Characteristics and Properties of Western Red Cedar Lumber
Western Red Cedar (Thuja Plicata) is renowned for its natural beauty & outstanding physical properties that make it one of the best softwoods (Redwood is another) for greenhouse construction.
This exceptionally beautiful wood has natural coloring in mellow ambers, reddish cinnamons and rich sienna browns. Its warm coloring is complimented by a uniform, fine-grained texture with a satin luster. Slow growing and durable Red Cedar is the preferred wood where attractive appearance or resistance to weather & insects is important.
Western Red Cedar has one of the longest lifespan of any North American softwood. It produces long lengths of timber with true, straight grain. It is free from pitch and its heartwood has natural decay resistance. Its low density gives it an insulation value superior to most other species. Light weight, easy to work, easy to finish, possessing outstanding dimensional stability.
Red Cedar formed an integral part of the spiritual and practical life of the Northwest Coast Indians. Cedar was used for constructing the walls and roofs of lodges, totem poles, canoes and utensils while the bark was used for weaving baskets, mats, rope and clothing, Native art, lifestyle image, totem pole. The hallmark of Western Red Cedar, it's natural durability, has preserved examples of this lifestyle for hundreds of years.
Natural Durability: Western Red Cedar is one of the few wood species that are naturally at home in the outdoors. It is classified as a durable wood by the building codes across North America, which permits the use of its heartwood in exterior applications without preservative treatments. The heartwood contains extractives that are toxic to decay causing fungi. The two principal extractives that are responsible for the decay resistance are Thujaplicans and water soluble phenolics. The tree’s ability to produce these extractives increases with age making the outer regions of heartwood the most durable.
Growth and Harvest Regions: Western Red Cedar grows on the western edge of the coastal mountains from southern Alaska to northern California. The principal supplying region is the coastal forest region of British Columbia. Cedar grows in mixed forests with other species such as Douglas Fir, Pacific Coast Hemlock, Balsam Fir and Sitka Spruce. Forestry practices are guided by the internationally recognized sustainable forest management system elements of ISO 14001 as part of the CSA Z809 Canadian national standard. These high standards of sustainable forestry are audited by third party inspection agencies to insure compliance with the certification standards. Forest management plans control harvest levels and require reforestation to enhance natural regeneration and insure regional biodiversity.
Durability Classification: The study of durability is a test of resistance to decay brought on by wood destroying fungi which, given the right conditions, establishes itself in wood. Actual test methods vary, however, in each test the samples are exposed to conditions conducive to the growth of various wood destroying fungi. The decay is measured by the weight loss over time. Weight loss is directly correlated to loss of strength and, therefore, durability. It is important to note that all studies of durability of wood focus on heartwood. In general, sapwood, regardless of species has a low resistance to decay.
Thermal Insulating Properties: Western Red Cedar is an excellent thermal insulator. The low density and presence of air spaces make it the best insulator of any available softwood. Its thermal conductivity factor K is 0.74 BTU in / ft2 h F and its R-value is 1.35 per inch of thickness. These exceptional thermal insulating properties protect a building from the extremes of heat and cold. Cedar sidings provide far superior thermal protection to alternatives such as concrete, brick and stone.
Acoustic Properties: The open cell structure of Western Red Cedar has demonstrated an ability to absorb and dissipate sound energy. The cell structure converts the sound energy into heat by friction and viscoelastic resistance. The use of cedar for walls and ceilings provides a level of sound insulation that will make rooms a little quieter.
Flame Spread and Smoke Development Ratings: Western Red Cedar has flame spread and smoke development classifications that are superior to the minimums set by the building codes. These ratings permits cedar to be used in many interior applications without treatment. The surface burning characteristics are used to regulate and control the rate of flame spread in case of fire. Lower ratings indicate more resistance to the spread of fire. The rating for Western Red Cedar has a class II rating of 69. This compares to Canadian and American code requirements of 150 and 200 respectively. The smoke development classification for Western Red Cedar is 98 which less than the code specifications of 300 and 450 for Canada and the US respectively. Further information on this topic is available from the Western Wood Products Association.
Workability: Western Red Cedar has a fine, straight grain and uniform texture that make it easy to cut, saw and nail with common tools. These features also contribute to its ability to be planed to a smooth surface or machined to any pattern. Cedar is highly resistant to splitting caused by fasteners. It is suggested that screws be lengthened approximately 1/3 when specified for use with Cedar. Cedar’s freedom from pitch and resin make it an excellent base for all types of paints and stains.
Gluing Properties: The lack of pitch and resin allows Western Red Cedar to hold glue bonds from a wide range of adhesives. Finger-jointed siding is an excellent example of the application of this feature to create a highly desirable product.
Extractive Bleeding: Western Red Cedar contains water soluble extractives that contribute to its color, durability and aroma. The presence of moisture on exterior surfaces can bring these extractives to the surface and leave a reddish brown stain after the water has evaporated. The stains can be removed with detergent and water when they are first on the surface however they can be more difficult to remove after exposure to the sun. Controlling the extractive bleeding process is a matter of moisture control. When primers are required prior to the application of a solid color coating, an alkyd oil primer is recommended because of its superior ability to block out moisture. This will limit the potential for extractive stains to appear on the coated surface. Removal of mature extractive bleeding stains is accomplished with an oxalic acid solution. Oxalic acid is available at most paint and hardware stores.
Iron Stains: The extractives in Cedar are also prone to staining when they are in contact with iron. The most common source of iron is the fasteners. The stain is a reaction to the water soluble polyphenols resulting in a blue-black blot or streak that follows the moisture pattern in the area of the iron source. Care must be taken not to use wire brushes to clean Cedar or to allow iron filings from other work projects to come into contact with Cedar. The use of common steel or electroplated fasteners will lead to staining. The solution to iron staining is to select fasteners made from stainless steel, aluminum or double hot dipped galvanized steel. Stainless steel fasteners are best and recommended for deck and siding applications where the fasteners are highly visible
Termite Resistance: The death rate of termites consuming Western Red Cedar varies with fiber source and the species of termites from 100% in several days to 40% in several weeks. Termites prefer food sources other than Western Red Cedar, however in the absence of alternative food sources, some termites will attack Western Red Cedar. It is best to consult local experts on their experience with Cedar’s resistance to the species of termite that inhabits the region. In the absence of local knowledge it is recommended that preventative treatments be made to insure consistent resistance to attack in areas that are prone termite attacks.
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