... structure can make practical use of wood as a framing material, employing carpenters who can rapidly construct a timber frame for an earth-sheltered house can decrease labour costs. To use wood to its best advantage and most effectively in engineering applications, specific characteristics or physical properties must be considered. Classes of woods Hardwoods and Softwoods Trees are divided into two broad classes, usually referred to as hardwoods and softwoods. These names can be confusing since some softwoods are actually harder than some hardwoods, and conversely some hardwoods are softer than some softwoods. For example, softwoods such as longleaf pine and Douglas-fir are typically harder than the hardwoods basswood and aspen. Botanically, hardwoods are Angiosperms; the seeds are enclosed in the ovary of the flower. Anatomically, hardwoods are porous; that is, they contain vessel elements. A vessel element is a wood cell with open ends; when vessel elements are set one above another, they form a ...

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