Fibre Reinforced Facade Encyclopedia: Design and detailing
Thermal bridging is heat flow through a localised part of the building envelope that bypasses the insulation layer, usually through a metal component that penetrates or interrupts it. On a cladding facade the bridge is almost always the bracket: a steel or aluminium element that carries panel dead load and wind load back through the insulated zone to the structure behind. Every bracket is a short circuit around the insulation, and there are commonly two to four of them per square metre.
Stainless steel conducts heat roughly forty times better than the insulation it passes through, and aluminium roughly four hundred times better. A bracket occupying less than one thousandth of the wall area can still account for a tenth or more of the heat loss through it.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Thermal conductivity, aluminium | about 160 W/m·K | The worst common bracket material |
| Thermal conductivity, stainless steel | about 15 to 17 W/m·K | The usual bracket choice for this reason |
| Thermal conductivity, mineral wool insulation | 0.033 to 0.040 W/m·K | The layer being bypassed |
| Thermal conductivity, isolator pad | 0.2 to 0.4 W/m·K | Glass fibre reinforced polymer or rigid thermoset |
| Thermal conductivity, GRC | about 0.4 W/m·K | ShapeShell-RC published value 0.39 W/m·K |
| Thermal conductivity, FRP laminate | 0.2 to 0.35 W/m·K | Glass and polyester laminate, typical |
| Bracket density | 1.5 to 4 brackets per m² | Set by panel size and design wind pressure |
| Point transmittance per bracket | 0.005 to 0.05 W/K | Typical range; depends on section, isolator and insulation depth |
| Effect on wall U-value | 10% to 40% increase | Unmitigated steel brackets through continuous insulation |
Repeating, linear and point bridges
Thermal bridges come in three shapes and the distinction matters for how they are counted. A repeating bridge occurs at regular intervals within the wall area, such as a stud or a rail, and is normally built into the U-value calculation itself. A linear bridge runs along a junction, such as a slab edge, a parapet, a window jamb or a base course, and is accounted for by a linear transmittance value, psi, in watts per metre kelvin. A point bridge is a discrete penetration such as a cladding bracket or a tie, and is accounted for by a point transmittance value, chi, in watts per kelvin.
Cladding brackets are point bridges, and they are the ones most often left out of an energy calculation entirely. A wall modelled as continuous insulation with no allowance for brackets can overstate its performance by a wide margin, and the error shows up as condensation risk and as a failed measured performance, not as a calculation error.
Why a cladding bracket is the problem
The bracket has a difficult job. It must carry the panel dead load and the wind load, resist buckling over the depth of the insulation, allow three-axis adjustment to absorb structural tolerance, and do all of this while conducting as little heat as possible. Those requirements pull against each other. A stiffer, deeper, wider bracket is structurally easier and thermally worse.
The two design decisions that matter most are material and count. Moving from aluminium to stainless steel reduces conductivity by roughly a factor of ten for the same section. Reducing the number of brackets reduces the bridge in direct proportion, and the way to reduce bracket count is to reduce the load each bracket carries, which means lighter panels. See substructure for how the bracket and rail system is put together, and dead load for how panel weight drives the bracket schedule.
Reducing the bridge
- Use stainless steel rather than aluminium for brackets that pass through the insulation.
- Fit a low conductivity isolator pad between the bracket base and the structure, typically a glass fibre reinforced polymer or rigid thermoset plate 5 to 10 mm thick.
- Reduce the bracket contact area at the structure, and use a perforated or webbed bracket section where the structural design allows.
- Increase panel span so that fewer brackets carry the same wall area, which lighter panels make possible.
- Keep the insulation continuous and outboard of the structure, with the cladding cavity outside it, so that only the bracket crosses the layer.
- Insulate the bracket arm within the insulation zone rather than leaving an air gap around it.
Lightweight panels shorten the bridge list
Bracket size and bracket count are both consequences of panel weight. A cladding system at 5 to 32 kg per square metre imposes a small fraction of the dead load of a precast panel at 250 to 500 kg per square metre, so the brackets can be smaller in section, fewer in number, and often stainless rather than galvanised mild steel. A glass fibre reinforced concrete panel at 30 to 50 kg per square metre sits between the two and still allows a much lighter bracket schedule than heavyweight cladding.
The panel material itself is a poor conductor in both cases, around 0.4 W/m·K for glass fibre reinforced concrete and lower still for fibre reinforced polymer, but that is not where the benefit lies. In a ventilated cavity the cladding skin contributes almost nothing to the thermal performance of the wall, because the cavity is at outside air temperature. The benefit of a lightweight panel is entirely in the bracket schedule. See lightweight cladding and ventilated facade.
Calculating it, and where condensation happens
Two-dimensional and three-dimensional numerical modelling to ISO 10211 is the accepted method for linear and point transmittance values. ISO 14683 gives default linear values where a calculation is not warranted. For a proprietary bracket, the manufacturer should be able to supply a calculated chi value for the specific bracket, isolator and insulation depth; a value quoted without those three parameters means nothing.
Standards and references
- NCC 2022 Volume One Section J, energy efficiency (check the edition adopted in your jurisdiction)
- AS/NZS 4859.1 and AS/NZS 4859.2 Thermal insulation materials for buildings
- ISO 10211 Thermal bridges in building construction: heat flows and surface temperatures, detailed calculations
- ISO 14683 Thermal bridges in building construction: linear thermal transmittance, simplified methods and default values
- ISO 6946 Building components and building elements: thermal resistance and thermal transmittance
- ISO 13788 Hygrothermal performance: internal surface temperature to avoid critical surface humidity
- BRE IP 1/06 Assessing the effects of thermal bridging at junctions and around openings (United Kingdom)
- ASHRAE 90.1 and ASHRAE RP-1365 thermal performance of building envelope details (United States)
Related terms
Questions specifiers ask
How much do cladding brackets affect a wall U-value?
Unmitigated steel brackets passing through continuous insulation typically increase the wall U-value by 10 to 40 percent, depending on bracket section, spacing and insulation depth. A wall modelled as continuous insulation with no bracket allowance will overstate its performance.
Are stainless steel brackets better than aluminium?
Thermally, yes, by roughly a factor of ten. Stainless steel conducts at about 15 to 17 W/m·K against about 160 W/m·K for aluminium, so for the same section the heat flow through the bracket is far lower.
Do lightweight panels reduce thermal bridging?
Indirectly but significantly. Lower dead load allows smaller bracket sections and fewer brackets per square metre, and bracket count is directly proportional to the total point transmittance of the wall.
Does the cladding panel itself help the U-value?
In a ventilated cavity system, almost not at all. The cavity sits at outside air temperature, so the outer skin is thermally outside the insulated envelope regardless of its own conductivity.
What is a thermal isolator pad?
A low conductivity plate, usually a glass fibre reinforced polymer or rigid thermoset 5 to 10 mm thick, placed between the bracket base and the structure. It interrupts the metal-to-metal contact without removing the structural connection.
Reducing bracket count starts with reducing panel weight. ShapeShell-RT runs from 5 to 32 kg per square metre and ShapeShell-RC from 30 to 50. Use the facade calculators
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.