Steel Side-Hung Windows – Outward Opening


Also known as the casement window, its sash is attached to the either side of the frame and opens outward. Depending on the design requirements, friction stays or butt hinges are used for hinging the sash to the frame.

With their slim sightlines, steel side-hung windows offer a sleek and modern aesthetic in buildings. Their versatility makes them suitable for various architectural styles,  from classic to contemporary homes.

Design and Aesthetic


  • Thermally broken profiles as standard 
  • A basic depth for thermally broken steel windows is between 50-70mm.
  • Slim sightlines

Materials and Surface Finishes


  • Strip galvanised steel (Allowing full range of standard powder coated RAL colour options)
  • Corten
  • Stainless steel
  • Marine grade powder coated for for use in marine and coastal environments

Size Limitations


  • Standard sash sizes for steel side-hung window are up to 1 metre in width and 2.3 metres in height.
  • A steel side-hung window sash may weigh up to 150kg. 

Opening options


  • Outward opeing side-hung window (with visible butt hinges)
  • Outward opeing side-guided window (with concealed friction stays)
  • Outward opening double side-hung window (also called french windows, no mullion in the centre when both sashes are open)

Safety & Security Options


  • Steel side-hung windows come usually with standard multi-point locking systems.
  • Burglar resistance classes of RC2, RC3 or PAS24 are available as security options,
  • Restrictor can be used to limit the amount of opening of the side-hung windows for safety.

Glass Options


  • Double glass option for a standard size side-hung window: 4-20-4, toughened glass, 20mm argon filled cavity, Ug-value of 1.0 W/m2K, low-e coating, warm edge spacers, light transmission over 70%) 
  • Triple glass option to achieve better thermal performance.
  • One pane of glass unit can be built with laminated glass for additional security or safety for preventing fall through, overhead glazing and full height glazing.

Thermal Performance


  • Thermal performance of a steel side-hung outward opening window depends on its frame and glass combinations.
  • A typical outward opening steel side-hung window can achieve a U-value less than 1.4 W/m2K with a double glass (Ug=1.0 W/m2K).
  • For better U-values, triple glass must be choosen.

Weather-tightness Performance


A typical outward opening steel side-hung window should meet the following minimum weather-tightness performance values:

  • Air tightness: Class 4 (600 Pa)
  • Water tightness Class 9A (900 Pa)
  • Wind load resistance: Class C4 (1600 Pa)

Regulations and Standards


Any steel window to be installed in residential properties is subject to building regulations and certain standards:

  • Windows to be installed on the ground floor of new residential buildings must have PAS24 securilty level. (Part Q, Read More >> )
  • Windows to be installed on residential properties must comply with Approved Document L in terms of thermal performance ( Read More >> )
  • Windows must comply trickle vent requirements specified in Approved Document F (Read More >>)

Buyer’s Guide to Steel Windows



Common applications of outward opening steel side-hung windows

  • Casement window is a traditional window type in the UK and is used in all types of buildings including historic or modern residential buildings and commercial buildings.
  • As they can be easily opened and closed, they can be used any locations in the buildings. 
  • As they do not occupy any interior space when opened, they are an ideal solution for tight spaces, such as narrow corridors or small rooms. 
  • They can serve as an alternative escape route, as they allow for easy exit without obstruction from inside.
  • They are ideal for rainy climates as they prevent water ingress during rain  compared to inward-opening windows.