Design & Supply is proud to announce the launch of Therma-Line, a new range of high-performance thermal steel doorsets developed to meet rising demands for energy efficiency without compromising strength, durability, or compliance.
With thermal performance achieving U-Values as low as 1.3 W/m²K, Therma-Line doorsets support compliance with Part L of the Building Regulations. As a result, they are suitable for both new-build and refurbishment projects across commercial, industrial, and public-sector environments.
Energy efficiency is now a key consideration in modern building design, and thermal performance plays an increasingly important role in external door specification. Part L of the Building Regulations sets clear limits on U-Values to help reduce heat loss and improve overall building performance.
For new dwellings, external doors (including glazed doors) must achieve a maximum U-Value of 1.6 W/m²K. In new-build applications where external doors are predominantly glazed, the requirement becomes more stringent, with a maximum permitted U-Value of 1.4 W/m²K or a minimum Doorset Energy Rating of Band C.
Different thresholds apply to replacement doors in existing buildings. For external fire doorsets, as defined in Approved Document B, a maximum U-Value of 1.8 W/m²K is permitted.
With thermal performance achieving U-Values as low as 1.3 W/m²K, Therma-Line steel doorsets not only meet these requirements but exceed them. This gives specifiers and contractors confidence that Part L compliance can be achieved comfortably as standards continue to evolve.
Rather than designing to minimum thresholds, Therma-Line provides additional performance headroom – helping future-proof projects while maintaining the strength, durability, and compliance expected from a steel doorset.
Many thermally efficient doorsets rely on alternative materials to achieve low U-Values.
By contrast, Therma-Line doorsets are fabricated in steel, delivering superior strength, durability, and resistance to damage.
Advanced insulation, precision engineering, and robust sealing systems work together to minimise heat loss.
At the same time, the doorset retains all the inherent benefits expected from a high-performance steel solution.
This makes Therma-Line suitable for projects where thermal performance, durability, and compliance must be achieved together.
Thanks to their enhanced thermal performance, Therma-Line doorsets are ideal for:
In addition, all Therma-Line doorsets are manufactured in the UK. This ensures consistent quality, reliable lead times, and full technical support throughout the specification process.
The launch of Therma-Line reinforces Design & Supply’s commitment to developing future-ready steel doorsets. These products respond directly to evolving building regulations while maintaining the performance standards expected from a specialist manufacturer.
Crucially, specifiers no longer need to choose between thermal efficiency and structural integrity. Therma-Line delivers both in a single, fully engineered solution.
For further information on Therma-Line thermal steel doorsets:
Our specialists are available to provide guidance from early specification through to manufacture and delivery.
Read more about Part L of the Building Regulation’s here: Approved Document L Volume 1, 2021 edition, page 23
