Vacuum Insulated Glazing VIG

Vacuum insulated glazing (VIG), also known as vacuum glazing, is a form of insulated glazing unit in which the cavity between the two panes of glass is evacuated to a vacuum rather than filled with air or an inert gas. Because a vacuum transfers almost no heat by conduction or convection, the cavity can be extremely thin — typically a fraction of a millimetre — so the finished unit approaches the thermal performance of triple glazing at a fraction of the thickness and weight of a conventional double glazed unit.

[edit] How it works

A vacuum glazed unit consists of two panes of glass, at least one of which is usually a low-emissivity (low-E) pane, hermetically sealed together around their perimeter. The cavity is evacuated, and an array of very small support pillars (micro-spacers), each typically less than 1mm in diameter and laid out in a regular grid, prevents atmospheric pressure from pushing the panes together. The pillars are barely visible in normal viewing conditions, though they can be noticed in raking light. A getter (a reactive material inside the cavity) absorbs residual gas molecules to help maintain the vacuum over the unit’s service life. Manufacturer warranties of 15 to 20 years are typical.

Because the perimeter seal and pillar grid are formed during manufacture, vacuum units cannot be cut down on site; each unit is made to order to the required dimensions.

[edit] History

The concept was proven at the University of Sydney in the 1990s, with initial commercialisation by Nippon Sheet Glass in Japan in 1996. Pilkington consider their Spacia unit, on sale from 1997, to have been the world’s first commercially available vacuum glazing. A number of manufacturers now produce vacuum glazed units, and hybrid products are also available that combine a vacuum unit with a conventional argon-filled cavity for further performance gains.

[edit] Performance and dimensions

Overall unit thickness starts at around 6mm — less than a third of a typical 24–28mm double glazed unit — with common heritage-retrofit formats around 8–14mm, and hybrid vacuum-plus-argon units at around 25mm. Centre-pane U-values as low as 0.4 W/m²K are certified for current products, with other vacuum products typically in the 0.4–1.1 W/m²K range; standard double glazed units are typically 1.2–3.0 W/m²K. The sealed vacuum also provides good acoustic performance for the thickness, with weighted sound reduction figures around 36–41 dB depending on the unit. Vacuum glazed units cost more than conventional double glazing because of the precision of their manufacture.

Some vacuum glazing products are certified through European Technical Assessments; others are certified through independent test-institute reports, as no harmonised CE marking route exists for vacuum glass as a category.

[edit] Use in historic buildings

The main application of vacuum glazing in the UK is upgrading single-glazed windows in historic buildings, because the thin unit can often be glazed into existing or refurbished timber sashes and casements — retaining the original joinery, sightlines and glazing bars in a way that thicker units cannot.

Historic England’s Advice Note 18, ‘Adapting Historic Buildings for Energy and Carbon Efficiency’ (2024, revised February 2026), states at paragraph 81 that installation of slim-profile or vacuum double glazing within historic frames “will generally be acceptable”, subject to conditions such as retaining original glazing bars and excepting windows with historic glass of interest.

Two local planning authorities have made listed building consent orders that pre-consent the replacement of single glazed panes with insulated or vacuum glazing units in Grade II listed buildings, subject to conditions on materials and dimensions: the Royal Borough of Kensington and Chelsea (order sealed 2023, running to 2028) and Babergh District Council in Suffolk (Local Listed Building Consent Order No. 1, in force from August 2025). In October 2025, a Planning Inspectorate appeal decision in Bristol allowed the use of vacuum glazing in non-original windows of a Grade II listed cottage while dismissing it for the original windows — illustrating that consent typically turns on which fabric is affected and the quality of the evidence submitted. In most cases, listed building consent is still required, and applications are expected to justify the intervention against alternatives such as repair and secondary glazing.

Pressure to improve the energy performance of historic buildings is increasing: the UK government’s January 2026 response to its EPC reform consultation removes the automatic exemption previously enjoyed by many listed buildings, with changes phased in from late 2026.

[edit] Considerations

• Higher unit cost than conventional double glazing.
• Micro-spacer pillars can be visible in some lighting conditions.
• Units are made to order and cannot be resized on site.
• In listed buildings, consent is normally still required, and proposals affecting original fabric or historic glass may be refused.
• Sash windows may need rebalancing where the new unit changes the sash weight.

[edit] Related articles on Designing Buildings

• Conservation rooflights.
• Domestic windows.
• Double glazing.
• Double glazing v triple glazing.
• Glass.
• Glazier.
• Glazing.
• Low-E glass.
• Patent glazing.
• Secondary glazing.
• Security glazing.
• Stained glass.
• Structural glass assembly.
• Suction lifter.
• Tempered glass.
• Triple glazing.
• Types of window.
• Window.
• Window frame.

[edit] External references

• ‘Adapting Historic Buildings for Energy and Carbon Efficiency’, Historic England Advice Note 18 (HEAG321), Historic England, v1.1, February 2026.
• ‘Vacuum glazing planning precedents’ — a compiled list of UK planning decisions, consent orders and appeal decisions concerning vacuum glazing in listed buildings, with links to the source documents.