Why does thermal performance matter for spandrel panels?

Spandrel panels form an important part of a building’s façade, and their performance can have a notable impact on the overall fabric performance and energy efficiency of the structure.

When specifying, however, you need to look not only at the declared thermal performance of the product, but also its design and how easy it is to install accurately – as these can have a significant impact on real world performance. In this blog, we'll look at how the thermal performance of spandrel panels is measured, and how you can use specification to help eliminate the performance gap between design and actual performance.

What is thermal bridging in a curtain wall façade?

Thermal bridging (also known as cold bridging) occurs in a façade when the design of an external wall product or system provides a clear path for heat to escape, bypassing other insulative materials. This often occurs in areas such as window frames where a highly conductive material (such as a metal) allows heat to bypass more insulating materials, or where there are gaps in the insulating layer.

Understanding U-values, R-values and Lambda values

A U-value is the sum of thermal resistances through a structure, which can either be a single material or an entire composite.

A centre pane U-value, also known as a the Ug-value, is a simple measure through the centre of a unit, such as a spandrel panel, considering the thermal resistances and thicknesses of each material in the build-up. It’s measured in units of W/m2K, which indicates how much heat is transmitted through the element – with a lower U-value indicating a better insulating product.

An overall U-value is the sum of thermal resistances through a whole structure – such as an entire spandrel panel in a curtain wall – considering all additional ancillaries such as fixings or gaps. Given that this encompasses the whole frame, which varies from project-to-project dependent on design and the other unknown products and systems, these will vary dependent on the build.

An R-value is the converse of a U-value, indicating the ability of a material to resist heat flow. R-values are measured in units of m2K/W, but unlike U-values, the higher the R-value the better insulating the product or system is.

A Lambda value (also known as a k-value or λ-value) describes the ability of a material to conduct heat and is measured in W/mK. Unlike the above, since it looks at a material and not a product or system, the result is irrespective of thickness, and simply indicates a material’s innate ability to conduct heat.

How does thermal performance differ between composite and built up spandrel panels?

The traditional approach of building façade spandrel panels up on site leaves room for variation and error. Curtain walled buildings often have tens or hundreds of spandrel panels across their façade, so the quality of on-site cutting, assembly and installation can hugely impact the thermal performance of the spandrel panel and the wider façade. If components are fitted poorly, with irregular gaps and cold bridges, the designed thermal performance is often not achievable in the final build. Given the nature of this unpredictability, this also isn’t reflected in the designed U-values of a product, forming a performance gap between initial intention, and final real-life performance.

Composite pre-insulated panels, on the other hand, offer repeatable quality and consistent fit and finish. Fabricated off site in factory-conditions, they arrive on site as complete units, simply being glazed into the façade with no complex assembly. This ensures that each and every panel performs as designed, with tight, dependable tolerances across the façade’s spandrel zone. This repeatability ensures that final, installed performance is as close as possible to initial design intentions and calculations, allowing buildings to be more efficient, more comfortable and more predictable.

What should I look for in a pre-insulated composite spandrel panel?

Not all designs of composite spandrel panels perform as effectively in the real world.

Some designs are mechanically bound, where metal fixings are used to hold component parts together. Often extending through the whole spandrel panel, these mechanically bound products provide the perfect path for thermal bridging through the unit, compromising its insulative qualities.

Spandrel panels which take advantage of high-performance adhesives, however, do not suffer from this fixing-induced issue. Instead, their components are bonded together in factory conditions, and offer reliable thermal and fire performance at scale. This factory-engineered design helps to ensure the final, installed product is as closely aligned to initial designs and calculations as possible.

Speedpanel A2® spandrel panels were designed alongside a world-renowned adhesive specialist, to develop a unique bonding layer that removes the need for mechanical fixings. This ensures the Speedpanel A2® range achieves A2-s1,d0 certified fire performance whilst retaining consistent, repeatable centre pane U-values as low as 0.26 W/m2K.

To learn more about spandrel panels in relation to facade retrofit or refurbishment projects, explore our blog.

To dive even further into the topic, our technical team also offer in-person CPD sessions centred around the needs of contractors and specifiers in façade retrofit projects. Get in touch to arrange a free session.