The floor is framed with 2x6's, 16-inches on center, in order to be strong enough to carry the weight of the green lumber. Lumber should be preservative treated if in contact with the soil. Paper backed fiberglass batt insulation was installed between the framing members (3). The interior and exterior are covered with 3/8" plywood (exterior grade plywood suggested). The inside plywood is painted with 2 coats of freshly mixed aluminum paint,(4) which, when dry, will act as an excellent vapor barrier. A 3rd coat of flat black paint is applied to the interior. The exterior is also painted, but a vapor barrier should not be used--if any moisture does migrate into the walls, it must have an easy way to escape to the outside. For this same reason,paper backed insulation rather than foil backed insulation is suggested.The roof is framed on fairly wide spacing. This spacing may have to be adjusted to accomodate the width of the covering material and any anticipated snow loads. The clear covering can be transparent polyethylene or other plastic sheets, but these coverings may deteriorate with heat, ultraviolet radiation, and continious fluttering and flexing (from the fans). The most durable covering would be ordinary,almost transparent, corrugated fiberglass, available at most building supply firms. Two layers of covering,seperatd by a dead air space, are suggested.
The dryer has 2 access doors at each end (east and west walls) to permit periodic examination of the lumber and measurements of moisture content. In addition, the Virginia Tech dryer has the roof hinged to the north wall and the south wall hinged to the floor. This permits the roof to be raised and south wall lowered to facilitate loading and unloading.
The vents on the north wall are framed openings with a small piece of plywood that acts as a door.
The fans are 3 speed window fans with thermostatic off-on control(5). The fans are fastened to the roof framing about 18" in front of the north wall with a plywood shroud or baffel around them extending downward 3 feet below the rood and running the full length of the dryer in order to force the air through the lumber pile.
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(3)/If foil backed insulation is used, the foil must be perforated throughout to destroy the vapor barrier properties.
(4)/ Aluminum paint can be made by mixing 18 grams of aluminum powder with 102 grams of spar varnish.
(5)/ Caution: Whenever the dryer will be left empty and fans will not be operating, the roof should be propped open slightly. If kept closed, temps at the peak can exceed 200^ F.
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