Dimensional Stability Test reports from Certified Kiln Dried the USDA Forest Products Laboratory show that redwood has less volumetric Siding Patterns and and tangential shrinkage than any other domestic softwood. This means that The CRA trademark is on products of Applications redwood siding will lay flat and straight member mills of the California Redwood throughout the life of the structure with Association only and is an additional minimal warping, cupping, checking and Redwood is synonymous with quality assurance of quality. nail popping. With tighter joints, redwood architecture. No other siding material Redwood grades are established by the provides better siding performance adds value to a home or commercial Redwood Inspection Service in the than other woods. building like redwood. The value of Standard Specifications for Grades of redwood’s beauty is immediately appar- Finish Retention California Redwood Lumber. Properly ent and the value of its long-lasting Redwood has an open cellular structure grademarked lumber will bear the RIS performance is appreciated for decades. and contains relatively little pitch or mark. The RIS is the exclusive rules- Architects and builders specify redwood resins. This enables redwood to absorb writing agency for redwood lumber. with confidence, knowing that exceptional and retain all types of finishes better than Quality redwood siding is available in performance is grown into every board most other woods. As a result, projects the architectural grades: Clear All Heart, and that redwood will add value and look better over a longer period of time. Clear, Heart B and B Grade. sales appeal to their projects. Protective finishes last longer and work better. Refinishing is required less often. Clear All Heart is a superior grade for Redwood’s Total Performance fine sidings and architectural uses. It is Redwood’s performance characteristics Resistance to Decay and Insects all heartwood and the graded face of are unique among American softwoods. Redwood heartwood has grown-in each piece is free of knots. resistance to decay and insects that is Its superior stability is especially suited to Clear is similar in quality to Clear All present throughout the lumber, not just the demands of siding applications. Its Heart, except that it includes sapwood on the surface. Wood exposed through finish retention, weatherability, flame in varying amounts. Some boards may sawing, boring or nailing is as decay- resistance and insulation properties have one or two small, tight knots on resistant as the surface. make it ideal for virtually any project and the graded face. even the most extreme climate. Heart B is an economical all-heartwood grade containing a limited number of tight knots and characteristics not permitted in Clear or Clear All Heart. It is graded on one face and one edge. B Grade is an economical grade con- taining a limited number of tight knots with sapwood accenting the heartwood. Specifying Redwood Siding Specifying To ensure delivery of the proper siding Application product, the specifications should Storage & Handling include: use, grade, grain, seasoning, General Application Information pattern description and number, and Careful attention to construction detailing surface texture. Grain is necessary to prevent moisture pene- Redwood lumber has either flat or vertical For Example tration into the siding and the wall cavity. grain. Siding Is considered vertical grain Redwood lumber for 1exterior siding shall Flashing over window and door headers when the annual growth rings form an be CRA-RIS grademarked redwood, and at other horizontal siding breaks angle of 45 degrees or more with the 2Heart B grade, 3mixed grain. 4Certified should be sufficiently sized, well placed, surface of the siding. If the angle is less Kiln Dried, 51x8 channel V shiplap, tightly anchored and sealed with caulk- than 45 degrees, the siding is known 6pattern 785R, 7saw-textured face to ing. Thorough caulking of all joints with a as flat grain. Vertical grain siding pos- be exposed. non-hardening compound is important, particularly at the butt joints of short sesses enhanced dimensional stability 1Use 5Pattern and will hold paints and finishes better 2 6 length siding laid vertically. High per- Grade Pattern Number formance caulks such as polyurethane, than flat grain. 3Grain 7Texture 4 polysulfide or acrylic latex are recom- Vertical Grain Flat Grain Seasoning mended for best results. In addition, the Installation section of the The lowest edge of siding should be at specification should specify: non-corro- least 6 inches off the ground to prevent sive fastener materials, type and size; moisture problems. It is particularly bearing and fastener spacing require- important that end grain at the bottom ments; water repellent application as ap- Annual rings Bark side Pith side of vertical siding be coated with water propriate, and field priming of cut edges. repellent. The use of a drip cap at the Seasoning lower edge of the siding is recommended. Clear All Heart, Clear, Heart B and B Storage and Handling Grade sidings are available Certified Kiln Redwood siding and trim are quality A water repellent building paper, with a Dried for applications requiring minimal finish products and should be handled permeability rating of at least 5 perms, shrinkage and top performance. with care. At the job site, redwood siding should be applied over sheathing. This will Redwood kiln dried to accepted stan- should be kept completely under cover help reduce water and wind penetration. and off the ground. Water-proof cover- dards will include the words “Certified Note: There have been reports of prob- Kiln Dried” or the initials “CKD” in the ings should allow air to circulate between the covering and the siding. Keeping the lems arising from the combination of grademark on each piece or package of wood siding and rigid plastic foam siding or be so specified on the invoice. siding clean and dry will help to eliminate the possibility of finish problems. For sheathings. CRA advises caution. Patterns protection, redwood siding is now avail- Request Redwood Technical Data Sheet Standard redwood siding patterns able wrapped in moisture-proof paper at Using Redwood Siding Over Rigid include: bevel, rabbeted bevel, tongue the sawmill and it should not be un- Foam Sheathing. and groove, shiplap, channel shiplap and wrapped until installation begins. V shiplap. Board and batten siding is laid up using standard size boards. Priming It is recommended that a water repellent Pattern Numbers containing mildewcide be applied to all Each siding pattern has a pattern num- surfaces of redwood siding before ber. To ensure delivery of the proper construction begins. This will inhibit the product, the pattern number should be movement of moisture as well as mildew included on specifications and invoices. growth, two conditions which can Pattern details are given in CRA’s severely damage a finish coating. When Architectural Guide and Redwood a clear, bleached or semitransparent Pattern Book. finish is to be applied later, a preliminary coat of water repellent will protect Textures against weathering and construction Surfaced sidings have a smooth, planed staining prior to final finishing. For best face, emphasizing the wood’s grain performance, special care should be and color. given to end grain; cut ends should be Saw-textured sidings have resawn faces coated before installation. Redwood providing a rough textured appearance siding should always be back-primed. that holds finishes extremely well. Factory priming or pre-finishing is highly recommended. Measuring and Cutting Preventing Moisture Problems causes of structural and finish failures. It All butt joints must occur over a stud or moves as invisible moisture vapor from solid blocking. Be sure that siding fits the warm interior of the house toward the snugly against corner strips and trim. Stop cold exterior. Vapor travels through Mitered corners, sometimes used with Moisture plaster, insulation and wood and may Stop Moisture Vapor From thicker patterns, should be cut in a miter From Outside Inside condense into water as it approaches the box. Plain bevel siding requires a com- colder exterior surfaces of the sidewall. Siding Wallboard pound miter. Predrill nail holes for all Finished This can sometimes result in structural ends, especially mitered ends. On All damage as well as siding cupping and Surfaces Vapor Barrier nail popping. Water entering the siding Using bevel cuts at a 45° angle (see illustration) can minimize the appearance can also cause finishes to blister, peel Insulation and discolor. of gaps if end shrinkage does occur. Vapor barriers are necessary to prevent Bevel Cut Siding Sheathing migration of moisture vapor. They must Building be applied to the warm side of the stud Paper wall, directly under the finish material. There are several types; the most fre- Sheathing quently used are either plastic or alu- Stud minum sheet material with a rating of one perm or less. Those sheets should overlap at least 2 inches at their edges. Do not reduce CRA lap recommenda- Ordinary building felt is not a vapor barrier. tions as this can result in damage from Proper interior and exterior wall construction When residing an existing house without wind-driven water. Carefully observe prevents moisture problems. Building paper a vapor barrier, an effective solution can should have a permeability rating of 5 perms, expansion clearance requirements for the vapor barrier, a maximum of 1 perm. be to paint the inner side of the exterior the siding pattern selected. walls with a vapor barrier paint. Nailing Attic areas should be adequately vented Nailing recommendations refer to nailing Moisture is the largest cause of siding to prevent vapor from condensing on siding to every stud or (for vertical cours- and finish problems. Most problems can cold surfaces or penetrating through the ing) each 2x4 blocking line, at not more be avoided if precautions are taken ceiling. Critical sources of humidity, such than 24 inches on center.