Head-of-Wall Joint Calculator

A head-of-wall joint is the gap left on purpose between the top of a fire-rated partition and the underside of the floor or roof deck above it, so the structure can flex without cracking the wall — and like the standalone Expansion Joint Gap Calculator, sealant quantity here scales with Joint Width more aggressively than with any other input, since the engine sets sealant depth to half the width and then multiplies width against that same depth, giving a near-quadratic relationship. Deflection Ratio is a different kind of output entirely: it divides Expected Deflection by Joint Width to check the joint against a rule of thumb that the ratio should stay under 50% for standard sealants, so widening the joint actually lowers the deflection ratio even though it raises material quantities elsewhere on the page. Wall Type (1 = gypsum, 2 = CMU/masonry, 3 = curtain wall) is a coded selector, not a continuous scale — it applies a flat cost multiplier (1.0, 1.3, or 1.6) to materials rather than changing any physical dimension, reflecting that masonry and curtain-wall assemblies are generally more labor- and material-intensive to firestop than gypsum.

Fire rating (hrs) genuinely does move the labor- cost figure (linearly, at $2.45 per linear foot per hour), unlike some of this hub's other calculators where the same field is inert — but it never appears in the mineral wool, sealant, or deflection-ratio math. This tool assumes a single continuous joint condition; it does not account for penetrations, corners, or T-intersections along the run.