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Thermal Performance of minimal windows® Glazing Systems

When it comes to modern building design, thermal performance is becoming an increasingly important factor. This applies to all aspects of the building envelop, including the glazing. 

Thermal performance is the one of the most critical subjects when choosing the best glazing for residential or commercial projects. Having an ideal temperature in the internal spaces is important to provide comfortable living and working temperatures.  

Incorporating oversized, thermally efficient glazing also has additional benefits such as maximising natural light and offering stunning, uninterrupted views of the outdoors. 

Some architects may have concerns with highly glazed building designs as in the past, glazing was not as thermally efficient as other elements of a building. Modern and new technologies now give us the ability to manufacture and install high thermal performance glazing systems. 

So how is the thermal performance of aluminium glazing systems measured? 

large slim sliding glass doors in a modern rear extension
new build home in cornwall with aluminium slim sliding glass doors

What are U Values?

To show the thermal performance of a glazing system, a combination of a value will be shown as Uw, and it is measured in Watts per metre squared Kelvin, shown as W/m2K. 

Uf, Ug, PSIG and Uw 

A Uw value refers to the thermal performance of the overall system and is calculated using a formula that takes into account the thermal performance of the glass panes, framing profile and warm edge spacers. This Uw value shows the heat loss through the installation or a material.  

The Ug value is the thermal performance of the glass panels, and UF value is the thermal performance of the frameworks. PSIG is the thermal performance of the glazing spacer. 

All these three elements along with opening configurations, size and framing design can all affect the thermal performance of a glazing system. As each minimal windows systems is manufactured completely bespoke, if a specific Uw value is required for a project we can work closely with the architect to ensure this is met. 

Aluminium and steel framed glazing should always use a thermal break – without this the conductive metal allows heat energy to pass through. minimal windows systems utilise a full polyamide thermal break resulting in excellent U values.  

With Uw values, the lower the better! The value refers to how much heat energy can pass through the glazing. The glass is always the best performing part of the system and so will have the lowest value, whereas in the frame will always be the higher value.  

This is why it is vital when specifying glazing that you ensure the U value your glazier is quoting is the Uw value and not the Ug value. 

minimal 4 pane slim sliding door
juliet balcony with sliding glass door and glass balustrades

What is a Thermal Break?

Even the framing of a glazing looks like the smallest element of the system, it is very important when designing a highly insulated building. If the framing used is not thermally broken, the Uf value will be high, resulting in a higher, and therefore worse overall Uw value for the system.  

A thermal break in the simplest of terms is a non-conductive material that is placed between the internal and external parts of the framing profile. We utilise polyamide as this prevent almost all heat energy from passing through. 

Combining modern thermal break technology with a low maintenance, durable material such as aluminium allows the glazing systems to achieve low Uw values whilst creating a system with a long lifespan and can be designed to suit any building style. 

minimal windows high performance glazing systems use high quality aluminium framing profiles that are fully thermally broken and lightweight, making to control manually. 

new build cornwall house with large aluminium slim sliding glass doors
ultra slim sliding glass doors in a contemporary holiday home in conrwall

Low E Coatings

Another way to improve the thermal performance of an external glazing system is to use a low e coating within the glazing. Low e is short for low emissivity which refers to how much radiant heat energy a surface can absorb and emit.  

By applying a low e coating to the internal side on the inner glass pane, this prevents the glass from absorbing heat from the internal living spaces and transferring it through to outside.  

This helps to keep the heat within the building and when used in insulted glazing systems brings the Ug value down and in turn the overall Uw value. 

minimal windows use a low e coating as standard on all of our glazing systems. This is not something that we charge extra for as  we believe it should be a part of all glazing systems to achieve the best Uw values possible at all times. 

floor to ceiling slimmest sliding glass doors in a new build house in mawgan port
double height slim sliding glass door in a traditional house in London

Thermal Performance of Triple Glazing

Triple glazed systems have better Uw value than double glazing due to the additional glass pane and insulating gas cavity. As our glazing systems also come with a low e coating as standard triple glazed systems also has an additional coating.  

In terms of the framing profile for triple glazed systems, in order to accommodate for this extra pane and gas cavity the framing profile is deeper which also means a thicker and therefore more effective, thermal break is used, again contributing to a better Uw value.  

Our minimal windows 4+ framing profile can be used to manufacture oversized, triple glazed sliding doors, pivot doors and vertical sash windows. The 4+ profile  can accommodate glass thicknesses of up to 54mm and have slightly thicker sightlines. However, even with this profile our sliding door system still has an ultra slim sightline of just 26mm. 

The standard minimal windows Sliding Door achieves Uw values of around 1.1W/m2K, but the 4+ triple glazed sliding door can achieve Uw values as low as 0.8W/m2K.  

floor to ceiling large sliding glass doors with high thermal performance
juliet balcony with framesless glass balustrade and thermally broken sliding glass door

Sustainability and Glazing

Although thermal performance has always been a big deciding factor when specifying gazing, as sustainability is becoming more important in building design this now carries more weight.  

When talking about sustainability and glazing there are tow sides to it. Firstly the materials used and the manufacturing of the systems and secondly how it can be used to enhance a sustainable building design and reduce its carbon footprint.  

Aluminium of 100% recyclable and when manufacturing framing profiles using recycled aluminium the embodied carbon is significantly reduced, which is why minimal windows aluminium frames use 70% recycled aluminium.  

A large part of sustainability in building design is how thermally efficient the building envelope is as this reduces the energy needed to cool the internal spaces in the warmer months and heat them in the colder months. 

This is why for low carbon builds, specifying glazing with high thermal performance is essential.  

thermally broken open corner configuration sliding glass door
thermally broken pivot door in a traditional house rear kitchen extension in London

Building Regulations for Glazing Thermal Performance

Building Regulations Part L focuses on the conservation of fuel and power and  outlines the required U values of glazing for both dwellings and non-dwellings, and divides these by whether it’s a new build or work to an existing build.  

The thermal performance requirements for glazing is slightly different in each of these four sections and so it is important to read through each carefully. The 2022 changes to Approved Document L includes new required Uw values and brings new building works in line with the government’s aims to achieve zero-carbon homes by 2025.  

If you are unsure if the new Approved Document L requirements will affect your project, contact your local building control body.  

minimal windows glazing is all about maximising views without compromising on performance values, and not only is the thermal performance unparalleled in comparison to other systems, but with the PAS24 certification of our sliding door system we can offer security and a modern design.  

If you would like to learn more information about our systems or to discuss and upcoming project, contact our team today.