This was formerly a very heavy piece of lumber casting a lot of shade. Modern builders realize this, and it is now only four or five inches by one and one-half inches. If you hinge at the ridge the hinge is on top of the ridge, if you open ventilators at the ridge then the cap closes over the ridge and there is no strength needed in the ridge piece.

The main support to keep a house rigid and perfectly straight and true, as long as it will stand, and that is, we trust a long time, is a 1 1/4-inch iron pipe straight under the ridge. If the ridge is thus supported the whole weight is really taken off the walls. In wind storms the roofs of our greenhouses are severely tested, and this center support should be screwed into a fitting which has a shoulder that fits under and screws on to the side of the ridge.

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At the bottom or floor this should be screwed into a circular plate which should be screwed into a short post securely set into the ground a couple of feet. Some only rest the bottom of this iron pipe on a stone. That is good enough for all weight from above, but in case of great wind storms, when a vacuum is formed in the house, I have seen the iron supports lifted clear off the stone, which is a wrenching of the roof and conducive to cracked glass.

In houses such as we have endeavored to describe, intended for plants in pots, if planted out to smilax or asparagus they would be on the ground, and wheeling on the benches would not be necessary.

The neatest way to support the purlins is. by getting the fittings made by Jennings Bros., of Philadelphia. They are made to go over a 1 1/4-inch pipe with a branch, one in each side, with a socket for a 1-inch pipe. They are fastened at any height on the center 1 1/4-inch pipe by a set screw and have knuckle joints so that the 1-inch pipe leading from them can be set at any angle.

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It 'will be readily seen that the weight from the purlins pressing to a common center must be the best of support. The purlins, one on each side of the ridge, should be situated about halfway between ridge and gutter or plate; or if you use a heavy bar let it be a little nearer the ridge than the gutter, because it will keep the bars more rigid near the ventilators. There should be 1-inch pipe set every eight feet (same distance apart as the center posts). You must put in a tee into which will screw the 1-inch pipe that leads from the fitting on the center post.

The bars are fastened to the purlins neatly and quickly by a steam fitter's galvanized iron clip, which you buy by the weight. The clip is screwed into the bar with a 7/8 -inch screw and holds the bar firmly, but not so firmly but what a rap with the hammer will move it either way when you are glazing. Be sure that you get the pattern for the bar the exact bevel both for the ridge and plate. Nothing looks worse than an ill-fitting open joint at the heel of the bar on the plate. Once get your pattern correct and the mitre box laid out right and you will have every joint correct.

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When putting on the bars we put up the ridge the whole length, nailing up a bar on each side every five or six feet, but only temporarily, and then the iron work is put up. By sighting along the bars the fitting that controls the purlins can be raised or lowered till you can get an exactly straight roof.

Glazing has been dealt with in another chapter.