Course Description:

Getting the base-of-wall right is one of the most consequential decisions in enclosure design, and one of the easiest to get wrong. Where insulation meets the foundation, where thermal mass meets resistance, and where air barriers have to transition across assembly types, the details stack up fast. Skipping or simplifying any one of them can compromise the performance of everything above.

In this live studio broadcast, RDH Building Science specialist James Bourget deconstructs an at-grade wall assembly to show how insulation placement and thermal mass work together to reduce heat flow and improve overall enclosure performance. Participants will see firsthand how interior thermal mass and exterior resistance complement each other and why getting that balance right matters for long-term energy efficiency.

The session also walks through the air barrier transitions that occur at grade level, comparing approaches across different assembly types. Drawing on real project experience, James highlights common decision points, trade-offs, and the factors that should drive material and detail selection at this critical enclosure zone.

This session is ideal for builders, architects, and trades who want a clearer picture of how at-grade decisions affect the whole enclosure system, and who want practical strategies they can apply on their next project.

Course Learning Objectives

By the end of this course, participants will be able to:

1. Understand the benefit of using thermal mass on the interior, with resistance to heat flow on the exterior.
2. Identify various air barrier transition options based on assembly type.
3. Discuss the factors that contribute to selecting an air barrier transition option based on assembly type and site conditions.
4. Recognize how insulation placement decisions at grade impact the buildability, continuity, and effectiveness of the overall enclosure air and thermal barrier strategy.

PRESENTED BY: James Bourget | RDH Building Science

*This webinar is supported by  

This High-Performance Enclosures: Starting at the Bottom webinar is Part 3 of RDH’s five-part High-Performance Enclosures series.