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Specifying Glass Extensions with minimal windows

High Performance Glazing for Bespoke Glass Extensions

Glass extensions come in many shapes, sizes and specifications. From glass box extensions to highly glazed double height extensions, our high performance glazing systems can be designed to fit in with any design.  

All the minimal windows slim framed glazing systems have flexible designs including a range of glazing options and frame finishes. This allows each system to be manufactured completely bespoke to meet specific project requirements.  

When specifying glass extensions with high performance glazing, there are a few key points to consider. The first is the thermal performance of the glazing. The required Uw value  may dictate whether double or triple glazing is needed.  

Secondly, especially with the rising temperatures across the UK, many homeowners are concerned about overheating in highly glazed extensions. This can easily be prevented using triple glazing, solar control glass or external shading solutions 

Then other performance values need to be looked at when specifying glass extensions, such as air permeability, water tightness, and wind load. The size of the glazing needed will also affect which glazing solutions would be best to specify. 

When creating a new extension or additional building to a property you have unprecedented options over the finishes around your slim framed sliding doors, creating as minimal appearance as possible. 

90 degrees open corner sliding glass doors in an extension in London
open corner sliding pocket doors in home extension

Glazing Options for Glass Extensions

The new Approved Document O and updates to Approved Document L of the UK building regulations mean that triple glazed systems with low e glass and solar control coatings will start to become the standard when specifying glass extensions, especially for highly glazed extensions designs.  

All minimal windows high performance glazing systems are manufactured with a Low E coating as standard, enabling them to achieve unparalleled thermal performance values.  

This prevents heat from escaping through the glazing, keeping internal spaces warm during the colder months, and helping to reduce heating costs needed in winter.  

For the warmer months, if overheating is a concern, then our high performance glazing systems can be specified with solar control glass. This thin metal oxide coating reflects the suns infrared rays away, reducing solar gain.  

Many other glazing options are available when specifying glass extensions with our bespoke glazing systems, such as low iron glass, low maintenance glass and electric glazing solutions.  

open corner slim sliding doors in home extension
triple glazed sliding glass door in a contemporary building in Scotland in double height

Specifying Glass Box Extensions

Glass box extensions are often designed using a combination of frameless structural glazing and slim framed glazing solutions 

A common glazing specification is a glass box extension with a solar control structural glass roof and slim framed sliding doors. Automated opening rooflight systems can also be utilised alongside the slim sliding doors to increase the levels of ventilation. 

These types of glass extensions give the new living spaces a vast amount of natural light and a strong connection to the outdoors. 

An excellent example of this is this traditional style home in Leicester. The homeowners wanted to expand their home and create a light-filled open plan kitchen and dining area.  

Therefore, a glass box extension was installed at the rear of the home with a large structural glass roof and biparting triple glazed sliding doors from minimal windows. 

flush threshold 26mm slim sliding glass door in an extension in Scotland
specifying glass extensions

Double Height Glass Extension Specification

When specifying glass extensions that require double height glazing, looking at glazing systems that can reach these heights without having to compromise on performance values is essential.  

minimal windows® systems can easily be specified as double height glazing solutions and are able to reach incredible heights, with one of our triple glazed sliding doors being installed at a staggering height of nearly 6m in a luxury London townhouse extension and refurbishment.  

There are tested maximum sizes for all minimal windows systems to achieve certain performance values, but they can be specified as larger sizes depending on several factors.  

For example, this 6m tall sliding door in London was able to be specified at that height as the wind load requirements for that area is lower, meaning that we could go outside of the tested sizes to manufacture a double height sliding door with a lower wind load.  

Our team can work closely with architects to help them specify high performance glazing for glass extensions that meet all requirements, in terms of both performance values and design.  

high security sliding glass door with pas24 certification in a contemporary house in the uk
triple glazed ultra-slim sliding glass door in a contemporary extension in Leicester

Specifications for Glass Extensions to Listed Buildings

Any renovation or extension work to a listed building needs careful consideration as listed building status is applied to preserve and protect the unique and best examples of the country’s rich traditional heritage for future generations. 

This means the building itself should be altered in any way, however, extensions can be added, and renovation carried out is necessary to preserve the building if the original character of the build is preserved.  

Highly glazed extension designs are often favoured, especially when low iron glass is specified, as the clear nature of the glass and minimal design does not detract from the surrounding building.  

A project in the Cotswolds included a massive extension to a small Grade II Listed gamekeepers’ cottage in the Cotswolds. This extension was granted planning permission under paragraph 80 due to the unique design.  

One significant element of this was the sustainability of the extension. The south facing elevation is made from mostly glass, including minimal windows sliding doors, and the solar gain from this is used as a heat source in the new internal living spaces.  

glass extension with double opening aluminum pivot doors from minimal windows
modern London home extension with a slim sliding glass patio door in a pocket configuration

Glass Extensions with Open Corner Sliding Doors Specified

Open corner sliding doors are the first choice is you are looking to completely merge your indoor and outdoor spaces.  

Depending on the structure of the building, there may even be no need for a support post, meaning that when to doors are slid open it creates a floating roof effect.  

Open corner doors can also be specified as pocket doors, again this depends on the building structure as a wall cavity will be needed for the system to slide into.  

By designing the internal and external floor finishes at the same level you can create a flush floor finish across the minimal windows® tracks.  

Below the external finished floor level, you can introduce a traditional pea shingle drainage channel for a discrete drainage option, alternatively you can integrate a flush external drainage channel from IQ Glass to maintain that flush floor finish whilst ensuring adequate water drainage. 

floor to ceiling ultra-slim sliding glass door in an extension in London

Specifying Glass Extensions with Pivot Doors

Many glass extension projects that use minimal windows® systems opt for slim sliding doors, however, our high performance aluminium pivot door should not be overlooked.

This slim framed pivot door is unmated in performance levels, especially water tightness as the minimal windows Pivot Door has a magnetic seal in the base. When the door is closed this rises up and interlocks with the base profile of the sash. 

When specifying glass extensions with slim framed pivot doors, it is important to remember that the stainless steel pivot mechanisms in the heed and base must be a minimum of 10mm form the closing edge.  

For wide systems, the pivot mechanisms can be in the centre of the sash, something not commonly seen but in the right glass extension can create a unique glazing feature.  

The minimal windows Pivot Door can also be specified in a double opening configuration, as seen in our Princelet Street project, a rustic style glass extension with a unique green toned finish to the glazing frames.

London home extension with large aluminium pivoting patio doors
sliding glass pocket door from minimal windows in a modern rear extension in London

Specifying Glass Extensions with Marine Grade Glazing

If the glass extension is located within five miles of a large body of water such as within five miles of the sea, then we recommend specifying glass extensions with marine grade glazing.

Marine grade glazing can mean many things, with the most basic being the metal framing profiles finished in a marine grade polyester powder coating (PPC) of around 50 microns thick. 

minimal windows system use marine grade PPC as standard on all of our system to ensure the highest levels of durability and protection.

For glazing in a marine environment, we would also recommend pre-anodising the framing profiles and then finishing with a marine grade PPC for ultimate protection. 

For the actual glass specification, locations by the coast often have a higher wind load and these winds can carry salt and sand deposits when can be left on the glass.

Specifying glass extensions with low maintenance coatings can help prevent the build-up of dirt and debris and decrease cleaning time. 

triple glazed ultra-slim sliding glass door in a contemporary extension in Leicester
structural glazing, structural rooflight and minimal windows slim sliding glass doors

Specifying Glass Extensions in Conservation Areas, AONB and National Parks

If the extension is a single story extension of up to 3m (or 4m for a detached property), then planning permission is not required. Anything over this, such as side extensions and two-storey extensions,  you will need to apply for planning permission.

When it comes to the design of the extension, there tends to be a lot of freedom as the buildings within these areas vary greatly in terms of style and character. Contemporary extensions are welcome, however, they may need to include certain materials to ensure they do not alter the overall look of the land or stand out too much.

Contemporary glass extensions are often preferred as they enhance the surroundings. Glass is an ideal way to do this, making contemporary glass extensions a popular choice in conservation areas.

No external building cladding is permitted to be added to any buildings within conservation areas, AONB or national parks.

It is recommended that even if your contemporary extension meets the requirements to go ahead with permitted development, you still consult the local authorities to ensure the project goes ahead without any unexpected delays.

structural glazing with aluminium door
large contemporary extension with sliding glass pocket doors

What's the difference between a glass extension and a conservatory?

Glass extensions differ from conservatory’s as they are usually merged with the rest of the home, sharing the same central heating system and glazing here must meet certain thermal performance values 

As a conservatory is now part of the main home’s building envelope there is no thermal performance requirement (hence why they tend to overheat in summer and be freezing in winter). 

There are more advantages to adding a glass extension to your home, as this space can be created as a secure, thermally efficient living space that can be enjoyed all year round.  

Whether you’re looking to specify a bespoke extension with oversized pivot doors or a double-height extension with triple glazed sliding doors, minimal windows systems can help enhance the glass extension design. 


For more information on glass extensions, contact the minimal windows® team today.