Building or buying our own house or apartment is very often an investment we can afford once in a lifetime, so we must approach the subject with special care. Some of the mistakes made will translate into lower comfort, others will cost us a lot throughout the time we live in the building.
One of the biggest challenges for general contractors and private investors alike is to make the property as energy efficient as possible – that is, to ensure that we don’t have to drastically cut back on electricity or heat consumption for fear of very high bills.
Meanwhile, all it takes is a minor oversight – the use of inappropriate materials or carelessness at the construction or insulation stage – for a building to develop a thermal bridge. What is a thermal bridge? What are the types of thermal bridges? How to eliminate thermal bridges in buildings? Here is everything you should know about thermal bridges.
What is a thermal bridge?
Let’s start at the very beginning, i.e. with a definition. Thermal bridge – what exactly is it? For the phenomenon known as a thermal bridge, the definition is quite simple. It is such a place in the building through which most heat penetrates. Answering the question of what is a thermal bridge, it should therefore be noted that, although undesirable, it is nevertheless natural. This is because in every building there are places that, by design, let more heat through than others. These may include parts of the roof slope, for example, or around doors and windows. These places may have poorer thermal insulation performance than the areas they are adjacent to. So while thermal bridges in a house are not unusual, they remain very undesirable for the builder and the user.
However, it is not enough to answer the question of what thermal bridges are – it is still necessary to verify how much heat actually escapes through a given insulation or construction element. Some phenomena cannot be stopped. There are no completely airtight buildings – and if there were, we would rather not want to live in them, as they would resemble futuristic hubs known from movies about astronauts exploring alien planets.
There are standards that determine the maximum amount of heat that can escape through thermal bridges. If they are exceeded, then the energy efficiency of the building drops sharply, and we begin to look forward to each subsequent energy bill with trepidation. It is also more difficult to sell for a good price a house in which numerous thermal bridges are present.
But high bills are not all that the owner of a building with heat bridges will face. Because in their vicinity the interior wall is colder than the temperature in the house, a thermal bridge can lead to the dew point – a situation where the water vapor present in the room condenses. The wall becomes damp, which in turn creates ideal conditions for mold growth. Mildew on the wall is dangerous for householders, as it is the cause of many very serious diseases, aside from aesthetic issues.
Thermal bridges – where do they occur?
In the case of the unpleasant phenomenon of thermal bridging, the definition often also includes the identification of the places where excess heat loss is most common. This is because thermal bridges in buildings occur in very specific areas, related to the structure of the house and its thermal insulation. Among the most common are thermal bridges at windows and doors. The culprit in this case is both inadequate insulation and the very nature of the door and window frames. Heat loss through windows and doors cannot be avoided completely, but it can be counteracted by choosing woodwork with better parameters and carefully sealing the installation site.
Very often thermal bridges are formed in the highest parts of the house – heat escapes from the building through the roof. The phenomenon of warm air rising upward is normal, and the team responsible for erecting the house or building the roof slope, must be aware of it.
Inadequate insulation between the upper surface of the exterior walls and the roof slope means that we can’t achieve a satisfactory temperature in the house despite turning up the heaters, for the heat consumption is brilliantly visible on the bills. Suspicion of the existence of a thermal bridge at the junction of the wall and the roof should arise especially in winter, when we notice that the snow accumulated on the roof melts much faster at the junction lines of the walls and the roof. A place prone to too much heat transfer is also the chimney. In this case, observing the snow won’t do us any good, because the chimney in use is, by definition, warmer than the roof.
From the very top of the building, let’s move to the very bottom. Inadequate foundation insulation is another cause of thermal bridging. In this case, the problem is more one of too much cooling passing into the building. It is the problem of maintaining high energy efficiency that is one of the main reasons (second only to the cost of construction) why more and more investors are abandoning the construction of a basement.
Thermal bridging in a block of flats, in a single-family house or in any other building can also occur in external walls. Once again, we are talking about a natural phenomenon, which with current technology we are not yet able to eliminate completely. The cause of thermal bridges in this case is the combination of materials characterized by different heat transfer coefficients. This means that some building materials conduct heat more easily than others. Fortunately, there are already ways to level thermal bridges in walls – both multi-layer and single-layer. However, it is best to think about them while the building is still being erected.
It is also very difficult to provide thermal insulation of such places, which by design are intended to be used for cooling and serve as open. This primarily refers to balconies and loggias. This is why modern energy-efficient and passive houses are devoid of them. However, if you are buying a house with a balcony, or at the design stage you do not want to deprive yourself of the joy of having one, you need to take even more care to ensure proper insulation.
Types of thermal bridges
When it comes to thermal bridges, the types mentioned most often are point bridges and linear bridges. What are the characteristics of each and what are their specifics?
- Point thermal bridges: are limited, single places characterized by higher thermal transmittance. They are formed where external elements are anchored to the wall structure, thus cutting through the insulation layer. Point bridges include places where Styrofoam, balustrades or canopies are attached.
- Linear thermal bridges: are much more extensive than point thermal bridges. They are formed at the junction of various structural elements of the building, hence their linear nature. A standard example is the line of intersection of thermal insulation through the balcony slab, as well as the line of contact between the exterior walls and the roof slope.
It is worth noting that the formation of thermal bridges in each of the examples mentioned is basically inevitable. Convection is a natural phenomenon and will occur wherever there is a temperature difference. So by using the right building and insulation materials, we will not ensure 100% airtightness of buildings, but we can significantly reduce heat loss.
How to eliminate thermal bridges?
The best way to eliminate thermal bridges is to prevent their formation – however, we only have this possibility at the stage of building construction. When we are already using the house and only then we notice excessive heat loss, the range of our options is limited – which does not mean that nothing can be done.
The first step is to order a thermal imaging survey of the building. Not every thermal bridge will be easy to locate by home means. Methods suggested on the Internet (e.g., infecting the house with a substance that causes visible smoke and observing its movements) can be unreliable and help partially locate air leaks themselves, rather than changes in energy conduction. They can also be dangerous. By analyzing thermograms, we will see which areas need our attention.
Once we know where the greatest heat loss occurs, we can take a number of measures to increase a building’s energy efficiency. Sometimes small investments are enough to achieve spectacular results. For example, if we discover that doors and windows are the most problematic, they will need to be properly sealed once again. In the case of older buildings, they will probably need to be replaced – the woodwork is working and gaps can appear over time.
A more complete thermal modernization of the building will already be more expensive. Some techniques are quite easy and insulation can be handled by people without advanced construction knowledge (e.g. spray foam insulation), for others it is worth engaging professionals (e.g. styrofoam insulation). It’s also worth checking the municipality’s current thermo-modernization subsidy programs – this is the best way to significantly reduce the cost of renovation. Everyone will benefit: thermal bridges when insulating disappear, as a result we use less energy for heating. We pay lower bills and reduce our impact on the environment.
Thermal bridging in the block and in the house – how to reduce them?
If you don’t want to be disappointed by the effects of thermal upgrading, you need to think about thermal bridges while you are still building or buying the property. In the former case, make sure the general contractor knows his job and can reduce heat loss in the house. Ideally, commit the contractor to specific U-factors or fRsi, or n50 airtightness. Then conduct a thermal imaging survey for acceptance of the work and a leakage test. If you are buying an apartment in a block of apartments or a detached house, the seller (whether a private individual or a developer) is obliged to provide you with the building’s energy certificate, from which you will learn how much energy needs to be consumed to ensure that users have access to electricity and heat at a satisfactory level for comfortable living. However, the MPC is only a purely theoretical evaluation of a more design and technical intent with declared values. The values calculated according to the methodology are not an assessment of the actual quality of workmanship and materials used.
