R-Values That Strain Credulity

Abstract

Rastra blocks are a type of insulated concrete form made of recycled expanded polystyrene beads mixed with cement. Apex Construction Systems of Portland, OR, which sells a Rastra-like block, recently announced that its 10-inch thick blocks have an R-value of 52. Since 10-inch thick Apex blocks are honeycombed with voids designed to be filled on site with concrete, the R-value claim of 52 strains credulity. After reviewing the California Institute of Electronics and Materials Science report, Dave Yarbrough, a research engineer at R & D Services in Cookeville, TN, and a well-known insulation expert, concluded, the test report is incomplete. The company should not market on the basis of this evaluation.