Types of Window Frame Material and Glazing
Choosing the right window materials can be the key to any project. They are the most eye-catching element of a building, giving personality and identity to a home. Additionally to letting light in, insulating the inside from cold, heat, rain, wind and adverse weather, windows have become a way of bringing the outdoors in and connecting interior rooms with external spaces. The materiality of windows chosen may change based on the style, location, age and exposure of a building as well as budget and design.
Below we will explore some of the main frame materiality choices as well as glass specification and share construction details of how these fit within a wall buildup. We will also share some of our recommended details for all the different window material options, so make sure you read to the end.
Choosing the right window frame material
The main materials available in the UK for domestic windows are timber, uPVC, aluminium and composite (timber frame with external aluminium cladding).
Timber Window Frame
Timber windows can be bought thermally broken or as traditional solid frames from a wide variety of wood species. Timber windows have good environmental merit, but a lower natural durability. Preservative treatments must be used in order to extend the life of timber windows. Timber is a popular choice due to its natural appearance, however it can be expensive. They are great for heritage projects when replacing existing windows and upgrading to double glazing within new frames whilst maintaining the character of a building. Thermally broken timber windows also work well in modern buildings.
uPVC Window Frame
Modern uPVC windows have a great life expectancy, with little maintenance required during that time. Historically uPVC was difficult to recycle and therefore was not considered to be a good environmental option. However, advances in research and innovation have led to uPVC being recycled. The window frames can be recycled and repurposed up to 10 times before there is a deterioration in quality or performance.They tend to be the cheaper options in many projects although the lack of manufacturer’s detail information for designers and difficulty of installing within the insulation zone of a wall can sometimes mean that the seal around the window is not as efficient as possible, allowing air leakage and less thermal performance. They also tend to have a thick frame, reducing the light internally.
Mixed / Composite Window Frame
It is common to see aluminium clad timber windows that provide the thermal and aesthetic benefits of timber with the durability of aluminium cladding externally. They can also be specified so that all the external aluminium colours match if you have different frame types such as aluminium only sliding doors.
Aluminium Window Frame
Aluminium windows have become popular over recent years due to their robust low maintenance frames, with profiles much thinner than uPVC allowing for more glass. Strong frames allow for large glazing sizes. Within a domestic setting they are used more for large pieces of glazing such as sliding doors, rooflights and structural glazing.
Other window frame materials
Fibreglass, steel framed, U Shaped Profile Glass, polycarbonate panel.
Fibreglass windows are not widely available in the UK although are more popular in countries like the US. The finishes and look is similar to uPVC although they are stronger and can be used as a cheaper alternative to aluminium. They are not easy to recycle although they are durable.
These are used mainly in renovation projects of conversions of existing industrial buildings due to their bold typically black painted steel frames and small panes of glass. They do not perform the best thermally and are therefore not recommended in new building projects.
Comparison of Window Materials
Below is a table showing a comparison of timber, uPVC, composite and aluminium windows within a domestic setting, including key features such as durability, sustainability, energy efficiency and aesthetics.
[To download this guide and table as a handy pdf scroll to the end]
Different manufacturer’s will provide certain guarantees based on the product, sometimes the cheaper product will have shorter warranties or have shorter times for different elements of the window such as the handles, hardware or glass.
Choosing the right glazing for you window frame
When specifying windows, the window manufacturer can install different types of glass to suit different uses. Below is a list of the most commonly used within residential settings.
This is the standard glass used in windows when areas are not in critical zones.
Laminated Safety Glass
Laminated glass is a safety glass which is created with an internal film between two layers of tempered glass. When struck, the glass will remain adhered to the film, preventing the glass from falling through the frame.
This glass is typically used on the external pane of ground floor windows to increase security and prevent someone entering the building through the window. It is also used internally, for glazing which falls below the 800mm guarding height to avoid the risk of falling if broken or where the risk of glazing being struck is high, just as full height doors leading to a terrace.
Tempered / Toughened Glass
Toughened glass is a type of safety glass which when broken crumbles into small granular chunks instead of splintering into jagged shards.
This type of glazing is used in areas which may be liable to knocks from users such as doors onto a terrace area, but where there is no risk of falling. Other applications include small areas of glazing on timber doors and shower doors.
This type of glazing has been largely replaced with laminated glass as it prevents the glass from being broken and allowing entry. Wired glass is still used in historic applications and can deter forced entry with the visible wires.
This is where one of the glass panes is tinted a certain colour. This is less common in domestic settings. Stained glass which is where coloured glass is connected with lead or other metals to form a pane of glass is more common in older properties.
Low-E glass stands for low-emissivity glass. This is glass with a microscopically thin coating on an internal pane that is transparent and helps to reflect heat to improve the thermal performance of the glass. Depending on the required levels, the finish can reduce the luminosity internally.
Privacy film / frosted glazing
When designing windows on a boundary where privacy is a planning requirement or bathrooms to private rooms such as bathrooms, different types of glazing can be used.
Frosted glazing has one of the panels of glazing which is permanently frosted, usually kept internal to the air barrier so the glass on both external sides is flat to the touch and easy to clean. Privacy film can be applied after the window manufacture to create a non-permanent frosting which can be removed by the user. This option may not be possible in areas where a planning requirement requires frosted glazing.
This type of glass also provides privacy. Is made with a mirror coating which reflects from the outside but allows views out from the inside. The finish reduces the luminosity internally.
Obscured / back painted glazing with insulated panel behind
Obscured or back painted glazing is usually used in window panel systems in areas where visibility is not wanted, such as window panels in front of kitchen counters or bathrooms. This is used more commonly in large facades with repetitive windows rather than on single family homes.
This type of glass helps to reduce noise levels from the outside. This can be done in a number of ways. The increased depth of gap between the panes performs better acoustically. Triple glazing tends to perform better than double glazing. Asymmetric thicknesses of glass can also help to disrupt the soundwaves. Some acoustic glass also has a sound-dampening laminate between panes to further reduce noise. However, key design decisions when specifying acoustic glazing is to make sure the wall construction and installation is also robust, any air leakage can allow sound inside. Trickle and other background vents should be suitable for the noise reduction needed.
What does thermally broken mean?
Thermally broken refers to a construction technique used to improve the energy efficiency of the window and reduce heat transfer between the interior and exterior of a building. It is an important feature in modern window design, particularly for regions with extreme weather conditions, as it helps to enhance insulation and reduce energy costs.
A thermally broken window frame is typically made of two or more materials with different thermal conductivities, often aluminium or metal on the exterior and a non-metallic material like PVC or timber on the interior. These materials are separated by a thermal barrier, usually a material with low thermal conductivity, such as a polyurethane or a specialised plastic strip. This thermal barrier effectively breaks the thermal bridge that would otherwise allow heat to flow freely from the interior to the exterior (or vice versa) through the window frame.
Choosing a window material
There are many options to picking a window material beyond what it will look like. Different projects will require the use of different materials, shapes and openings to suit the new or existing building. There are also many ecological features to bear in mind as well as cost, designability and energy efficiency amongst others.
Written by Aida Rodriguez-Vega, architect and researcher. At the Detail Library, Aida keeps busy by carrying out technical research and drawing new details for the ever-growing library.
Source URL: https://www.archdaily.com/300175/slip-house-carl-turner-architects
Image URL: https://images.adsttc.com/media/images/50b7/d9ba/b3fc/4b23/9a00/00f9/slideshow/Slip_hs-2729.jpg?1414039260
Architect credit: Carl Turner Architects [https://turner.works/]
Photographer credit: Tim Crocker [https://www.timcrocker.co.uk/]
Source URL: https://www.themodernhouse.com/past-sales/the-yard-house/
Image URL: https://tmhmedia.themodernhouse.com/uploads/2018/06/TMH_LordshipLane_web-36-1600×1067.jpg
Architect credit: Jonathan Tuckey Architects [https://jonathantuckey.com/]
Photographer credit: The modern house
Aluminium window example
Source URL: https://neildusheiko.com/projects/dalston-house/
Image URL: https://neildusheiko.com/projects/dalston-house/#images-9
Architect credit: Neil Dusheiko [https://neildusheiko.com/]
Photographer credit: Tim Crocker [https://www.timcrocker.co.uk/]
Timber window example
Source URL: https://www.dezeen.com/2022/05/15/architecture-for-london-stone-house-extension/
Image URL: https://www.dezeen.com/2022/05/15/architecture-for-london-stone-house-extension/
Architect credit: Architecture for London [https://architectureforlondon.com/]
Photographer credit: Building Narratives [https://www.buildingnarratives.co.uk/]
Composite window example
Source URL: https://www.dezeen.com/2021/02/05/ar-residence-dedraft-london-house-extension/
Image URL: https://static.dezeen.com/uploads/2021/02/ar-residence-dedraft-architecture-residential-extension_dezeen_2364_col_23-852×1032.jpg
Architect credit: DeDraft [https://dedraft.co.uk/]
Photographer credit: Nick Dearden/Building Narratives [https://www.buildingnarratives.co.uk/]
Steel framed windows
Source URL: https://www.dezeen.com/2016/10/04/blee-halligan-architects-victorian-house-extension-renovation-highgate-hill-london/
Image URL: https://static.dezeen.com/uploads/2016/10/highbury-house-extension-victorian-terrace-residential-architecture-blee-halligan-architects-london-uk_dezeen_2364_col_2-852×568.jpg
Architect credit: Blee Halligan Architects [https://www.bleehalligan.co.uk/]
Photographer credit: Robert Battersby [https://www.robbattersby.com/]
Source URL: https://www.pinterest.co.uk/pin/399694535682231476/
Image URL: https://i.pinimg.com/564x/70/c2/1e/70c21e5cebeeca2a70294e746d7de88f.jpg
Architect credit: VEKA window frames