A home wood kiln can be a useful resource for anyone who uses a lot of lumber, is partial to expensive or exotic wood or simply wants to enjoy the satisfaction of personally preparing raw timber for use in woodworking projects. The easiest way to get started with timber drying is to build a backyard solar kiln, which is essentially a specialized shed that uses the sun's light to heat and dry raw, or "wet," boards. With a little planning and some basic construction know-how, you can build a solar kiln with ease and confidence.
Start at the Top
The amount of wood your kiln can dry depends on the size of the roof, which will be a 45-degree slope of clear polycarbonate running between a low front wall and a taller rear wall. For every 10 feet of lumber you hope to dry, plan on 1 square foot of roof area. It is easy to cover a portion of the roof to reduce the solar energy flowing into your kiln, but there is no easy way to increase your kiln's capacity, so err on the high side.
Work Your Way Out
The size and angle of the roof will help to determine the dimensions of your kiln's walls and floor, but you can still adjust the exact layout to your preference. Be sure to give yourself enough floor space to accommodate a large stack of timber with at least a foot on each side to let the air circulate. Factor in at least one wide doorway in at least one wall to let you load and remove boards easily. Your rear wall needs to be high and wide enough to give you room for several wall vents, and the interior height should accommodate several dangling frames or boxes to hold a series of fans. Both of these elements are necessary to ensure proper airflow for thorough drying.
Cover and Seal
A solar kiln is effective only if you can absorb and contain the sun's heat, so it is important to seal your kiln well. You should cover the floor frame with plastic sheeting to lock out ground moisture, and then nail plywood to the floor and to the inside and outside of the walls. A coat of rubber-based sealant on the inside walls and floor will help absorb sunlight and trap heat, while ordinary exterior paint outside will protect your kiln from the elements. A single layer of polycarbonate on the roof should be sufficient, but you can nail sheets of polycarbonate to the underside of the roof frame as well for extra insulation in cold climates.