Liquid Membranes for Light Gauge Steel Frame (LGS)

Liquid Membranes for Light Gauge Steel Frame (LGS)

Achieve airtightness, fire compliance and facade waterproofing on LGS structures — liquid-applied solutions compatible with all LGS substrates, factory-applied or on-site.

Light gauge steel frame structure showing interlocking steel studs and trusses used in modern construction

The Challenge of Airtightness in LGS Construction

Light gauge steel frame is one of the fastest-growing construction methods in the UK — used in residential, student accommodation, build-to-rent, hotels and commercial buildings. However, achieving the airtightness requirements of Part L 2021 and Passivhaus on an LGS structure presents unique challenges.

Steel studs conduct cold from outside to inside (thermal bridging), and the interfaces between panels, around window openings, and at service penetrations are notoriously difficult to seal with tape-based sheet membrane systems. The rigid nature of steel also means any building movement can crack traditional applied finishes, creating hidden air leakage paths.

Key issue: Steel and infill materials (board, plasterboard, insulation) expand and contract at different rates. Passive Purple's flexible formulation accommodates this movement without cracking — maintaining the airtight layer for the lifetime of the building.

Why Liquid-Applied Membranes Are Ideal for LGS

Adheres Directly to Steel

Passive Purple bonds directly to steel substrates without primer — eliminating a preparation step and reducing the risk of adhesive failure at the membrane-to-steel interface.

Bridges Panel Joints

Panel joints and interfaces in LGS construction are sealed by the liquid membrane conforming to the surface — no lapping, taping or additional detailing required at the joint.

Fire Rated

Passive Purple X carries a Class B fire rating — suitable for LGS high-rise residential, student accommodation and commercial projects requiring fire-rated external envelopes.

Factory or Site Application

Products can be applied in the factory (for volumetric modules or factory-built panels) or on-site after erection, giving flexibility to the programme.

Fast Programme

Spray application at up to 300m²/day means the airtight membrane is not a programme constraint — critical on fast-track LGS projects.

Works on All LGS Substrates

Passive Purple adheres to steel, OSB, cement board, plasterboard, concrete block infill and masonry — covering all the substrates encountered in a typical LGS build.

Passive Purple X liquid airtight membrane applied in light gauge steel construction, sealing window reveals and floor junctions

Recommended Products for LGS

Product Where Used Certifications
Passive Purple Internal (Spray) Internal face of LGS panels and infill boards Passivhaus, BBA, WUFI
Passive Purple Brush Panel joints, service penetrations, window reveals Passivhaus, BBA
Passive Purple X (Spray) External fire-rated applications on LGS facades Class B Fire, Passivhaus
Passive Purple X (Brush) Details and junctions on fire-rated applications Class B Fire, Passivhaus
Passive Purple External External face — airtight, weatherproof facade membrane Passivhaus, Fire Rated

3D cross-section of a steel frame wall and ventilated cold roof showing Passive Purple External on the facade and Passive Purple Internal on the warm side

Applicable Building Types

  • Low-rise and mid-rise LGS residential
  • High-rise LGS residential (Approved Document B compliance)
  • Build-to-Rent and student accommodation
  • Hotel and hospitality (modular LGS)
  • Commercial and mixed-use LGS structures
  • Volumetric modular construction
  • Hybrid concrete core / LGS structures

LGS Project Support

We work with LGS manufacturers, main contractors and offsite specialists. Contact us to discuss your project — we can advise on fire ratings, airtightness strategy and factory-applied options.

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