epartment of Energy scientists have developed a method for measuring the effective R-Values of walls. Their new formula considers the performance of insulation along with the heat losses that occur at corners, through studs, around windows and where walls meet roofs, floors and foundations.

These thermal breaks can cut the heat flow resistance to way below the R-value of the insulation in the wall. This new calculation allows builders to estimate a typical wall's real insulation performance much more closely and to make accurate comparisons to other types of wall systems; such as steel framing or foam core panels.

The method uses a computer model to predict wall performance based on the known properties of the wall's materials. Results of this new testing method show structural insulated panels as the big winner.

While their testing is mostly done on styrene panels (which have a much lower R-value than urethane) the general results are interesting.

For more information follow the links below to some technical abstracts from studies done at the Oak Ridge National Labs.