68 GREENHOUSE CONSTRUCTION AND HEATING. 
edges of the glass ; though, failing this, a fillet, or bit of 
beading, tacked on will answer nearly as well. 
When the ventilators are placed opposite each other along 
the ridge of a span-roofed, or three-quarter-span, house, 
or in the case of a lean-to structure, the plan just described 
is an excellent one, and may be safely adopted, provided 
that the ventilators are not very long. But when they 
are placed alternately on each side of the ridge, according 
to the usual and proper practice, this objection to the plan 
of cutting the ends of the bars off beneath the ventilators 
occurs—that the thrust of the bars or rafters on the 
opposite side of the ridge-plank forces the latter, unless a 
very heavy one, slightly out of line, and then the ventilators, 
or the hanging-pieces, do not fit well, gaping at each end, 
unless hollowed a little in the middle. It is, consequently, 
better to carry the bars right through to the ridge, certainly 
where the usual three-square ventilators are employed, 
fitting short lengths of ‘seat’ in between the bars, and 
thus ensuring a straight ridge. With continuous ventilators 
it will usually suffice to carry every alternate or third bar 
‘through ; though these should be opposite each other on 
each side, and where principal rafters are used these only 
need be of the full length, with a stout seat to carry the 
ends of the smaller bars safely. 
Glazed side- or front-ventilators are framed together 
in exactly the same manner as those in the roof, with two 
styles, a top rail of the same thickness, and a thinner and 
wider one at the bottom, and two, three, or more light 
sashbars disposed equidistantly between. In conservatories 
and other large structures the side-lights are usually of 
considerable depth—from 3ft. to 5ft., or more—and, as a 
4 
