Thermal Break

A thermal break, also called a thermal barrier, is a piece of low-conductivity material placed inside an assembly to interrupt a path that would otherwise let heat flow easily from one side to the other. The idea is simple. Wherever a conductive material such as aluminium, steel or concrete runs continuously from a warm interior to a cold exterior, it acts as a shortcut for heat. Cut that shortcut and fill the gap with something that conducts heat poorly, and the heat flow drops sharply.

The shortcut is called a thermal bridge, and the thermal break is the fix. Thermal breaks are found in aluminium window frames, curtain walls, balcony connections, steel beam penetrations, cladding attachments, refrigerated display cases and many other places where a strong or stiff material has to pass through an insulated layer. This article explains the physics, the main types of thermal break, how their performance is measured, what building codes and standards now require, and where thermal breaks fall short.

Thermal bridges: the problem a thermal break solves

What a thermal bridge is

A thermal bridge, sometimes called a cold bridge or heat bridge, is an area or component that has a higher thermal conductivity than the materials around it. Heat follows the path of least resistance, so it crowds through the bridge. The result is that the whole assembly insulates less well than its insulation alone would suggest.

The materials that make buildings strong are mostly good conductors of heat. In his 2008 essay "A Bridge Too Far," the building scientist Joseph Lstiburek of Building Science Corporation put it bluntly: steel, concrete, aluminium and glass are all thermally conductive, and "except for concrete, we make frying pans out of all of them." He wrote that modern buildings are built "like heat exchangers with protruding fins," with exposed slab edges, concrete frames and cantilevered balconies carrying heat straight through the envelope.

Why it matters so much

Thermal bridges cause three kinds of problem.

Extra heat loss and gain. In winter, heat escapes through the bridges. In summer, heat flows in. Either way, the building uses more energy for heating and cooling than its designers expected. Wikipedia's article on thermal bridges notes that simple one-dimensional calculations can substantially underestimate heat transfer when thermal bridges are present, so a building's predicted energy use may be too low.

Cold surfaces, condensation and mould. Where a bridge carries heat out, the interior surface around it becomes colder than the rest of the wall. If warm, humid indoor air touches a surface below its dew point, water condenses. Repeated condensation feeds mould, damages finishes and degrades insulation. An article in Construction Canada notes that unmitigated slab-edge thermal bridges can drop interior surface temperatures to about 13 °C (55 °F), which can be a condensation risk in cold climates, depending on indoor humidity. Thermal bridges at windows can also cause frost and ice on frames and glass.

Ghosting and comfort. Dust and soot tend to deposit on cold areas, leaving visible stripes on walls and ceilings over studs or other bridges, an effect called ghosting or thermal tracking. Cold surfaces also make rooms feel draughty and uncomfortable even when the air temperature is fine.

Where thermal bridges occur

Common thermal bridge locations include:

• floor-to-wall junctions, especially concrete slabs that run through the wall to the outside
• balcony-to-wall connections
• roof-to-wall junctions and parapets
• window and door frames, and the junction where they meet the wall
• steel, wood or concrete studs and framing
• metal ties in masonry cavity walls
• shelf angles (relieving angles) that support brick veneer
• steel beams and columns that pass through the insulation
• brackets, clips and girts that attach cladding through exterior insulation
• recessed light fittings that penetrate an insulated ceiling
• gaps in insulation, or poorly installed insulation

Not every bridge can be removed. Structure has to reach the outside to hold up balconies, canopies and cladding. A thermal break is the tool engineers use when a conductive connection is unavoidable.

The physics of heat conduction

Conductivity and Fourier's law

Heat flows by conduction through solids from hot to cold. The rate of steady heat flow through a slab of material is given by Fourier's law:

P = k × A × ΔT / d

where P is the heat flow in watts, k is the material's thermal conductivity in watts per metre per kelvin (W/(m·K)), A is the cross-sectional area the heat passes through, ΔT is the temperature difference across it, and d is its thickness. Insulating ability is the inverse of conductivity. A low k means a high thermal resistance, which in building practice is expressed as an R-value.

The single most important number for a thermal break is k, and the differences between materials are enormous.

Values are typical figures from engineering reference tables and manufacturer data. Real products vary with grade, density, moisture and temperature.

The table explains why thermal breaks work. Aluminium conducts heat roughly 700 to 850 times better than polyamide (215 ÷ 0.31 ≈ 690; 215 ÷ 0.25 = 860). Carbon steel conducts about 1,700 times better than polyurethane foam at 0.03 (50 ÷ 0.03 ≈ 1,667). Even a small amount of metal running through a wall can carry as much heat as a large area of insulation.

It also explains why stainless steel is used in many structural thermal breaks. It still conducts heat, but at about 15 W/(m·K) against about 50 for carbon steel it carries roughly 70% less heat for the same cross-section. That figure is from a Schöck technical comparison. Stainless steel also resists corrosion where it crosses from the warm interior to the wet outside.

Series and parallel paths

Heat flowing through a sequence of layers meets each layer's resistance in turn, and the resistances add up like resistors in series. That is how a thermal break works: placing even a thin layer of a poor conductor in the path adds a large resistance.

Heat flowing through side-by-side materials, such as studs alternating with insulation, takes the parallel paths at once. The most conductive path dominates. Doubling the insulation's R-value between steel studs does little if most of the heat is going through the steel. This is the core of the thermal bridging problem.

A worked example (hypothetical)

Consider a steel element, such as a beam stub or a heavy bracket, passing through 200 mm (0.2 m) of insulation. Suppose its cross-section is 0.005 m² (50 cm²), the indoor temperature is 20 °C and the outdoor temperature is 0 °C, so ΔT = 20 K. Take carbon steel at k = 50 W/(m·K).

The steel's thermal resistance is d ÷ (k × A) = 0.2 ÷ (50 × 0.005) = 0.8 K/W. The heat flow is ΔT ÷ R = 20 ÷ 0.8 = 25 watts.

Now replace the same 50 cm² of steel with insulation at k = 0.03 W/(m·K). The resistance becomes 0.2 ÷ (0.03 × 0.005) ≈ 1,333 K/W, and the heat flow is about 0.015 W. The steel element carries about 1,700 times as much heat as the insulation it displaces.

Finally, insert a 25 mm (0.025 m) pad of a polymer at k = 0.3 W/(m·K) across the steel path, in series with the steel. The pad's resistance is 0.025 ÷ (0.3 × 0.005) ≈ 16.7 K/W. The total is 0.8 + 16.7 = 17.5 K/W, and the heat flow drops to 20 ÷ 17.5 ≈ 1.1 W, a cut of more than 95% in this simple model.

This is a one-dimensional idealisation and overstates the benefit. Real connections need bolts that pass through the pad, the steel spreads heat sideways into the surrounding structure, and the pad area may be larger than the steel cross-section. Real-world tests and three-dimensional models give smaller improvements. A Schöck summary of a study by Oxford Brookes University, for example, reported that one stainless-steel thermal break module cut heat loss at a steel beam connection by 48% compared with a continuous beam. The example does show why even a thin break helps so much: in a series path, the poor conductor sets the overall rate.

Measuring thermal bridges: U, psi and chi

Building scientists describe heat flow through envelopes with three related quantities.

U-value (U-factor). The rate of heat flow per square metre of an assembly per kelvin of temperature difference, in W/(m²·K), or Btu/(h·ft²·°F) in US practice. It describes a "clear field" of wall, roof or window. In US standards, repeating elements spread across the area, such as studs, masonry webs, ties, girts and fasteners, are counted as clear-field thermal bridges and folded into the assembly's U-value.

Psi-value (Ψ). The linear thermal transmittance, in W/(m·K): the extra heat flow per metre of length per kelvin caused by a linear bridge such as a slab edge, balcony line, parapet, window perimeter or shelf angle.

Chi-value (χ). The point thermal transmittance, in W/K: the extra heat flow caused by a single discrete bridge, such as a beam penetrating a wall, a column penetrating a roof, or an anchor attaching something to the building.

The total heat loss of an envelope can then be written as the sum of three terms: U times area for each assembly, plus Ψ times length for each linear junction, plus χ for each point bridge. These definitions match those adopted in ASHRAE Standard 90.1-2022.

Psi and chi values are found by detailed two- or three-dimensional heat-flow simulation. International standards such as ISO 10211 set out how such calculations are done, and ISO 14683 provides default values for common junctions. Catalogues such as the BC Hydro Building Envelope Thermal Bridging Guide, developed by Morrison Hershfield with BC Hydro Power Smart and other partners, and the ASHRAE research project RP-1365, list calculated values for many common details.

Typical numbers for balconies

Concrete balconies are the classic linear thermal bridge, because a solid slab runs straight out through the wall. Construction Canada gives these indicative ranges:

Exact values depend strongly on the specific product, wall type and insulation position.

A worked example (hypothetical)

Imagine a ten-storey residential building with 40 m of balcony connection on each floor, or 400 m in total. Take a conventional balcony at Ψ = 0.9 W/(m·K), the middle of the range above, and a thermally broken version at Ψ = 0.2 W/(m·K).

• Conventional: 400 m × 0.9 = 360 W per kelvin of indoor-outdoor temperature difference.
• Thermally broken: 400 m × 0.2 = 80 W/K.

Over a heating season of 3,000 kelvin-days (a heating degree-day total typical of a cold-temperate climate), the energy lost through the balcony lines is the W/K figure × 24 hours × 3,000 ÷ 1,000:

• Conventional: 360 × 24 × 3,000 ÷ 1,000 = 25,920 kWh
• Thermally broken: 80 × 24 × 3,000 ÷ 1,000 = 5,760 kWh

The difference is about 20,000 kWh a season for this hypothetical building. That is before counting the comfort and condensation benefits of warmer slab surfaces. The numbers are illustrative. Real savings depend on climate, heating system efficiency and the actual details.

Main types of thermal break

Thermally broken aluminium windows, doors and curtain walls

Aluminium is light, strong, durable and easy to extrude into complex shapes, which is why it is so common in windows, storefronts and curtain walls. Its weakness is very high thermal conductivity. The Efficient Windows Collaborative notes that in cold climates a plain aluminium frame can get cold enough for condensation or frost to form on its inside surface. It says the condensation problem, more than heat loss, drove the development of better-insulated aluminium frames.

The fix is to make the frame in two parts, an inside and an outside, joined by a less conductive material. There are two main manufacturing methods, described by the Aluminum Extruders Council:

Pour and debridge. A single aluminium extrusion is made with a channel. A two-part liquid polyurethane is poured into the channel, where it hardens. The channel walls are first conditioned to create a mechanical lock with the polymer. The metal bridge at the bottom of the channel is then cut away, leaving the two halves of the frame connected only through the polyurethane. Patent literature describes it as the older method that is still widely used. The width of the break is limited by the width of the saw cut.

Insulating strip (crimped polyamide). Two separate aluminium extrusions are joined by rigid polyamide strips. Knurling wheels cut small teeth, 0.15 to 0.30 mm long, into pockets in the aluminium. The strips are pulled or pushed into the pockets, and three sets of wheels crimp the aluminium closed onto the strips under more than 1,300 pounds of force in stages. The teeth bite into the polyamide and give the joint its shear strength, making a load-bearing composite. Manufacturers test samples periodically to confirm that strength. Strips come in many shapes, and wider or multi-chambered strips give better performance. The Aluminum Extruders Council says polyamide strips have been used for more than 30 years overseas and for more than a decade in North America.

The thermal improvement is large. The Efficient Windows Collaborative says standard thermal breaks reduced aluminium frame U-factors from about 2.0 to about 1.0 Btu/(h·ft²·°F). A continuing-education course citing the 2001 ASHRAE Handbook of Fundamentals gives frame U-values of 1.92 for an aluminium frame without a thermal break and 1.13 with one. In metric units those are roughly 10.9 and 6.4 W/(m²·K) (multiplying by 5.678). The same source lists 0.51 for an aluminium-clad wood frame, showing that a thermally broken aluminium frame is still well behind wood or composite frames.

The frame is only part of the window. Whole-window U-factors on certified labels, such as those from the US National Fenestration Rating Council, combine frame, glass, spacers and sash. The same course reported whole-unit U-values for thermally broken aluminium windows ranging from 0.35 with low-e triple glazing to 0.64 with clear double glazing. In hot climates, solar heat gain through the glass usually matters more than conduction through the frame.

Because the polymer joint carries structural loads and goes through daily heating and cooling cycles, its durability is tested. The American Architectural Manufacturers Association's AAMA 505 test procedure covers dry shrinkage and composite performance under thermal cycling.

Structural thermal breaks for balconies and slabs

For a cantilevered concrete balcony, the balcony slab must be firmly connected to the floor slab inside, because the inside slab is what holds it up. A structural thermal break replaces the continuous concrete at the wall line with a manufactured module. A typical module is a block of insulation, roughly the thickness of the wall insulation, through which pass:

• stainless steel tension bars at the top, which carry the bending moment that holds the balcony up
• compression elements at the bottom, often high-strength concrete or polymer-concrete bearings, which push back against the inside slab
• shear bars that carry the vertical load

The insulation lines up with the wall insulation so that the thermal envelope is nearly continuous, and only the small cross-section of stainless steel and bearing material crosses it.

The German company Schöck says it launched the first commercially available structural thermal break, the Isokorb Type M, in 1983. The product was developed by the company's founder, Eberhard Schöck. That date and the "first" claim come from the company's own materials. Several manufacturers now offer similar products for concrete-to-concrete, concrete-to-steel and steel-to-steel connections, as well as retrofit versions for adding or replacing balconies on existing buildings.

Alternatives for balconies

A structural thermal break is not the only answer. Lstiburek listed several:

• support balconies on separate columns or offset point supports, so the slab does not have to cantilever through the wall
• use precast balconies set slightly apart from the wall
• hang balconies from tie rods anchored to the structure
• build stand-alone balcony structures in front of the building
• use thermal-break foam blocks with stainless steel rods at the slab-to-balcony connection
• or leave balconies off altogether

Each has costs and trade-offs in structure, appearance, drainage and fire safety.

Steel beam and column thermal breaks

Where steel beams pass through the envelope to support canopies, sunshades, roof dunnage or balconies, the beam is often cut at the insulation line. The two halves are bolted together through a thermal break. Two main approaches are used:

• Thermal pads. A layer of low-conductivity, high-strength material is clamped between the end plates. The bolts still cross the break, so stainless or low-conductivity bolts and adequate pad thickness matter.
• Engineered modules. Manufactured units with stainless steel elements and insulation fillers are fixed between end plates, designed to carry tension, compression, shear and moment.

Material choice matters. Schöck warns that some graphite-enhanced insulation pads can make heat loss worse than an unbroken beam in certain configurations, so designers need tested data rather than assumptions.

Shelf angles and cladding attachments

Brick veneer on tall buildings is usually supported floor by floor on steel shelf angles (relieving angles) fixed to the slab edge. A shelf angle fixed tight against the structure interrupts the exterior insulation along a continuous line at every floor. Lstiburek's solution is to hold the angle off the face of the structure with intermittent stand-offs, so the insulation can run continuously behind it and only the small stand-offs cross it. He wrote that this also lets designers use a small, standard angle, because the stand-offs take the bending forces.

Cladding attachments are a similar problem at a smaller scale. Rainscreen systems hold panels on rails and clips that pass through the exterior insulation. Continuous metal girts carry a lot of heat. Intermittent clips, often with low-conductivity isolators or made of stainless steel or fibre-reinforced polymer, carry much less.

Steel stud walls

Light-gauge steel studs are an extreme thermal bridging case. Lstiburek described a steel stud as a thin web with fins (the flanges) on both sides, an ideal heat-exchanger shape. His essay stated: "Put an R-19 batt in a steel stud wall and you are lucky to get R-5 to R-6 in the real world," roughly a 75% loss of the insulation's nominal resistance. He argued that about 1 inch (25 mm) of rigid insulation outside the studs would match that real-world performance. Other sources give similar results. A Masonry Advisory Council summary of ASHRAE 90.1 data puts the effectiveness of batts between steel studs at about 35% to 60%, depending on stud spacing and insulation level.

The usual thermal break for steel stud walls is continuous exterior insulation. It does not stop heat moving through the studs themselves, but it puts an unbroken layer of insulation outside them, so the stud heat has to pass through that layer before reaching the outdoors. Lstiburek's recommendation was simple: put the insulation on the outside of steel studs and structural frames, and leave the cavity empty.

Other applications

Thermal breaks appear wherever two zones at different temperatures must be connected by a solid part:

• Refrigerated display cases and cold rooms, where aluminium frames are thermally broken to stop condensation on the warm side, an application the Aluminum Extruders Council lists alongside windows and doors.
• Doors, including insulated metal entry doors and overhead doors with thermally broken frames or panels.
• Mechanical systems, such as insulated pipe hangers that support a cold pipe without letting the support become a condensation point.
• Roofs, where rooftop equipment supports and dunnage steel penetrate the insulation.

A brief timeline

Thermal breaks did not arrive as a single invention. They grew out of separate industries, windows, precast and cast concrete, and steel, each tackling its own condensation and heat-loss problems, and only later converged under the shared language of psi and chi values. The dates below are the ones that can be pinned down from the sources used for this article.

The pattern is clear. Products came first, driven by condensation complaints and by architects' wish to keep balconies and slim metal frames. Measurement came next, through simulation research that showed how much heat the details were losing. Regulation came last, once there were enough tabulated values for code writers to set requirements that designers could actually check.

Codes, standards and design criteria

ASHRAE Standard 90.1-2022

For many years, US energy codes treated the opaque envelope mainly through an overall U-factor and assumed perfect connections between building elements. An article in the June 2023 ASHRAE Journal by Len Sciarra and colleagues explains that as required insulation levels rose, the gap grew between how buildings are actually built and the idealised models used for compliance. Research projects, including ASHRAE RP-1365, BC Housing's guide to low thermal energy demand for large buildings, and the BC Hydro thermal bridging guide, documented the effect.

The 2022 edition of ASHRAE Standard 90.1, the main US commercial energy standard, added explicit thermal bridging provisions in Section 5.5.5. They are prescriptive and "tradeable" rather than mandatory. The section covers five common types of thermal bridge:

Projects that cannot meet the prescriptive requirements can use the envelope trade-off method or whole-building performance modelling. In that case, they enter psi and chi values from Table A10.1 of the standard, which gives both "mitigated" (default) and "unmitigated" values, or from another recognised source. A design that uses a high-performance structural connection better than the prescriptive requirement can receive credit for it. There is an exception for materials with a thermal conductivity below 3.0 Btu·in/(h·ft²·°F), or 0.433 W/(m·K), which is characteristic of wood. The standard's Informative Appendix K provides illustrations of the thermal bridge categories.

Canada

The National Energy Code of Canada for Buildings 2020 includes thermal bridging provisions in Section 3.2.4. Canadian work, particularly the BC Hydro guide developed in British Columbia, has been influential across North America in quantifying psi values for common details.

Passive House

The Passive House standard, developed by the Passive House Institute in Darmstadt, Germany, treats thermal bridges very seriously. It uses the term "thermal bridge free design." The Institute's Passipedia explains that for ordinary building geometries, the thermal-bridge-free requirement was almost always met when every linear thermal bridge had Ψ ≤ 0.01 W/(m·K). That threshold became the simplified working criterion. Passive House energy calculations use the building's external dimensions, so some junctions, particularly outside corners, come out with negative psi values. That is an artefact of measuring area to the outside surface, not a sign that the junction gains heat. Certified Passive House components list their junction psi values, many below the 0.01 threshold.

By comparison, the indicative values above for conventional balconies (0.6–1.2 W/(m·K)) are 60 to 120 times the Passive House threshold, and even good thermally broken balconies (0.15–0.30) are well above it. This is why many Passive House designs avoid cantilevered balconies entirely or use separately supported balconies.

Design and installation considerations

Structure first

A structural thermal break is part of the structure. It must carry the design loads, including bending moments, shear, and for balconies the guard loads. It must limit deflection, since a balcony that sags at its tip is a problem even if it is safe. Construction Canada notes that balcony connections are commonly designed to limit vertical deflection to span/360 or tighter where glazing or brittle finishes are present. Structural engineers must be involved in selecting and detailing breaks, not just energy consultants.

Fire

A thermal break replaces solid concrete or steel with insulation and polymers. Codes require fire resistance at floor slabs and other separations, so structural thermal breaks used in those locations need tested fire ratings, often achieved with fire-protection boards or intumescent materials at the edges of the module.

Moisture and corrosion

The parts of a thermal break that cross the envelope link a dry, warm interior to a wet, cold exterior. Stainless steel is often specified for the elements that cross the break because it resists corrosion. Polymer components must tolerate moisture and ultraviolet light where exposed. The break must also be integrated with the air barrier, water-resistive barrier and flashing, because a thermal break that leaks air or water causes new problems.

Construction tolerances

Concrete slab edges are rarely perfectly placed. Construction Canada notes that high-rise slab-edge tolerances commonly vary by ±25 mm (about ±1 inch), and that these deviations accumulate up the building. Thermal break modules, shelf-angle stand-offs and cladding clips need enough adjustability to cope.

Continuity

A thermal break only works if the insulation on either side lines up with it. A break placed outside the plane of the wall insulation, or a gap between the break and the insulation, leaves a new bridge. This is why standards like ASHRAE 90.1 describe the location of the insulation relative to slabs, window frames and supports, not just the presence of a break.

Cost

Thermal breaks cost money. A 2014 news report on an earlier edition of the BC Hydro guide estimated that a thermally broken concrete balcony could cost about $266 more per metre ($81 more per foot) than a continuous concrete balcony. Whether that pays back depends on energy prices, climate, and how much value is put on comfort and avoided condensation damage. The guide's broader argument was that the cheapest improvements often come from fixing the worst bridges rather than adding more insulation to the clear field.

Limits of thermal breaks

They reduce, not eliminate, heat flow. A thermal break still conducts some heat, and the metal parts that cross it, such as stainless bars and bolts, carry heat too. A thermally broken balcony is much better than a continuous slab but is still a significant linear bridge by Passive House standards.

More insulation elsewhere does not fix a bridge. Because heat favours the conductive path, adding insulation to the clear field of a wall while leaving bridges in place gives diminishing returns. Lstiburek's point about expensive spray foam in steel stud cavities is an example: higher-resistance cavity insulation barely helps when the studs dominate.

One-dimensional calculations miss the effect. Simple U-value calculations assume heat flows straight through each layer. Thermal bridges create two- and three-dimensional heat flow that those calculations do not capture, so a design can look compliant on paper and perform worse in reality.

Climate matters. In cold climates the main benefits are lower heating demand and avoided condensation. In hot climates the energy effect of frame conduction is often small next to solar gain through glass. The Efficient Windows Collaborative notes that in hot climates a better glazing system usually matters more than an insulated frame.

Durability must be proven. Polymer components in windows and structural breaks must hold up through decades of thermal cycling, loading, moisture and in some cases fire. That is why testing standards such as AAMA 505 exist and why structural breaks carry product approvals.

Common misconceptions

"A thermal break is just insulation." Insulation fills large areas. A thermal break is a targeted interruption of a conductive path, often a structural component that must carry loads while insulating.

"Wood framing needs thermal breaks like steel." Wood conducts heat far less than steel: roughly 0.12–0.17 W/(m·K) against about 50 for carbon steel. Wood framing is still a thermal bridge compared with insulation, but a much milder one. ASHRAE 90.1-2022 exempts materials with conductivity below 0.433 W/(m·K), which is characteristic of wood, from some of its thermal bridging requirements.

"Thermally broken aluminium is as good as wood or vinyl." A thermal break roughly halves an aluminium frame's U-factor, but in the ASHRAE example, a thermally broken aluminium frame at 1.13 was still more than twice as conductive as an aluminium-clad wood frame at 0.51.

"If the wall meets the R-value requirement, it performs." Nominal R-values describe insulation, not assemblies. Lstiburek pointed out that "nominal" means "in name only," and that an R-19 batt in a steel stud wall delivers far less.

"Exterior insulation fixes the studs." Exterior insulation does not reduce the heat moving through the studs themselves. It puts a continuous layer outside them, which greatly improves the whole wall's performance.

"Negative psi values mean a junction gains heat." In calculations based on external dimensions, negative psi values often appear at corners because the clear-field areas already overcount the heat loss there. They are a correction, not a gain.

Frequently asked questions

What is the difference between a thermal bridge and a thermal break? A thermal bridge is the problem: a conductive path through the insulation. A thermal break is the solution: a low-conductivity element placed in that path to interrupt it.

How do I know if a window has a thermal break? Look at the frame cross-section or the manufacturer's literature. A thermally broken aluminium frame has a visible band of polymer, often dark, separating the inside and outside metal. The whole-window U-factor on an NFRC or similar label is the best guide to overall performance.

What materials are used in thermal breaks? Polyamide strips and poured polyurethane in aluminium windows and curtain walls. Insulation blocks combined with stainless steel bars and compression bearings in structural balcony connections. High-strength polymer or fibre-reinforced pads in steel connections. Low-conductivity clips and isolators in cladding systems.

Do thermal breaks prevent condensation? They greatly reduce the risk by keeping inside surfaces warmer. The Efficient Windows Collaborative notes that condensation on cold aluminium frames was the main reason thermally broken frames were developed. Whether condensation still occurs also depends on indoor humidity and outdoor temperature.

Are thermal breaks required by code? Increasingly. ASHRAE 90.1-2022 added specific thermal bridging provisions for commercial buildings in the US, and the National Energy Code of Canada for Buildings 2020 includes thermal bridging rules. Requirements depend on the code edition adopted locally, the climate zone and the building type.

How much energy does a thermal break save? It depends on the detail, the climate and the building. In the hypothetical example above, reducing a 400 m balcony line from Ψ = 0.9 to 0.2 W/(m·K) cut the seasonal heat loss through that line from about 25,900 kWh to about 5,800 kWh in a 3,000 kelvin-day climate. A real building's savings must be calculated from its own details.

Can thermal breaks be added to existing buildings? Sometimes. Existing exposed frames and steel stud walls can be reclad with continuous exterior insulation, which Lstiburek called an easy fix for exposed frames. Existing balconies are harder. Options include cutting off and replacing them with thermally broken or separately supported balconies, or wrapping them in insulation. Several manufacturers make retrofit balcony connectors.

Is stainless steel a thermal break? No, but it is a less conductive structural metal. At about 15–17 W/(m·K) against about 50 for carbon steel, it carries much less heat, which is why it is used for the bars that cross structural thermal breaks.

Summary

A thermal break is a low-conductivity element placed in a conductive path to interrupt heat flow through an insulated envelope. The need for it comes from a basic mismatch: the materials that make buildings strong, such as aluminium, steel and concrete, conduct heat hundreds or thousands of times better than insulation. Wherever these materials cross the envelope, at window frames, slab edges, balconies, beams, shelf angles and cladding supports, they create thermal bridges that waste energy, chill interior surfaces and invite condensation and mould. Thermal breaks range from the polyamide strips in aluminium windows, which roughly halve frame U-factors, to engineered structural modules that hold up balconies through a few stainless steel bars. Building codes are catching up. ASHRAE 90.1-2022 and Canada's NECB 2020 now address thermal bridges explicitly, and the Passive House standard sets a demanding target of Ψ ≤ 0.01 W/(m·K). Thermal breaks reduce heat flow but do not eliminate it, and they work only when they are continuous with the insulation, structurally sound, fire-safe and durable.

Sources

• Thermal break (Wikipedia)
• Thermal bridge (Wikipedia)
• Building Science Corporation: BSI-005 A Bridge Too Far (Joseph Lstiburek, 2008)
• ASHRAE Journal: Thermal Bridging Requirements in Standard 90.1-2022 (June 2023)
• Passipedia: What defines thermal bridge free design
• Construction Canada: Where facades fail first, managing continuity at slab edges and connections
• Aluminum Extruders Council: Aluminum extruders provide a thermal barrier
• Efficient Windows Collaborative: Metal frames
• Continuing Education Center: Greater Vision, alternate window materials in commercial buildings
• Engineering ToolBox: Thermal conductivity of common materials
• Schöck: A comparison of thermal break solutions for structural steel
• Schöck: 40 years of Isokorb
• Building Design + Construction: New guide on prevention of thermal bridging in commercial buildings
• Masonry Advisory Council: Steel stud wall systems R-value
• Phius: A comparison of calculation methods for thermal bridges in building enclosures