Spandrel Glass: What It Is and Where It Belongs on a Facade

Why it matters on a facade project

A glazed elevation is not glass all the way down. Behind every apparently continuous run of glazing sits a floor slab, a ceiling plenum and the services threaded through it — typically 900mm to 1,400mm of structure and duct that nobody wants to look at. Spandrel glass is what hides it.

Get it wrong and it shows in two expensive ways: panels that crack in the first summer, and an elevation where the spandrel bands read as a visibly different colour from the vision glass under certain light.

How it is specified in practice

Parameter	Typical position	Why
Glass treatment	Heat-strengthened, occasionally toughened	The cavity behind traps heat; annealed glass fails on thermal stress
Opacifier	Ceramic frit or opaque film	Frit is more durable; film is cheaper and easier to match
Cavity ventilation	Vented or sealed, decided early	Drives both condensation risk and panel temperature
Back-up insulation	Mineral wool, thickness per ECBC	Counted as opaque assembly, not glazing

Common mistakes

• Specifying annealed glass to save cost. The cavity behind a south-facing spandrel can run 30-40°C hotter than the vision glass. Annealed panels crack, and replacing them means returning to a sealed facade at height.
• Leaving the colour match untested. Vision and spandrel glass reflect differently because one has a lit interior behind it and the other has a dark cavity. Match them on a mock-up, in daylight, not from a sample board.
• Forgetting insulation behind the spandrel. It is opaque assembly under ECBC, and it is usually the cheapest place to recover an envelope shortfall.
• Deciding vented versus sealed late. It changes the panel temperature, the glass grade and the condensation strategy — all of which are fixed by the time the facade is ordered.

Standards referenced

Safety glass requirements follow IS 2553 (Part 1). Where spandrel forms part of the opaque envelope, its assembly U-value is assessed under ECBC 2017.