The 2021 Midwest Building Science Symposium brought together some of the country’s most knowledgeable high-performance builders, including Travis Brungardt of Catalyst Construction, for a town hall-style exchange of practical building knowledge. Hosted by Fine Homebuilding’s Patrick and Rob Wotzak, the symposium tackled the core challenges of modern residential construction: how to build homes that are durable, energy-efficient, comfortable, and healthy. The discussions ranged from air barrier systems and insulation strategies to moisture management and the real-world economics of high-performance building. This article distills the essential lessons from that symposium for builders and homeowners alike.
What Building Science Means for Residential Construction
Building science is the study of how a home performs as a system. Every component—the structure, the insulation, the air barrier, the mechanical systems, the windows—interacts with every other component. When one part fails or is installed incorrectly, the whole system suffers. The 2021 symposium emphasized that understanding these interactions is not optional for modern builders; it is a fundamental requirement for delivering durable, comfortable homes.
The House as a System
A home operates through four primary control layers: water management, air control, vapor control, and thermal control. These layers must be continuous across the entire building envelope. A gap in any one of them can lead to energy loss, moisture damage, or indoor air quality problems. The symposium presenters stressed that the most successful high-performance homes are those where builders design and install these layers with intentionality, not guesswork.
- Water management: Rain screens, flashing, and drainage planes that direct bulk water away from the structure
- Air control: Continuous air barriers that stop uncontrolled airflow through the envelope
- Vapor control: Smart vapor retarders that allow drying in at least one direction
- Thermal control: Continuous insulation that minimizes thermal bridging
Why Performance Testing Matters
One of the recurring themes at the symposium was the value of testing. Blower door tests, infrared thermography, and duct leakage tests are not optional extras for high-performance builders; they are essential quality assurance tools. Travis Brungardt shared that his team tests every project, often multiple times during construction, to catch problems before they are buried behind drywall. This commitment to verification separates true high-performance builders from those who merely claim to build well.
The Art and Science of Air Sealing
Air sealing emerged as one of the most discussed topics at the symposium, and for good reason. Uncontrolled air leakage can account for 30 to 40 percent of a home’s heating and cooling load. It also carries moisture into wall cavities, where it can condense and cause rot, mold, and failed insulation. The builders at the symposium shared their preferred air sealing strategies, emphasizing that an effective air barrier must be both continuous and durable.
Key Air Sealing Locations
- The top plate and attic plane: Every penetration through the top plate, whether for wiring, plumbing, or ductwork, must be sealed. The attic floor is often the single largest source of air leakage in a home
- The rim joist area: This intersection of foundation, floor framing, and exterior wall is notoriously difficult to seal but critically important. Rigid foam with spray foam edges is a common solution
- Window and door rough openings: The gap between the frame and the rough opening must be sealed on both the interior and exterior sides. Compressible gaskets and low-expansion spray foam are preferred over caulk alone
- Penetrations through exterior walls: Every electrical box, exhaust vent, and pipe penetration through the exterior wall needs a sealed boot or gasket
Choosing Air Barrier Materials
| Material Type | Typical Application | Permeance | Durability |
|---|---|---|---|
| Liquid-applied membrane | Sheathing seams, complex details | Variable | High when properly applied |
| Self-adhered membrane (peel-and-stick) | Window rough openings, transitions | Low (Class I or II) | Very high |
| Fluid-applied flashing | Penetrations, small gaps | Moderate | High |
| Compressible gaskets | Between framing and rigid insulation | N/A | Moderate |
| Spray polyurethane foam | Rim joists, irregular gaps | Closed-cell: Low | High |
Builders at the symposium also stressed the importance of air leakage testing to verify that the installed air barrier actually performs as designed. A blower door test before drywall installation allows crews to locate and fix leaks while they are still accessible.
High-Performance Wall Assemblies and Insulation Strategies
The symposium featured extensive discussion of wall assembly design, with several builders presenting their preferred approaches for different climate zones. The consensus was clear: there is no single best wall assembly, but all successful high-performance walls share common attributes—including continuous insulation, an effective air barrier, and the ability to dry if they get wet.
Comparing Wall Assembly Approaches
Three wall assembly types dominated the conversation at the symposium. Each offers different trade-offs between cost, complexity, and performance.
Double-stud walls consist of two separate rows of stud framing that create a deep cavity for insulation. This approach eliminates thermal bridging through the studs and allows for R-40 or higher insulation values using relatively inexpensive materials like dense-pack cellulose. The downside is the increased wall thickness, which reduces interior floor area and complicates window and door installation details.
Exterior insulated walls use rigid foam or mineral wool board applied to the exterior side of the structural sheathing. This strategy keeps the structural frame warm, reducing the risk of condensation in the wall cavity. It also interrupts thermal bridging through the studs. The symposium builders noted that this approach works well with standard framing techniques, making it accessible to crews that are not yet familiar with advanced framing methods.
Structural insulated panels (SIPs) offer a factory-built solution with integrated insulation and structural sheathing. SIPs provide excellent air tightness and insulation continuity, but they require careful planning for penetrations and can be challenging to modify in the field. Several symposium attendees shared stories of successful SIP projects where the key was investing in detailed shop drawings before fabrication began.
Insulation Material Selection
The choice of insulation material has a direct impact on both thermal performance and long-term durability. The builders at the symposium emphasized that high-performance wall assemblies require matching the insulation material to the specific assembly design and climate conditions.
- Dense-pack cellulose: Excellent thermal performance, low embodied energy, good acoustic damping, and the ability to settle into irregular cavities. Must be protected from bulk water
- Spray foam: Exceptional air sealing and insulating properties. Closed-cell foam also adds structural strength. Higher cost and environmental concerns around blowing agents
- Mineral wool: Fire resistant, water repellent, and dimensionally stable. Provides good sound control. More expensive than fiberglass but easier to install tightly
- Fiberglass batts: Lowest cost option but requires meticulous installation to avoid gaps and compression. Best suited for simple cavities with minimal obstructions
Moisture Management and Long-Term Durability
Moisture is the single greatest threat to building durability. The 2021 symposium devoted significant time to moisture management strategies, with experienced builders sharing hard-won lessons from projects that failed and those that succeeded. The unifying principle was simple: control bulk water at the exterior, manage vapor diffusion thoughtfully, and design every assembly to dry in at least one direction.
Exterior Moisture Management
The first line of defense against moisture damage is the exterior cladding and drainage system. Properly installed rain screens, flashing at all transitions, and generous roof overhangs all reduce the amount of water that reaches the sensitive layers behind the cladding. The symposium panelists emphasized that flashing details, particularly at windows, doors, and deck attachments, are the most common points of failure in otherwise well-designed homes.
Interior Moisture Control
Inside the home, moisture is generated by occupants, cooking, showering, and mechanical equipment. The symposium builders recommended balanced ventilation systems with heat or energy recovery to manage interior humidity without wasting conditioned air. They cautioned against relying solely on exhaust-only ventilation, which can depressurize the home and draw moisture into wall cavities from the exterior.
Building Durability Through Design
The most durable homes are those designed with redundancy in their moisture management systems. A wall assembly that relies on a single line of defense, such as a vapor barrier or a single layer of weather-resistive barrier, leaves no margin for error. The symposium participants advocated for a belt-and-suspenders approach: proper flashing and drainage at the exterior, a well-designed air barrier system, and building energy efficiency measures that also improve durability, such as conditioned crawl spaces and insulated slabs.
Lessons for the Modern Builder
The 2021 Midwest Building Science Symposium reinforced that high-performance building is not about exotic materials or unaffordable upgrades. It is about doing the fundamentals correctly: designing continuous control layers, testing the work, and detailing every connection with care. Builders who embrace these principles deliver homes that are more comfortable, more durable, and less expensive to operate over their lifetime. The symposium proved that the Midwest building community is leading the way in turning building science theory into real-world practice.