Expanded polystyrene foam (EPS) has melting point of 165°F, or about 73°C. When the foam melts, it may not necessarily liquify (although if faced with direct heat like that of a fire it will), but it tends to shrink, which will cause it to pull away from the lamina, which consists of the base coat, the reinforcing fiberglass mesh and the finishing top coat. If the foam pulls away from the lamina enough, the lamina can end up loose, hanging or falling off completely.

Whether the EPS foam used in Exterior Insulation Finishing Systems can be affected by heat from different sources depends on many variables:


Even though during some of those cold winter days it seems unbelievable, Ontario receives a large amount of direct, hot sun especially at mid day. While the average temperature outside will rarely exceed 35°C on even the hottest summer days, you can get a good idea of how the sun affects different materials by touching the hood of a car or road pavement. Many different surfaces in Ontario can become hot to the touch simply from the bright sun, even on winter days.

The orientation of the wall to which the EIFS is clad can also cause similar issues to arise: northern- and eastern-facing walls will stay far cooler than their southern- and western- facing counterparts, but if your house is in a highly forested area, you may run less of a risk than other homes that receive full sun.


There’s a reason your black car might conveniently melt away any snow or ice buildup before your neighbour’s white car. Darker colours absorb light, and therefore more heat, whereas lighter colours will reflect it. That’s why the black pavement mentioned earlier becomes so hot. If your EIFS is darker in colour it may absorb heat at a rate much higher than any lighter-coloured EIFS would.

Other surfaces nearby

Your neighbour’s driveway might be positioned just so that when they pull their car in, the rearview mirror or windows are primed to reflect or focus a concentrated beam of searing sunlight right into your exterior wall. Anything shiny, glass or reflective put in the right position or location can have this effect on your wall. Many have seen or can picture what a magnifying glass will do to an ant, and just imagine these beams being concentrated on your EIFS.

All of this concentrated sunlight or excess heat on your EIFS can cause an issue called “delamination”, where the lamina detaches from the foam, which has melted or shrunk because of the heat. Plastic foam doesn’t sizzle or fry, but rather shrivels up. Imagine a styrofoam peanut placed next to a flame, or conduct this experiment yourself, albeit outdoors. The styrofoam will shrivel and retreat, away from the heat. This is exactly what happens to the EPS in your EIFS.

Fixing delamination

Repairing EIFS ravaged by delamination can be a daunting and expensive endeavour. In an ideal world, the lamina could be removed and replaced as it comes off. However in reality, the delamination will not be evenly distributed throughout the whole of the wall.

Of course, the whole delamination problem is because of one core problem – the melting foam. Obviously once the foam has shrunk or melted, it too must be repaired or better yet replaced. And, the removal of the foam will likely damage the substrate, which in turn, means you will have to redo the whole thing.

So, repairing delamination is much more trouble than simple prevention will ever be. While delamination is not overly common or something to live in fear of everyday, simple mitigation measures can be put in place to help avoid it:

  • Keep an eye on the proximity of reflective or glass surfaces to the EIFS and monitor how they reflect or concentrate light.
  • Warn all who have their minds set on choose darker colours about the possible ramifications they may have with regards to their absorption of heat and light.
  • Ensure that all parties involved in the design, construction and installation of the project as a whole are aware of the previously mentioned factors that add to the risks of EPS melting and EIFS delamination.
  • Don’t hesitate to utilize sensors or monitoring equipment if the variables surrounding an EIFS job suggest it might get too hot. Accurate, average temperature readings will give you a rough idea of what to expect.

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