Casing
Two layers of VERMICULUX^® board (see TABLE 4 for thickness) edge screwed with 60mm x 5mm wood screws at 200mm centres.

Layers offset at circumferential joints to form 100mm overlap; boards screwed together at the overlap with 35mm x 4mm (60 minutes), 45mm x 4mm (90 minutes) and 50mm x 4mm (120 minutes) screws at 100mm centres. The screws should be located at the centre of overlap. Screws must be inserted from outside of the duct.

Suppports
8mm diameter threaded rods and 15mm x 30mm x 15mm x 5 mm steel channel rails at 1220mm centres near circumferential joints. Stress on support sections should not exceed 10N/mm²

Filler
Joints and screw heads are filled using INTUMEX^® AN Acrylic Sealant.

VERMICULUX^® boards are suitable for protecting smoke extraction ducts in buildings where the means of escape could be severely contaminated with smoke and become impassable.

The boards can provide self-supporting ducts offering up to 120 minutes fire resistance level (FRL) for stability, integrity and insulation in accordance with the criteria of BS476: Part 24: 1987.

Maximum duct size is up to 750mm x 300mm.