- 1). Determine your kiln size. The kiln is basically a wood box with a full-size back wall opposite a very short front wall, and roof sloping at a 45-degree angle between them (see Virginia Tech site in References for photos and illustrations). The roof, which is made of clear, corrugated polycarbonate that is greenhouse-rated, provides the drying power by allowing sunlight to heat the air in the kiln. Ideally, you want to have 1 square foot of roof area for every 10 board feet of lumber being dried. Keep in mind that you can reduce the solar collecting area (to accommodate smaller amounts of wood) by covering part of the roof with an opaque tarp or cloth. Your kiln should be long enough to accommodate the boards you plan on drying, and wide enough to allow a foot of empty space on either side of the stacked lumber.
- 2). Build the floor. Using standard construction framing methods, build a floor using 2 by 6 lumber with joists 16 inches apart. Place insulation between the joists, and cover the entire floor with a sheet of plastic (stapled in place) and then a layer of plywood (attached with framing nails).
- 3). Build the walls. Use 2 by 4 lumber to frame the four walls according to your design. Be sure to include large doors in the back or one side to give you access to place and remove lumber. Also, frame openings for one or more vents high in the wall opposite the sloped roof. Place insulation between the studs, and attach plywood to both sides (interior and exterior) of the wall frames.
- 4). Coat the walls. Paint the interior walls with a black sealant, such as rubber-based concrete or roof sealant. If you like, you can begin with a layer or two of aluminum paint to create a moisture seal, but be sure to finish with a coat of black rubberized sealant, which helps to absorb sunlight. Paint exterior walls with latex paint to protect the wood.
- 5). Build the roof. Construct the roof frame using widely spaced 2-by-4s to create a rectangular grid. The boards should be close enough to create a sturdy frame, but distant enough to minimize blocked sunlight. Place a layer of clear polycarbonate atop the frame and attach it with framing nails.
- 6). Place vents and fans. Place wall vents in the framed openings in the back wall. Use 2-by-4s to create frames for the window fans. The frames should hang from the roof and hold fans in position roughly 1.5 to 2 feet in front of the back wall and 3 feet from the ceiling. Place the fans in these frames.
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