The Roof as a Loa arrier and Ventilator
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Providing for the Accommodation of Goods in Roof Enclosures on Vans and for Effective Ventilation of the Cab and Loading Space
WHEN a bulky load, such as furniture, is being transported from the factory on a lorry, the loading capacity of the vehicle is frequently increased by means of a platform built over the cab roof. The amount of comparatively flat space available on the cab roof itself is limited, because the sides are usually rounded and the cab is 10 ins. or 12 ins, narrower than the body.
To give more space a platform is built which is the same width as the body. If the cab be specially constructed it may have a flat roof, so as to provide a good foundation for the cross-bearers which support the platform. The back of the landing is supported on the front boarding of the loading portion.
For a light load, the cab platform may be supported on side brackets from the front of the body.
The number of vans of all sizes designed to carry roof loads does not diminish. The roof is not used only for empty tins and cases, but often
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accommodates loaded crates. The market van is a familiar example. The roof is also a convenient place for carrying ladders and lengths of piping.
The usual method of equipping the load-carrying roof is to fit it with a set of wood battens, which may be set out either lengthwise or crosswise. The load is kept in position by encircling it with rails, boarding or netting. The boarded .surround is preferred if extra space for writing display be required.
When the battens are screwed directly to the roof, each screw—and there are probably two dozen of them —which pierces it is a point where water may enter. In order to avoid injury to the roof, the slatted platform may be made as a unit, without any actual fastenings to the top of the roof.
This unit consists of a set of lengthwise battens made up into a mat by fastening to them three or more crosswise battens on the under side. The mat is held in position transversely by stays, the lower halves of which are shaped to fit the curved sides of the roof.
How the Stays are Fitted.
The foot of the stay takes a bolt, which secures it to the cantrail. The upper half of the stay is vertical and carries at the top the roof rail. It also has a lug or flap for securing it to the roof mat. Instead of making the mat stay and rail support in one piece, the upright portion may be bolted on separately.
Any lengthwise movement of the battens may be prevented by making them the full length of the roof. The end crosswise slat has an angle plate fastened to it, which forms a lip below the top of the roof and has a bearing on the front and back rails of the roof framework. A continuous angle plate is not essential and, instead', two or three small lip plates may be used, fastened either to the battens or the rail of the body.
When piping, mouldings or bar iron is carried on the roof of a box van, the load is not a heavy one. If a heavy burden of this description is to be transported, it will be carried on a lorry, with a gantry or side troughs. For a comparatively light load, the full width of the roof is seldom required and the weight may be concentrated in the centre.
For the roof of a small van there is a pair of stirrups with cross-bars supported between a pair of brackets. These three-cornered brackets and a cross-bar provide plenty of convenient points for tying the load. This operation can be facilitated also by Welding eyes or hooks to the brackets. For a larger roof, there is a 'Centre pair of brackets and a crossbar.
The feet of the brackets may be screwed or bolted directly to the roof, or they are first mounted on a skeleton wood framework.
Preventing Condensation.
The van should he ventilated when foodstuffs are carried. Efficient ventilation also keeps the inside of the vehicle dry, and prevents condensation on the inside surfaces of the panels and framework. When louvre panels are inserted, they should be as close as possible to the underside of the roof, where the heated air collects.
If the loading portion be higher than the cab, the front and back louvres may be arranged at the same level and good circulation of fresh air ensured.
Ventilation of the cab is even more important. In this instance, louvres may be inserted in the curved sides of the roof. The cantrail position is also a good place for inserting louvres in the loading portion of the van.
When louvres are placed in the top of the door and are 5-6 ins, below the roof line, their effectiveness may be increased by inserting a small deflector panel under the roof. This will direct the currents of air directly to the louvres and prevent pockets of air from being set up between the top of the louvre panel and the roof.
There are several types of ventilator designed for placing in the roof itself. The roof ventilator is often an extractor and the currents of air which flow over the roof set up a partial vacuum at the ventilators, either by flowing over or through them. The ventilator is constructed
so that it is effective whatever the direction of the wind.
A simple type of roof ventilator is the hinged-flap pattern. This is fitted so that the flap or lid opens towards the front and thus forms a deflector, which creates suction of the air behind it. This pattern may have a glazed lid, thus forming a roof light.
The clerestory roof is specially designed for ventilation. The heated air collects in the higher central portion, which has opening windows on` each side. These windows may be hinged on their top or bottom edges, or vertically at either end, so that they act as_ air inlets or extractors, according to the position of the window opening in relation to the direction of the vehicle.
If half the number of lights be hinged on the back edge and the other hall on the front face, the lantern roof has one set of openings for admitting fresh air and another set for drawing out the vitiated atmosphere.