Western hemlock (Tsuga heterophylla) is also known as West Coast hemlock, Pacific hemlock, and British Columbia hemlock. It is found along the Pacific coast of Oregon and Washington and in the northern Rocky Mountains north to Canada and into southern Alaska.
A close relative of western hemlock is mountain hemlock (T. mertensiana), which grows in mountainous country from central California to Alaska. It has similar processing properties.
There is more than 380 billion board feet of Hem-Fir sawtimber on the managed timberlands of the Western region. Western hemlock is the state tree of Washington.
Western hemlock is a magnificent tree reaching 120 to 160 feet high with diameters of 3 to 4 feet at maturity. The lower 3/4 of the main stem will be free of branches.
Native Americans used western hemlock for medicine, food, dye, and to tan hides; to fashion small implements; to make articles of clothing, such as skirts made of boughs; to ensure hunting or fishing success by rubbing their bodies with boughs; and to ward off evil spirits.
Today, western hemlock is used for pulpwood, lumber, and plywood. In the early 20th Century, western hemlock was considered a weed tree. It was only in the 1940s that its true value was discovered.
Hem-Fir lumber products are available in structural, appearance and remanufacturing grades. Hem-Fir is a combination of western hemlock and five true firs. In fact, Hem-Fir is the second most important grouping in the West. Appearance and reman grades are used for many products including wood paneling, cabinets and trim, solid wood doors, louvers, shutters, moulding, casegoods, and furniture.
When severely bacterially infected, logs will not float; they are called sinkers. Shelling is common with this wood, especially after drying. Drying is difficult. Bacterial infection can be identified by the foul odor, high MC and shake (cracks run parallel to the growth rings, rather than across the rings). When possible avoid bacterially infected logs and lumber.
The wood, although having limited natural decay resistance, treats well with standard preservatives.
Processing Suggestions and Characteristics
Density. The density is about 28 pounds per cubic foot at 10 percent MC. This means that a dried piece of lumber 1 inch x 6 inches x 10 feet (actual size ¾ inch x 5-1/2 inches x 10 feet) will weigh 8 pounds. This is over 30 percent heavier than eastern white pine, but is about 10 percent lighter than southern pine.
Sawing is moderately easy. If there is a market for quartersawn lumber (such as flooring), the standard quartersawn sawing patterns can be used.
With flatsawing, there will be a large amount of clear or nearly clear lumber with older, large diameter trees. Second growth trees will likely have a few more knots, but for many products, these knots, if round and not spike, will not hurt the value.
Drying and Stability. One of the troublesome problems with western hemlock is the presence of a bacterial infection in the tree. This increases the moisture content of the tree, weakens the wood and imparts an objectionable odor to the wood.
There are a variety of kiln schedules, depending on wood quality and the quality of the lumber. See Dry Kiln Schedules for Commercial Woods, or Oregon State’s Forest Products Lab Extension personnel.
Shrinkage of western hemlock is moderately high: 6 percent in width and 3 percent in thickness for flatsawn lumber.
For construction, the typical target for kiln drying is 15 percent MC or under. For boards, 12 percent MC and under.
Gluing and Machining. Hemlock glues well with standard adhesives. As with most softwoods, over-dried (under 10 percent MC) wood does not machine as well. Shelling is likely if too dry or if bacterially infected.
Stability. Hemlock is moderately stable. It takes a 4 percent MC change for a 1 percent size change in the width of flatsawn lumber, and 7 percent MC change for a 1 percent change in the width of quartersawn stock.
Strength. Western hemlock is moderately light in weight and moderate in strength. It is also moderate in hardness, stiffness, and shock resistance. The strength (MOR) is 11,300 psi; the stiffness (MOE) is 1.63 million psi; and the hardness is 540 pounds. Corresponding eastern white pine values are 8600 psi, 1.24 million psi, and 380 pounds. In other words, it is considerably stronger, stiffer and harder than EWP. Similarly, western hemlock is much stronger stiffer and harder than the SPF lumber grouping.
Hemlock splits when nailed or screwed near the end of a piece, so predrilling may be required.
Color and Grain. The heartwood and sapwood of western hemlock are almost white with a purplish tinge. The sapwood, which is sometimes lighter in color than the heartwood, is generally not more than 1 inch wide, so it seldom will be found in lumber.
The wood often contains small, sound, black knots (They are black because the branch wood was dead when the wood from the main stem grew around the branch. that are usually tight and dimensionally stable.
Dark streaks are often found in the lumber; these are caused by hemlock bark maggots and generally do not reduce strength.
The grain is straight and even with a medium to fine texture.
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