As U-Values improve, thermal bridging becomes the next challenge for building fabric performance

As UK and Irish building regulations continue to push U-values lower, one of the industry’s experienced technical voices has given a warning. The junctions between insulated elements rather than the insulation boards themselves are now where much of the performance is being lost.

In a recent video produced with the Insulation Manufacturers Association (IMA), Eamonn Clarke, Technical Manager at Unilin Insulation and a member of the IMA’s technical committee, addressed persistent and largely preventable sources of underperformance in construction: thermal bridging at junction details and poor on-site installation practice for PIR insulation.

For decades, the insulation industry has witnessed a steady improvement, providing thinner boards, lower thermal conductivities and better U-values. Eamonn’s message is that this progress has created a new problem. As the flat areas of a building envelope become better insulated, the proportional impact of gaps, junctions and thermal bridges grows rather than shrinks.

Poorly detailed junctions, such as where a wall meets a floor, a window reveal, a parapet or a balcony connection can bypass the insulation layer entirely and undermine the fabric performance that the rest of the design has worked to achieve. Research from BRE Group have stated that thermal bridging can be responsible for up to 30% of a building’s total heat loss, even in otherwise well-insulated structures.

Eamonn’s point is clear for both designers and installers. A specification sheet showing an excellent U-value is only as good as the junction detailing that supports it on site. As the sector works toward tighter Building Regulations and Part L compliance targets, he argues that attention now needs to shift from the product itself to the detail, so that what is specified matches what is built.

This has real consequences across a project. From a compliance perspective, as-built performance can fall short of the design stage calculations if junctions aren’t properly modelled and detailed. It also has implications for embodied carbon, since wasted heat from thermal bridging drives up operational energy use and undercuts the sustainability gains that the insulation is meant to deliver. It also affects the occupant’s comfort too, as cold spots at junctions increase condensation and mould risk, which is a growing concern under evolving health and building safety standards.

As U-values of insulation boards continue to fall across UK and Irish building regulations, the industry’s next real gains won’t come from the insulation board alone. Future gains for effective thermal bridging will rely of the addition of detail around the insulations board and the buildings perimeter. Eamonn Clarke’s message is a timely one for architects, specifiers and contractors; closing the gap between what’s specified and what’s built at every junction is now just as important as the performance figures on the data sheet. The future aim of getting the detailing right isn’t just a technical necessity anymore, it’s what determines whether a building performs the way it was designed to.

This article is based on video content produced by the Insulation Manufacturers Association (IMA) featuring Eamonn Clarke, Technical Manager at Unilin Insulation.

Watch the interview here!