Curtain Wall Sealant Calculator

Aluminum's coefficient of thermal expansion (23.1x10⁻⁶/°C) is roughly 2.5x glass's (9.0x10⁻⁶/°C), so an aluminum panel expands and contracts proportionally more across the same Temperature Range -- and since Thermal Movement feeds directly into Design Joint Width, that larger movement typically requires a wider joint to keep the sealant within its rated stretch capability.

Thermal Movement is pure physics: Substrate material's coefficient of thermal expansion times Substrate Length times Temperature Range, full stop -- the aluminum panel expands and contracts by the same physical amount whether a low-cost butyl bead or a premium structural silicone ends up sealing it, because the metal doesn't know what sealant was specified. Design Joint Width is a design decision layered on top of that physics: it takes the SAME Thermal Movement number and asks how wide a joint a given sealant needs to absorb it without exceeding its rated stretch. So Sealant Class reshapes the joint the movement gets built into, but never the movement itself -- swap sealants on an already-built structure and the panel keeps moving exactly as much as it always did; only the joint sizing that should have accommodated it changes.

The total material order, not the joint geometry. Design Joint Width comes from a per-location calculation -- Thermal Movement plus Construction Tolerance, divided by sealant capability -- that never references Total Joint Length at all; a single 1500mm panel joint and the same joint repeated across a 100,000m perimeter both come out to the identical width, depth, and backer rod diameter. What DOES scale with Total Joint Length is everything downstream of that fixed per-metre design: Total Sealant volume, the cartridge and sausage counts, and backer rod length all multiply directly with it, because more linear metres of an identically-sized joint simply need proportionally more material to fill.

Substantially -- at this calculator's default substrate and temperature inputs, moving from Sealant Class 1 (silicone, ±50% movement capability) to Sealant Class 3 (butyl/acrylic, ±12.5%) roughly quadruples Design Joint Width, since a sealant rated for a quarter of the movement range needs roughly four times the width to absorb the same absolute movement.

More than its small absolute size suggests, and the answer depends entirely on Sealant Class. Design Joint Width is Total Movement divided by (2 x the sealant's movement capability), so Construction Tolerance's contribution gets divided the same way Thermal Movement's does. With silicone (Class 1, ±50% capability) on this calculator's default aluminum panel and temperature swing, the tolerance's full 0-to-15mm range moves Design Joint Width from 6mm (the practical floor) up to 18mm -- a threefold jump. Switch to butyl/acrylic (Class 3, ±12.5% capability) on the same panel and the same 0-to-15mm tolerance range moves Design Joint Width from 12mm to 72mm instead -- a 60mm swing on its own, six times larger than silicone's. A fixed, capped construction tolerance can dominate the joint-sizing math far more under a low-movement sealant than a high-movement one, even though the tolerance input itself never changes.