27 



Lapped glass is commouly, almost entirely, used in the United States. This 

 means that the glass is laid up in the same manner as shingles, one light overlap- 

 ping the one underneath it. The lap is usually 3/16 or ^ inch. Any more makes 

 a poor job and dirt collects in the small space, and becomes very unsightly and 

 causes a certain amount of shade. With the lapped glass construction the glass 

 is usually bedded in putty, while with the bar and cap no putty is used nor no 

 glazing point. A zinc strip attached to the gutter or eave holds the bottom 

 light in place and the others above rest on it. If lapped glass is to be laid, 

 only first class greenhouse putty should be used. Ordinary putty secured from 

 a hardware store will not do. It will crack and peel off in a^bout two years time, 

 necessitating going over the whole house again. 



This grade of putty will cost a few cents more per pound Taut will save in 

 the long run. It cost some growers in the States this last year several hundreds 

 of dollars to re-putty their houses because they used an inferior putty at the 

 start. This can be pi-ocured from any reliable firm who make and handle green- 

 house materials. 



Glass should be laid convex side up or with the bowed side to the weather, 

 practically all American houses are equipped with lapped glass, and practically 

 all Ontario houses have butted glass. The butted glass is handier in some cases to 

 put on in case of breakage, and yet the close fits and the! Jagged edges sometimes 

 found tend to cause more breakage. If there is any jar or move of the frame one 

 piece of glass is pushing against another in the case of the butted glass, whereas 

 with the lapped glass the one light has a chance to slide on the one beneath 

 before it will break. Lapped glass properly toedded in putty will give a warmer 

 house than the butted one. There is always an opening between the best butted 

 glass, and this allows for the escape of warm air and permits rain and moisture 

 to get in. More unsightly houses, due to collecting of dirt on the lights which 

 has run in through the butt opening and down the inside of the light, will be 

 found than from dirt collected under the lap in a well bedded house. 



The objections to lapped glass encountered more than anything else was 

 that it was awkward to fit a broken light. This point was admitted by many 

 growers, but they have a counter claim that the breakage is not one-quarter that 

 of a butted glass house. The glass in the latter is simply shoved in at the 

 bottom, thus shoving all the lights up until there is sufficient room for the light 

 being replaced. 



Glass comes in boxes holding 100 square feet. There is always more or 

 less ^breakage in them, but the huilder should insist that he is given D. D. 

 English 21 oz. glass or he should get double strength (D.S.) American glass. 



HEATING. 



Hot Water Heating. — The heating is the next point which must be 

 considered. Hot water and steam are the two sources of heat for green- 

 houses yet. A great deal can be said for and against each kind of heating, and 

 it is a problem to say which is used the most. Both systems have been improved 

 in the last 10-15 years, and both systems are Ibuilt to give maximum service. 

 Hot water heating may be divided into two systems; the gravity system and the 

 pressure system. In the gravity system the water circulates from the boiler 

 through the coils and back into the boiler again, because after it reaches a certain 

 point there is a drop in the pipe system and the water naturally seeks its own 



