The Future Buildings Standard means vacuum glass is being considered as an alternative to triple glazing – George Barnsdale’s Tom Wright looks at the options.
The Future Buildings Standard is looming over the horizon in 2025 and is likely to mean a big increase in the use of triple glazing to meet the lower U-values. However, specifiers are starting to consider vacuum glass as an alternative but which is better? Well, it depends.
The Government has outlined its plans to deliver “zero carbon ready” buildings via the Future Buildings Standard. It aims to ensure that no new buildings from 2025 will require further retrofitting, with an uplift in energy efficiency standards, improved ventilation and requirements to mitigate overheating in residential buildings. A start was made on this last year with the changes to Building Regs (Parts F, L and O).
Following an industry consultation, a Notional Building Specification has been developed which states that window U-values will need to be 0.8 W/m2.K down from 1.2 W/m2.K currently. Doors will need to be 1.0 W/m2.K from 1.2 W/m2.K (where they are more than 60% glazed).
This is likely to lead to triple glazing becoming the norm in most windows for new build or retrofit projects that want to achieve the highest performance.
Up to now, many of our clients have opted for triple glazing in areas where they require high acoustic performance, with this comes much better thermal performance, saving money on fuel bills.
The advantages of triple glazing are firstly its excellent thermal performance, in order to meet the new Future Homes Standard, meaning it will save money on heating. It also has great acoustic performance – ideal for blocking out noisy roads, aircraft noise etc, better security, having thicker units that are harder to break, and it can help to reduce condensation.
WHAT ARE THE DISADVANTAGES OF TRIPLE GLAZING?
Triple costs more than double glazing, but usually not as much as vacuum glazing.
Also, the windows end up heavy which means they require chunkier frames and stronger fixings, all of which increase the price further.
Aesthetically, some customers dislike the look of the triple glazed windows because they aren’t as sleek as their single or double glazed counterparts.
Lastly, because triple glazing units limit the amount of heat from the sun, they limit thermal gain. Harnessing solar energy is something homeowners have done for centuries, and this is harder with triple glazed units.
WHAT IS VACUUM GLAZING?
Vacuum glazing manufacturing takes two pieces of glass with a tiny gap (0.1 mm, in one example) and removes the air in order to create a vacuum.
The units used to have unsightly plugs where the air was extracted, but the latest technology means this is no longer the case. They can be ultra thin, from as little as 7.7 mm compared to 44 mm for triple glazing.
THE BENEFITS OF VACUUM GLAZING
Vacuum glazing is three to four times thinner than triple glazing, and looks more like single glazing. It has the same thermal performance as triple glazing, for example 0.7 W/m2.K, which is better than the target the Government is aiming for in the Future Homes Standard.
Vacuum glazing also lasts longer – because it doesn’t have gas between the panes which can leak over time. The units provide better solar gain – allowing more sun heat into the room and thereby helping reduce energy bills, and are also much lighter than triple glazing.
In addition, it’s been shown that 15% more light is allowed into the room compared with triple glazing. Vacuum glazing being much lighter means environmental savings on transport and less product used, plus as they last longer there is a lower replacement requirement.
Vacuum glazing is designed to provide great acoustic performance, and is thought to be better aesthetically – especially for historic properties, listed properties and modern contemporary builds that want to avoid heavy frames and fixings. Lastly, it’s designed to be easier to install.
WHAT ARE THE DISADVANTAGES?
Typically vacuum glazing is the most expensive option compared with double and triple glazing; this is thought to be due to there being no UK manufacturers making it, and the inherent cost of the materials; some use silver for example.
Also, it has low impact resistance – where micro pillars are used it can put high stress on the glass. It can cost up to 60% more than double glazing and around 35% more than triple glazing (although prices may vary depending on size and spec).
SO WHICH SHOULD BUILDERS AND ARCHITECTS CHOOSE FOR 2025?
Inevitably, it will end up coming down to price in most cases. We predict that most people will opt for triple glazing unless something drastic happens to the price of vacuum glazing, which may happen as the product becomes more popular and their production efficiencies improve. However, for anyone looking to balance compliance with the new regulations with heritage detailing, vacuum glass is the option that makes this possible.
We are getting more and more enquiries about vacuum glass from architects and specifiers who like it for its performance and great aesthetic qualities, however often value engineering means they have to fall back on triple glazing.
Tom Wright is managing director at George Barnsdale