Wood Engineering Wood Structural Design Data, NFPA (National Forest Products Assn.), 1250 Connecticut Ave., NW, Washington, DC 20036, 1978. 240 pages, $20. by Paul Hanke Wood is becoming an almost unrecognizable product. The contemporary builder is faced with a plethora of "reconstituted" sheets, Ibeams, and glulams-all stronger than the original lumber, and making more efficient use of trees that are declining in size and quality. Each of these products has its own special characteristics, applications, and span ratings, and every year they find a wider share of the market. For those purists-or Neanderthals- among us who still use "real wood," Wood Structural Design Data is an essential reference. It will tell you the span capabilities of a remarkable range of timber sizes.