Why Below DPC Insulation Matters More Than You Think

When we talk about improving thermal performance and insulation, the conversation usually starts – and often ends – with façades. Architects and specifiers are now well-versed in selecting non-combustible external wall systems to meet the latest Building Regulations on properties over 11 metres in height, but there’s a critical zone that has long been overlooked: what happens below the damp proof course (DPC) and at the base of the system on balconies and walkways.

Updated UK Building Regulations require that materials used on buildings over 11 metres achieve a minimum A2-s1,d0 fire classification. While this has driven innovation in façade insulation, the treatments used at ground level – around plant rooms, walkways, balconies and below the DPC – have typically remained disconnected, untested, and in many cases reliant on combustible coatings such as bitumen.

This creates a gap in performance and compliance. A building envelope is only as strong as its weakest point, and if the base of the system is not fire-tested to the same standards as façades, can we really say the full building envelope is safe?

That’s the challenge addressed by SOQEL A2, the UK’s first fully fire-tested external wall insulation (EWI) system designed specifically for use below the DPC. Developed by Wetherby Wall Systems, part of the ROCKWOOL Group, in collaboration with HECK in Germany, SOQEL A2 brings continuity to insulation design – extending fire-safe performance all the way down to the ground.

The system uses Coverrock X2 insulation with a durable factory-applied coating that protects its A1-rated stone wool core during installation and improves adhesion for finishing layers. Reinforced with Heck K+A SL basecoat and Heck CER Mesh, SOQEL A2 is engineered for lasting durability, resisting moisture and weather extremes at the most exposed part of the building envelope.

The SOQEL A2 system also provides increased impact resistance, achieving up to 60 joules in comparison with the 10 joules required by standard façade system testing. In areas likely to suffer impact damage from foot traffic, bins, or heavy objects, this represents a significant improvement to the system in a zone that needs robust protection.

One of the barriers to specifying robust below-DPC solutions has been aesthetics. Traditional treatments can compromise the visual continuity at the base of the system, breaking the clean lines of a façade. SOQEL A2 solves this by integrating Heck 4S Silicone Render, which can be colour-matched to the upper façade finish. The result is a seamless, unified appearance that doesn’t compromise fire performance.

By extending tested fire performance to ground level, SOQEL A2 addresses a blind spot in current practice. As Joe Ragdale, Technical Director at Wetherby Wall Systems, explains:
“SOQEL A2 is the first system of its kind to undergo full fire testing for below DPC use. It’s a major step forward in ensuring fire safety compliance across the entire building envelope.”

For specifiers, this marks an important shift. Building safety isn’t just about façades – it’s about continuity, durability, and integrity from the ground up. With SOQEL A2, that safety gap has finally been closed.