How, why and where does thermal bridging occur?
Thermal bridging has been recognized as a significant heat loss problem by building scientists and engineers for decades. The appreciation of thermal bridging and how much energy is wasted with it has been quantified, and brought into focus by three dimensional thermal computer modeling. Energy conservation in buildings can be greatly improved when thermal bridging areas are designed with thermal breaks to insulate and reduce the losses at these critical details.
Because of the focus on sustainable building practices, and conservation, professional organizations such as ASHRAE and IECC have raised standards, and put pressure on architects and builders to find ways to build better, more efficient buildings. By addressing the thermal bridging challenges alone, energy efficiency can be improved by 30%-60% on average, according to engineering and building experts. Proven methods that mitigate these heat leaks and bypasses have been aided by the development of material that have high structural properties and low conductivity.
To understand thermal bridging, we need to begin by looking into different building connections and transition stages of a construction. Often structural components, like steel beams and balconies, extend through the conditioned, heated or cooled space, into the outside environment. This creates a conductive pathway where heat can travel on the path of least resistance. When heat passes through and along these “thermal bridges”, material that is more conductive than the materials surrounding it at these connections, this is a thermal bridge. 3–D thermal modeling has quantified the losses attributed to thermal bridging and found it accounts for a significant portion of preventable heat loss or gain.
These bridges can greatly reduce the efficiency of a building envelope by bypassing insulation. High strength insulation materials, known as thermal breaks, are now manufactured with load bearing qualities while also insulating difficult areas of a building. Thermal breaks are an effective solution to control thermal bridging, and reduce heat loss by 30%-60% on average..
The usual suspects…
There are several details where thermal breaks prove to be beneficial including foundation walls, balcony or canopy installations, roof penetrations, masonry shelf angles, column bases and cladding attachments and more. These are all key areas where energy-saving thermal breaks are essential to improving the overall efficiency of the structure.
Thermal break materials are made of inert, closed cell polymers, that are structurally sound, unaffected by water, and have good insulating properties. There are several ultra-high density materials available, to satisfy structural and thermal resistance requirements. These materials make it possible to insulate, and reduce heat losses at steel, aluminum or concrete transition areas without compromising structural integrity.
Steel has long been a favorite material to build with due to its design flexibility, strength and durability. Most commercial construction uses steel as a structural subframe. For all of its positive attributes, steel buildings can be difficult to insulate, especially when beams or bolts “bridge” the thermal envelope at shelf angles, balconies, canopies, shading devices, signs, or roof penetrations. These steel connections, from inside to outside, can be thermally broken (insulated) with high strength, low conductive material like Armatherm FRR, or a variety of Armatherm 500 ultra-high density polyurethane products.
Masonry shelf angle applications
When working with masonry veneer walls, galvanized steel shelf angles have to be specified to assist with the load bearing. These assist with transferring the masonry load back to the building’s structural frame – usually the steel or concrete slab edge, interrupting the continuous insulation of the wall assembly. Unfortunately, shelf angles can cause significant thermal bridges, making it difficult to meet energy codes. Many energy codes now require thermal breaks at these transitions.
A thermal break solution can help with this. Armatherm™ FRR structural material can be used behind the shelf angle to act as a thermal break on plane with the insulation layer. The Armatherm™ thermal break will result in signiﬁcantly reduced heat loss at the shelf angle connection.
Balconies and canopy connections
Balconies and canopies often use cantilevered or steel elements, connected to slab edges or spandrel beams on the inside of the thermal envelope, passing through the insulation and air barrier layers. Thermal breaks are capable of transferring load in moment and shear connections, without creating significant rotation. It’s imperative that a structural thermal break maintains the integrity of these connections while also minimizing the heat flow.
Cladding is where we see the most common causes of continued insulation being bridged and compromised. The steel clip and girts used often create thermal bridges when connected to steel stud framing, but the efficiency of wall assemblies are improved considerably with the addition of an effective thermal break solution. This works towards preventing heat loss and minimizing subsequent condensation issues caused by thermal bridging. Simply changing from steel z girts to Armatherm non-metallic, FRP Z Girts, can improve the effectiveness of continuous wall insulation by over 90%, and the installation of the Armatherm Z Girt is exactly the same as traditional steel z girts!
On the roof of a commercial building you will often find penetrations such as davits, anchors and supports for dunnage and HVAC equipment, which extend through the envelope and roof insulation, resulting in non-continuous insulation. They’re usually connected to the interior structural elements or trusses which can cause heat flow and transfer. Armatherm FRR or 500 materials can provide a secure, non-conductive base plate to attach through, breaking the conductive pathway and saving energy.
Specifying a thermal break at any of these connections will increase efficiency by up to 60%, while also helping to prevent condensation issues when colder temperatures are transferred inside and cause cold spots on interior walls or ceilings. Neglecting energy transfers can encourage condensation on these spots that can lead to the formation of mold. You can often see the presence of this on ceilings where roofing systems have been installed, or the interior walls of buildings that feature cladded façades or balconies which have not been isolated correctly, or haven’t been isolated at all. Mold can cause serious health issues if it goes untreated, so it’s a detrimental issue which can not only affect the aesthetic of a room, but result in costly remediation projects to eradicate the issue.
Foundation wall connections
Thermal bridges in foundation walls create heat loss within the foundation perimeter, reducing the exterior wall’s effective R-value. The intersection at slab on grade to foundation wall and exterior wall to foundation transition are both key areas where heat can flow out of a building. This occurs when there is a lack of continuous insulation materials.
Heat loss at the base of the foundation wall can be prevented by as much as 60% by using efficient, structural thermal breaks. The Armatherm™ 500 product is a load bearing, thermal break material available in several different densities to provide a range of load capacities with R-values as high as R 3.8 per inch. Thermal bridging at foundation wall applications can also be reduced further by increasing the length and thickness of the slab insulation.
It is especially important for buildings with large, consistent temperature differences, such as cold storage or freezer building to maintain a continuous, monolithic insulation barrier without omissions. Columns in these special buildings must be thermally separated from the relatively warmer earth with structural, load bearing thermal breaks. Not doing so would result in melting and puddling at the column bases. There is also a large saving in the operating cost of these buildings. The cold storage industry has an appreciation for building envelope insulation and continuity.
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