May 9, 2023

The Future Buildings Standard which is looming over the horizon in 2025 is likely to mean a big increase in the use of triple glazing in order to meet the lower U-values that will be required. However, specifiers are starting to consider vacuum glass as an alternative but which is better? Well, it depends….

What does the Future Buildings Standard say about U values?

The Government has outlined its plans to deliver a “zero carbon ready” building strategy through its 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 and parts F, L and O which we have covered in previous blogs .

Following public 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 more than 60% glazed)

This is likely to lead to triple glazing becoming the norm in most windows for new buildings or retro fits that want to achieve the highest performance.

Triple glazed window at Florence Boot Hall, Nottingham
Triple glazed window recently installed at Florence Boot Hall, Nottingham University

What is triple glazing?

Very simply, triple glazing is an extra pane of glass added to the two used in double glazing but the benefits can be great. 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.

What are the advantages of triple glazing?

  • Excellent thermal performance that meets the new Future Homes Standard, will save you money on heating
  • Great acoustic performance – ideal for blocking out noisy roads, aircraft noise etc
  • Better security – thicker units are harder to break
  • Can help to reduce condensation

What are the disadvantages of triple glazing?

  • It costs more than double glazing but usually not as much as vacuum glazing.
  • The windows are heavy which means they require chunkier frames and stronger fixings, all of which increase the price further.
  • Aesthetically, some people dislike the look of the triple glazed windows because they aren’t as sleek as single or double glazed ones.
  • Reduces the amount of heat from the sun limiting 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 takes two pieces of glass with a tiny gap (0.1mm in the case of Fineo) and removes the air to create a vacuum.

Fineo vacuum glass
Fineo vacuum glass

They used to have unsightly plugs where the air was extracted but the latest technology means this is no longer the case. Ultra thin from as little as 7.7mm compared to 44mm for triple glazing, it’s great for listed historic properties or new builds looking for a sleek slimmer aesthetic.

What are the benefits of vacuum glazing?

  • 3-4 times thinner than triple glazing, looks more like single glazing
  • Same thermal performance as triple glazing. Fineo states 0.7 W/(m2K) which is better than the target the Government is aiming for in the Future Homes standard.
  • Lasts longer – because it doesn’t have gas between the panes which can leak over time
  • Better solar gain – allows more sun heat into the room helping reduce energy bills
  • Much lighter than triple glazing
  • 15% more light is allowed into the room compared with triple glazing
  • Environmentally better – much lighter saving on transport and less product used plus last longer so less need to replace
  • Great acoustic performance
  • Better aesthetically especially for historic properties, listed properties and modern contemporary builds that want to avoid heavy frames and fixings
  • Easier to install

What are the disadvantages of vacuum glazing?

  • Typically it 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
  • Low impact resistance – where micro pillars are used it can put high stress on the glass.

How much does vacuum glazing cost?

Vacuum glazing can cost up to 56% as much as double glazing and around 35% times as much as triple glazing*.

*Prices may vary depending on size and spec.

So which should builders and architects choose from 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 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, but often value engineering means they have to fall back on triple glazing.

Tom Wright, MD, George Barnsdale