The unfavorable reports and condemnation of this system are largely from two sources, mostly by men who never tried in the right way, or perhaps tried it on an old house that was formerly glazed with putty, and the other people whose houses were not built accurately enough and made straight and true. Square cut glass will not fit crooked plate and bars.
In the first place you must use the cypress cap and bar that are especially made for the purpose and your bars must be put on true and parallel. One-sixteenth of an inch is all you want for play between bars. It should be just that and nothing more nor less; this is very particular. Some carpenters mark out 011 the ridge and plate the place for the bars; others will cut strips of hardwood, one to be used at ridge and one at plate. If the strip is one-sixteenth inch longer than width of glass and the bar is nailed up to the stick carefully every time, top and bottom, you can't go very far wrong; yet every ten bars or so you should prove by a rod that you are keeping the bar at top and bottom parallel. You can make up any discrepancy with putty. Putty, like charity, covers a multitude of sins. With butted glass you must be correct, and it is just as easy to be so.
Don't trust to any carpenter, however many houses he has built; prove for yourself that he is right. When the bar is nailed to the plate see that the face of the bar on which the glass rests and the slope of the plate are exactly flush. If the bar is a trifle below the plate it is difficult to remedy. If it is a trifle above it can easily be taken off with a chisel. The bar can always be straightened on the purlin when you lay the glass, or straightened by a straight-edge and fastened in place before you begin to lay the glass.
The glass should not be lapped on the plate more than half an inch; the less glass there is resting on the wood the less likelihood of breakage by ice. The glass should always be laid with the rounding part up; all glass is more or less convex and concave. The thin edge of the glass (if there is a choice) should always lead up the bar. If you were to put the thick edge up and it butted against a thin one there would be a small space for the water to lodge. The man who lays the glass, if he has any brains at all, will be able to see these points at a glance and lay it about as quickly as a boy can hand it to him. Remember that is all he has to do; there are no putty and no brads, no squeezing and thumbing, no squinting and swearing; it is only to lay the glass in, and so you go on to the top.
In laying out the length of the bar we try to make it so that a certain number of lights just fill up from plate to ridge. If that is not convenient you can always make it so that a half light will finish at the top. When you know exactly what size of fraction of a light you need (if any) you will have them all cut ready; it is just as well to use the small piece at the bottom.
Before we lay any glass we drive in two wire 6-penny nails, half an inch below the edge of the plate, but only drive them in a small depth, just enough to hold the lights while you are laying them. This can be done before you begin to glaze and by a man standing on the ground. When the whole run of glass is in and before you screw down the cap the man nearest the bottom, with the end of his chisel handle, gives the glass a good push up, closing up any space, however small, and then drives in his bottom nails. They should be driven close down to the glass or they will impede snow and ice slipping off. Now this effectually prevents the glass from slipping, and if the bottom light does not, how can the others?
We have found with further experience that if the roof is any length, say sixteen feet, that the weight of glass on the nails will cause the nails to grind themselves into the glass, affording the chance for a slight space between some of the lights, so instead of the two nails at the bottom we now prefer a strip of wood (cypress is best) half an inch wide and an eighth of an inch thick, well painted. After all the glass is tight, nail down this strip and you will be bothered with no slipping or cracks between the lights.
One and one-eighth inch round-headed brass screws are used to fasten down the cap. Be sure you use the brass screw. They cost more than the iron but never rust, and when the iron screw rusts it decays the wood and very soon the cap is loose. We used to put a screw at every joint, or where the two lights butted. We found the middle of the glass a better place; the glass being laid with the convex up if they are tight on the bar in the middle they are bound to be at both ends. A boy can get these caps ready because you will have one cap as a pattern, and with a ratchet drill the caps can be ready with the screws already lightly tapped in, and when the two men laying the glass call for the cap, up it goes, and the men who have ratchet screw-drivers soon have the screws down in their place. Don't screw down too tightly, just firm and solid is enough. You will, of course, need one screw within an inch or so of the ridge.
Be sure to have the ventilators made the same way with cap and bar, and to take the same size glass. Have but one size glass on the place, if possible, and as little cutting as possible. I do not like to disparage any device that is made and sent abroad in good faith by a fellow florist, but in justice to those who will follow my advice I must candidly say the zinc strips that are made to go between glass when butted are a miserable failure and a nuisance. You want nothing between them or under them; simply the cap.
Any size glass can be butted. We have it on 12-inch, 14-inch and 16-inch square and always double thick. We prefer to use glass that is square, that is, 14x14 or 16x16. Then you have the choice of two edges, and if one is a little rough you can use the other. If glass is laid as described above it will save you many dollars. It is a smooth, fine roof, more air-tight than lapped glass. The drip is nothing, absolutely nothing, if well and properly laid; if there should be a trifle it is always at the bottom, which in commercial houses would fall in the path. And if a little dust creeps in. and it will creep in where Mater won't, it can be washed annually as clean as the day you put it up.
In our last addition we used cast iron gutters. If you should have occasion to put in these iron gutters see that the check in the gutters that the bottom light butts against is a full one-eighth of an inch. In the cast iron gutters we have, though satisfactory in every other respect, the check is scarcely one-sixteenth of an inch and occasionally a light slips over.
Fancy the luxury of painting such a house. Remove the glass, thoroughly paint and relay again. If you were visited by a hail storm you have only to break out the shattered lights, shove up the sound, and before night you are whole.
Without considering these contingencies, it is the ideal way for a commercial man to build. I have twenty-two houses glazed with butted glass. I had no one to tell me how, but I persevered, and when 1 had built five or six I had it down fine and have given you the mature fruits of my experience.
Most of the above was written eight years ago and since then we have built and rebuilt more than a dozen houses, but have never altered our mind with regard to glazing. We have heard lately extravagant praise as well as censure of this method. If houses are truly and squarely built and the butting method is properly followed it has many points in its favor over lapping and the use of putty.