This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
INTERIOR VIEW OF MODERN GREENHOUSE.
120 ft. long, 40 ft. wide, with hot-water pipe overhead. Erected by Messrs. W. Duncan Tucker & Sons.
A tank for keeping the pipes supplied with water must be placed somewhere where it can be filled easily. This tank should not be too small, or when the water in the pipes gets hot the expansion will cause an overflow and a consequent shortage when the water cools again; 20 gal. will do for a small house or two, but a 30- or 40-gal. tank will not be a bit too big for say 1500 ft. of pipe. An expansion pipe must be fitted to the boiler, and should be 1 1/4 in. diameter for anything but a very small boiler; this pipe should rise to a height of 6 ft. above the highest point in the pipes. When setting the boiler, a good rise should be given to it. The makers will say what rise to give their special boiler, but any of the forms of saddle boiler will want a rise of 3/4 in. to the foot.
With regard to water supply, for forcing, it will be necessary to have tanks in the houses, and for obtaining warm water one of the pipes should be taken through the walls. To do this a sliding collar with a joint formed with indiarubber rings must be put on to the pipes where they will pass through the walls of the tank, and this must be done before the pipes are joined together. These collars are built into the walls of the tank, and the pipe inside is thus free to move a little with the expansion and contraction due to the temperature. If this is not done the movement will crack the walls of the tank. Tank walls should be 6 in. thick, made of good concrete, and faced with sharp sand and cement in the proportions of 1 part cement to 2 parts sand. When the facing is set it should be brushed over with a wash made of neat cement, or, better still, let the walls get quite dry and then paint over, first with a solution of Castile soap, 3/4 lb. to the gallon of water, allowing twenty-four hours for drying, and then with a hot solution of 2 oz. of alum to the gallon. This process can be repeated if necessary; but it is said that four coats are impervious to a head of 45 ft. of water, so that one coat should be sufficient for a greenhouse tank. When ground clinker is used for making the concrete it may be economized by making old bricks or the concrete to a batter, and as it is filled into the mould any kind of hard rubbish can be bedded in it. Long tank walls should have old lengths of gas pipe put in to strengthen them, and pieces of small pipe or iron bar should be bent round and set in the corners. Corner irons should be put in the greenhouse wall as well.
To return to the actual building of the house, some form of gearing should be fitted to the ventilators, and there are several good and cheap forms on the market: but the bottom gearing is more difficult to do cheaply, and the only thing to do is to have one worked by levers fitted to a gas pipe running in bearings screwed to the louvre framing, the movement being applied by means of a worm wheel and cog.
The glazing can be let out piecework at 2s. 6d. per 200-ft. box of glass, unless time is no object. Brass brads should be used for fixing the glass and no top putties. The lowest panes should have three brads at the bottom edge to make sure they shall not slip down. In some way or other these bottom brads work out and let the glass slip down; and the only suggestion I can make is, that the drip, freezing round brads lifts them out a little at a time till they are quite loose. The best hinge for ventilators and louvres is that supplied by Messrs. Paine, Main-waring, & Lephard, of Worthing, whose patent it is. I am not aware of any other patent makes, and so feel at liberty to mention this form as better than the common cross garnet or the water - joint ┬ hinges, which soon wear or rust out. The ventilators can be glazed before they are hung. Before the glazing is done a couple of wind stays should be put in at each end of the house; these are made of pieces of l-in.-by-3-in. batten, the longer the better. These pieces of batten are carried from the under side of the top end of the rafters to the plate, as far back in the house as the battens will reach, and a screw is put through into every bar where they cross; but the glass gauge should be put in while the stays are being fixed to the bars, to make sure that they keep the right distance apart. As the end rafters are 1 in. deeper than the glass bars the stays will have to be let in; this makes all the stronger job.
Allowance must be made for carrying off the rainwater from the roof. A cheap form of gutter can be made of wood. Instead of using the usual narrow drip, l-in.-by-3-in. batten is nailed in its place, and to the outer edge of this pieces of l-in.-by-4-in. batten are fixed by screws placed at every foot. The joints between the ends of the pieces are made by making a saw-cut right down the middle of each end, and then when all the pieces are in position short pieces of hoop iron are driven up the cuts; when the gutter is well tarred there will be no leak. Outlets can be made into the tanks, and the waste water from the ends can be carried off into a drain.
Where it is important to save all the water it is best to take the rainwater from the end of the gutter through 2-in. gas. pipe laid under the border to the first tank; then if the tanks are joined up the water will fill all at the same time. If iron guttering is preferred, the narrow drip is used and the gutter fixed to the plate under it. As soon as the glazing is finished the last coat of paint should be got on, and for inside work some special greenhouse paint should be used; it may cost a shilling a gallon more, but it will last much longer. There is also a special greenhouse putty called "Plastine". This is double the cost of ordinary putty, but it never gets hard, and repairs can be carried out with the greatest ease; there is also less shrinkage with this, and consequently less leakage. All ironwork should be coated with iron-oxide paint.