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

> Spandrel glass is the opaque glazing used to conceal the floor slab, ceiling void and services between one floor's vision glass and the next, so a facade reads as continuous glass from outside.

## 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**.

## Frequently asked questions

### Can spandrel glass be the same glass as the vision area?

Visually yes, and it is usually the same product with an opacifier applied to the back. Thermally no — the concealed cavity behind spandrel runs far hotter than the vision area, so the panel must be heat-strengthened or toughened to survive the stress.

### Does spandrel glass count towards the window-to-wall ratio?

No. Spandrel is an opaque assembly, so ECBC treats it as wall rather than glazing. This matters because pushing insulation behind spandrel is often the cheapest route to an envelope compliance shortfall.

## Sources

- [IS 2553 (Part 1)](https://standards.bis.gov.in/website/published-standards/department-wise) — Safety glass — architectural
- [ECBC 2017](https://beeindia.gov.in/) — Envelope — opaque assembly U-value

---

Source: https://hagerstone.com/glossary/spandrel-glass