Thermal Bridging Research: Foundation to Wall Transitions

One of our many in-house research efforts is a large, collaborative project. We investigated the Thermal Performance of Façades through the AIA Upjohn Research Initiative.

Thermal bridging in building construction occurs when thermally conductive materials penetrate through the insulation creating areas of significantly reduced resistance to heat transfer. These thermal bridges are most often caused by structural elements that are used to transfer loads from the building envelope back to the building superstructure. Though design professionals generally understand that thermal bridging is a concern, few can quantify the extent of its impact on building performance.

Small changes in designs can still lead to dramatic improvements in performance. With careful detailing and attention to the issues of thermal bridging, the design and construction industry can improve the performance of our building envelopes.

Today we’re sharing our findings regarding foundation to wall transitions.

The wall transition above the foundation wall is a consistently problematic area for thermal performance. This transition has been observed to affect the wall R-value by as much as 70-75% for three factors. The transition of wall assemblies is usually necessary because most wall assemblies above grade are not able to withstand conditions below grade. The switch of wall assemblies usually results in an offset and discontinuity of the insulation. The second reason this is a difficult area to detail is that this offset typically occurs at the termination of waterproofing, which results in the metal flashing spanning across the insulation, creating an additional thermal bridge. The third factor to take into account is that the transition often occurs where the slab on grade meets the foundation wall. The structural stability of the connection creates another discontinuity of the insulation that is hard to overcome.

To determine ways to improve the performance we looked at a number of options for improved details. The first was a structural thermal break in the concrete slab where it connects to the foundation wall for a foundation wall that was insulated on the interior. This allows for some thermal continuity between the slab insulation and the interior insulation. The most improved option was a concrete foundation wall built of a sandwich panel with insulation integral within the concrete. This allowed the insulation to be as continuous as possible with the above grade insulation and minimizes the shelf condition at grade.

Related:
Thermal Performance of Facades: Final Report
Thermal Bridging Research: Curtain Walls
Thermal Bridging Research: Investigating Insulation Thickness for Renovations
Thermal Bridging Research: Masonry Veneer Walls
Thermal Bridging Research: Window Transitions