How to Design a Functional Glass Box Extension

27 February 2024

Light Is the New Luxury 

The contemporary aesthetic of architectural glazing has taken over the modern design industry with its sleek finishes and outdoor living feel, making it one of the most highly desired trends to date.  Glass box extensions are very popular amongst modern and traditional homes as it adds a touch of luxury to any type of property. Many clients will initially browse their Pinterest / Instagram feeds to gather inspiration for their dream extension, whilst not taking into consideration the specifications required to ensure it’s also functional.  That is where the architect/ designer would come in and ensure clients are provided with the relevant knowledge.

Advantages of having a glass box extension: 

  • On trend, contemporary aesthetic
  • Bespoke solutions to meet size/ configuration requirements
  • Indoor-outdoor open plan layout
  • Offers excellent energy performance
  • Encourages and influx of natural lighting into the interior
  • Planning permission not always required for more info click here 
  • Multiple functionality options

Disadvantages of having a glass box extension:

  • Overheating due to direct sunlight
  • Glare from the sun due to direct sunlight
  • Lack of privacy from surrounding properties/neighbours
  • Likely to lose heat during the winter months
  • Hard to keep clean

So how do we ensure a glass box extension is both aesthetically pleasing and functional?  Firstly, clarifying whether a glass box is actually the best option for the client is the first step as there are many different structural glazing options available which can still provide the luxury aesthetic and modern style without the disadvantages that come with installing an entire glass box extension such as:

Eaves Windows

Where a vertical panel of glass at the edge of a roof overhang to the face of the wall and project over the side of a building creating uninterrupted views of surrounding areas. IQ Glass can create bespoke and complex structural glass Eaves Windows to meet any size and configuration.

Glazed Side Infills:

This style is generally used on Victorian/ Georgian style homes as they are smaller and extending into the rear of the property is a great way to open your downstairs living spaces whilst improving access into the garden.  The use of large glass panels maximises the natural light influx to create a lighter, airy space.

For more structural glazing options click here.

If the client prefers the glass box extension after gaining the relevant knowledge of the pros and cons, then there are plenty of options to make their design functional. Clarifying the orientation of the property to the sun is a sensible place to start, as a south-facing glass box extension can invite in too much sunlight during the summer months causing overheating of the property and an uncomfortable glare from the sun. Whereas, a north-facing property can bring in light to the duller parts of the home, of which you would be less likely to need any solar shading solutions installed. An east-facing extension will get sun in the morning whilst a west-facing property will get sun in the evening.  The orientation of the building will be a big part of determining the solar shading solution used, if any.

Technical Glass: Solar Control Glass

With the growing demand for large structural glazing projects, it is recommended that the use of a Solar Control Coating is used to reduce solar gain whilst maintaining light transmission and clarity. This creates a comfortable internal environment without losing the aesthetic of the minimal glass desired. There are different levels of solar control coating available depending on the level of light transmission you want to allow through. It’s the metal oxide coating that reflects the infrared parts of solar energy and absorbs the ultraviolet wavelengths which reduce the amount of heat that flows into the interior of the home.  

Technical Glass: Switchable Privacy Glass

A thin layer of liquid crystals is laminated between two pieces of toughened glass of which, when an electrical current pass through the film, between the interlayers, all the crystals within the film align, switching the glass from translucent to transparent. If using Switchable Privacy Glass, you would not need the Solar Control Glass as it also has solar control properties. The switchable glass technology alone is impressive and provides the wow factor, but to take it to the next level you can control the glass via a smartphone or tablet with the integration of a home automation system like IndigoZest who are also based at The Sky House Design Centre.

Grants Blinds

Blinds are a great option for a solar shading solution and are a more cost-effective option than the technical glass.  Grants blinds create bespoke solutions for your project with a wide range of fabrics and styles readily available for you to choose from.  A disadvantage of using blinds are the fact that this would take away from the clean look of structural glazing however Grants Blinds have a concealed blinds option where the use of their patented system, ‘Blind Space’ comes into play. This concealment system has been designed to future-proof window/ door openings for a clean finish which is installed inside the wall or ceiling. Grants Blinds use IndigoZest as one of their main suppliers to integrate their motorised blinds into a smart home automation system which is becoming the standard in smart homes.


Shading timber louvres have become increasingly popular as a solar shading solution for residential properties.  Avino has a selection of timber cladding and shading systems which are easy to install for even the most eloborate of projects. The different options of timber species, sizes and styles available allow for a cohesive design throughout a property.  From fixed louvres to partitioning systems and slim framed timber windows and doors.   


All options above can be found at The Sky House Design Centre, to visit us please book an appointment in advance and one of our technical specialists will take you on a tour.  

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