Buying freshly sawn timber and drying it in a home wood kiln can be less costly and more satisfying than buying pre-dried commercial wood. Using a personal solar kiln to dry lumber can take several weeks, but the opportunity to treat even exotic hardwoods and prepare them to your liking can make building your own wood drying kiln an appealing project.
Plan your kiln. It should have a tall rear wall, a low front wall, a sloped roof of clear polycarbonate (usually at an angle of 45 degrees) joining them and wood side walls cut to fit. For every 30 cm (1 feet) square of roof area, your kiln can process 3 metres (10 feet) of timber. Choose your roof size and plan the other dimensions accordingly. Keep in mind that your kiln needs to be long enough to hold raw timber and wide enough to leave 30 cm (1 foot) of open space on each side of the stacked wood.
Construct a floor frame using 5 by 15 cm (2 by 6 inch) boards with joists every 40 cm (16 inches), and lay in insulation between each pair of joists. Staple plastic sheeting over the whole frame, and then nail plywood over the joists to create a sturdy floor.
Construct the wall frames using 5 by 10 cm (2 by 4 inch) wood with joists every 40 cm (16 inches). Your frame should include wide doors set into the back wall or sides (to enable easy transfer of timber) and vent openings near the top of the rear wall. Lay in insulation between each pair of studs, and nail plywood over both sides inside and outside the frame.
Paint the inside walls with a rubber or aluminium-based sealant, such as the kind used for concrete or roofing. Make at least the top coat black to promote absorption of sunlight.
Paint the outside walls with the latex exterior paint of your choice.
Construct the roof frame using 5 by 10 cm (2 by 4 inch) timber with joists spaced wide enough to maximise the amount of sunlight passing through, but narrow enough to be structurally sound. Place a layer of clear polycarbonate over the frame and nail it into place. If you will use your kiln during cold months, consider nailing a second layer of polycarbonate to the underside of the frame for extra insulation.
Set the wall vents into their frames in the rear wall.
Construct frames for the window fans using 5 by 10 cm (2 by 4 inch) timber. Each frame should be attached to the roof frame and allow the fan to rest 60 cm (24 inches) from the rear wall and 90 cm (3 feet) below the roof. Place the fans in the frames.
When choosing a site for your kiln, leave plenty of open space around the kiln for easy transfer of long timber, and try to face the roof south for maximum exposure to sunlight.
When your kiln is empty, leave the doors open to allow the heat to escape. An empty kiln can easily reach temperatures over 93 degrees C (200F).