, CCPF becomes the material of choice for refrigeration, freezers become "frost free".
1970's, CCPF becomes insulation of choice for cold North West and continues it's growth into mainstream national building practice.
2013, still using a 64 year old rating system (R-Value) to evaluate space age technology.
The building industry is in desperate need of a valuation system that takes into consideration the following:
Air movement, not only wind, but static pressure and convection looping.
Vapor drive, not only within the envelope, but inside the wall cavity.
Emulation of thermal Mass, i.e. R-Value.
This new term will be called the Z-Value
The R-Value has been interpreted in so many ways. Because of this, we have endeavored to create a term that is truly the final say in the worthiness of the thermal envelope, hence the "Z". The "Z" has two short, equally sized legs representing "Vapor Drive" and "R-Value", and one long leg representing "Air Loss and Gain".
In order for a product to receive a Z-Rating, the product on its own must be tested to the ASTM-E-96 (Vapor Drive), ASTM-E-2178 (Air Penetration) and ASTM C-168 (R-Value). The better a product is at stopping air movement, vapor drive, and thermal transfer, the higher the Z-value it will receive.
- Z-Value Videos
Published Articles, Scientific Research and Testing Results
- Contact Us
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