20 VEGETABLE FORCING 
unsuitable for vegetable forcing, especially during the 
short days of winter. 
Even-span houses (Figs. 6 and 7) are in common use 
among vegetable growers. In this type of house the 
roof-bars on both sides of the ridge are of equal length, 
and are pitched at the same angle. As previously stated, 
the houses may or may not be connected at the sides, 
although the tendency is to connect them. Even-span 
houses are preferred by many growers. 
Although uneven-span houses are popular in some sec- 
tions, they are not used so generally in vegetable forcing 
Fig. 6.—Typical even-span range of narrow units. 
as are even-span structures. In this form, the roof-bars 
on one side of the ridge are longer than those on the 
other side. These houses usually run east and west; the 
southern slopes, being longest, admit the most light 
during the short days of winter. Some growers who pro- 
duce cucumbers and tomatoes in midwinter claim great 
superiority for the uneven-span house, and others are 
doing equally well in even-span houses in which the dis- 
tribution of light is more perfect. The length of the two 
spans varies more or less. 
The three-quarter span is the most common. It is used 
almost exclusively in the Boston section (Fig. 2), where 
