In large roofs, especially those which are subject to vibration, as in the case of railway stations, or those subject to hot fumes such as arise from some workshops, it is desirable to avoid the use of putty, which becomes dried and loose, and is shaken out so that leaks are caused in the roof.

Every good system of glazing without putty should have the following characteristics.

a. It should be simple in construction, so as to be easily repaired by ordinary workmen. Broken panes should be easily replaced.

b. It should allow of expansion and contraction of the roof (if it is of iron) under changes of temperature without breaking the glass.

c. It should be of such a structure and strength that men can easily get at any part of it for cleaning and repairs.

d. The fastenings and metal parts should be so placed as to be protected from corrosion by the weather.

e. It should not be obscured by heavy framing or sash bars, but should give a good proportion of light for the area it covers.

Of late years many systems of glazing have been introduced in which the use of putty is altogether avoided.

Of those now in use the principal forms are shown in Plate XIII. The writer has had most of these forms tried. He prefers, however, not to make any invidious comparison between them. Sometimes a system not suitable for one structure is suitable for another.

1 Seddon's Builders' Work.

Plate XIII.

Glazing Without Putty 200283