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Understanding R-Value & Aged R-Value

Home built with Thermocore SIPS with afternoon shadows


The term R-Value is the most popular term used to measure various insulating materials. Unfortunately, what is printed on the bag or on the material itself often gives a poor representation of how the product performs in the field. In order to better understand how insulating products work it is important to understand what R-values measure. R-value is the measurement of resistance of heat flow through a particular product. The higher the R-Value, the greater the product's resistance to heat transfer.

Here are a number of other terms used when describing a products energy rating:

  • Thermal Mass - Thermal mass such as logs or concrete slow the transfer of heat but do not reduce heat transfer. This is why most basements are insulated before they are finished.

  • Advertised R-Value - This is the manufacturer's stated R-Value for the product as it is tested. This R-Value is often never achieved in real world applications. Example: Many builders are moving towards framing with 2x6 material in order to gain a higher R-Value. Unfortunately R-19 batt type insulation needs a space of 6-1/2″ in order to achieve its stated R-Value. A 2x6 is only 5-1/2″ thick. When the R-19 insulation is installed it must be compressed thereby reducing its stated R-Value to 16. Likewise, doubling up on fiberglass batts will not increase their overall R-Value, in fact it lowers it significantly.

  • Thermal Breaks - Thermal breaks occur when a conductive material is placed in a wall and comes in contact with the two outer skins of the wall. An example of a thermal break is the studs in a typical frame wall. It is important to note that metal studs “conduct” cold much more effectively than wood.

  • Whole Wall R-Value - Whole wall R-Value is the measure of a wall system as it appears on the house. This would include the measure of heat loss due to window openings, electrical boxes and studs. The whole house R-Value is the best measurement for a product's performance in a home application. Example: When fiberglass batts are used in a typical stud wall, the combined R-Values of the 2xs material and the batt insulation must be used to determine the correct R-Value. Test have shown the actual whole house R-Values for 2x4 walls with R-13 batts to be R-10 and for 2x6 walls with R-19 to be R-13.8. This is hardly what one would consider to be “R-VALUE”.

When choosing methods to insulate your home, the products with the greatest return on investment are those products with little or no thermal breaks, that have a high resistance to heat transfer and that can be installed in a manner that conforms to their true R rating. Thermocore consistently performs to its stated R-Value when used in home construction, giving you the greatest value for your money and the highest return on your investment.

Special Note

It has become more popular to frame homes with 2x6″s rather than 2x4″s to increase R-value. The fact is that the true R-value for a wall framed with 2x6″s never reaches the intended R-value of 19. It is in fact R 13.69 a reduction in R-value of 28%. The same problems occur with 2x4 construction. The intended R-value is intended to be 13 but in fact it is truly R 9.58 a loss of 27%. This phenomena does not occur with Thermocore Panel Systems. The R-value is in fact its stated value. The question is: where is the true value in R-value? Clearly the answer is panels.

Data Source: Oakridge National Laboratories.

Aged R-Value

Aged R-Value is the long term R-Value of a given insulator. Many factors can affect the long term performance of an insulation product, including dirt, settling, moisture absorption, UV rays, and out gassing.

Out gassing is a process by which fumes or gas 'escape' from a product over time. All living creatures out gas as well as most manufactured products such as cabinets, carpet, paints, and fabrics.

Polyurethane gains its superior R-Value rating due to its unique cell structure and polyurethane's ability to create a higher density of cells. The polyurethane used to manufacture Thermocore's panels is a closed cell, class 1 rated, structural foam.

If the surface foam of polyurethane is exposed directly to atmospheric pressures for an extended period of time and air is allowed to permeate the foam, the outermost cells can rupture, releasing their inert gas and losing their R-Value. This process takes place over the first two years of the product and usually results in a drop of R-Value of 15%.

Placing a coating or facing directly onto the polyurethane skin can eliminate any reduction of R-value from out gassing. This fact has been proven in study after study. The question then remains: Is OSB board a suitable facing as to eliminate any out gassing and reduction in R-Value? The answer is a resounding YES!

There have been many documented studies to determine whether the skins on OSB foam core panels would eliminate out gassing. The following are a summary of some of the studies:

  1. The Alchem study measured a door panel for R-Value after eight years. Result: No noted loss of R-Value
  2. Lars-Erik Larsson studied the effects of skins on panels over a seven year period. Result: No loss of R-Value.
  3. A further study of a home after an 11 year period found no loss of R-Value.
  4. Thermocore has its own panels tested after a period of three years and found no measurable loss of R-Value.

The conclusion is clear. There is no measurable out gassing or loss of R-Value when polyurethane is protected by wood skins. After all, would refrigerator manufacturers, cooler manufacturers or refrigerated semi-trailer manufacturers use polyurethane as their first choice if it was going to lose all its R-Value? Have you ever seen your refrigerator out gas? Is there a warning label for out gassing? Polyurethanes are in everything from the dash board of your car, to the bottom of your shoes to the cushions on your couches and chairs. If out gassing were a problem, these products would not be available for public use. Out gassing in structural insulated panels is nothing more than a rumor by manufacturers of inferior products.

Thermocore SIPS home under construction

“Panels make the finish work much easier than stick built. Window openings are machine cut to exactly the manufacturer's specification and square to boot. All the drywall and trim work is much easier to do and with less waste and hanging cabinets was a breeze!”

- Chris F. (Builder),