Improving the thermal performance of a building enclosure and minimizing the energy use of buildings has received increasing focus in the drive for sustainability and energy security. We have seen the adoption of increasingly stringent enclosure thermal performance requirements in building codes, ASHRAE and voluntary programs such as LEED. These include requirements aimed at controlling heat flow through the opaque portions of the building enclosure. Adding insulating materials to the enclosure assemblies is one obvious way to do this, but insulation is not effective if there are easy heat flow paths around it. This is why codes and standards are progressively moving to requirements based on Effective Thermal Resistance; which requires identifying and mitigating thermal bridges.
Thermal bridges in building enclosures can be defined as localized areas with higher thermal conductivity than the adjacent areas. A typical thermal bridge in a building enclosure would be where a material of high conductivity, such as a structural attachment or metal flashing, penetrates the insulation layer. The presence of a thermal bridge in a building assembly could result in:
- Higher heat transfer through the assembly
- Colder surface temperatures on the warm side of the assembly
- Warmer surface temperatures on the cold side of the assembly
The possible consequences of these conditions include:
- Higher energy use for heating
- Higher energy use for cooling
- Noncompliance with energy code requirements
- Discomfort due to cold surfaces
- Condensation or frosting on chilled surfaces, which could lead to:
− Corrosion of metal elements and structure
− Decay of wood-based materials
− Visible patterns on interior or exterior surfaces due to variations of surface temperature and drying potential
- Mold growth and associated health concerns
A primary design goal for any building enclosure assembly in cold climates is to have a continuous and aligned layer of insulation, minimizing the number, size and impact of thermal bridges. Many designers are not fully aware of how significantly some common thermal bridges compromise the value of the installed insulation.
As shown later in this Design Guide, the heat transfer through common thermal bridges in a building can easily exceed the heat transfer through the insulated opaque enclosure assembles (reference ASHRAE RP-1365). If designers do not consider the impact of thermal bridging, they will not meet the intent of energy standards such as ASHRAE 90.1 and ASHRAE 189.1, and voluntary sustainability programs such as LEED, Green Globes and Passive House.
Schöck provides product solutions specifically designed to mitigate or eliminate structural thermal bridges in commercial building construction. For over 30 years, Schöck has developed research and expertise in building physics and understanding the problems of thermal bridging to provide the most effective solutions.
The intent of this manual is to provide designers with:
- A better understanding of how heat moves through building assemblies and how this affects the surface temperatures and condensation control of building assemblies
- Methods to calculate the impact of thermal bridges on the energy flows, temperature and moisture performance of building enclosures
- Examples showing how the impact of thermal bridges can be mitigated during design, both in general and using Schöck Isokorb® thermal breaks
- Example procedures to evaluate energy benefit using whole building energy modeling
- Design guidance on how best to integrate Schöck Isokorb® thermal breaks for performance and code compliance