Thermal bridging can have a major impact on a dwelling’s overall thermal efficiency, even in very well-insulated homes. According to recent studies, thermal bridging has been found to be responsible for up to 30% of a home’s heat loss.
In this blog, I will show you what exactly is thermal bridging, its consequences, causes, types and strategies to reduce them. Let’s get started.
What is a thermal bridge?
A thermal bridge is a part of an object that has a higher thermal conductivity than the surrounding areas. This allows heat to flow through it with the least amount of resistance. The object’s thermal resistance is reduced as a result of thermal bridges. It is also known as a cold bridge, heat bridge, or thermal bypass.
Thermal Bridging is the phenomenon by which heat easily flows away through a part of the construction that has very less thermal resistance compared to its surroundings. This leads to uneven heating in a building.
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Thermal Bridging Consequences
- Thermal bridging in buildings will increase the amount of energy needed to heat and cool a room.
- Results in condensation of moisture inside the building envelope
- Cause thermal discomfort.
- Causes additional heat losses in colder climates and require more energy to mitigate.
Thermal Bridging Causes
Thermal bridging can be caused by:
- The points where the wall and the floor come together
- Wall-to-roof junctions
- Pipe and cable access holes in the building envelope
- Window and door reveals
- Steel wall links in masonry work, (e.g. cavity walls)
Thermal Bridging Types
There are several types of thermal bridges, which can be further classified as follows:
Repeating Thermal Bridges
Repeating thermal bridges follow a trend. And it is “repeated” over a large area of the building’s thermal envelope. The examples include:
- Steel wall ties used in masonry cavity wall construction
- Ceiling joists used in cold pitched roofs when insulating at the ceiling level
- Split created by timber framing when insulation occurs between the studs
Repeating thermal bridges are normal and predictable. But still, they result in significant heat loss. Because of that, we should consider thermal bridging when calculating the U-value and during planning, design, and construction.
Non Repeating Thermal Bridges
- Thermal bridges appear periodically. And, they are located where the building’s thermal insulation has a split in it.
- Non-repeating thermal bridges can form where materials with different thermal conductivity come together to form the envelope.
- Examples include reveals around windows and doors, loft hatches, and other openings in the building’s thermal envelope.
Geometrical Thermal Bridges
Geometrical thermal bridges are induced by the building’s geometry, as the name implies. They are more likely to occur with complex building forms. So it’s best to keep the overall design as simple as possible to avoid them. The examples include:
- Corners of exterior walls
- Wall-to-floor junctions
- Wall-to-roof junctions
- Junctions between adjacent walls
Why should we avoid thermal bridging?
Let me give you a set of reasons that would prompt you to avoid thermal bridges during construction of a building.
Decreased Insulation Effectiveness
- Buildings that are airtight and have high levels of insulation may be more vulnerable to thermal bridges.
- When high levels of air tightness and insulation are present, thermal bridges can account for up to 30% of heat loss.
- During the warmer months of the year, thermal bridges can actually cause an increase in heat gain. This can contribute to overheating of the indoor room.
Increased expenditure of energy
The amount of heat lost depends on the intensity and frequency of thermal bridges. it’s best to design and construct buildings with no thermal bridges. If you don’t, you’ll end up spending more money to maintain a constant and comfortable indoor air temperature. This will undermine the intention of installing energy efficiency measures in the first place.
Greater risks of Condensation, mould, and rot
- Thermal bridges can cause interstitial condensation within walls and other building elements.
- Since it cannot be seen from the inside or outside of the house, interstitial condensation can be extremely hazardous.
- As the interior temperature falls below the dew point, moisture in the warm air condenses into water droplets.
- Mold growth is one of the most common side effects of condensation.
- Invisible mold can develop out of reach, resulting in poor indoor air quality and negative health effects for building occupants.
Strategies to reduce Thermal Bridging
Depending on the source, site, and form of construction, there are many methods that have been proven to minimise or eliminate thermal bridging. The aim of these approaches is:
- Either create a thermal break where a building component would otherwise stretch from outside to inside.
- Or, minimise the amount of building components that span from outside to inside.
These are some of the strategies:
- Using a continuous thermal insulation layer, such as rigid foam board insulation in the thermal envelope.
- Lapping of insulation where direct continuity is not feasible.
- Usage of Wall assemblies with double and staggered walls.
- Using Insulating Concrete Forms (ICFs) and Structural Insulated Panels (SIPs).
- Reduce the framing factor by removing unnecessary framing members.
- Increased insulation depth by using raised heel trusses at wall-to-roof junctions.
- Installation of high-quality insulation with no voids or compressed insulation.
- Adding a gas filler and a low-emissivity coating to double or triple-pane windows.
- Installing windows with thermally broken low conductivity frames.
Keep this strategies in mind so that they can help you construct a building with zero thermal bridges. Hope you found them useful. Let’s know in the comments.