FOREST SERVICE WATER SrRAY DRY KILN. 15 
ROOFS. 
The roof may be built of wood, concrete, or tile and concrete. 
Wood roofs should be ceiled on the underside to prevent excessive 
heat loss; and in case of long kilns it is advisable to fur down the 
ceiling to make it level and create an ample air space between the 
ceiling and the roof. (See fig. 1.) Such space should have grated 
openings for ventilation; otherwise it becomes saturated with mois- 
ture and destroys the insulating effect. 
The absorption of moisture and the heat loss is much less in the 
tile and concrete roofs than where concrete slabs are used and the 
construction is much lighter. By casting the roof slab flat and using 
a cinder filling graded to gutters for roof drainage, a level ceiling can 
be obtained. 
It is advisable to build tile or concrete roofs in such a manner as 
to have expansion joints over each bearing or division wall; for in 
monolithic roofs with a solid continuous slab the expansion is mul- 
tiplied and causes the outer walls to be pushed out of alignment. 
FLOORS. 
The floor of the kiln should be concrete, pitched toward the gutter 
one-fourth inch per foot. It is advisable to lay the floor on a cinder 
foundation; in the absence of cinders sand should be used. The 
floor need not be over 3 inches thick, but should be troweled smooth 
to permit flushing with a hose. 
GUTTERS. 
The gutters should be the full width of the spray chamber, at least 
3 inches deep at the shallow end and pitch evenly to the drain not 
less than 1 inch in 8 feet. A floor-drain grating, without trap, 
should be set over the opening to the drain piping. For installation 
of drain for return water see " Water supply." 
WELLS. 
The wells should be built of concrete, made watertight with integral 
waterproofing. For size and shape see "Water supply." 
ELECTRIC WIRING. 
Electric lights spaced from 20 to 25 feet apart along the spray 
chamber make it easy for the operator to examine the sprays readily 
to see whether all heads are in operation and also to note the condi- 
tion of the lumber. A switch should be provided outside the door. 
All fittings inside should be waterproof or marine type and all wire 
lead-covered. 
INSULATING MATERIALS. 
Materials for insulation in kilns should be nonabsorbent and 
capable of standing high temperature and moisture conditions without 
damage. Ordinary building paper is practically worthless. Water- 
