The increasing urgency to reduce the environmental impact of energy use in all sectors of society is driving energy conservation in buildings. As building enclosures seek to become more airtight and highly insulated, the use of foam insulation is increasing. Unfortunately, foam insulation currently has high environmental impacts itself, relative to other types of insulation like fiberglass, cellulose and mineral wool. Polystyrene board stock, polyisocyanurate board stock and polyurethane spray foam (SPF) create health risks during manufacture and contain chlorine or bromine-based flame retardants that are listed as persistent organic pollutants by the Stockholm Convention on Persistent Organic Pollutants.(1)

Perhaps more troubling, some foam insulation contains bubbles of blowing agent which when released into the atmosphere are strong greenhouse gases, a thousand times stronger than carbon dioxide. Even at the relatively low blowing agent leakage rate of 1.5% per year acknowledged by American Plastics Council (2) and assuming a 25% release rate during manufacture, (3) 2/3 of the blowing agent will be released into the atmosphere over a 50 year product lifetime. This does not include the inevitable additional release from demolition and disposal of the product. So most of this stuff will eventually end up back in the air.

All foam insulations do not pose equal global warming risk. Extruded polystyrene and SPF contain hydro-fluorocarbon blowing agents that are much more damaging than the pentane blowing agent used in expanded polystyrene and polyisocyanurate. The relative environmental impact of insulation can be assessed by comparing the global warming potential of the blowing agent release to the global warming avoided by reduced building heating and cooling energy use. The accompanying graph shows the reduction in the CO2 equivalent greenhouse gas emissions from R10 insulation added to a base R15 wall compared to the equivalent greenhouse gas released by various insulation types over their lifetime. This information is for a cold climate like Minnesota (Zone 6).(4)
foam ghg comparison 85 ppi
The green bar at the left of the graph represents the impact of the R10 insulation through 50 years of reduced natural gas use for heating. The other bars represent the 50 year impact of leaked blowing agent at 1.5% per year for various insulation types. Note that the blowing agent damage from extruded polystyrene takes back about 60% of its environmental benefit and SPF offsets almost 40% of its benefit. And these figures do not account for blowing agent release during demolition and disposal. Polyisocyanurate and expanded polystyrene foams produce much less environmental damage than extruded polystyrene and SPF. The most benign insulation types – mineral wool, fiberglass and cellulose – produce even less environmental damage than foam.

There are situations when extruded polystyrene and SPF use are difficult to avoid. Extruded polystyrene appears to be the best insulation for below grade use. SPF works well in cold climates for remodeling walls and ceilings when exterior foam cannot be used because wall cladding or roofing will not be removed; by spraying it on the interior of the sheathing, an air barrier can be created and the condensation potential at the sheathing can be reduced. But given the global warming potential of these insulations in their current formulation, they should be used only when other insulation types cannot. For instance, why use extruded polystyrene on the exterior of walls when fiberglass-faced polyisocyanurate, foil-faced polyisocyanurate or high density mineral wool can be used instead?

Changes are coming from the foam industry that will improve the situation. Dow Chemical and Johns Manville are working to eliminate or reduce the toxicity of the flame retardants in some of their products. The EPA will phase out the use of most HFC blowing agents and refrigerants by 2021 under the Clean Air Act. Dow says it will eliminate HFC-134a in extruded polystyrene by 2020. BuildingGreen guesses that the new blowing agent may be Solstice, a hydrofluoroolefin (HFO) with a very low global warming potential produced by Honeywell.(5) This blowing agent is currently coming on the market for SPF. There are no other HFO’s in the market place yet so “clean” SPF is currently too expensive to have much impact. Likewise, the new line of cleaner extruded polystyrene board may be expensive until competition drives the price down.

Third Level Design 2015

  1. “Avoiding the Global Warming Impact of Insulation”, Alex Wilson, BuildingGreen, 2012
  2. “Plastics Energy and Greenhouse Gas Savings Using Rigid Foam Sheathing Applied to Exterior Walls of Single Family Residential Housing in the U.S. and Canada – A Case Study”, Franklin Associates as prepared for the American Plastics Council, 2000
  3. “Net Climatic Impact of Solid Foam Insulation Produced with Halocarbon and Non-halocarbon Blowing Agents”, L.D. Danny Harvey, University of Toronto, 2006
  4. The physical properties of insulations and blowing agents are based on the paper in note iii above and on the “Insulation GWP Tool” spreadsheet developed by David White with support from BuildingGreen
  5. “Styrofoam’s Chemistry Becoming Less Hazardous, Gradually”, Alex Wilson, BuildingGreen, 2015