16 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE 
sirable in the interests of fire protection. The great variation found 
in existing yards indicates a failure to appreciate the value of cross 
alleys. Some yards 2,000 feet in length have none. 
SPACING BETWEEN PILES 
The necessity for proper spacing between the piles on the same 
alley can not be emphasized too forcibly. The primary purpose 
of these openings is to aid air circulation, not only to supplement 
the alleys in building up general air currents in the yard, but also 
to exert a very definite effect on the horizontal circulation in the 
lumber pile. The front and usually the rear of a pile, because of 
the location of the crossers, present an almost solid face. The sides 
of the pile offer the only easy inlet and outlet for downward air 
currents. A very definite circulation along the sides of the pile 
is essential to effective drying. To obtain this, a spacing of at least 
3 feet and preferably 4 feet should be used. Where local air move- 
ment is sluggish, a spacing of 5 or 6 feet may be justified. A second- 
ary benefit from adequate pile spacing is that as the width is 
increased the direct rays of the sun strike farther along the sides 
of the pile during a greater part of the day. 
If the relation of adequate pile spacing to the air-seasoning process 
is appreciated by the lumber industry of the West, it is not apparent 
in present practice. Although a maximum spacing of 6 feet is 
occasionally used, the average is about 2 feet, and many yards have 
still narrower spacing. In certain yards where slow drying and 
the resultant difficulties exist, the most effective single improvement 
would be to widen materially the spacing between the sides of the 
iles. | 
7 In order to cbtain the maximum benefit from local wind currents, 
the openings between the sides of the piles should be continuous 
from alley to alley, providing unbroken channels from one side of 
the yard to the other. (Pl. 2, B.) This arrangement is especially 
desirable where the prevailing winds come from the east or west 
and the main alleys are laid out from north to south. To effect 
this arrangement it is necessary to segregate stock lengths in the 
yard by blocks rather than by alleys unless a uniform width of pile 
foundation is used throughout. 
The advantage of this type of layout is recognized to some extent. 
Tt is commonly found in the California pine region and occasionally 
in the Inland Empire and Douglas fir regions. Oddly, in the red- 
wood region, where climatic conditions make for generally slow 
drying, this arrangement is not in use. 
TRAMS 
The use of trams in the drying yard should be discussed in connec- 
tion with layout, for where the ground is very uneven trams may 
seem desirable for facilitating yard transportation. Also, higher 
piles can be erected by hand in tram yards. But the hindrances to 
seasoning inherent in trams may more than offset their benefits. Air 
movement below the level of the tramways is seriously retarded, just 
where it is of greatest importance in order to maintain a positive 
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