The variety of forms of these is very great; one or two different kinds are shown in the accompanying illustrations.
In Fig. 282 the ventilator has a central cast-iron standard in addition to T iron standards on each side, the latter being filled in with wooden louvres. The covering to the ventilator is the same as that of the roof, i.e. slating on boards fixed to angle irons filled in with wood.
Fig. 307 is an enlarged section of the lantern and ventilator surmounting the roof in Fig. 284.
Fig. 307. Scale, ½ inch = 1 foot.
The construction is evident from the figure, and requires but little explanation.
The skylight itself is supported by a central cast-iron standard bolted to the head, which receives the rafters, and has side standards of the same material, with galvanised iron louvres. It is covered by an ordinary wooden skylight sash, having deep bars filled in with glass.
Surmounting the skylight is a ventilator open at the sides, which are formed by cast-iron standards, supporting a covering of corrugated iron bolted to flanges formed upon their upper extremities.
The coverings used for wooden roofs have already been described at p. 140, Part I., and p. 61, Part II.
Most of these can be used for iron roofs, in some cases with slight modifications in the way of laying.