SPANDREL AREA IN CURTAIN WALLS

SPANDREL AREA IN CURTAIN WALLS

Are we protecting the building... but forgetting the glass?

The Spandrel Zone is one of the most critical areas in a curtain wall system, even though it is usually hidden behind opaque glass.

A typical spandrel assembly may include:

🔹 Rock / Mineral Wool

🔹 Back Pan / Back Panel

🔹 Perimeter Fire Stop / Safing

🔹 Smoke Seal

🔹 Spandrel Glass

These components are essential for fire safety, thermal performance and building protection.

But there is another important aspect that should not be overlooked:

☀️ THERMAL STRESS ON SPANDREL GLASS

Solar radiation can be absorbed by the spandrel glass. When insulation and back-pan components are installed behind the glass, heat dissipation may be restricted, creating a heat-trap condition.

This can increase the temperature difference across the glass and potentially lead to thermal stress and glass breakage if the complete assembly is not properly designed.

⚠️ The solution is NOT to remove the Rock Wool or Fire Stop.

The real solution is to coordinate the complete system:

Fire Safety + Thermal Performance + Glass Selection + Proper Clearance + Thermal Stress Assessment

For example, Viracon recommends maintaining a minimum 1-inch (25 mm) clearance between spandrel glass and insulation in relevant applications.

Are we designing the Spandrel Zone only to protect the building from fire and heat — or are we also considering the thermal conditions that our own design creates for the glass?

A successful curtain wall is not just a collection of components.

It is a complete engineered system.

💬 Have you ever experienced spandrel glass thermal breakage due to heat build-up behind the glass?

I would be interested to hear the experience of other façade professionals.