Cladding for portal frame buildings
Cladding is the complete envelope system for a steel portal frame — roof, walls, and all the elements in between. Choosing the right cladding type depends on the building's use, thermal requirements, budget, and programme. This section covers the main cladding types used on UK portal frame buildings, with specification data, U-values, and fire classification reference sourced from manufacturer technical documentation.
Which cladding type do I need?
| If you need… | Use | Typical U-value | Best for |
|---|---|---|---|
| A single insulated panel for roof or wall | Composite panel | 0.18–0.35 W/m²K | New-build, fast programme, guaranteed U-value |
| An outer weatherskin for a built-up system | Single-skin profile | N/A — outer skin only | Built-up systems, re-cladding, agricultural |
| Separate liner + insulation + outer sheet | Twin-skin built-up | 0.20–0.40 W/m²K | Thick insulation, retrofits, walls |
| Low-pitch roof with no exposed fixings | Standing seam | Depends on build-up | Architectural, low pitch (3–4°), long runs |
| Natural daylight through the roof | Rooflights | 1.9–5.7 W/m²K | All portal frame buildings — typically 5–10% roof area |
| Natural daylight through a wall | Translucent wall panels | 1.1–1.9 W/m²K (PC multiwall) | Agricultural, industrial, north-facing walls |
Cladding reference pages
Composite panels
Insulated sandwich panels for portal frame roofs and walls. Kingspan QuadCore, Steadmans AS35, Tata Trisomet — U-values and thickness options by core type.
Single-skin profiles
Profiled steel roof and wall sheeting from Steadmans, Cladco, and Tata Steel. Profile depths, cover widths, gauges, and coating systems.
Twin-skin built-up systems
How built-up cladding works: liner, spacer rails, insulation quilt, VCL, and outer sheet. U-values with cold bridge correction and comparison with composite panels.
Standing seam systems
Secret-fix standing seam roofing from Euroclad, Lindab, Cladco, and Tata Steel. Minimum pitches, seam heights, and when to specify over box profile.
Rooflights
GRP barrel vault and polycarbonate multiwall rooflights for metal roofs. Brett Martin, Hambleside Danelaw, Xtralite — U-values, light transmission, and fire classifications.
Translucent wall panels
Polycarbonate multiwall and GRP flat sheet panels for daylighting in wall runs. U-values, light transmission, fire ratings, and GRP yellowing guidance.
Common questions
What cladding is used on a steel portal frame building?
The most common cladding for UK portal frame buildings is composite (sandwich) panels for the roof and walls, or single-skin profiled steel sheet in a twin-skin built-up system. Composite panels are faster to install and give a factory-guaranteed U-value. Built-up systems are more flexible for thick insulation depths and retrofits. Standing seam systems are used on low-pitch roofs and architectural projects. Rooflights (GRP barrel vault or polycarbonate multiwall) are a standard element of every portal frame roof, typically covering 5–10% of the roof area.
What is the difference between composite panels and built-up cladding?
A composite panel is a factory-made sandwich of outer steel skin, insulation core, and inner liner, installed as a single element on site. A built-up system assembles the same three layers on site — liner sheet to the purlins first, then spacer rails and insulation quilt, then the outer weathersheet. Composite panels are faster and give a more predictable U-value, but cost more per square metre of insulation. Built-up systems allow greater flexibility in insulation depth, are easier to achieve very low U-values on a budget, and are the norm for retrofit overcladding.
What U-value is required for portal frame cladding under UK Building Regulations?
Under Approved Document L (2021) for non-domestic new builds, the typical elemental targets are 0.25 W/m²K for roofs and 0.35 W/m²K for walls. These are elemental limiting values — your actual compliance target may be lower depending on the notional building specification used in your energy calculation. Rooflights and translucent panels have much higher U-values than the surrounding insulated cladding and must be accounted for in the overall calculation.
How is SteelSpec cladding data sourced?
All cladding data on SteelSpec is sourced from publicly available manufacturer technical data sheets, product brochures, and published standards. Where specific values have been calculated from manufacturer-published parameters (such as indicative U-values from declared lambda values), this is clearly noted alongside the data. SteelSpec is an independent data registry — data is published on its own terms from public sources, and all values should be verified against current manufacturer documentation before use in a project specification.