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Properties Of Western Red Cedar
Density - (at 12% mc): 368kg per m3 (21 lbs per ft3)
Western Red Cedar is one of the lightest softwoods commercially available.
Specific Gravity- (at 12% mc): 0.34
Western Red Cedar is an excellent dampener of sound transmission.
Western Red Cedar has a coefficient of thermal conductivity (k value) at 12% moisture content of 0.74 BTU inch/ft2h degrees F. The R value, (the reciprocal of k) for Western Red Cedar is R1.34 per 25mm of thickness.
This equates to an R1 for 18mm thick cladding.
Under the Australian durability ratings, Western Red Cedar is rated as Class 2 for both in ground and above ground applications.
Flame Spread and Smoke Development - more >>
NOTE: Consideration of the Flame Spread and Smoke Development properties for timber products is normally not required for single unit residential buildings - however, we recommend checking all compliance requirements with applicable code authorities and local fire departments.
The Flame Spread Rating for Western Red Cedar is 69 (class II rating)
The Smoke Developed Classification for Western Red Cedar is 98. 98 k value (12% mc): 0.74 BTU in/ sq. ft. h F
Western Red Cedar has a very low shrinkage factor and offers superiority in resistance to warping, twisting and checking.
Workability – more >>
Western Red Cedar is easy to cut, saw, nail and glue.
Fasteners should be corrosive resistant and preferably non-ferrous.
Paints, stains, varnishes, oils and waxes all work well.
Although cedar is a naturally durable species, leaving it untreated is not recommended because a finish or protective coating will greatly increase its service life.
Cedar is free of pitch and with its high degree of dimensional stability, it is the best of the softwoods for accepting paints, stains, oils and other coatings.
Acoustic Properties
An important acoustic property of wood is its ability to damp vibrations. Wood has a cellular network of minute interlocking pores which converts sound energy into heat by frictional and viscoelastic resistance.
Because of the high internal friction created by the cellular pore network, wood has more sound damping capacity than most structural materials. Floor, ceiling and wall assemblies of wood can provide effective economical sound insulation and absorption when properly utilized.
Western Red Cedar is particularly effective in this regard and can be used to help reduce noise or to confine it to certain areas. It is an excellent dampener of sound transmission.
Wood is an excellent thermal insulator. This is an important characteristic since good thermal insulators help keep buildings cool in the summer and reduce heating costs in the winter.
The conduction of heat in wood is directly related to its density. Woods with low density have the highest thermal insulating value because such woods contain a high proportion of cell cavities. In dry wood, these cavities are filled with air which is one of the best known thermal insulators.
With its low density and high proportion of air spaces, Western Red Cedar is the best thermal insulator among the commonly available softwood species and is far superior to brick, concrete and steel. It has a coefficient of thermal conductivity (k value) at 12% mc of 0.74 BTU inch/ft2h degrees F. The R value (the reciprocal of k) for Western Red Cedar is 34mm of thickness.
Cedar's low density enhances its insulation value.
Thermal insulation depends on the ability of timber to trap air pockets in its cellular structure. Woods with a low density have the highest thermal insulating value. Western Red Cedar with a density of approximately 368kg/m3 is one of the lightest commercial timbers thereby giving it the best thermal insulating rating of most timbers and exceeds most other common building materials.
Durability
The natural durability rating of a timber species is a rating of the timber's resistance to attack by wood destroying fungi and wood destroying insects. The sapwood of all timber species has poor resistance and so the natural durability rating applies only to the heartwood of a timber species. The rating is based on the testing of stakes and poles embedded in the ground and on expert opinion of historical performance. There are 2 sets of ratings: one for above ground use and one for in-ground contact use. The lower the number the higher the performance in terms of durability. This information is useful for specifying material for external or exposed applications.
Western Red Cedar is rated as Class 2 under the Australian durability ratings. That is, the timber has a high natural resistance to decay and termite attack. Timbers of this rating are most suitable for use in exposed, aggressive environments.
The long-term performance of timber in an external environment is primarily a function of dimensional stability and resistance to decay of the timber.
All woods absorb or discharge moisture to attain equilibrium with the surrounding atmosphere. This activity is responsible for the seasonal movement of timber. Western Red Cedar however, has a very low shrinkage factor and therefore resists the forces that create warping, twisting and checking.
Historically, native peoples of the Pacific coast prized cedar for its long lasting qualities and used wood and bark from cedar trees for most of their building needs. Evidence of cedar's durability are the many cedar artifacts still in good condition today.
Properly finished and maintained, cedar will deliver decades of trouble-free service. If exposed for prolonged periods to conditions where decay could be a factor, such as where the wood is in contact with the ground, cedar should be treated with suitable wood preservatives.
Flame Spread and Smoke Development Ratings
Flame spreading ratings describe the surface burning characteristics of interior finishes. They are used to regulate the use of interior finish materials to reduce the probability of rapid fire spread. Materials are burned in a test furnace for a relative assessment of flammability. The lower the flame spread rating, the more the material resists the spread of fire.
Building codes in North America generally define as interior finish any exposed material that forms part of the building interior. This usually includes interior wall and ceiling finishes, flooring, windows, doors and other wood products. US codes set the maximum flame spread rating for interior wall and ceiling finishes in most buildings at 200. The flame spread rating for Western Red Cedar is 69 (Class II rating).
Smoke developed classifications reflect the amount of smoke released by burning material. They are used in conjunction with flame spread ratings to regulate the use of interior finish materials where the potential to generate smoke or control smoke movement is of major fire safety importance.
US codes set the maximum smoke developed classification for interior wall and ceiling finishes in most buildings at 450. The smoke developed classification for Western Red Cedar is 98.
Western Red Cedar's flame spread rating and smoke developed classification compare well with the ratings of many other species of both softwood and hardwood. Because of its favorable performance, Western Red Cedar can be used for interior finish in some building applications where other species would not be permitted.
In relation to fire hazards, North American codes set the maximum flame spread rating for interior wall and ceiling finishes in most buildings at 200. The flame spread rating for Western Red Cedar is 69 (Class II rating). The codes set the maximum smoke developed rating for interior wall and ceiling finishes in most buildings at 450. The smoke developed rating for Western Red Cedar is 98.
Dimensional Stability
Like all woods, Western Red Cedar is hygroscopic and will absorb or discharge moisture to attain equilibrium with the surrounding atmosphere. However, it has a very low shrinkage factor and is superior to all other coniferous woods in its resistance to warping, twisting and checking.
Shrinkage of Western Red Cedar
Radial shrinkage applies to the width of vertical grain (quarter sawn) timber.
Tangential to the width of flat grain (back sawn) timber.
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Direction of Shrinkage
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Shrinkage in Percentage
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From green (25% or greater moisture content) to:
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From kiln dried (15% average moisture content) to:
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15%
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12%
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6%
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15%
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12%
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6%
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Radial
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0.96
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1.2
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1.8
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0
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0.3
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1.0
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Tangential
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2.0
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2.6
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3.8
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0
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0.7
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2.1
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Western Red Cedar is rated amongst the highest of softwood species for stability.
Workability
With its straight grain and uniform texture, Western Red Cedar is among the easiest and most rewarding woods to work with. It takes a fine finish in all hand and machine operations, takes fasteners without splitting and is easily sawn and nailed. When working with Western Red Cedar, sharp cutters are recommended. It is easy to cut, saw, nail and glue.
Fixings
Fixings and fasteners should be corrosive resistant and preferably non-ferrous.
Stainless steel, aluminium, brass, silicone bronze are preferred, with hot-dipped galvanised, or electroplated acceptable.
Western Red Cedar has good fastening properties but its natural preservatives have a corrosive effect on some unprotected metals in close contact, causing as well, a black stain on the wood.
Nails and screws used to fasten Western Red Cedar should be about one-third longer than those used to fasten hardwood species.
Because it is free of pitch and resin, Western Red Cedar has excellent gluing properties. It works well with a wide range of adhesives.
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