Structural Glass Extensions

By using glass panels, structural glass extensions are a modern architectural element that expands a building’s space. Incorporating glass walls, floors, and ceilings, glass extensions create a seamless transition between indoor and outdoor spaces while allowing natural light to illuminate the interior.

These extensions can create stunning visual appeal, making them popular choices for contemporary architecture. They offer a unique and captivating way to enhance space and elevate architectural aesthetics in a variety of settings, including residential, commercial, and public spaces.


  • Glass options for panels: Single, double or triple glass options (toughened or laminated-toughened)
  • Glass thickness: The thickness of the glass depends on its intended role. For instance, if it needs to withstand high wind loads, it will be thicker.
  • Low-iron glass: It is manufactured with lower iron content than standard ‘clear’ glass and doesn’t have a greenish tint. When incorporating thick and layered glass components, such as glass beams and fins, are to be used, it is recommended to consider low-iron glass in order to minimise any greenish tint.
  • Depending your safety and security conditions, we use toughened and/or laminated glasses
  • Solar glass coating: It helps reduce the transfer of heat from the sun into your glass extension. A glass with a low solar factor (g-value) helps prevent the interior space from overheating on sunny days.
  • Low-e coating for increasing thermal performance

Size Limitations

  • Contrary to traditional framed glass, which is limited in size by the weight of the glass, structural glass has no maximum size restriction. However, the largest possible size of a glass panel that can be made in the UK is 6000 X 3210mm.
  • Site access and installation constraints are taken into account when determining glass sizes.

Opening Elements

  • A glass door can be incorporated into the glass extension for accessing the outside and also providing natural ventilation.
  • Single-leaf or double-leaf hinged glass doors are a popular choice for the glass-box extensions.
  • Instead of a traditional hinged door, a pivot glass door or slimline sliding door can be added to the glass link for a contemporary look.  Steel supporting elements are necessary for this integration.

Thermal Insulation

  • Choosing the glass with minimum U-value reduces heat transfer between interior and exterior of the glass extension. 
  • Choosing the insulated glass with low-e coating helps to prevent heat from escaping through the glass by reflecting it back into the interior
  • Opting for thermally broken frames enhances thermal insulation and prevents thermal bridges.

Weather Tightness

  • The glass extensions are required to be constructed in a way to withstand any type of wind force, prevent any water infiltration and air leakage. 
  • The proper drainage system such as guttering and flashing must be considered at the design stage.  It is important that the aesthetic of the glass extension should remain intact when designing the drainage system. 
  • Insufficient air tightness leads to air infiltration from outside because of differences in pressure and wind forces. To avoid air leakage between interior and exterior,  it is crucial to choose high-quality sealants and apply them correctly to all joints  to withstand wind and water. 
  • The glass extensions must be resistant to wind and snow loads. The vertical structural support for wind load is usually provided by glass fins. The lateral structural support for the roof section is provided by steel or glass beams. The minimum thickness of glass fins and beams is determined with structural calculations.  For the UK, the average design wind load is usually 1200 N/m2 and the snow load is 600 N/m2.  However, simply using these averages may result in the glass being over specified or under specified for the job.

Safety and Security

  • Toughened glass is the standard choice for safety purposes.
  • Laminated glass is used for safety and security. 
  • Laminated glass is used for safety where containment is needed (protection against falling).  
  • When extra security is needed, laminated glass will be used.  
  • The inner pane of the glass panels used on the roof section must be  laminated for safety. 
  • If the extension includes an opening element, a strong locking mechanism must be equipped. 

Glass Extension Cost

  • Every project is unique and needs different specifications for glass, supporting elements, materials and installation requirements, meaning the prices vary or there is no standard rate.  
  • The cost of a glass box extension depends on a variety of factors such as total size, glass panel size, number of supporting elements, glass thickness, and glass features required. 

Frameless glass box extension

Building Regulations for Glass Extensions

  • Glass box extension requires to meet the building regulations.
  • Part K: Glass box extension must comply with Building Regulations Part K in terms of safety requirements.
  • Part L: Any glazing element must meet Building Regulations Part L in terms of thermal insulation and energy efficiency. Glass box extensions are considered as over-glazed extensions (the total area of glazed elements exceeds 25% of the floor area). So that, Standard Assessment Procedure (SAP) can be used to achieve compliance. SAP calculation should be carried out by an approved SAP assessor.