18 THE CONSTRUCTION OF THE FORCING-HOUSE. 
roof with an even span, those with a lean-to or true shed 
roof, and those with an 
uneven or broken roof. 
These various types of 
houses are illustrated in 
LE ED ea the aC =e 
x iii orams. Figs. 1 and 2 
s show the ordinary types 
aa of an even-span house, 
2. A simple Ses eo house, Figs. 3 and 4 (page 19) 
forms of an uneven or 
broken span, and Figs. 5, 6 and 7 (pages 20, 21 and 22), of 
a lean-to or shed house. The older type of forcing-house 
was rather narrow in proportion to its width; that is, it 
was rarely more than 20 feet wide, whilst the length might 
vary from 50 to 300 feet. A house of this width is propor- 
tionately more difficult to heat and to manage than one of 
greater width, and the tendency at the present time is to- 
wards much wider houses, especially in establishments 
where a large product is expected to be grown. The wide 
house, however, when built with a gable roof, becomes too 
- 
~ 
= 
3: A broken or uneven span, 20 feet wide, on a side hiil. 
high to admit of economical construction and heating, and 
the plants are also too far removed from the glass for 
best results. It is necessary, therefore, in these very 
