LaboratoryDesign|MAR|APR 2014 15
used in the design of contemporary research labs. Because the insulation
typically lies behind the cladding and ventilated cavity, but before the
supporting stud or structural wall, the rails, hat channels, Z-girts and clips
required to support that exterior rainscreen all become thermal bridges.
Typically made of highly conductive aluminum, continuous supports
such as Z-girts were observed to decrease the R-value of the assembly by
45 to 60% from the design-intended R-value. Rainscreens that employed
discontinuous supports, like clips, showed a significant improvement
in thermal performance, though the R-value was still determined to fall
short of the theoretical design value by 15 to 25%.
Because supports like Z-girts are so widespread in commercial con-
struction today, and have been noted in the industry as common thermal
bridges, a number of manufactures have developed alternative solutions.
These thermally broken, off-the-shelf products have been developed to
meet the structural requirements to transfer the load of the exterior cladding, while not allowing continuous aluminum to pass through the insulation. By limiting the penetrations to only screws and fasteners, and providing insulating pads between metal attachments, we can now achieve
the elusive goal of providing continuous insulation. Based on our heat
flow simulations, these thermally broken support systems allow a wall to
achieve an R-value that is only about 5% less than the clear wall R-value.
While each manufacturer has their own strategy deterring the flow of
heat, the options that exist give designers the opportunity to find the
rainscreen attachment system that works best for their project conditions.
The significant impact observed from thermal bridging suggests a more
substantial problem than simply one of condensation risk in a humidified
lab environment. The data collected thus far shows that thermal bridging
can easily double the conductive heat transfer over what was intended
for the design. As we strive to reduce air change rates within the lab
environment, we are seeing that envelope heating and cooling loads are
an increasingly significant portion of the building energy demand. This
research shows that thermal bridging already has a significant impact on
the performance of our buildings, and that controlling this path for heat
transfer is the key to achieving to truly high-performance façades.
Not surprisingly, the majority of the typical problems identified in this
research have centered on transitions between systems and the structural
assemblies necessary to support exterior cladding. While many building products exist on the market and it’s easy to implement alternative
designs that improve thermal performance, it’s clear that not all manufacturers are equally sensitive to the magnitude of the problem and
marketing material must be scrutinized carefully. As we seek to achieve
higher-performing research buildings, careful attention and analysis is
needed during design to minimize thermal bridges and deliver buildings
that perform as anticipated.
1. Morrision Hershfield. (2011). “Thermal Performance of Building
Envelope Details for Mid- and High-Rise Buildings” (ASHRAE 1365-
RP). Atlanta: ASHRAE Technical Committee 4. 4.
2. Madding, R. (2008). “Finding R-Values of Stud Frame Constructed
Houses with IR Thermography.” Inframation 2008 Proceedings vol. 9.
Charles Klee drives Payette’s Research and Innovation Initiative, bringing
a detailed understanding of emerging building science and sustainable technologies. Andrea Love leads Payette’s sustainability initiatives. Combining
her background in architectural practice and building science, she provides
sustainable design knowledge and energy expertise. Kansas City, MO | 800.821.5525
The Protector® XStream®
a fraction of the
energy used by
Regardless of desired
face velocity, high-performance Protector®
XStream® Hoods consume the lowest CFM —
and we can prove it. They
t Unobstructed sight line of 37-1/2”
t Significant savings to your bottom line
t Unmatched containment for an extremely safe
Visit www.labconco.com/ProveIt or call
800.821.5525 to learn how our full-line of
high-performance fume hoods will save you money.
Now that’s worth smiling about.
can give you something
to smile about