This is from the Sto specifications: “Select finish coat with a light reflectance value of 20 or greater. The use of dark colors is not recommended with systems that incorporate EPS”
Anyone dealt with this before? I have spec’d hundrends of EIFS projects and this is the first time i have heard of this. Thoughts?
Yes, this is real.
A very dark color top coat can and will heat extruded polystyrene beyond its melting point. This applies to EIFS (and Single-Ply Roof assemblies as well). The melting point of EPS is about 160 degrees F (going on memory here)and that can be reached under the right field conditions.
A related concern I have heard of is the combination of a dark color EIFS panel in proximity to a highly reflective glass or metal surface where the combination of direct sunlight and reflected light can heat the surface to beyond melting point.
I included mention of single-ply roofing because we had a wonderful example a few years ago of an Owner messing with the Architect’s specifications and getting in trouble as a result.
We had specified a “cool roof” light colored single-ply product for a project in Utah. The Owner had little concern for the environmental value of our selections and accepted a lower cost substitution without reviewing the change with us, his Architects. The substituted product was a fine, jet black EPDM membrane. No one in on this change, including th esales reps for the new roof membrane or the installers, stopped to consider the overall roof assembly, including the sub-strate EPS insulation board.
Apparently, some time after the roof was installed, the “architect” of this change took a walk on his new roof only to have his shoes sink into a roof that had the consistency and give of a water bed. The EPS had melted!
EPS is expanded polystyrene, not extruded; that is XPS. There was a discussion here earlier this year about the differences. In your roof story, Steven, was it EPS (expanded) or XPS (extruded) that melted?
George,
Sorry for mis-reading the original post and running on like that. Yes, it was extruded polystyrene that turned a roof into a science project.
Is the same true (melting point issues) of expanded polystyrene or just extruded?
I would suggest that the problem is the same for both extruded and expanded polystyrene. Both products are covered in ASTM C578 which states “Products manufactured to this specification are intended for use as thermal insulation for temperatures from -65 to +165F…”.
I would be interested in what the perceived differences between these two products are.
Sounds like testing is needed. Anyone have a couple of scraps and a lighter? Sometimes the direct approach tells you a lot, even if it’s not an ASTM test.
I’m interested in hearing if anyone has had forensic experience with a XPS exceeding service temperature when installed directly under metal roofing. We receive substitution requests for XPS but have continued to require polyiso due to its higher service temperature.
See the July 2007 issue of the Construction Specifier for the article, “Taking a Look Under the Roof Membrane”:
Expanded Polystyrene (EPS)
"…Care should be taken when specifying EPS with certain roof systems. While it can be used in hot asphalt systems, it is limited to applications where the temperature of the asphalt is less than 121 C (250 F).
Extruded Polystyrene (XPS)
“As with EPS, the use of extruded polystyrene foam is not recommended where sustained temperatures exceed 74 C (165 F); intermittent heat exposure during installation and use should not exceed 82 C (180 F).”
Discusses other differences as well.
From my Foam Insulation rep:
There are three types of rigid foam insulation; Polystyrene Molded Bead Foam (EPS), Polystyrene Extruded Foam (XPS), and Polyisocyanurate Foam.
Polystyrene Molded Bead Foam:
Tiny beads are placed in the forming chamber
which looks like a large metal box. The amount
beads placed in the chamber determines the
density of the finished product. The R value of
bead foam is provided by the air space between
the beads (typically R 3.8/inch). Unfortunately,
this also provides a path for vapor and moisture
so bead foam is not to be used in moist areas.
Polystyrene Extruded Foam:
Although it is polystyrene, it is a completely
Different product with billions of tiny cells, all
of which share cell walls with adjacent cells.
This means that vapor and moisture cannot get
through the board so it is designed for use in
wet areas. In fact, it is Coast Guard approved
for use as exposed floatation for boat docks. None of the other rigid boards are.
Robin: I believe that statement about the dark colors has been in EIFS guide specs for a while … In addition to the issue related to the insulation, I believe it is also because the dark colors are not as UV stable as other paint coatings that get clear coats for example, and they can and will fade.