Stainless Steel: A Cool Option for Building Exteriors

Airports with stainless steel roofs help with cooling efficiencyFred Nolan of NOW Specialties Inc.

Recently The Metal Initiative sat down with Jim Halliday of Contrarian Metal Resources, to discuss the solar reflectivity of stainless steel, and its many applications in the building envelope.

TMI: You recently reminded us of something we all seem to know intuitively: that stainless steel has a very low thermal conductivity. 

CMR: Anybody who has used a stainless steel pot to cook may have noticed that the handles are often cool enough to the touch to handle a vessel with boiling water. The user may have even been aware of copper, aluminum or carbon steel being used on the bottom or encased inside the body of the pot to facilitate heat transfer in the cooking process. Imagine then, taking that vessel, removing the thermally conductive metal coupled with it, flipping it over and calling it a building.

Theoretically it would be more energy efficient. While thermal conductivity is a factor, the real story is that stainless, unlike every other outdoor metal people have day-to-day experience with, doesn’t get burning hot in the sun. This is counter-intuitive. People are used to metals which oxidize and the oxide coatings have high absorption of solar energy (low solar reflectivity, or low SRI). Stainless doesn’t behave like normal metal. Its passive film is not an oxide so its surface behaves like a bare metal and reflects incoming electromagnetic energy, including sunlight.

TMI: Do you care to describe your Eureka! moment?

CMR: I was on top of the Doha airport roof inspecting the installation of our company’s stainless steel.  I was taken aback when I was able to place my hand comfortably on the metal surface on a sunny 118°F day. That’s when it really hit me that there was a whole lot more to the story of stainless steel as a building material.

As a result, Contrarian Metal Resources is undertaking research to understand the properties of stainless steel, and how they relate to energy efficiency, as well as the heat island effect of stainless-clad buildings. While we are not quite ready to release our findings, this research shows promise that we can demonstrate how stainless steel building envelopes save energy and help reduce urban temperatures.

TMI: Do any specific applications come to mind, in which stainless steel exteriors could have an immediate, positive impact?

CMR: It’s the long-term impact that probably means the most. As long as a stainless building exterior has been properly specified and installed, it will last indefinitely with very little maintenance. With no need to replace the system and little more than periodic washing to maintain the original appearance, the building owner will save a considerable amount of money in the future. Coupling that with potential energy savings, the owners of stainless steel clad buildings can win big, while at the same time respect the environment.

TMI: Does material thickness or finish have any impact on thermal conductivity?

CMR: The finish certainly does have an effect on how much energy is transmitted to the back side of a steel stainless steel panel. A dark body, as in the case of a black colorized or painted stainless steel, will absorb more heat and therefore have more available to transfer through the material. A light body, such as an uncoated stainless steel surface, will absorb and therefore transfer less. Thickness may also have an effect, but to a lesser degree.

TMI: With all factors considered, which is the more exciting product in this regard: titanium or stainless?

CMR: Stainless steel is a more exciting opportunity for the construction market, given the current price premium for titanium. In fact, our company has succeeded in introducing duplex alloy stainless steel for building envelope applications in severe environments like the Middle East. Prior to our efforts in this area, titanium was the low cost sustainable metal building solution where conventional grades of stainless steel would not perform.

Building with Stainless Steel Walls

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