Spandrel glass — the opaque panels doing the hiding.

Not every panel in a curtain wall or window wall is meant to be looked through. Between each floor's vision-glass band sits a spandrel zone — the opaque panel that conceals the slab edge, perimeter mechanical, ceiling cavity, and structural connections that nobody wants visible from the street. It's doing an architectural job, not a daylighting one: hide the guts of the building while keeping the same glazed module and sightline as the vision glass above and below it. For the plain-English version of what spandrel is and how it's used, see our spandrel glass glossary explainer; this page is the commercial spec, thermal-risk, and replacement reference.

There are two standard ways to build a spandrel panel:

• Ceramic frit spandrel. A single lite of glass with opaque ceramic ink fired onto the interior-facing surface — typically a solid, 100%-coverage frit pattern on spandrel, though dot-pattern and gradient frit exist for other applications. It's the lower-cost, thinner-profile option, and the one most commercial jobs default to.
• Shadow box spandrel. A vision lite — clear or low-E — with an opaque insulated panel set back 6 to 12 inches behind it. The setback creates real depth and a shadow line that reads differently in daylight than a flat frit panel does. It costs more and needs more room in the wall section, but it's the higher-end look architects reach for on a prominent facade.

Both approaches solve the same problem — hide the structure, keep the module — with different cost, depth, and appearance trade-offs. Neither is "better" outright; the choice comes down to budget, wall-section depth, and how much the design wants the spandrel band to read as a shadow versus a flat color field.

Thermal stress cracking on spandrel glass almost always starts at the edge — the part of the lite sitting in the shade of the frame while the center of the same panel is heating up in direct sun. The bigger that center-to-edge temperature gap, the more tension the edge carries, and heat-treated glass exists specifically to give the panel enough strength margin to survive that gap without cracking.

A few conditions make that gap worse, and they're all things a spec reviewer or GC can actually check for before glass gets ordered:

• Dark, solid frit colors absorb more solar radiation at the panel's exposed center than a lighter color or a dot-pattern frit does.
• Insulation touching the back of the glass creates a hot spot right where the panel needs to shed heat — published guidance recommends maintaining a real air gap between the spandrel glass and any insulation or back-pan behind it, rather than letting the two touch.
• Shadow box cavities with poor ventilation can trap heat behind the vision lite, raising the temperature the inner glass has to tolerate.
• Partial shading — an overhang, an adjacent building, a sunshade — that shades part of a panel but not all of it can create a sharper temperature gradient across a single lite than full sun or full shade would.

Florida's solar load doesn't create a different failure mechanism than anywhere else — it's the same edge-tension physics everywhere. What it does is push more panels into higher-risk territory on the margin: more hours of direct, high-intensity sun on south- and west-facing spandrel bands means the center-to-edge gap referenced above runs hotter, more often, on a Florida facade than on an equivalent building in a milder climate. That's a reason to take the frit-color and ventilation details seriously at the design stage, not a reason to assume every Florida spandrel panel needs to jump straight to fully tempered — the right call is still project-specific and belongs in a thermal stress analysis, not a rule of thumb.