Sigma® II
High performance. Low carbon. Designed for results.
Sigma® II Build System closed panel
High performance. Low carbon. Designed for results.
Sigma® II from Donaldson Timber Systems is the optimum closed-panel timber frame solution for today’s housing market, combining speed, precision, and performance in one complete, factory-engineered system.
Developed to help housebuilders meet Future Homes Standard, net-zero, and low-carbon targets, Sigma® II delivers a high-performance building fabric with reduced site labour, improved productivity, and total confidence in quality.
Performance driven by design
Sigma® II is a closed-panel timber frame structure prefabricated in our offsite manufacturing facility for maximum quality control and precision. Each panel is fully insulated, engineered, and factory-sealed, ensuring predictable performance and faster installation on site.
Key features include:
-
Factory-fitted insulation and service zones for enhanced thermal and air-tight performance.
-
Optional pre-installed windows for increased Pre-Manufactured Value (PMV) and faster build programmes.
-
Solid-stud and I-stud wall options with a choice of 140 mm, 184 mm, 195 mm or 235 mm stud widths.
-
Factory-finished internal and external sheathing boards with reflective foil breather membrane.
-
30- or 60-minute fire-rating options.
-
Fully accredited to NHBC Accepts, BOPAS, BBA, LABC with full EPDs and STA Gold Standard.
The result is a robust, precise, and energy-efficient timber frame system that simplifies construction and improves site performance.
Reduce cost and improve programme efficiency
Sigma® II provides a lower-cost alternative to other construction methods by integrating insulation, membranes, and service zones within each panel, minimising materials, trades, and delays on site.
-
First-fix can begin immediately after frame installation.
-
Reduced on-site labour – fewer trades, less rework, lower overheads.
-
Shorter build programmes – faster weather-tight stages and earlier internal progress.
-
Reduced waste and storage – panels arrive ready for installation, manufactured just in time.
For housebuilders and contractors, that means faster completions, improved margins, and more predictable project delivery.
Precision engineered for performance
Every Sigma® II Build System is manufactured in a controlled offsite environment using high-quality, standard materials. The Sigma II Build System provides:
-
Air-tightness levels of <3 m³/h·m² achievable.
-
U-values from 0.21 W/m²K down to 0.12 W/m²K, with full condensation-risk analysis and Psi-value calculations.
-
Interlocking panel details reduce shrinkage and settlement.
-
Factory-fitted air-tight seals at vertical and mid-floor junctions ensure consistent performance.
-
Certified 60-year design life verified by BOPAS+.
This combination of fabric efficiency and build quality allows housebuilders to meet and exceed energy and regulatory targets for Future Homes Standard 2025 compliance.
Simpler installation, less labour
Sigma® II has been designed for straightforward installation by qualified installation teams.
Structural sheathing on both sides of each panel provides rigidity and reduces the need for additional racking walls.
Pre-installed windows and internal service zones remove multiple site processes.
Fewer materials to handle, store, and dispose of on site.
In short, more work happens in the factory, not on site, cutting risk, increasing quality, and saving time.
Low carbon, high PMV
Sigma® II combines low embodied carbon with a high level of Pre-Manufactured Value (PMV) — typically 55.7% to 58.4%, verified through independent assessment by CAST Consultancy.
That means every Sigma® II build system contributes to lower carbon while supporting MMC and compliance frameworks.
The use of responsibly sourced structural timber locks carbon into every home, delivering sustainability you can measure.
Fully supported by our expertise
When you choose Sigma® II, you also gain access to our Technical Hub, providing:
-
Comprehensive construction details and BIM objects.
-
U-value and thermal-bridging data for integration into your design process.
-
Project-specific support from our design, engineering, and technical teams.
Combined with our local construction teams and qualified installation partners, we ensure Sigma® II performs exactly as designed, from factory to site.
Proven and accredited
When you choose Sigma® II, you also gain access to our Technical Hub, providing:
-
Sigma® II is independently tested, certified, and trusted across the industry:
-
NHBC Accepts, BBA, BOPAS, and STA Gold Standard approvals.
-
Validated 60-year design life under normal maintenance and weathering conditions.
-
Meets or exceeds UK building regulations and Future Homes Standard performance criteria.
With over 50 years of timber frame innovation and more than 150,000 homes delivered, we give you proven performance, backed by the stability and investment strength of the Donaldson Group.
The smarter way to build
Sigma® II represents the next step in offsite construction, a high-performance, modern method of construction (MMC) that simplifies processes, cuts waste, and delivers measurable results.
Whether you’re building new homes, apartments, or mixed-use developments, Sigma® II provides the quality, speed, and sustainability you need to stay ahead.
More from Donaldson Timber Systems
Open panel systems
Timber frame build systems and certified closed panel solutions
Learn More
Open panel systems
Timber frame build systems and certified closed panel solutions
Learn More
Open panel systems
Timber frame build systems and certified closed panel solutions
Learn More
