High-Rise Curtain-Wall Firestop: ASTM E2307, Perimeter Fire Barrier and Leapfrog

In glazed high-rises, the perimeter void (slab edge) between the unitized curtain wall and the floor slab is the main path for fire to leap from the façade to the floor above — the leapfrog effect. If you leave this gap improperly sealed on site, your 2-hour fire separation is gone in an instant. Three separate tests apply: ASTM E2307 for the perimeter fire barrier, ASTM E119 for wall fire resistance and ASTM E814 for firestop penetrations. After Grenfell 2017, façade combustibility classifications were tightened worldwide; in Turkey we follow the same line for buildings taller than 28.50 m (BYKHY Article 27(1)).

Perimeter Void Risk

• Slab edge: the gap between slab and façade is typically 25-150 mm and must be firestopped. BYKHY Article 27(1) also requires façade-to-floor junctions to be sealed for the fire resistance period of the floor, so that flames cannot jump to the adjacent floor.
• Spandrel panel: the narrow band between windows at floor level; it must not be all glass — back it with a fire-resistant build-up
• Mullion: the vertical frame of the curtain wall; a 2-hour firestop detail is required where it crosses floors
• Insulation vs. barrier: thermal insulation and the fire barrier must not be confused; assuming one layer does both jobs is a common trap
• Leapfrog fire: the window below breaks, flame exits, climbs the façade and enters through the glass of the floor above — this is how fire skips floors even when interior separations are rated

ASTM E2307 Test

• Test rig: a full-scale two-storey façade mock-up
• Duration: minimum 2 hours; results reported as integrity (F rating) and temperature (T rating)
• Fire scenario: interior room fire plus the flame plume projecting from the window
• T rating: temperature rise on the upper floor slab below 140°C
• F rating: no flame passage for the test duration
• Mineral wool: the most common solution; we use 4 pcf (≈ 64 kg/m³) density at 4 in (≈ 100 mm) thickness

Spandrel Panel

• Height: in Turkey, BYKHY Article 27(1) requires at least 100 cm of fire-resistant solid façade vertically between the unprotected openings of two floors; the alternative is sprinklers inside the façade at no more than 2 m spacing and no more than 1.5 m from the façade
• Back-up: cement-based board or a fire-resistant metal build-up; ordinary particle board or decorative panels will not do
• Shadow box: the detail behind the glass that hides the interior; any colored films used there must be fire-rated
• Insulation: mineral wool preferred; PE-core aluminum composite panel (ACM) strictly prohibited
• Grenfell lesson: replace PE-core ACM panels with A1 or A2 class mineral-core panels

Firestop Design

• Mineral wool compression: 20-35 percent; less leaves gaps, more breaks the fibers
• Smoke seal: fire-rated silicone sealant on top of the mineral wool
• Safing clip: Z-shaped metal clips hold the wool in place — compressing it by hand and leaving it is a serious error
• Movement: building sway can reach about 25 mm; the firestop detail must absorb it
• UL HW/CW systems: choose a UL-listed head-of-wall or curtain-wall detail and install it exactly as listed

Worldwide Incidents

• Grenfell Tower, London 2017: 72 dead; the main culprit was PE-core ACM cladding
• The Address Downtown, Dubai 2015: a typical façade leapfrog fire that wrapped the hotel from outside
• Mermerler Residence, Istanbul 2012: one of the most discussed façade fires in Turkey
• Beckton, London 2019: façade fire involving high-pressure laminate (HPL) cladding
• Regulation: Turkish BYKHY Article 27(1): external facades of buildings with a building height above 28.50 m must be limited-combustibility (zor yanıcı), which Annex 2/Ç defines as Class A2-s1,d0

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