A Homemade Solar Lumber Kiln

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UNCLE SAM TO THE RESCUE

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The material arrived in record time. I opened the envelope and-lo and behold!—found a set of plans for building a solar kiln, including charts that specified the drying periods required for various species and thicknesses of wood. At that time (about two years ago), the Forest Service experiments were still in their infancy, so the amount of information contained in the charts was fairly scanty, but it was enough to turn my "have to" concern into a "want to" determination.

According to the Forest Service data, inch-thick boards could be dried in as little as 30 days in the kiln . . . while two-inchers would take from 45 to 90 days. Now that may sound like a long spell to sit around waiting for lumber to dry . . . but in fact, it's impressively brief when compared with the time required for air-drying lumber: approximately one year per inch of thickness. And even after all that time, air-dried planks frequently aren't dry enough for my purposes.

For example, here in Ohio the moisture content of lumber stored outside rarely drops to as low as 15%. (I just bought some pine that had been stacked outdoors for five years, and it tested 14%.) And if the chances of warping are to be kept to a minimum, construction lumber should have no more than 10% moisture content, while 8% is recommended for furniture work.

GETTING STARTED

The pictures accompanying the Forest Service plans showed a small building, similar to a chicken shed, with solar panels on its south-facing side. A materials list for the entire assembly and specific directions for building the solar panels were included with the package. In short, the whole project looked so marvelously simple that I wondered why I hadn't thought of it myself. I realized that I'd have to make a few minor changes in the plans to suit my particular needs, but the basic concept certainly appeared to be workable.

My son and I launched the kiln project by felling a few trees and sawing out enough boards and beams to do the framing-in. (I'm fortunate enough to have a 40-acre woodlot, a chain-saw lumber mill, and a 25-year-old son who's strong as a bull . . . but even working alone, you shouldn't have any problem building a kiln with simple electrical and hand tools.)

MATERIALS

I decided to use 4 X 8's for the beams, 2 X 8's for floor joists, and 2 X 4's for wall studs and rafters. We covered the outside walls of the little building with scrap aspen, sliced 3/4" thick and left with the bark still on its edges. My lumber purchases were limited to two sheets of plywood for the doors, three sheets of 1/4" Masonite hardboard for solarpanel backing, and some 1 X 3 furring strips for the roof frame.

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