18 DEPARTMENT BULLETIN 1425, U. S. DEPT. OF AGRICULTURE 
unit type is cheaper to construct, more easily kept in repair, and, if 
the yard is properly laid out, assures adequate and uniform spacing 
of the piles. It is generally more flexible than the continuous type, 
as it can easily be changed to accommodate different lengths of stock 
and to make repairs. 
Another style of foundation, which has much merit, is illustrated 
by Plate 4, A. It is the most rigid type in use and definitely pre- 
cludes any variations in the spacing between the sides of the piles 
when once the yard is built. One admirable feature is that the 
stringers upon which the lumber is piled are not attached to the 
permanent part of the structure, but can be moved to support stock 
of different lengths. This type assures a firm bearing at each tier 
of crossers. Obviously, much better original material and a higher 
labor cost are required than for the other two types. Also, because of 
the cross and lengthwise bracing, more obstruction is offered to air 
movement under the pile. In Plate 4, B is shown a good type of 
pile-bent foundation, necessary where the yard is located over water. 
These examples of construction are above the average for the 
western softwood territory generally. Very poor foundation con- 
struction is too often found. Local conditions will affect the choice 
of structure, but whatever type is preferred the chief functions of the 
foundation should always be clearly kept in mind. The use of con- 
crete piers or treated wood supports for the foundation stringers 
has much merit. Moist air and damp soil beneath the lumber pile 
are naturally favorable to decay, and untreated members in contact 
with the soil require constant replacement if poor alignment is to 
be avoided. 
NUMBER OF FOUNDATION STRINGERS 
In general, a stringer should be provided for each tier of crossers 
in the piled stock. The number of crossers that should be used to 
each course of the lumber will be covered later under “ Pile construc- 
tion,” but as a broad principle it may be stated here that for western 
softwoods the maximum distance between supports should be 8 feet. 
In order that different stock lengths may be provided for, the type of 
bottom shown in Plate 4, A is very desirable as being the most fiexible 
in this respect. With other types, special foundation must be pro- 
vided for different length piles. Plate 4, C illustrates the effect of 
insufficient bearing. 
HEIGHT OF FOUNDATION 
Actual study has shown that adequate unobstructed clearance be- 
neath the lumber pile is a basic factor in effective air seasoning. 
Controlled yard tests have demonstrated that as the foundation 
height is increased the inherent lag in drying between vertical sec- 
tions of the pile is decreased; final moisture content of the stock is 
more uniform throughout the pile and during a given period will 
reach a lower average; and, in pine, depreciation from stain is re- 
duced, particularly in the lower third of the pile where blue-stain 
development is ordinarily greatest. In drying redwood, a difference 
of 12 inches in the rear height of the foundation resulted in a final 
average moisture content of 18 per cent for the stock on the higher 
bottom and of 12 per cent for that on the lower. Stock in the higher 

