Vacuum Glass Windows – Triple-Pane Performance, Slim Wood Frames
For centuries, a wood window was a slender thing. A single pane of glass, about 1/8 inch thick, sat in a light sash with narrow muntins – the proportions you still admire on old townhouses, French châteaux and farmhouses. Then came insulated glass. Double pane brought the glass to about 1 inch, triple pane to almost 2 inches, and the wood had to grow with it: deeper sashes, wider muntins, heavier frames.
Vacuum insulated glass (VIG) changes this. Two panes of glass with a vacuum between them insulate like triple-pane glass in a unit only about 5/16 inch thick. That means we can build wood windows with the slim lines of the past and the energy performance of a high-performance European window.
What Is Vacuum Insulated Glass?
Vacuum glass works like a thermos bottle. Two panes of glass are sealed together all around the edge, and the air between them is pumped out to leave a gap about as thin as a sheet of paper. Without air, heat cannot travel by conduction or convection, and a low-E coating on the inside face sends most of the radiant heat back where it came from. Tiny support pillars, less than half a millimeter wide and set on a regular grid, keep the two panes apart against the atmospheric pressure. From a normal viewing distance they are almost invisible.
The technology is not new: vacuum glass has been in commercial production since 1996, and today it is tested for long-term durability to the international standard ISO 19916-1. What is new is the performance level and the choice now offered by Europe’s leading glass makers – tempered, laminated, acoustic, solar control, and even historic-look glass for restoration work.
Back to the Proportions of Historic Windows
For us this is the most exciting part. Because the glass is so thin, the glazing rebate in the wood can be small again. The sash does not need to be deep to hold almost 2 inches of glass, the muntins of a true divided lite window can stay narrow, and the glazing bead can be drawn the way a joiner drew it 150 years ago. The result is a window that looks right on a historic facade, in an Old World design or in a classical French home, without giving up comfort or energy savings.
It also works for modern architecture. A slimmer sash means more glass and more light, and vacuum glass weighs about one third less than triple-pane glass, so large sashes and French doors are easier on the hinges and easier to operate, year after year.
Vacuum Glass at a Glance
- Insulates like triple pane: center-of-glass U-value from about 0.12 down to 0.07 BTU/hr·ft²·°F (0.7 to 0.4 W/m²K), depending on the configuration
- Only about 5/16 inch thick, versus about 1 inch for double pane and 1-3/4 inch for triple pane
- About one third lighter than triple-pane glass
- More daylight: around 78 to 80% light transmission with clear glass
- Quieter rooms: sound reduction up to Rw 39 dB with acoustic versions
- Warmer glass surface, less condensation and no cold draft near the window
- No argon or krypton that can slowly escape over the years
- Historic-look glass available for restoration and Old World projects
Vacuum Glass and Passive House
A Passive House window in a cold climate must reach a whole-window U-value of about 0.14 BTU/hr·ft²·°F (0.80 W/m²K). Until now the only way to get there was triple-pane glass and a deep, heavy frame. Vacuum glass opens a new path. A standard vacuum unit already matches the center-of-glass performance of a good triple-pane unit. For the most demanding projects, a hybrid unit – vacuum glass combined with an extra pane and an insulating cavity – goes beyond triple pane while staying thinner than a typical triple-pane unit.
Thinner glass also means less material. A vacuum unit uses two panes instead of three, with no spacer bar and no gas fill, and the glass makers expect a service life of several decades. Combined with a responsibly sourced wood frame, it is one of the most efficient ways to build a high-performance window.
For projects pursuing Passive House (PHI or Phius), LEED or local energy code compliance, we provide the glass data and the whole-window values for your energy model. See also our Passive House windows.
Where Vacuum Glass Makes the Difference
- Historic homes and landmark districts – new windows with the slim look of the originals, a look that respects the architecture when a preservation commission reviews the project. See our landmark and historic district wood windows page.
- Old World and classical French designs – true divided lites with narrow muntins, flush sashes and a real crémone bolt, with modern comfort. See our French style windows.
- Passive House and net-zero homes – triple-pane level insulation without the deep, heavy sash.
- Large windows and French doors – lighter glass for big sashes and tall doors.
- City homes and busy roads – very good acoustic performance in a thin unit.
- Hot and sunny climates – solar control versions keep the heat out in Texas, Florida or California.
Vacuum Glass vs. Double and Triple Pane
| Historic single pane | Double pane | Triple pane | Vacuum glass | |
|---|---|---|---|---|
| Glass thickness | about 1/8 in (3 mm) | about 1 in (24 mm) | about 1-3/4 in (44 mm) | about 5/16 in (8 mm) |
| Center-of-glass U-value BTU/hr·ft²·°F |
about 1.0 | about 0.20 | about 0.09 – 0.12 | about 0.07 – 0.12 |
| Glass weight | about 1.5 lb/ft² | about 4 lb/ft² | about 6 lb/ft² | about 4 lb/ft² |
| Typical wood sash depth | about 1-3/8 in | about 2-11/16 in | 3-1/16 to 3-5/8 in | slim, close to historic proportions |
| Gas fill | none | argon | argon or krypton | none – vacuum |
Typical values for clear glass with low-E coatings. Exact figures depend on glass thickness, coatings and configuration, and we confirm them for each project.
Vacuum Glass - Frequently Asked Questions
Is vacuum glass really as good as triple pane?
For insulation, yes. A standard vacuum unit reaches a center-of-glass U-value of about 0.12 BTU/hr·ft²·°F (0.7 W/m²K), the level of a good triple-pane unit, at about one sixth of its thickness. Hybrid units go even further.
Can I see the support pillars?
If you look for them up close, yes – a regular grid of very small dots. From a normal distance, looking at the view outside, most people never notice them. We are happy to send a sample so you can judge for yourself.
How long does the vacuum last?
The edge seal is fully hermetic, and a small getter inside the unit absorbs any trace of gas over time. The units are tested for durability to ISO 19916-1, and the glass makers expect a service life of several decades.
Can it be used in true divided lite windows?
Yes. Vacuum units can be made in small sizes, so each pane of a true divided lite window can be its own vacuum unit, held in a narrow muntin. Very small panes have limits, so we check the pane sizes with you at the drawing stage.
Can it be used in doors?
Yes. Tempered and laminated versions exist for doors and safety glazing. Maximum sizes are around 5 x 8 ft depending on the glass type, which covers most French doors.
Is vacuum glass more expensive?
Yes, it costs more than standard double or triple pane. On a historic or high-end project it is often the only way to get the slim look and the performance together. We can price both options so you can compare.
Explore more: La Française French casement windows – French tilt and turn wood windows – wood + aluminum clad windows – specialty glass and divided lites – request a quote
Is Vacuum Glass Right for Your Project?
Every project is different. Window sizes, pane sizes, design, climate and energy targets all play a role. Send us your drawings, and we will tell you where vacuum glass makes sense, compare it with double and triple pane, and give you a detailed quote with full technical data.