Vacuum Glazing: How It Works, What It Really Achieves and What It Costs

Most of what you will read about vacuum glazing in the UK is written by someone selling one brand of it. Of the top results for the term, nearly all are distributors or fitters of LandVac, AGC's Fineo or a rival, and the headline number they lead with is a glass-only figure taken on the maker's chosen test. None of that makes the product bad. In the only independent test in a real UK window it was the best performer of every thin unit tried. But the gap between the glass figure and the window figure is large, the price evidence is thin, and both are worth knowing before a salesperson compares it with triple glazing.

How vacuum glazing works

Ordinary double glazing loses heat three ways: conducted and carried across the gas in the cavity, and radiated from pane to pane. Pilkington says that in a standard low-e unit the conducted and convected part can be 70% of the heat lost, which is why the cavity has to be wide, typically giving a unit of 24 mm. Take the gas away and that route closes, so the gap can shrink almost to nothing. A low-emissivity coating on one pane deals with the radiated part, as it does in a normal unit.

The gap is 0.2 mm in Pilkington's Spacia, 0.1 mm in AGC's Fineo, 0.3 mm in LandVac and 0.1 mm in Panasonic's Glavenir. A grid of pillars, 0.5 mm across in Spacia, stops atmospheric pressure pressing the panes together, and the edge is sealed airtight: welded, in Pilkington's description. A getter, a reactive metal inside the gap, soaks up stray gas molecules over the unit's life. Because the pillar grid and edge are made in the factory, a unit cannot be cut down on site; each one is made to order. Vacuum glazing has its own international standard, ISO 19916, rather than EN 1279, the sealed unit standard for gas-filled double glazing, so ask for test evidence against the right one.

What you actually see: pillars and the pump-out cap

The pillars are visible close up. Pilkington spaces Spacia's 20 mm apart and says that from 2 to 3 metres they "become imperceptible"; its tolerance allows up to two missing or misplaced pillars in any 540 mm square. AGC uses a 20 mm grid too. LandVac's distributor gives its pillars as about 55 mm apart, and a physicist who tested a sample in January 2026 found them visible on close examination but not at a distance. Historic Environment Scotland, which trialled vacuum panes in Edinburgh in 2009, notes that some observers comment on them close up, and a building industry wiki says they show most in raking light.

Pilkington's Spacia also has an evacuation port, the hole the air was drawn out through, capped by a small permanent plastic cap 12 mm across and 5 mm high, 50 mm in from a corner, in black or silver. It must face into the room and must not be removed. AGC says Fineo has no port, LandVac says its current Enhance unit has none, and Panasonic's annealed Glavenir has none. A Fineo fitter cites the visible cap as one reason Spacia lost ground, so ask which you are getting.

The products and what their makers claim

Every figure below is the maker's own, for the centre of the glass only, and the test methods differ. That is the single most important thing to know when two quotes cite different numbers.

Sources: Pilkington Spacia range brochure and technical data sheet (both September 2024); AGC Fineo data sheets (April 2022 and April 2025); Vacuum Glazing UK, LandVac distributor (2025 and 2026 pages); Panasonic Glavenir page. Research in lib/research/vacuum-glazing-2026.md.

For modern frames there are hybrids, a vacuum unit paired with a second pane across a gas cavity: AGC's Fineo Hybrid, 25.7 mm, at 0.5, and LandVac's Optimum, 25.1 mm, at 0.4. Guardian and Vitro make vacuum glazing for the North American market; neither has a UK product page we could find.

Why the published U-values disagree

Three reasons, and they stack. First, method: EN 673 is a calculation, EN 674 and ISO 19916-1 are hot-plate measurements, and Panasonic uses its own standard and says its values "are not guaranteed". Pilkington's own September 2024 brochure and data sheet cite different standards for the same numbers. Nobody we found has compared the methods head to head for vacuum units. Second, coating: LandVac alone spans 0.34 to 0.49 across its coatings. Third, and biggest, these are glass-only figures. LandVac's distributor says so in terms: asked whether 0.34 is a whole-window U-value, its answer is "No. It measures the glass only."

The independent evidence is Historic Scotland's. Its Technical Paper 9 (September 2010), by Changeworks, Glasgow Caledonian University and Heriot-Watt University, fitted a Pilkington vacuum unit, then sold as energiKare Legacy and later renamed Spacia, into a Georgian sash in an Edinburgh listed building. The maker said up to 1.3; it measured 1.0 W/m²K at the centre of the glass, one of only two units in the study whose specification did not overstate it. Technical Paper 20 (2013) measured a second unit at 0.9. Then it calculated the whole window, and the figure nearly doubled: 1.9for a six-over-six sash, 1.6 for two-over-two and 1.4 for one-over-one. The paper names the leaks: heat "transferred through the small support pillars separating the panes and the edge seal", and more frame and glass edge on a window with more glazing bars.

Sources: Historic Scotland Technical Paper 9 (September 2010) and Technical Paper 20 (2013); maker data sheets; this site's U-value research. The heritage rows are sash windows; the modern rows are modern frames.

A second, informal test points the same way. A physicist who tested a 35 cm square vacuum sample in January 2026, outside any standard method, found the edge losing three to four times as much heat as the glass itself, an effective 0.8 to 1.4 overall, and concluded that the specified figure "is no guide at all to the actual heat loss from the window in which it is installed". A LandVac distributor page concedes that insulation drops towards the edge. For modern frames, LandVac estimates 0.6 to 1.0 whole-window in uPVC, 0.9 to 1.0 in timber and 1.1 to 1.3 in aluminium for its hybrid; no independent measurement exists. One last trap: a 0.6 figure attributed to Historic England comes from a sentence about vacuum units used in secondary glazing, not in a sash. How the two kinds of figure relate is explained in our U-values guide.

A vacuum unit's glass figure is real, and in Historic Scotland's sash tests nothing thin beat it. But when a quote puts 0.4 beside a triple glazed window's 0.8, one is the glass and the other is the window. Ask which, and ask for the test method.

Double Glazing Cost Calculator Team

What vacuum glazing costs

We found no Checkatrade, MyJobQuote or Which? price for vacuum glazing, and no second independent UK price per square metre or per window. What exists is one fitter's glass prices, one fitter's installed prices, and a spread of premiums from people with a product to sell.

Every row is a single fitter. The Independent (November 2025) quotes the same £340 to £390 per m² from Six Over Six rather than confirming it. Research in lib/research/vacuum-glazing-2026.md.

On the premium over ordinary double glazing, the sources disagree widely and we have not averaged them. The LandVac fitter above says £200 to £400 more per window. A timber window maker (May 2023) says up to 56% more than standard double glazing and 35% more than triple, with no source given. The Independent (November 2025) says vacuum "could easily add 50 per cent" to a uPVC window costing under £600. An editorial site that sells nothing (July 2026) calls two to four times the cost of standard double glazing a heavily hedged rule of thumb. Historic Environment Scotland says only that vacuum units are "more costly than other options", and AGC itself says an average price per square metre is difficult to give.

Set against the options already priced on this site: fitting double glazing into existing sash frames runs £650 to £1,300 a window on Checkatrade's July 2026 figure, a new timber heritage sash £1,330 to £2,850, a uPVC casement £400 to £1,000, and secondary glazing £300 to £500 for a standard window. Lead times add up too: four to five weeks for Fineo 8 and six to eight for the toughened Fineo 10 in 2024, and around 16 weeks reported for Spacia, shipped from Japan. For a new period window, the sash window calculator and timber window calculator price the frame; the glass is a specification to discuss with the maker.

Vacuum glazing in listed buildings and period windows

Historic England's Advice Note 18, revised in February 2026, puts vacuum and slim-profile units together: installing either "within historic frames will generally be acceptable", with three exceptions, windows that retain historic glass of interest, frames or glazing bars that cannot support the units, and leaded lights, and with listed building consent "likely to be required, unless replacing panes in modern windows". Its web guidance says inserting double glazing into historic windows "will usually require Listed Building Consent", and that it has no role in decisions on unlisted buildings in conservation areas, which are the council's. Its 2017 window guidance, still online and marked as under review, is far less encouraging. None of these names a product; a seller's claim that its brand is "approved by Historic England" is not something the guidance says. The cost side of consent is on our listed building costs page.

Thin is not the same as drop-in. Historic Environment Scotland says vacuum glazing "is thin enough to directly replace single glazing" and weighs only a little more than a standard sheet. But Historic England's 2017 guidance draws a 6.5 mm vacuum unit with a 10 mm edge seal needing, on the maker's own recommendation at the time, a rebate of 11 mm or more and a glazing bar of 26 mm or more, against 4 mm and 12 mm for the original single pane: the widest bar of the three units it drew. And the minimum pane sizes matter on a Georgian sash: 200 by 400 mm for Spacia, 190 by 230 mm for LandVac Enhance, 200 by 200 mm for Fineo (600 by 300 mm for the toughened version). Ask for the minimum before anyone measures. On putty, Pilkington says traditional putty may be used with Spacia but compounds containing acetic acid should be avoided; Historic England's general advice is that linseed oil putty can damage the seals of sealed units. Follow the maker's instruction for the product you buy.

The Building Regulations follow the same split as for any glass. In England, Approved Document L paragraph 10.6 says replacing glazing in an existing frame is not a controlled fitting and need not meet the energy requirements. A new window must reach 1.4 W/m²K or band B, or, where a building's character must be kept, a centre-pane figure of 1.2 (paragraph 4.10), which every vacuum unit in the table above claims to beat. The 2026 edition, in force from 24 March 2027, keeps both rules. The wider rules are in our Part L guide, and the planning side in our guide to conservation area window rules.

The downsides and limits

• Safety glass. Spacia is annealed and needs a professionally fitted safety film, or the laminated Shizuka version, in a critical location. Fineo 8 is not toughened, and one fitter warns it can break in delivery; Fineo 10 T is toughened, and Fineo comes laminated. LandVac says all its units are toughened, and Panasonic makes a tempered Glavenir.
• Minimum size. Small Georgian panes can fall below what a maker will make, which is the one limit Historic Environment Scotland names alongside cost.
• Edge heat loss.The glass figure hides it (above). One joiner who fits slim gas units says it causes condensation round the perimeter; that is a competitor's claim and we found no independent test of it.
• Thermal stress. Pilkington warns of a higher risk of thermal fracture for Super Spacia in double glazing, depending on orientation, frame and shading, and not to use Spacia where the air may exceed 50°C without consulting it.
• Failure.No maker or heritage body we found says what happens when a unit loses its vacuum. One Fineo fitter says failures that do happen usually show in the first year, and LandVac's distributor admits rare cases of pillars dropping to the bottom of the unit.
• Supply.Spacia is made in Japan, LandVac in China and Fineo in the EU, with lead times to match. Pilkington Spacia's UK availability is disputed: three sellers of rival products say it is no longer available here, while Pilkington's UK site still listed it on 19 September 2026 with data sheets dated September 2024. Confirm with Pilkington UK.

How long it lasts

The warranties are longer than on slim gas units and the evidence is shorter. Pilkington gives the installer ten years; AGC gives 20 years and claims a 60-year life; LandVac's UK distributor quotes 10, 15 and 25 years on different pages. A building industry wiki (August 2026) calls 15 to 20-year warranties typical, and The Independent's 10 to 25-year lifespan has no source. The structural argument is the edge: Historic Scotland and Northern Ireland's heritage division both note the Spacia panes are welded together, with no polymer seal to perish. The only independent record is two years: Technical Paper 20 found the vacuum unit showed no significant deterioration. No heritage body has put a service life on vacuum glazing.

Vacuum, slimline or secondary glazing

In Historic Scotland's tests the ranking was clear: the vacuum unit beat secondary glazing, which beat the gas-filled slim units, with one minor exception. Whole-window, 1.9 for vacuum against 2.0 for secondary glazing on a six-over-six, and 1.4 against 2.1 on a one-over-one. Our guide to slimline double glazing covers the gas-filled alternative, which is thicker and measured mostly near 2.0 at the centre of the glass. Secondary glazing costs less still, needs no seal, usually needs no listed building consent, and Historic England rates it better than double glazing for noise; makers' lab figures put vacuum units at 35 to 39 dB against 31 for a standard 4-16-4 unit. The costs are on secondary glazing costs, and Historic England's own first step, draught-proofing, costs least of all.

Getting it priced

Vacuum glazing is fitted by few firms and priced by fewer, so a written quote on your own windows is the only reliable figure. If you want vacuum units, slim glazing, secondary glazing or new windows priced, tell us what you have and Leads 2 Trade will arrange quotes from installers covering your postcode.

Price-checkedLast reviewed 19 September 2026

Reviewed byDouble Glazing Cost Calculator TeamCross-checked against Checkatrade, the FMB & GreenMatch