Here at Colin’s Sash Windows we often get asked about triple glazing. Our stock answer is no, in our climate it’s not worth the additional expense. We use low E glass in all our windows. Glass with a low E coating keeps your home warmer by reflecting a higher proportion of the heat back into your home and can keep you cooler by reflecting solar thermal energy from outside. The only exception to have triple glazing might be in North facing rooms where low E glass is not so effective.
In sash windows it simply isn’t possible. The sealed unit can only be 24mm thick as opposed to 28mm in our other windows. This means there would only be 6mm between the panes. Additionally, the sealed units would be too heavy for the frames.
Here’s what warrants consideration when deliberating the advantages and disadvantages of investing in triple glazing:
Understanding Triple Glazed Windows
To put it succinctly, triple glazing comprises three glass panes encased within a sealed frame, mirroring the structure of double glazing with two panes. Between each glass pane lies an insulating layer of air or an inert gas, like argon. Argon, being denser than air, functions as an effective insulator for both heat and noise.
The addition of a third glass pane, positioned between the inner and outer panes of double glazing, creates two air chambers, significantly boosting the energy efficiency compared to regular double glazing by approximately 50%.
Further advancements in energy efficiency stem from variables such as the choice of gas or air in the space between panes, warm edge spacer bars that minimize heat transfer at the perimeter, and specialized glass coatings that curtail energy loss from the interior. The window frames themselves, alongside providing insulation, play a crucial role in overall performance and insulation. Look for frames with commendable airtightness ratings to bolster energy efficiency.
Energy Performance Analysis
A common metric for gauging window energy performance, analogous to how we assess walls, floors, and roofs, is the U-value measurement.
Glass manufacturers have perfected the art of applying coatings and tints to glass surfaces, enhancing heat retention, mitigating excessive sunlight, reducing glare, and even facilitating self-cleaning. This innovation has significantly reduced the U-values of glazing.
Single glazed windows can possess U-values around 5.0W/m²k.
While double glazed windows initially hovered above 3, they can now achieve values as low as 1.4
In comparison, walls adhere to a U-value requirement below 0.3, underscoring windows as potential weak points in a building’s thermal efficiency. This has prompted intensified efforts to further enhance their performance.
Progress in Glazing Manufacturing
Innovations that have propelled advancements include:
- Increased spacing between the two glass panes (optimal distance around 16mm).
- Incorporation of low-emissivity coatings on glass surfaces to curtail heat escape.
- Infusion of an inert gas, typically argon, into the cavity.
- Elimination of cold bridges, like aluminium spacers encircling glazed units. All our sealed units are made with warm edge spacers.
Switching from single to double glazed windows brings substantial energy savings. However, the difference between U-values of around 1.4W/m²k for double glazing and approximately 0.8W/m²k for triple glazing translates to a less substantial improvement in overall energy performance—perhaps a 5% enhancement for a new house. (Windows typically contribute to about 20% of overall heat loss.) Converting this improvement into cost savings might yield around £20 to £40 annually on heating bills, contingent on the residence’s size.
Traditional payback calculations don’t neatly justify the additional cost of triple glazing being recouped over 10 to 15 years through energy bill savings.
The primary advantages primarily revolve around heightened comfort. If the walls, roof, and floor of a dwelling are well insulated, neglecting the glazing can lead to cold spots around windows, fostering drafts, sapping warmth when seated close by, and fostering condensation buildup.
Essentially, the quality of glazing must mirror the insulation standards in the rest of the house to ensure consistent warmth enveloping the residence.
Thermal Comfort: While double glazing suffices, triple glazing takes comfort a step further by retaining heat more effectively. Modern, energy-efficient double glazed upvc windows maintain a surface temperature of 16°C in a room heated to 21°C, while triple glazing can maintain 18°C.
Acoustic Performance: There’s not much difference between double glazing and triple glazing if you use acoustic glass in your double glazed windows. There’s also a security benefit because the glass is laminated meaning it’s virtually impossible to smash.
Reduced Condensation Risk: The lower U-values of triple glazed windows aid in minimizing internal condensation issues by retaining heat inside the building and curbing the interaction between cold external temperatures and warm indoor air that leads to condensation. (Note that internal condensation is primarily influenced by high humidity levels and inadequate ventilation.)
Higher Cost: Triple glazing typically incurs greater costs.
Potential for Wall Damage: Due to their heavier frames, improper support during installation could damage walls.
Installation Precision: Needless to say, correct installation is paramount to maintain performance.
Evaluating Window Ratings, Heat Absorption, and Solar Gain
Windows differ from walls and roofs in their capacity to absorb heat when exposed to sunlight. Some high-end double glazed windows can even contribute net heat over a heating season. Conversely, triple glazed windows slightly reduce the heat absorption properties.
Recognizing these intricacies, the British Fenestration Rating Council introduced an energy labelling system for windows, ranging from A to G. The highest rating signifies windows that absorb as much heat as they lose, encompassing both double and triple glazed variants.
If you live in a very strict conservation area or listed building where double glazed windows and definitely triple glazed windows are not allowed your only option is secondary glazing. This is an extremely effective option for energy savings and sound reduction.
I'm the founder of Colin's Sash Windows. I disrupted the sash windows market in the UK in 2014 by introducing fixed prices for uPVC sash windows in the UK. Before this they were generally only available at very high prices through window installers. Today our business is one of the market leaders in supply only windows, doors and roofs in the UK.