Treated Wood Transition Henry Walthert Executive Director Canadian Institute of Treated Wood The pressure treated wood market in Canada will have a different face in 2004. New preservatives to treat wood first introduced in early 2002 will become the mainstay of the industry in the coming year. ACQ (amine copper quat) and CA (copper azole) will replace the traditional CCA (chromated copper arsenate) in the treatment of pressure treated wood products destined for residential applications. CCA will continue to be used to treat wood for industrial, commercial and agricultural uses. In addition, existing inventories of CCA treated wood produced before January 1, 2004 can be sold into the residential market until exhausted.     The Pest Management Regulatory Agency, Health Canada announced in March 2002 that the manufacturers of CCA had requested a change to their pesticide registration in order to eliminate treatment with this product for the residential market. This would facilitate the introduction of new preservatives. Effective date for the change is January 1, 2004. The transition requires pressure treating plants across Canada to complete the retooling of existing or the installation of new processing equipment by December 31, 2003. This conversion began immediately after the announcement. A few plants converted and introduced the new products to the retail marketplace during the summer of 2002. Volumes increased throughout 2003 as many retailers chose to introduce these products to their customers before the deadline. Wood products treated with the new preservatives are similar in appearance with the familiar green colour. Left to the elements treated wood will weather to a honey brown colour and eventually silver gray. Recommendations for the safe use and handling of wood treated with the new preservatives are identical to those first recommended for CCA. The transition is nearing completion as most treating plants have now converted and are actively producing treated products for the 2004 market. The Canadian Standards Association A366 Technical Committee is currently developing product standards for this application to be introduced in 2004. Purchasers of treated wood can check for labels or ask their retailer to determine the type of preservative used. The transition in the United States has followed a similar pattern since the original announcement by the U.S. Environmental Protection Agency in February 2002. The American Wood-Preservers' Association has established standards for the new preservatives and treaters across the country have converted their plants. Retail chains have been selling the new products since early 2002. The deadline for the transition is identical to Canada December 31, 2003. For more information on the treated wood transition, please contact The Canadian Institute of Treated Wood (CITW) at (613) 737-4337 or by e-mail to citw@citw.org. Insulation and Ventilation of Wood-Frame Roof Assemblies Part 1 - Moisture Control and Climate Types Michael Steffen Ventilation of insulated roof assemblies has become standard practice in the design and construction of wood-frame buildings throughout North America. These practices have developed as much from myths and misunderstanding as they have from documented and validated research. Regulations and codes concerning ventilation have been based on general assumptions regarding insulation type and climate that often do not account for the specifics of a building뭩 design or location. Historically, wood roof assemblies were open to heat and moisture flow so durability problems related to moisture were rare. With increased levels of insulation, the wetting potential from condensation is greater, while drying potential has been reduced from loss of heat flow and increased use of vapor impermeable materials. Current Code Requirements Building codes generally require that the minimum net free ventilating area for attic vents be a 1/150 ratio of the area of the attic space being ventilated. The codes also generally allow the ratio to be reduced to 1/300 if the venting is 밷alanced,?and a vapor retarder of 1 perm or less is installed on the warm 밹eiling?side of the insulation. Balanced ventilation means that 50% of the ventilation is provided low on the roof, while the other 50% is placed high. These requirements, however, have been developed and enforced largely without regard to: climatic differences, roof configuration, cathedral ceilings vs. open attics, and differences in the properties of materials used in roof assemblies. Outside of code requirements, many feel that ventilation can help control roof temperatures to 1) extend the service life of asphalt shingles and 2) reduce cooling loads in warm seasons. TenWolde and Rose [1999] conclude that shingle color, not venting, likely has greater effect on shingle durability. They also found that the quantity of attic insulation and location of ducts are most important to lowering attic temperatures. Ventilation is also seen as a strategy to prevent or minimize the occurrence of ice dams. Moisture Control for Roof Assemblies The key to moisture control is establishing a balance between wetting and drying. Design and construction must minimize the potential for wetting and maximize the potential for drying. Climate is another important factor because moisture control strategies that work in one climate do not necessarily work in another. In fact, ventilation is not necessary in all climates, and in some climates may actually lead to moisture and durability problems. For example, venting a roof in warm, humid climates tends to increase rather than decrease the moisture level in a roof space. From a performance standpoint, moisture control is important for preventing mold growth as well as physical deterioration of framing components within roof assemblies. In roofs with cavity insulation, mold growth can occur at the underside of roof sheathing in cold, heating climates, or on a ceiling-side vapor retarder in warm, humid, cooling climates. If moisture levels are excessive, deterioration of the sheathing can occur, particularly in cold climates. Moisture control for roof assemblies in all climates should begin at the 뱒upply?side, using the primary strategies of: 1) interior humidity control, 2) air leakage control and 3) vapor diffusion control. Michael Steffen is a registered architect and Quality Director at Walsh Construction Company in Portland, Oregon. Part 2 of this article will discuss supply side moisture control, climate-specific controls and roof configurations. A longer version of this article is found in the Spring 2002 issue, Number 19 of Wood Design & Building. For more information visit www.woodmags.com, click on the Wood Design & Building logo, and then MagRack.

Seismic Redundancy Factor in WoodWorks USA Shearwalls 2004 The November edition of Wood-in-Sited listed new features of WoodWorks USA Design Office 2004. These new features are also described on the WoodWorks Software website. One of the new features, calculation of seismic redundancy factor, is described in more detail below. WoodWorks Shearwalls 2004 calculates seismic reliability factor, . The seismic reliability factor takes into account structural redundancy in the lateral force resisting system, and is used to modify any forces induced by horizontal earthquake loads as described in Section 9.5.2.4, pp 128-9 of ASCE-7 and Section 1630.1.1, p 2-13 of the UBC. In general, this factor applies to buildings that are much longer than they are wide, or have very short shear resisting elements along the shearlines. Applicable Seismic Zones The application of this factor is restricted to UBC Seismic Zones 3 and 4, and ASCE-7 Seismic Design Categories D, E, and F. Shearwalls implements these restrictions. Most heavily loaded element The calculation of involves the shear applied to the most heavily loaded element on a story. Shearwalls considers an 밻lement?to be a full height sheathing segment between openings. Maximum Element-to-Storey Shear Ratio rmaxx or ri This is the ratio of the design storey shear resisted by the most heavily loaded single element, to the total design storey shear. For shearwalls, the ratio is modified so that concentrations of load in short segments result in a higher ratio. Where: c1=10.0 (feet) or 3.3(metres) lw = the length of the element. Calculation of According to UBC 1630.1.1, pg. 2-13 and ASCE-7 9.5.2.4.2 , pg. 128 where c2 = 20 (feet) or 6.1 (metres) and A = floor area. Limits for Shearwalls implements the limitations of the value in both codes to between 1.0 and 1.5. Structure Shearwalls implements the following methods: ASCE-7 method determines a maximum and floor area A for each floor to determine a for that floor, then takes the maximum for all floors. UBC method determines the greatest for all floors at or less than 2/3 building height, and uses it and the base floor area A determine the for the structure. Design cases A separate calculation is performed for each direction of earthquake force, and for each of rigid and flexible distribution. Sequence of operations The program calculates on each storey for the flexible diaphragm method, then calculates a structure for the flexible method. It then redistributes the flexible forces to the shearlines with this value, designs the flexible method walls, and uses their capacity as relative rigidities for the rigid method. It then calculates for the rigid method, applies this value to the rigid shearline forces, and designs the shearwalls for the rigid method. This procedure relies on the fact that for the flexible method, the value of will not effect the relative distribution of forces to the shearlines, but it does for the rigid method. Display The program displays loads unfactored by and shearline forces factored by . It displays a line on the screen in which is indicates the value in the earthquake load combination. Design results The program outputs a new Seismic Information table that lists Building Mass, Floor Area, as well as Story Shear, Shear Ratio rmax and Reliability factor, in each direction, for each story and for the structure. It displays separate tables for rigid design and for flexible design.