By Andrea Love, AIA, LEED AP and Charles
Klee, AIA, LEED AP
For a long time, the thermal performance of façades in research buildings has been undervalued because of the large volumes
of air being moved through the space. Using the
arsenal of strategies currently available to lab
designers—such as chilled beams and low-flow
fume hoods—air volumes in many contemporary research labs have been reduced to the
minimums needed to maintain health and safety, and the performance of the building envelope is having an increasing influence on the
building’s energy usage and thermal comfort.
Thermal bridging in building construction
is a well-understood phenomenon frequently
resulting from structural elements that penetrate through insulation layers and create a
path for unimpeded heat transfer. While the
construction industry has begun to develop
materials and assemblies intended to mitigate
this effect, there is little available research documenting the extent of the problem or the performance benefit that will result from the use of
these new products. Anecdotal reports suggest
that thermal bridges in conventional construction may reduce insulation effectiveness by as
much as 40%.1
Payette received funding from the American
Institute of Architect’s Upjohn Research Grant
to better understand and quantify the impact of
thermal bridging on the overall performance of
the building envelope. The intent of this research
is to bring rigor to the investigation of thermal
bridges in commercial construction by using
thermal imaging equipment to quantify actual
performance of built installations; and use these
results along with heat-transfer modeling software to suggest and then analyze performance
improvements. Preliminary results suggest that
through the use of readily available construction
materials and careful detailing, it’s possible to
effect a 50% or greater reduction in the impact
of common thermal bridges (Figure 1).
In order to understand how façades are per-
forming in the field, we used a thermal imaging
camera to determine the R-value and identify
sources of thermal bridges in recently complet-
ed projects designed by the firm. Teams were
deployed to locate and document a range of
façades and conditions. Using the methodology
tested by Madding, 2 we were able to measure
the exterior air temperature, interior air tem-
perature and radiant temperature in order to
calculate the R-value of the assembly.
We collected thousands of images from
visits to 15 buildings. These images were then
organized by assembly type, and we noted conditions that were likely to affect performance,
such as the transition to a foundation wall or
adjacency of a window. Having established a
library of data that was primarily focused on
thermal bridging, the research team was able
to identify typical problem areas thematically. We noted that they fell generally into two
categories: one that is related to structure that
supports façade and roof systems, and one that
is more about material transitions.
• Existing building façade renovations.
• Masonry wall systems.
• Metal panel wall systems.
• Curtainwall systems.
• Rainscreen wall systems.
Transitions and penetrations:
• Transitions between new and existing
• Transitions between different wall systems.
• Transitions between windows and walls.
• Foundation-to-wall transitions.
• Roof-to-wall transitions.
• Roof parapets.
• Roof penetrations.
• Seismic and movement joints.
• Louver openings.
Using heat flow simulation software, such
as Lawrence Berkley National Laboratory’s
THERM, it’s possible to study alternative
designs. The research team prepared THERM
models of the areas being studied which were
calibrated to the performance measured in the
field with the thermal imaging camera. With
validated THERM models in place, the research
team is currently testing the quantitative
impacts of potential design improvements.
The THERM modeling platform enables us to
probe a detail and effectively measure the changes
in heat transfer associated with different detailing
or materials selections. Using this approach, we’re
able to make quantifiable recommendations for
improvements that can then be rigorously evaluated on a lifecycle basis for a specific project.
CASE STUDY: INTERIOR SPRAY FOAM IN EXISTING
Preliminary findings in our research show
continued on page 14
The increasing significance of thermal bridging in
lab building envelopes
Figure 1: Diagram of thermal bridging on assembly U-value as insulation increases.