Rethinking Polystyrene Insulation

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