The Overlooked Detail in Exterior Insulation: Why Proper Bug Screens and Rodent Barriers Are Essential
As the construction industry shifts toward more energy-efficient building practices—especially with the increased use of semi-rigid exterior insulation products like Rockwool Comfortboard™ and Powerwool—there’s a growing oversight on many job sites: the proper detailing of bug screens and rodent barriers at the base of wall assemblies.
We’ve seen this firsthand on large-scale multi-family and commercial projects throughout BC. Despite the focus on high-performance envelopes, one small but critical detail is being missed—and it’s opening the door (literally) for costly infestations.
The Problem: Unprotected Insulation Is a Welcome Mat for Rodents
Mineral wool insulation is prized for its thermal, acoustic, and fire-resistant qualities. But there’s one thing it doesn’t do well on its own: resist pests.
Without a proper physical barrier at the base of the wall system, mice, rats, and insects can easily access the gap between the cladding and sheathing, burrowing into the mineral wool for shelter. The fibrous structure of semi-rigid insulation provides an ideal nesting ground, especially in colder months.
What starts as a small entry point can quickly escalate into a serious issue, leading to:
Damaged insulation and thermal bridging
Increased risk of moisture intrusion and mold
Potential code compliance issues
Pest infestations affecting tenants and requiring remediation
Expensive retrofits or teardown of finished cladding systems
The Solution: A Simple, Effective Perforated Flashing
The fix is incredibly straightforward: a perforated metal flashing that acts as both a bug screen and rodent barrier.
This Z- or L-shaped flashing is installed at the bottom of the rainscreen cavity and serves multiple purposes:
Blocks access to the cavity for pests and rodents
Allows for drainage and airflow, preserving the ventilation gap
Protects the insulation from mechanical damage near grade
Complies with Step Code and building envelope best practices
Reduces liability and costly callbacks
When properly integrated with the cladding, WRB, and insulation system, this flashing becomes a seamless part of a durable, high-performance envelope.
Why Is This Detail So Often Missed?
Despite its importance, many modern architectural drawings fail to include this component. We've reviewed countless construction drawings—especially on large-scale wood-frame and concrete developments—where the exterior insulation is fully detailed for performance, but no rodent screen or bug barrier is specified.
This happens for several reasons:
Assumption that cladding is a sufficient barrier (it’s not)
Oversight during fast-paced design or tender phases
Lack of field experience among design consultants
Value engineering efforts removing "non-essential" components
Unfortunately, when it’s left out of the plans, it’s often left out of the build—and the consequences can be significant.
Our Approach at White Glove Contracting
At White Glove Contracting, we treat rodent and insect protection as a non-negotiable detail in any exterior insulation installation. Whether it’s part of the spec or not, we proactively recommend perforated base flashings on all projects where semi-rigid insulation is installed. This isn’t an upsell—it’s about protecting the integrity of the building envelope.
We also work directly with architects and general contractors to flag missing details early in the construction phase and propose solutions that are cost-effective, code-aligned, and field-tested.
A Small Detail with Big Payoff
When it comes to building envelope performance, it’s the small details that make the biggest difference. A $10 piece of flashing can save thousands in repairs, tenant complaints, and pest control bills—not to mention the reputational risk of a poorly performing building.
If you’re planning a project that includes Rockwool, Powerwool, or any other semi-rigid mineral wool exterior insulation, make sure your details include proper rodent and bug screens at all terminations and penetrations. And if they don’t—White Glove Contracting is here to help.
Contact us today for expert exterior insulation installation and envelope consulting on your next project.