Polyiso and the LTTR Transition

August 2nd, 2011

One of the key performance factors in a commercial roof is energy-efficiency. Gone are the days when efforts to curb the cost of construction cause energy efficiency to take a back seat. On today’s highly competitive commercial landscape, construction costs must be economical, materials must be reasonable and operational performance of the completed structure is paramount.

Since the roof is a major component of operational performance, its energy-efficiency gained increased scrutiny during he last 30 years. Insulation is a key factor in determining the long-term performance of a commercial roof so the insulation industry and the commercial roofing industry along with engineers, specifiers and industry associations began to standardize ways to measure long-term energy efficiency, rate materials and develop benchmarks for local national and international codes and regulations.

Polyiso (polyisocyanurate) is the insulation of choice among commercial roofing contractors, materials manufacturers, architects and other specifiers. PIMA (Polyisocyanurate Insulation Manufacturers Association) has led the transition since the early 1980’s from measuring the performance of a commercial roof system using a polyiso product’s R-Value combined with suppositions, to a scientific standard called LTTR (Long-Term Thermal Resistance).

LTTR is a scientific methodology to determine a 15 year average, time weighted R-value of roof insulation components made from polyiso.

PIMA developed a certification process for manufacturers, architects, roof consultants, contractors, engineers and others who spec commercial roof insulation can be precise regarding product performance when specifying materials. This process incorporates the LTTR of a manufacturer’s polyiso product.

Atlas Roofing Corporation is a PIMA certified manufacturer of polyiso roofing components. Their ACFoam products are industry leaders in quality and versatility for commercial roof systems. Because Atlas understands the importance of creating energy-efficient structures they’ve simplified the process for specifiers to use ACFoam products in development of LTTR performance based commercial roofing solutions.

The LTTR Calculator from Atlas began around 2002 as a convenient digital tool. It was recently been updated with interactive functionality. Now constructors and specifiers have a drag and drop interactive tool to determine material grade and thickness for a job according to required R-Values. The system, found at www.GreenZone.com helps the user create a component package and determine LTTR value easily and quickly.