What is a light steel frame floor?
A light steel frame floor is a floor system whose load-bearing joists are thin-walled, cold-formed steel C or Sigma sections. The Dutch term is staalframevloer. The joists are usually spaced at 600 mm centres, so plasterboard can be fixed to the underside without extra battens. They are cut to size in the factory and assembled into frames, which are joined on site on the same principle as timber frame construction.
Build-up
- Sections. Galvanised steel sections a few millimetres thick form the structure.
- Infill. Insulation is usually placed between the joists, partly for sound absorption.
- Top. A board material, such as flooring-grade particleboard or OSB, forms the deck.
- Finishes. For better sound insulation and less noticeable vibration you can add a dry floating floor. Underneath comes a plasterboard ceiling.
Advantages
- Light. At a weight in the order of 175 kg/m², the floor is much lighter than concrete (a 200 mm solid concrete slab weighs about 480 kg/m²). That makes it suitable for adding storeys or inserting a mezzanine in tall industrial or listed buildings.
- Span. According to suppliers, spans of up to about 7.5 m are possible without intermediate support.
- Bespoke. Cantilevers, voids and irregular shapes are easy to make, and services run through openings in the sections.
- Demountable. The system can be taken apart and reused.
Application
- Have the existing structure checked. Even a light floor adds load. A structural engineer must assess foundations and load-bearing walls.
- Don’t drill the sections at random. Use the pre-punched holes in the web and never cut into the flanges.
- Fix boards with self-drilling screws suitable for thin steel, at the spacings the supplier specifies.
- Plan acoustics and fire in advance. A light floor transmits impact sound more easily, and thin steel loses strength quickly in a fire. Fire resistance comes mainly from the correct plasterboard lining.
Common mistake: finishing a light steel frame floor as if it were concrete, without a floating floor or decoupled ceiling. The result booms and transmits footfall noise.
Related terms
- Cold-formed steel
- Timber frame construction
- Topping up a building
- OSB board
- Plasterboard
- Structural steel sections
- Composite steel deck floor
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