The Case of the
Disappearing R-Value
The latest word on urethane and polyisocyanurate:
The older they get, the worse they look
by Paul Hanke
Most engineers, architects and builders
probably know that rigid foam insulation
boards (such as polyurethane and polyisocyanurate)
have relatively high R-values per
inch of thickness at the time of manufacture,
but that these values decline as the products
age. For this reason, the products have been
marketed on the basis of the so-called "aged
R-value, " which is determined by standard
testing procedures.
But now these aged R-values are coming
under fire by the Midwest Roofing Contractors
Association (MRCA). Citing MRCA
field tests of urethane and polyisocyanurate
materials, a group of panelists at the association's
convention