Which is worse, metal through-wall flashing or a big ‘ole insulation gap?

“Beauty is in the eye of the beholder.”

This holds true for building science details as well. As best-practice research from Passive construction standards is making its way into mainstream building codes, there are some simple (yet elusive) mentality shifts that need to occur.

Today, we will examine two specific details side by side to call attention to a small but impactful detail, and to investigate the significance of not questioning industry norms:

  1. A detail showing a 1″ gap in the exterior insulation, which most would identify as a construction defect.
  2. A flashing detail where a strip of aluminum drains to the exterior, which many consider a good solution.

While the occurrence of 1″ gaps in the exterior insulation of buildings is hopefully limited, metal flashing details can add up to hundreds of linear feet in single family buildings and thousands of linear feet in commercial buildings.

Now, the question arises: Which of these details is preferred?

From a thermal standpoint, both details actually perform virtually the same. In a laser-focused attempt to solve a moisture problem, we have created an energy-efficiency problem.

Fortunately, there is good news. We can achieve the same level of drainage detail by replacing the metal through flashing with non-metal flashing. By doing so, we maintain the integrity of the exterior insulation while still ensuring efficient drainage.

How much does this matter, you ask?

In a world where our buildings are becoming more and more efficient, the closer we get to zero, the more every detail counts. Through-wall metal flashing has made the difference in reaching thermal comfort goals in past Emu projects, and sometimes the difference in achieving Passive House certification.

In conclusion, when it comes to building science details, it is vital to consider the larger picture. While a 1″ gap in exterior insulation may be perceived as a construction defect, a flashing detail with metal components can have a similar impact. By specifying non-metal flashing alternatives, we can enhance the thermal performance of our buildings while continuing to address the very real potential for moisture damage.

The lesson of the story? Make sure your solution is not creating another problem!

If you found this interesting and want to challenge your brain to question other industry norms, consider joining one of our Passive Design/Build Boot Camps or one of our Online Crews, where we delve into the WHY behind our building science decisions from an un-sponsored, brand-neutral, research-led perspective.

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