There is a ceiling to what conventional double and triple glazing can achieve. No matter how many low-emissivity coatings you stack, or how much argon you seal into the cavity, a gas-filled unit will always transfer some heat through convection. For buyers who want the very best thermal performance available - not the best that is compliant, but the best that exists - vacuum glass skylight technology represents a genuine step-change.
A vacuum glass skylight removes the gas entirely, replacing it with a near-perfect vacuum that conducts virtually no heat at all. The result is a glazing unit that performs at a level that standard products simply cannot match, in a form factor slim enough to transform what is architecturally possible in overhead glazing. This guide explains the technology, sets out what it delivers, and helps you decide whether it belongs in your project.
What Is Vacuum Insulated Glass and How Does a VIG Skylight Work?
Vacuum Insulated Glass commonly abbreviated as VIG is a glazing technology in which the space between two panes of glass is evacuated to a very high vacuum, typically below 0.1 Pascal. At that pressure, the air molecules present are too sparse to transfer heat by convection or conduction. In practical terms, the vacuum cavity performs like the inside of a Thermos flask: heat simply cannot cross it in any meaningful quantity.
The structural challenge is significant. Without the internal gas pressure that standard sealed units rely on, the two glass panes would be forced together by atmospheric pressure - roughly 10 tonnes per square metre. To hold the panes apart, a VIG unit contains an array of tiny support pillars, typically made from stainless steel or ceramic, spaced at precise intervals across the cavity. These pillars are the reason a vacuum glazing unit can hold its form without imploding, and they are engineered to minimise their own thermal conductivity so they do not become heat bridges.
The perimeter seal is the other critical element. Unlike a standard glazed unit where the spacer bar sits within a gas-filled cavity several millimetres wide, a VIG unit requires a hermetically sealed edge that maintains the vacuum indefinitely. Modern VIG products use a low-melting-point glass solder or indium alloy seal, bonded at the factory under controlled conditions.
The result is a unit that can be as thin as 6–8mm in total yet outperform a 36mm triple-glazed unit on thermal performance. This is the engineering achievement that makes VIG skylight products so compelling for premium applications.
Ultra Efficient Glazing: The Numbers That Matter
For high-end buyers, thermal performance is best understood through U-values. A U-value expresses how much heat passes through a material per square metre per degree of temperature difference - the lower the number, the better the insulation.
As our 2026 rooflight U-value guide explains, the UK Building Regulation minimum for roof glazing is 1.2 W/m²K. High-performance triple glazing currently achieves 0.6–0.8 W/m²K in rooflight applications. Ultra efficient glazing using VIG technology pushes well below that - the best current commercial VIG units achieve centre-pane U-values of 0.4 W/m²K or below, with whole-unit values approaching 0.5–0.6 W/m²K depending on frame and edge seal specification.
VIG vs. Triple Glazing vs. Double Glazing: A Clear Comparison
|
Glazing Type |
Typical Centre-Pane U-Value |
Typical Unit Thickness |
Condensation Risk |
Key Advantage |
|
Standard Double Glazing |
1.1–1.4 W/m²K |
24–28mm |
Moderate to high |
Lowest cost |
|
High-Performance Double Glazing |
0.9–1.1 W/m²K |
28–32mm |
Moderate |
Budget-conscious upgrade |
|
Triple Glazing |
0.5–0.7 W/m²K |
36–44mm |
Low |
Strong all-round performance |
|
Vacuum Insulated Glass (VIG) |
0.3–0.5 W/m²K |
6–10mm |
Very low |
Best performance, slimmest profile |
|
VIG Laminate Hybrid |
0.4–0.6 W/m²K |
10–16mm |
Very low |
VIG performance with enhanced safety rating |
Values are indicative. Whole-unit U-values for rooflights vary with frame specification, unit size, and edge seal construction.
Where VIG Rooflights Make the Most Sense
Not every project justifies VIG glazing. But there are specific contexts where the premium is not just desirable - it is the rational specification choice.
Passivhaus and Near-Passivhaus Projects
Passivhaus certification requires the whole-building energy model to demonstrate very low heating demand. Rooflights are a thermal weak point in any Passivhaus scheme, and the gap between conventional triple glazing and VIG can be the difference between a scheme that passes certification and one that requires compromise elsewhere. For developers and self-builders pursuing certified Passivhaus performance, VIG rooflights remove one of the most difficult variables.
Heritage and Listed Building Applications
Listed buildings and conservation area properties often have strict constraints on frame profile thickness and visual protrusion above roof lines. Standard triple glazing frequently fails these constraints on aesthetic grounds. The slim profile of a VIG unit opens up rooflight possibilities in historic buildings that would otherwise be technically or visually unachievable. Specify a VIG unit in a slender aluminium frame and the rooflight reads almost as a cut in the roof surface - an outcome conservation officers consistently favour.
What to Consider Before Specifying a VIG Skylight?
VIG technology is maturing rapidly, but there are practical considerations worth understanding before committing to a specification.
Cost: VIG units carry a significant premium over conventional glazing — typically two to four times the glass cost of an equivalent triple-glazed unit. For a single rooflight, the difference may be a few hundred pounds. Across a large installation, it becomes a budget line that requires justification.
Availability and lead time: VIG for rooflight applications is a specialist product. Not all rooflight manufacturers offer VIG as a standard option; bespoke commissioning may be required. Lead times can be longer than standard products.
Safety specification: For overhead glazing, laminated safety glass is required under BS 6206 and BS EN 12600. VIG units for rooflight use are typically supplied as laminated composites - a VIG unit bonded to a laminated inner pane. Confirm the safety specification before ordering.
Long-term vacuum integrity: The vacuum seal must be maintained for the unit to perform. Reputable VIG manufacturers provide performance guarantees and accelerated life testing data; ask for it. The technology has been proven in commercial applications for over a decade, and well-manufactured VIG units should retain vacuum integrity for the lifespan of the building.
For buyers already researching glass performance options, our guide on solar control skylight glass covers how solar management coatings can be combined with high-performance glazing units - including VIG - for a fully optimised overhead glazing specification.
Final Thoughts
VIG represents the current ceiling of rooflight glazing performance - slimmer, warmer, and more refined than anything conventional glazing can offer at equivalent thickness. If your project demands the best available, it is worth the conversation. Explore our flat roof skylights and roof lanterns for premium-specified options.
