The current common types of rigid foam plastic continuous insulation used in exterior wall assemblies contain zero ozone-depleting chemicals and can be recycled through reuse. While made of petroleum-based products, they have low environmental impact. The impacts of raw material extraction, transport, manufacturing, and installation are minor compared to the savings gained in building heating and cooling energy, provided one takes into account the building lifecycle.
In a study done by Franklin Associates on several wall assemblies, exterior ci almost halved building heating and cooling energy consumption over the 50-year lifecycle, and greenhouse gas (GHG) emissions were substantially reduced (Figure 8).
An ongoing area of controversy is the use of flame retardants, specifically hexabromocyclododecane (HBCD), which is currently used in most expanded and extruded polystyrene (EPS and XPS) insulations. HBCD is on the U.S. Environmental Protection Agency’s (EPA’s) list of “chemicals of concern.” Polyisocyanurate (polyiso) insulation board manufacturers have converted to Tris (2-Chloro-1-Methylethyl) Phosphate (TCPP), which, based on current information, is “not considered to be toxic or bio-accumulative, and its environmental persistence is considered to be lower than other common foam plastic flame retardants.”
In all likelihood, HBCD will be replaced with a less environmentally controversial flame retardant in EPS and XPS. In fact, at least one XPS manufacturer has already introduced an alternative, though it is not yet commercially produced in North America.
As building codes have evolved to the point where continuous insulation is now mandatory for many wall assemblies, rigid foam plastic ci wall assemblies have become more prevalent than in the past. They have special design considerations, including fire safety, moisture-related durability, added design detail complexity, and cost control. Each category can be addressed at the design stage with an awareness of what the building code requires in relation to the use of foam plastics and their effects on the physics of the wall construction, as well as design details and the environment.
In some cases, engineering analysis of fire safety or structural adequacy is needed where prescriptive requirements or other direction does not exist in building codes. In other cases, testing is needed to verify performance. International Code Council Evaluation Service (ICC-ES) Evaluation Reports can be a valuable tool to assist in verifying code compliance and limits of materials and/or wall assembly performance.
Tom Remmele, CSI, is the director technical services/R&D for Sto Corp., a manufacturer of air barriers, coatings, exterior insulation and finish systems (EIFS), and stucco products. He has held technical management positions in the construction industry for more than 25 years. Remmele is a past Technical Committee chair of the EIFS Industry Members Association (EIMA). He can be reached at firstname.lastname@example.org.