Natural draught ventilator for roof mounting - has segmented and tapered base to allow thermal movement without damage to roof

摘要

The ventilator has base (3) which fixes to the roof, a cylindrical piece (1) rising from the roof and a cowl (2) at the top of the cylinder. It is weather-proofed by asphalt which is dressed over the base. The base forms an annulus and its outer part is divided by radial slots (5) into a series of segments (6). The cross section tapers from the inside down to the outside. The taper and segmentation permit the base to expand and contract without distorting. This prevents lifting and cracking of the asphalt with consequent damage to the weather proofing.