Thermal breaks are materials that stop or reduce energy transfer by interrupting a material with high thermal conductivity. Examples include steel wall ties, window frames and doors and plumbing pipes.
They can also cause a number of problems including lower energy efficiency, condensation and health risks. Here are the main reasons to avoid them:
Insulation Values
Many building professionals cite high insulation values and airtight buildings as the two most important factors in reducing energy consumption, but thermal bridging can undermine these gains. This is because when a thermal bridge is present, heat can bypass insulation and escape your home or building faster than it would if the structure were insulated continuously.
Wall studs, doors and window frames, and balcony and parapet walls are common examples of thermal bridging. They interrupt the continuous insulation layer and act as conduits for heat flow, increasing a building’s overall heating loss by up to 20%. Utility penetrations, like pipes and wires, can also create thermal bridges as they pass through the insulation layer.
To minimize the impact of thermal bridging, it is important to use a continuous insulation system and include thermal breaks where necessary. This means that insulation should be installed tightly around the edges of the frame, and fasteners should be either plastic or thermally broken. In addition, the choice of tape used to seal the insulation sheets together is critical as it can also affect the effectiveness of the insulation. To ensure the best performance, a tape with a low thermal conductivity is recommended. A thermally broken tape will also reduce the impact of any gaps that may be present between the sheets.
Condensation
Thermal bridges can undermine the energy efficiency of a home even if a high level of insulation has been installed. This is because the bridges are made of materials that are more conductive than the insulation and provide an easy pathway for heat flow. In addition, these areas often encourage condensation which has numerous negative impacts on a building and its occupants.
In new construction, a clear wall system reduces the impact of thermal bridging on overall performance by eliminating or minimizing thermal bridges in critical places such as slabs, parapets, corners and glazing transitions. In existing homes, installing insulation to reduce the amount of air escaping through the walls and properly detailing any transitions and penetrations will help to mitigate thermal bridging.
For steel-framed buildings, insulating the exterior sheathing is one way to prevent thermal bridging because it blocks the steel from the inside and outside of the walls. However, there is also a need to use a thermal break tape on any junctions or openings in the frame to further reduce bridging. For wood framed walls, putting insulation between the studs is another effective way to avoid thermal bridging. This is best done by wrapping the studs with insulation before attaching sheathing. If the insulation is not installed correctly, it may bind to the studs and not block the thermal bridge. This can lead to moisture damage which creates rot and rust, and it may not be visible because it takes place inside the walls.
Moisture Damage
A thermal bridge creates a path of least resistance for moisture, facilitating condensation when warm air meets cooler surfaces. This can damage building materials and lead to moisture-related problems, such as mold and mildew. These problems can cause health issues for building occupants, and they may result in higher maintenance costs.
The impact of a thermal bridge can be quite severe in high-performance buildings, particularly those that are designed to achieve very low U-factors. These buildings often have insulation requirements that must be met and that require a very tight enclosure. In order to meet these requirements, a qualified building envelope analysis must be performed prior to construction and monitored throughout the construction process. This can help to identify and correct the problem of thermal bridging so that the building performs as intended in terms of energy consumption, comfort for occupants, and use of the structure.
For new construction, continuous insulation and eliminating thermal breaks are key strategies for minimizing the negative impacts of a thermal bridge. This can be done by incorporating continuous insulation into the design of the wall, using foam strips for structural elements such as window frames, and adding insulation to gaps and compressions in walls. In existing homes, adding continuous insulation will usually require a renovation of drywall and trim to add the extra layer.
Health Risks
Many builders, energy auditors, and homeowners consider high-performance insulation and airtight building envelopes to be the key components to a building’s energy efficiency and comfort. Unfortunately, improper design and construction of a home or commercial building can lead to thermal bridges that dramatically reduce an insulation’s effective R-value and cause energy loss.
The primary impact of thermal bridging is that it allows conditioned air to escape the building, leading to higher energy bills in cold temperatures and hot weather. In addition, it leads to surface and interstitial condensation that encourages mold and mildew growth, as well as rot in materials such as wood and metal.
The good news is that there are ways to avoid thermal bridging, which include properly detailing at transitions between systems and using thermal breaks made of non-conductive materials such as foam board, expanded polystyrene, or closed cell spray foam. Thermal breaks stop conductive heat flow and break the path of least resistance that otherwise would bypass your fiberglass batts, sheep wool batts, or closed-cell spray foam. Properly locating and installing thermal breaks in the most problematic areas of your walls or roof can help you achieve higher R-values, minimize condensation, and avoid structural damage.