Rethinking Polystyrene Insulation


imagesFrom the Editors from Environmental Building News

Written by – Alex Wilson

Rethinking Polystyrene Insulation

Insulation is a critical component of our buildings, and providing high R-values must be a high priority in creating green buildings of nearly all types and sizes.

Toward that end, polystyrene insulation, both extruded (XPS) and expanded (EPS), plays a key role in many energy-efficient green buildings. And it is a key component of several specialized, high-performance building-envelope systems, such as structural insulated panels (SIPs), insulated concrete forms (ICFs), and exterior insulation and finish system (EIFS).

However, as our feature article this month points out, polystyrene is not a very green material. It is made from fossil fuels, and a key component, benzene, has a host of health and environmental problems. Polystyrene has no recycled content, and it is rarely recycled at the end of its life. Most significantly, all polystyrene building insulation today contains the brominated flame retardant HBCD, a persistent, bioaccumulative toxin (PBT) that is being targeted for much stricter regulation in Europe.

So what should we do about this? Based on our investigation over the past several months, EBN recommends that use of polystyrene insulation made with HBCD should be avoided in buildings as long as doing so will not sacrifice energy performance or durability. The green building community should pressure the polystyrene industry to find safer, non-halogenated flame retardants.

Until such alternatives are available, manufacturers should offer XPS and EPS insulation for below-grade applications that does not contain any flame retardant—a change that should lower manufacturing costs. Building codes do not require flame-retardant foam when separated from the interior by concrete or masonry. Such products, however, would have to be clearly labeled for their intended use.

The other option is to switch to alternative, safer insulation materials. For above-grade wall and roof applications, polyisocyanurate, rigid mineral wool, and rigid fiberglass can provide drop-in replacements for XPS and EPS, or wall systems can be changed to allow more fiber insulation (cellulose, fiberglass, or mineral wool batts) or to allow spray polyurethane foam insulation. With some substitutions, greater thicknesses will be required to maintain comparable performance, and careful attention needs to be paid to moisture dynamics and vapor profiles with alternative materials.

For below-grade foundation-wall applications, rigid mineral wool and rigid fiberglass offer good alternatives, though these materials are not widely stocked in the U.S. so may necessitate special ordering. They should also be investigated for sub-slab applications; Europeans are using rigid mineral wool for this application to some extent, and experts EBN spoke with do not foresee problems with its use here. Finally, spray polyurethane foam can be used on both exterior foundation walls and underneath concrete slabs. For the latter application higher-density roofing formulations may be recommended by foam contractors—and care is needed to achieve uniform thickness.

– Alex Wilson


  1. Although this article points out trade-offs in PS Insulation — positive and negative, it seems to weigh more heavily on negatives. My understanding of XPS and EPS is that the energy savings in their use is very significant which is why they are so often spec’d and have been for as long as I can remember. Not sure what has changed? Although probably boring, I plan to get a hold of the European risk assessment that looked at flame retarded PS insulation. Would also be interested in more depth about the trade-offs of the alternatives mentioned compared to cost/performance.

  2. Alex,

    I agree that we need to pressure the manufacturers of these products to replace harmful chemicals with friendlier ones, particularly because there is virtually no cost effective solution for replacing these materials in some particular wall assemblies (most notably basement retrofits where EPS moisture characteristics provide ideal wall solutions).

    It is also worth noting that polystyrene IS recyclable and the fact that it doesn’t get recycled isn’t something intrinsicly wrong with the product, but rather an indication that we need a sea change shift in the way we dispose of building materials.


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