While there is usually much consideration that goes into choosing the right style of windows and doors, all too often, one of the most important elements of this decision, the type of glass used to glaze them, is treated as something of an afterthought.
This is a huge mistake as the glass is one of the deciding factors in how all types of windows and doors perform, ensuring, amongst other things, that they keep your home at a comfortable temperature all year round, allow in enough light and keep you safe from both intruders as well as accidents.
So, if you were planning on plumping for just any old glass in your new windows and doors, wait right there. First, you need to hear what the experts have to say about how to choose the right glazing for your home, specific requirements and budget.
What factors should determine the type of glass you choose?
Rather than simply looking at a list of glass options and selecting the one that appears, on paper, to offer the best value for money, you need to start by assessing your particular requirements.
Charles Lowe, senior marketing executive at the IQ Glass Group, explains how best to start the selection process. "The glass specification should be developed around the individual building rather than selected as a standalone product. Orientation, the size of the glazed elevations, room use, local climate, surrounding shade, thermal targets, security, acoustic requirements and the risk of overheating should all be assessed before deciding on the appropriate glass build-up."
Edward Stobart, technical sales manager at IDSystems, goes on to set out, in detail, exactly what you need to be taking into account:
- Orientation of the house: A large, south-facing sliding door needs very different glass specifications compared to a north-facing kitchen window. South- and west-facing elevations receive direct sunlight and are therefore more prone to overheating, meaning choosing glass with a solar-control coating is important. North-facing elevations, on the other hand, receive no direct sunlight and therefore glass with a higher light transmittance is a crucial consideration.
- Acoustics: If the property is near a main road, railway, or flight path, choosing acoustic laminated glass is essential to dampen low-frequency noise.
- Safety and security: Building Regulations Part K specifies where toughened glass must be used, for example for doors and low-level glazing, whilst Part Q covers where security glass (most often laminated glass) must be used for ground-floor or easy access.
- Size and weight: Large architectural glass panels (like sliding doors or fixed frame picture windows) require thicker glass panes for structural stability against wind load. Thicker glass panes means heavier panels, which can place limitations on the sizes that can be achieved and the size of panels that can be created.
Charles Lowe is Senior Marketing Executive at the IQ Glass Group, leaders in high‑specification architectural glazing. The company design and install bespoke structural glass and ultra‑slim framed systems, with their speciality being bespoke structural glazing and precision-engineered slim sliding door systems.
A long serving member of the IDSystems team, for the past 20 years Edward has advised and supported self-builders and renovators to identify the most suitable glazing options for their project. He has recently finished a complete renovation and remodel of his own home, transforming a tired 1960s house into a stylish modern family home. His expertise ensures that each project is equipped with cutting-edge, bespoke glazing designs that enhance both functionality and aesthetics.
What are the main types of glass on offer?
While the array of glazing options might, at first, seem a little bewildering, it is actually possible to break the options down into categories which can make choosing much easier.
Single glazing
Realistically, very few people are going to opt for single glazing for new or replacement windows, although those living in a period property or listed building may well find this is something they have to live with and work around. "A single pane with almost no insulating value, around 4.8 to 5.8 W/m²K, runs cold and invites condensation. It rarely makes sense (unless it's legally required)," explains Megan Ebanks, director of MEA Studio.
Double glazing
"Double glazing is two panes with an argon-filled cavity and a low-emissivity coating, and for the vast majority of UK homes it's the sensible choice," explains Megan Ebanks. "A good modern unit reaches roughly 1.2 to 1.4 W/m²K, which is what Building Regs now ask for. It gives you a good balance of comfort and cost."
Triple glazing
This is becoming an increasingly popular option for UK homeowners. Megan Ebanks explains its benefits. "Triple glazing adds a third pane and a second cavity, taking you down to around 0.6 to 0.8 W/m²K. It comes into its own on north-facing elevations, in genuinely cold or exposed spots, in low-energy and Passivhaus homes, and anywhere the warmth of the internal glass surface matters to how a room feels."
Charles Lowe is keen to point out its disadvantages too. "While triple glazing can provide lower U-values and improved acoustic performance, it does create a thicker, heavier and generally more expensive glass unit. Whether triple glazing is worthwhile depends on the complete glazing system and the building’s performance targets, rather than simply assuming that an additional pane is always better."
Vacuum glazing
A relatively new kid on the block, vacuum glazing is fast becoming one of the most popular options. Megan Ebanks explains why. "Vacuum glazing is the newest choice and, on the right project, a great alternative to triple glazing. Two panes are separated by a vacuum barely a fraction of a millimetre thick, giving triple-glazing performance, roughly 0.4 to 0.7 W/m²K, in a sealed unit only 6 to 8mm thick. That slimness is the point: it fits into the delicate rebates of an original sash.
"On one of our listed projects, we used vacuum glazing to bring a heritage window up to modern thermal standards without altering how it looks or losing the original frames. The vacuum glazing costs more per unit, but where you need warmth and a heritage-honest profile, nothing else offers both. There is a slight trade-off which is if you look very closely, you can see the micro spacers which look like tiny dots. When looking through the glass into the distance, however, these are not visible."
Acoustic glazing
It is also worth looking into acoustic glazing vs triple glazing in some cases, according to Megan. "Acoustic glass uses a special interlayer between panes to damp sound, and is probably worth every penny near a main road, a railway or a flight path."
Laminated/safety glass
In certain cases, you will have no choice but to specify this type of glass. "Safety glass, toughened and laminated, isn't a comfort upgrade – it's a legal requirement in what the Regulations call 'critical locations', in and beside doors below 1500mm, any glazing below 800mm from the floor, and wet areas such as bathrooms," explains Megan Ebanks. "Toughened glass is around five times stronger than ordinary glass and crumbles safely; laminated holds together on impact and is the usual choice for balustrades and security. We always specify laminated glass in rooflights."
Low-iron glass
This is often combined with other types of glass within a unit. It has less iron oxide than standard glass, meaning it is far clearer – ideal for north-facing spaces. Interestingly, Fallingwater, by renowned architect Frank Lloyd Wright, was one of the first houses to incorporate low-iron glass.
"Low-iron glass provides greater clarity and reduces the green tint associated with standard glass, particularly where exposed edges or multiple layers of glass are visible," explains Charles Lowe.
Megan Ebanks (BA(Hons)DipArch RIBA), founded MEA, a RIBA Chartered Practice, in 2019. MEA is known for blending the historic with the contemporary, creating a sense of timeless luxury in heritage and modern buildings. Before founding MEA, Megan worked on high-profile projects for Foster + Partners and Bennetts Associates, including large-scale new build offices in the Kings Cross Development and the City of London, the refurbishment of significant listed buildings in an Oxbridge University and a new HQ for a prestigious Royal College.
What specialist glass coatings are available?
In addition to window styles and the type of glass you will be choosing from, there are also a range of glazing innovations that involve specialist coatings, designed with specific requirements in mind. The main two are solar control and Low-E.
Low-E glass is now almost seen as something that comes as standard, as Megan Ebanks explains. "Low-E glass isn't really a separate type of glass, more a near-standard coating that reflects heat back into the room. We assume any modern double or triple unit already has it, but it's always worth checking."
Solar-control glass is ideal where overheating could be an issue. "Solar-control glass carries a coating that turns away much of the sun's heat before it enters, dropping the g-value (the measure of solar heat gain) from around 0.76 for clear glass to roughly 0.28 to 0.42," says Megan. "Use it on large south- and west-facing glazing, on rooflights and glass box extensions – anywhere a room is prone to overheating.
"One practical note to bear in mind is that most solar-control glass carries a faint green tint," points out Megan. "It's barely perceptible from inside, but it can read from the outside, so it's worth checking against the look you want before you commit."
Are there any Building Regulations that could affect your choice?
Charles Lowe explains that it is not unusual to find that your glazing options will be partly dictated by the need to comply with the Building Regulations. "Depending on the project, the glass and complete window or door system may need to satisfy requirements relating to thermal performance, overheating, safety, security, ventilation and fire performance.
"These include Part L for energy efficiency, Part O for overheating in new residential buildings, Part K for safety and protection from impact, Part Q for the security of accessible windows and doors in new dwellings, and Parts B and F where fire safety or ventilation requirements apply," continues Charles. "The correct requirements depend on the location, building type and scope of work, and the regulations differ across England, Wales, Scotland and Northern Ireland."
"Part L, on energy, requires replacement windows in existing homes to reach 1.4 W/m²K and new homes target 1.2 W/m²K," picks up Megan Ebanks. "Part K, on safety, makes safety glass mandatory in those critical locations near doors, at low level and in wet rooms. However, I find it mad that it's not a regulation requirement to have laminated glass in a rooflight. Replacement windows generally need signing off, through a FENSA or CERTASS-registered installer or building control."
Will glass options be more limited for listed building owners?
If you live in a listed building or in a designated area, you may well find that your options when it comes to choosing double or triple glazing are more limited.
In these cases, secondary glazing can be a great way to reduce heat loss while keeping the conservation officers happy, according to Edward Stobart. "Secondary glazing, where a second window frame is fitted inside the original window, is the most common solution. While less optimal than double or triple glazing, modern secondary glazing with low-E glass can still reduce heat loss and offer improved acoustic performance without altering the external fabric of the listed building."
Vacuum glazing can also be an option in some cases, says Megan Ebanks. "Where consent allows the original glass to be replaced, vacuum glazing can be acceptable. Because the sealed unit is so thin it drops into the existing sash rebates, delivering more warmth while keeping the window's original character."
That said, it isn't just the glazing that needs to be taken into account when upgrading windows in period properties, as James Allsop, MD and bespoke joinery expert at JLA Joinery, explains. "When choosing glass for a period property, the decision cannot be made in isolation. The age and significance of the building, the depth of the original glazing bars, the condition of the timber frames and any planning restrictions all need to be factored in. The starting point should generally be to retain and repair windows wherever practical, rather than assuming they need to be replaced.
"If conventional double glazing is unsuitable, there may still be several ways to improve the energy efficiency," adds James. "This includes repairing the existing timber, discreet draught-proofing, secondary glazing, shutters or carefully chosen curtains."
Shop window upgrade solutions
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James Allsop is Managing Director of JLA Joinery, a family-run bespoke joinery company established in 1980 and based near Chichester, West Sussex. He specialises in staircases, staircase renovations, fitted furniture, doors and made-to-measure joinery, and frequently offers advice on home improvements, craftsmanship, timber, interiors and property renovation.
How much do different types of glass cost?
For many people, the cost of new windows will be one of the main deciding factors in the type of glass they choose.
While it is hard to give exact costs, it is possible to gauge how selecting one type of glass over the other could impact your budget, as Edward Stobart explains. "There are so many other variables – but as a guide, if we take a standard double-glazed unit with toughened glass as a basic specification, then change the specification to laminated glass for security or acoustic performance, this would typically add around 15% to the cost.
"With the same standard double-glazed unit, adding a solar-control coating to the specification would add around 8-12% to the cost, while upgrading to a standard triple-glazed unit would work out around 20-25% more expensive. The percentage figures are dependent on glass size, glass thickness and the system they are installed within so are a guide only."
FAQs
Can solar-control glass also keep heat in during winter?
Finding ways to prevent heat loss is often top of a homeowner's list of priorities once winter hits, and upgrading windows and doors can be a great way to do this. However, if you were considering using solar-control glass to mitigate heat loss, you might want to adjust your plan.
"Solar control and thermal performance are independent technology but need to be considered together when choosing the right glazing," picks up Edward Stobart. "Glass that prevents solar gain features a solar-control coating that is a microscopically metallic layer applied to the outer pane to reflect away infrared radiation while allowing light to pass through. The level of reflection is measured by the g-value of the glass.
"The specification of glass to keep homes warm in winter is dictated by low-E (low-emissivity) coatings and the insulating gas (argon or krypton) inside the double- or triple-glazed unit," continues Edward. "The performance of thermal efficiency is measured by the U-value of the sealed unit and of the window or door as a whole system.
"With this in mind, glass that prevents solar gain wouldn’t automatically keep your home warmer in winter – indeed reducing the solar gain from the weaker sun in winter months could potentially make a home feel cooler. However, combining both solar-control and low-E coatings, along with thermally efficient frames will ensure you have the optimal solution for both summer and winter."
Is it worth upgrading the glazing on a period house?
Finally, if you live in an old house and are considering replacing the windows, or are adding an extension to a period property, it is important to consider the energy efficiency of the building as a whole if you want to see any real benefits from your glazing upgrades.
"Glass alone won't fix a house that's leaking heat everywhere else," says Megan Ebanks. "Windows are usually a smaller share of the loss than an uninsulated roof, cold solid walls and, above all, draughts. The order that actually pays is nearly always draught-proofing and airtightness first, then loft and wall insulation, then glazing. Upgrade the glass in isolation and you can even push condensation and cold spots onto the walls, which are now the coldest surface in the room.
"There's a comfort and a health dimension here too," continues Megan. "Cold, damp and stuffy rooms are common in the older homes people love, and they affect how well you sleep and how a house feels to live in. The right glass, in the right place, sitting on a well-insulated and airtight home, is where the warmth, the quiet, the savings and the health benefits genuinely come from. Treat the house as one system and the glass does its job."
While choosing the right glass for your new windows and doors is hugely important, looking into insulating windows properly will also go a long way to ensuring your home feels comfortable and remains mould, damp and condensation free.
