TECHNICAL GUIDE Natural Selection, Installation & Finishing

Western Wood Products Association Contents Natural Wood Siding:

Grades ...... 2 Selection, Installation & Finishing Pattern Selection ...... 3 Moisture Content ...... 3 Checklist for a Natural Wood Siding Siding products are generally categorized as either premium or Siding Specification ...... 4 Solid wood has long been used knotty grades. as a siding material. Its natural Priming and Prefinishing ...... 5 Premium grades have fewer beauty is timeless and the color Installation ...... 5 characteristics such as knots, and textures available are streaks and so forth. The Pattern & Installation (Nailing) unmatched by other building highest designations are reserved Diagrams ...... 6 products. Such properties make for clear wood free of characteris- wood siding adaptable to a wide Nails & Nailing ...... 8 tics. These grades are generally variety of regional preferences, Finishing ...... 9 more expensive and usually sold architectural styles and climates. kiln-dried. Checklist for High When correctly installed and While some B&Btr is available, Performance Siding ...... 11 maintained, natural wood siding Select grades usually include C will last for decades and some- Coverage Calculations ...... 11 and D Select. (Equivalent grade times centuries. It is a prestige designations in Idaho White Additional Information ...... 11 product that adds value to a are Supreme, Choice and Quality.) Western Grade home or commercial building, Western Red Cedar may be Reference Chart . . . . . back cover reflecting both quality materials graded as Selects, or according and professional workmanship. to Cedar Rules where compara- ble grades are Clear Heart, A and Grades B grades. Finish grades include Building codes usually consider Superior and Prime, and can be wood siding a non-structural used for most Western species material and place few restrictions but are seldom used for the on its use. In addition, model cedars and . Additional codes do not require that it be grades for patterns are gradestamped. shown in Table 1. Specify exact However, all Western species grade desired, by grade rule book used for siding are listed under at and paragraph number. least one industry-recognized Knotty grades such as grade rule published by an Common, Alternate Board, Select American Lumber Standard Knotty and Quality Knotty are Committee, Inc. accredited rules- more abundant as they include writing agency, such as Western material with knots and other Wood Products Association characteristics. (WWPA). Knot size and quality are Western species of the United defined in the grading rules. States include Douglas and Sound, tight knots will not , Hemlock and the True , adversely affect the performance Ponderosa Pine, Lodgepole Pine, of the siding. However, encased Idaho White Pine, Sugar Pine, or unsound knots can become Engelmann , Sitka Spruce, loose and may eventually fall out. White Spruce and the Western WWPA knotty grades include 1, Cedars. 2 and 3 Common. (Equivalent Cedar’s weather resistance and grades in Idaho White Pine are dimensional stability make it Colonial, Sterling and Standard.) EADERSHIP. SERVICE. VALUE. particularly well suited to siding These grades are generally refer- L applications, with the added enced as 2&Btr Common and Western Wood Products Association benefit that cedar’s heartwood is 3&Btr Common for most Western 522 SW Fifth Avenue, Suite 500 naturally durable against decay. species. (Refer to notes under Portland, OR 97204-2122 Clear Heart and Clear VG Heart Table 1 for additional information.) grading rules include the heart The WCLIB knotty grades for 503-224-3930 designation. If heartwood is Alternate Boards are Select fax: 503-224-3934 desired in other grades, and Merchantable, and e-mail: [email protected] sapwood to be limited, then it Standard. Similar knotty grades website: www.wwpa.org must be so specified through for cedar siding are Select Knotty ©2002 WWPA buyer/seller agreement. and Quality Knotty. 2 When selecting knotty siding in combination of Select Knotty and Patterns not only allow for any species, specify the exact Quality Knotty, with a percentage different effects in design and grade or paragraph number of of the order in Quality Knotty. appearance but also affect perfor- the grade rule book from an mance. Patterns like tongued- ALSC-accredited agency. Pattern Selection and-grooved, which are primarily (Paragraph numbers are included paneling patterns, should only be Boards in standard dimensions in Table 1.) installed in exterior applications can be readily used for such Some manufacturers market where the greatest degree of pro- siding applications as board-and- their siding under a variety of tection from climatic conditions or board-on-board. names such as STK (select tight can be provided. Tongued-and- However, most siding products knot or sound tight knot) or NPS grooved patterns allow for very lit- are milled or run to a pattern. (no prior selection). These names tle dimensional change as the Standard patterns are published are helpful but it is important to siding acclimates to the environ- by the rules-writing agencies to understand that these are ment, or as a result of seasonal encourage uniformity and to serve marketing terms and not grade dimensional adjustments. as a common reference through- designations from grading Climate, humidity levels, architec- out the industry. The popular pat- agencies. tural detailing and exposure to terns are bevel or bungalow, Dolly There are no uniform standards prevailing weather conditions Varden and channel. (Refer to for STK, NPS, etc. Consequently should all be considered when Figure 3 for profiles of these and the products so-named may vary selecting a pattern. other patterns. WWPA’s Standard in quality from one source to As a rule of thumb, narrow Patterns can be downloaded another. STK cedar may be a patterns perform best because from www.wwpa.org.) there is less dimensional change in the siding as the environment changes from wet to dry, or from Table 1: GRADES the freezing conditions of winter General to the blistering heat of late sum- GRADES7 Categories Grade Rule Paragraph mer. Thicker patterns have less (Note that there WESTERN SPECIES CEDAR Numbers for are additional Reference & Specifying tendency to cup or split than do grades for bevel Western & pattern.) Selects1 Finish Canadian WWPA2 WCLIB3 NLGA4 thinner patterns. Siding surfaces are manufac- Clear Heart5 20.11 102-b 200a tured smooth, rough, or - A Grade5 20.12 102-c 200b C Select5 10.12 – – textured. The type of surface and Superior 10.51 – – pattern, in combination with the D Select5 10.13 – – finishing material, will affect

All Patterns Prime 10.52 – –

Premium Grades B Grade 20.13 102-d 200c performance. In general, saw- textured surfaces hold finishes Clear VG Heart5 21.11 106-aa 201a A Bevel5 21.12 106-a 201b longer than smooth surfaces. Superior Bevel 16.11 – – B Bevel 21.13 106-b 201c Moisture Content

Premium Rustic – – 201d C Bevel 21.14 106-c 201e As wood loses or gains moisture, it will shrink or swell Bevel Patterns Prime Bevel 16.12 – – until it reaches equilibrium with Additional Grades for Select Knotty6 ––205a

Knotty Quality Knotty6 ––205b the level of moisture in the air of its immediate surroundings. Commons1 Alternate Because of its cell structure, Boards wood shrinks primarily in thick- 2 Common Select Merch. – 30.12 118-a 114a ness and width and very little in Construction Select Knotty6 –111-e 204a 3 Common 30.13 118-b8 114b8 length. All Patterns Knotty Grades Standard Quality Knotty6 – 111-f 204b Wood siding is no exception. It 118-c9 114c9 will shrink and swell regardless

1 Equivalent grades, under the same paragraph numbers in WWPA Rules, are available in Idaho White Pine. Refer to of pattern or material quality. Western Lumber Grading Rules. Problems can occur after instal- 2 Western Wood Products Association’s Western Lumber Grading Rules. lation if the siding shrinks or 3 West Coast Lumber Inspection Bureau’s Standard Grading Rules for West Coast Lumber. 4 National Lumber Grades Authority’s Standard Grading Rules for Canadian Lumber. swells unevenly or very rapidly, 5 Some clear grades may be specified VG (vertical grain). Common practice is to ship orders as a combination of verti- particularly if it has been improp- cal and flat grain, unless specified otherwise. 6 The widely used marketing term, “STK” usually describes a combination of Select Knotty and Quality Knotty, some- erly nailed and its natural move- times marketed with approximately 15% of the order in Quality Knotty. ment has been restricted. 7 The grades listed in these three columns are arranged in order of highest to lowest appearance quality; Clear Heart However, problems such as twist, is the highest, and Standard and Quality Knotty are the lowest grades in this table. 8 Construction grade paragraph reference number. cup, warp, splits and checks can 9 Standard grade paragraph reference number. be minimized. The grade names in bold face type are the most widely available grades. These are often specified as a To avoid potential problems and grade combination that includes some portion of material in the next higher grade; i.e. C&BTR Select, D&BTR Select, to minimize dimensional change A&BTR Cedar, 2&BTR Common, 3&BTR Common or STAND&BTR (Standard & Better). 3 after installation, the moisture kiln-dried so that it will not exceed (spacers between the layers) in an content of the siding should 19% moisture content. Thus, area where there will be good air match the local climate as closely dry knotty siding will have a flow through the stack. This should as possible at the time of moisture content of 19% or less be done in an open garage or installation. and may be gradestamped other area that is protected from For instance, if the climate in a ‘‘S-DRY’’ or “KD”. However, knotty the elements. particular region causes wood to grades can be specified MC 15 or If stacked over concrete, use maintain 9% to 14% moisture KD 15, and are available through 2x4s or 2x6s on edge to elevate content, then the moisture con- a buyer/seller agreement, when a the first course of siding at least tent of the siding should be within maximum moisture content of 3¹⁄₂ inches above the surface of the that range when installed. 15% is desired. concrete. If the stack is over wet Siding can be dried at the time Method of Drying — Lumber ground or wet concrete, lay down of manufacturing to a variety of may be air dried or kiln dried. a vapor barrier so the wood moisture content levels or it can These terms do not necessarily doesn’t pick up moisture from be shipped from the mill un- refer to a specific moisture beneath the stack. seasoned or green. content but refer instead to the Allow air to flow through and Unseasoned or green wood method used for drying. Air- around the stack for a week to 10 has a moisture content of more dried lumber has been seasoned days for dry siding, prior to installa- than 19%. by exposure to the atmosphere, tion. Extend the time period to 30 Dry wood will be at a without artificial heat. Kiln-dried days or longer, for unseasoned maximum moisture content of lumber has been seasoned in a siding or if acclimating in excep- 19% or 15%. chamber with the use of artificial tionally humid conditions. Dry siding will take less time to heat. To assure compliance with a Further precautions must be acclimate to the air of its final moisture content level, a moisture taken if unseasoned or green surroundings (refer to Table 2) percentage should always be materials, with a moisture content and it will have less dimensional referenced. of more than 19%, are to be used change, before and after instal- Siding Storage — All siding successfully: lation, than unseasoned or green may pick up or lose moisture in 1) Allow materials to acclimate, as siding. transit or storage so it is described, over a longer period When ordering siding, specify important to allow it to acclimate —at least 30 days and longer in the required moisture content with the surrounding air of its final damp or humid conditions— level, but keep in mind the reality site prior to installation. before installation. of the marketplace: premium Stack the siding on evenly 2) Use patterns which allow for grades of siding are readily avail- spaced, vertically aligned stickers some shrinkage, such as bevel, able dry; some knotty grades are channel or board-and-batten. available dry. Remember too, dry These patterns have a profile has a different meaning for that includes a gap that can the premium grades than it does for the knotty grades. Dry for the premium grades Checklist for a Siding means that the siding has been Material Specification dried to a maximum of 15% ■ Select species suited to the moisture content (MC 15). In addi- project. tion, under WWPA rules, MC 15 ■ List grade names, paragraph means that at least 85% of the numbers and rules-writing pieces in the order will be at a agency. (Refer to Table 1.) moisture content of 12% or less. ■ When knotty grades are dried Specify surface texture for Figure 1: at the mill, the siding is air- or exposed face. STACK FOR ACCLIMATIZATION ■ Specify moisture content suited to the project. ■ If gradestamped, specify Table 2: MOISTURE CONTENT GUIDELINES lumber be stamped on back Recommended Moisture Content at Time of Installation or ends. (WWPA’s Lumber Use of Wood Most Areas Dry, Southwestern Damp, Warm South- Specifying offers additional in Exterior of the U.S. States eastern Coastal Areas information.) Individual Individual Individual ■ Specify VG (vertical grain) if Average1 Pieces Average1 Pieces Average1 Pieces Siding, Trim appropriate and available. and Sheathing 12% 9-14% 9% 7-12% 12% 9-14% (Refer to Table 1, footnote 5.) 1To obtain a realistic average, test at least 10% of each item, i.e. 10% of the siding pieces, 10% of ■ Specify pattern and size. the trim pieces and random checks of the sheathing material. It is particularly important to check the (WWPA’s Standard Patterns sheathing prior to the siding application if it has become wet after installation. offers additional information.) Source: Wood Handbook, 1999, from Table 12-2.

4 more easily accommodate rier, on the warm side of the insu- blends, polyurethane and dimensional change. lation, should be used to reduce polysulfide caulks should give 3) Use as narrow a width as moisture movement from inside.) satisfactory performance. possible. Dimensional change When sheathing material or 100% silicone caulks are not is proportional; the wider the sheathing wrap surfaces become recommended. width, the greater the change. wet, allow surfaces to dry before Theoretically, any pattern which the wood siding is nailed into can be installed in either direction, Priming and Prefinishing position. such as channel or tongued-and- Many patterns may be installed grooved, can also be installed Often, material which has been horizontally or vertically. Pattern diagonally. However, diagonal properly seasoned, stored and orientation should restrict the installation tends to channel water handled will pick up moisture after entrance of moisture and weather. directly into jambs, window installation but prior to finishing. Some patterns, such as board- casings or other joinery details on Later, when the siding loses that and-batten, may be installed only a structure. moisture, joints may open up. in a vertical fashion. Others, such If siding is to be installed Research from the U.S. Forest as bungalow, bevel and drop, diagonally, the project must be Products Lab indicates that siding may be installed only horizontally. designed from the outset to exposed to the elements for two Use caulk where siding abuts accommodate the direction of weeks weathers enough to openings or trim. Latex-silicone run-off. reduce the adhesion of film- forming finishes. Priming or prefinishing the Figure 2: siding (all sides, edges and cut CORNER DETAILS ends) after it has reached climatic balance but before it is installed can provide extra e protection and often prevent adhesion problems and/or b d premature finish failure. b Back-priming the siding elimi- b nates the leaching of chemical b a extractives, which have the poten- a tial to degrade sheathing wraps. e Prefinishing is recommended in d all circumstances. Prefinishing will d c minimize objectionable unfinished c lines where joints open up due to face-width shrinkage during a. HORIZONTAL SIDING a. HORIZONTAL SIDING exceptionally dry summers. b. BUILDING b. BUILDING PAPER c. TRIM c. CAULK Make certain the prefinish is d. SHEATHING d. CORNER BOARDS compatible with the final coat. For e. CAULK e. SHEATHING example, clear water repellents Inside Corner Detail-A Outside Corner Detail-A should not be used if a bleaching oil is to be the final finish. (Refer to the section on Finishing.)

Installation a Natural wood siding should be e b installed over a weather-resis- e c tive barrier regardless of the b sheathing material. A weather- b resistive barrier is a vapor-perme- able sheathing wrap that resists any liquid water that gets behind a d d the siding, and acts as a drainage d . There are three basic types c of sheathing wrap: asphalt felt, Grade D building paper and plas- tic housewrap. In order to func- a. HORIZONTAL SIDING a. PROVIDE ADDITIONAL STUD b. BUILDING PAPER TO ALLOW FOR NAILING tion as a drainage plane, a c. FLASHING OR BUILDING PAPER AT ENDS OF SIDING d. USE CAULK AT INSIDE CORNER OR b. BUILDING PAPER sheathing wrap should have an air OPEN JOINT. PROVIDE METAL FLASHING c. CAULK BEHIND JOINT IF CAULK IS NOT USED. d. CORNER BOARDS gap between the wrap and the e. SHEATHING e. SHEATHING siding. (An appropriate vapor bar- Inside Corner Detail-B Outside Corner Detail-B

5 Figure 3: SIDING PATTERNS, NOMINAL SIZES & RECOMMENDED NAILING

Nominal Sizes* Nailing Siding Patterns Thickness & Width 6" and Narrower 8" and Wider

TRIM Board Board Board and and on BOARD-ON-BOARD 1 x 2 Batten Batten Board BOARD-AND-BATTEN 1 x 4 Boards are surfaced 1 x 6 smooth, rough or saw- 1 x 8 textured. Rustic ranch- 1 x 10 style appearance. 1 x 12 Provide horizontal nailing members. Do not 1¹⁄₄ x 6 ¹⁄₂ through overlapping 1¹⁄₄ x 8 " pieces. Vertical 1¹⁄₄ x 10 applications only. 1¹⁄₄ x 12

Recommend ¹⁄₂" overlap. One Increase overlap proportion- siding or box nail per bearing. ately. Use two siding or box nails, 3-4" apart.

BEVEL or BUNGALOW ³⁄₁₆ ³⁄₁₆ Plain Plain Bungalow (“Colonial”) is ¹⁄₂ x 2 slightly thicker than ¹⁄₂ x 4 Bevel. Either can be used ¹⁄₂ x 5 with the smooth or saw- ¹⁄₂ x 6 faced surface exposed. Patterns provide a ⁵⁄₈ x 8 traditional-style appear- ⁵⁄₈ x 10 ance Recommend a 1" overlap. Do not nail ³⁄₄ x 6 through overlapping ³⁄₄ x 8 pieces. Horizontal ³⁄₄ x 10 applications only. Cedar Bevel is also available in ⁷⁄₈ x 10, 12. Recommend 1" overlap. One Recommend 1" overlap. One ¹⁵⁄₃₂ ³⁄₄ siding or box nail per bearing, siding or box nail per bearing, just above the 1" overlap. just above the 1" overlap.

⁵⁄₁₆ ¹³⁄₃₂ DOLLY VARDEN Rabbeted Edge Rabbeted Edge Dolly Varden is thicker Standard than Bevel and has a Dolly Varden rabbeted edge. Surfaced ³⁄₄ x 6 approximate smooth or saw-textured. ³⁄₄ x 8 ¹⁄₈" gap for dry material Provides a traditional- ³⁄₄ x 10 8" and wider style appearance Allows for a ¹⁄₂" overlap, includ- Thick ing an approximate ¹⁄₈" Dolly Varden ¹⁄₂" = full depth gap. Do not nail through 1 x 6 of overlapping pieces. 1 x 8 Horizontal applications 1 x 10 only. Cedar Dolly Varden 1 x 12 is also available in ⁷⁄₈ x Allows for ¹⁄₂" overlap. One Allows for ¹⁄₂" overlap. One 2 10, 12. ¹₃₂ ¹³⁄₃₂ siding or box nail per bearing, siding or box nail per bearing, 1” up from bottom edge. 1” up from bottom edge. (G-16) for scale profiles and actual dimensions of run-to-pattern(G-16) for scale profiles products.

DROP T&G T&G Shiplap Drop siding is available in ³⁄₄ x 6 Patterns Patterns Patterns Patterns 13 patterns, in smooth, ³⁄₄ x 8 rough or saw-textured ³⁄₄ x 10 surfaces. Some are T&G, others shiplapped. Refer Standard Patterns to Standard Patterns (G-16) for dimensional approximate ¹⁄₈" gap for pattern profiles. A variety dry material of looks can be achieved 8" and wider with the different patterns. Do not nail through overlapping pieces. Refer to WWPA’s Refer to WWPA’s Use casing nails to blind nail ¹⁄₂" = full depth Horizontal or vertical T&G patterns, one nail per of rabbet applications. Tongued bearing. Use siding or box nails Use two siding or box nails, edge up in horizontal *Note: to face nail shiplap patterns, 1" 3-4" apart to face nail, 1" up applications up from bottom edge. from bottom edge. 6 Figure 3: SIDING PATTERNS, NOMINAL SIZES & RECOMMENDED NAILING

Nominal Sizes* Nailing Siding Patterns Thickness & Width 6" and Narrower 8" and Wider

Plain TONGUED 1 x 4 Plain & GROOVED 1 x 6 Tongued & Grooved 1 x 8 siding is available in a 1 x 10 variety of patterns. T&G 1 x 12 lends itself to different effects aesthetically. Refer Note: T&G to Standard Patterns (G- patterns may 16) for pattern profiles. be ordered with Sizes given here are for ¹⁄₄, ³⁄₈, or ⁷⁄₁₆" Plain Tongued & Grooved. tongues. For Do not nail through over- wider widths, lapping pieces. Horizontal specify the or vertical applications. longer tongue Tongued edge up in Use one casing nail per Use two siding or box nails and pattern. horizontal applications. bearing to blind nail. 3-4" apart to face nail.

CHANNEL RUSTIC Channel Rustic has a ¹⁄₂" ³⁄₄ x 6 overlap, including an ³⁄₄ x 8 approximate ¹⁄₈" gap, and ³⁄₄ x 10 approximate ¹⁄₈" gap for a 1" to 1¹⁄₄" channel dry material when installed. The pro- 8" and wider file allows for maximum dimensional change with- out adversely affecting appearance in climates of highly variable moisture ¹⁄₂" = full depth levels between seasons. of rabbet Available smooth, rough or saw-textured. Do not nail through overlapping Use one siding or box nail to Use two siding or box nails pieces. Horizontal or face nail once per bearing, 1" 3-4" apart per bearing. vertical applications. up from bottom edge.

LOG CABIN siding is 1¹⁄₂" 1¹⁄₂ x 6 thick at the thickest 1¹⁄₂ x 8 point. Ideally suited to 1¹⁄₂ x 10 informal buildings in 1¹⁄₂ x 12 rustic settings. The pat- approximate tern may be milled from ¹⁄₈" gap for appearance grades dry material 8" and wider (Commons) or dimension grades (2x material). Allows for ¹⁄₂" overlap, ¹⁄₂" = full depth of rabbet including an approximate ¹⁄₈" gap. Do not nail through overlapping pieces. Horizontal or Use one siding or box nail to Use two siding or box nails, vertical applications. face nail once per bearing, 1¹⁄₂" 3-4" apart, per bearing to up from bottom edge. face nail. (G-16) for scale profiles and actual dimensions of run-to-pattern(G-16) for scale profiles products.

Siding Installation Tips ■ Do not nail through overlapping pieces. Use stainless , high tensile strength aluminum, or hot-dipped galvanized nails with ring or spiral-threaded shanks. Use casing nails to blind nail; siding or box nails to face nail.

Standard Patterns ■ Horizontal applications only for Bevel, Bungalow and Dolly Varden. ■ Vertical applications only for Board-on-Board or Board-and-Batten; bevel cut ends of pieces and install so water is directed to outside. ■ Horizontal or vertical applications for Tongued & Grooved, Channel Rustic, Log Cabin or Drop patterns. Tongued edge up in horizontal applications of Drop and T&G patterns.

Refer to WWPA’s Refer to WWPA’s ■ Read the section on Nail Penetration and Spacing to determine nail size. ■ Read the section on Moisture Content and Prefinishing before installing siding. *Note:

7 When wood siding is installed This will reduce the potential for Nail Points over metal studs, concrete or chipping and the subsequent The most commonly used nail , provide 2x nailers of suf- potential for corrosion. points include: ficient spacing and size to meet 4. Other . Other types Blunt — reduces splitting. the nailing requirements. This pro- of corrosion-resistant fasteners Diamond — most commonly cedure is sometimes used when may perform satisfactorily. used. wood siding is installed over foam Before selecting an alternative Needle — should be avoided sheathing. (Refer to Nail , check with the fasten- as needle points tend to cause Penetration and Spacing.) er manufacturer to determine splitting. whether or not it is suitable Nails and Nailing with the species of wood used Nail Penetration and Correct nails and nailing for the siding. Avoid fasteners Spacing practices are essential in the prop- that may result in stains. Do Recommended penetration into er application of wood siding. In not use staples or electro- studs or blocking, or into a com- general, siding and box nails are plated nails. These fasten- bination of wood sheathing and used for face nailing, and casing ers often result in black iron these members, is 1¹⁄₂". nails are used for blind nailing. Nail stains which can be Penetration is 1¹⁄₄" with ring locations are included with the permanent. shank nails. individual patterns in Figure 3. Copper nails are not suitable for Vertical siding, when applied Western Red Cedar as cedar’s over wood-based sheathing, Recommended Nails natural extractives will react with should be nailed to horizontal Nails must be corrosion- the copper, causing the nails to blocking or other wood resistant, and preferably rust corrode and resulting in stains on members not exceeding 36" on proof. Avoid using staples. the siding. center when face-nailed, or 32" While budgets are always a on center when blind-nailed. 1. Stainless Steel. The best consideration, high-quality nails choice. Vertical siding, when installed for solid wood siding are a wise without sheathing, should be 2. High Tensile Strength investment. The discoloration, nailed to wood framing or block- Aluminum. An economical streaking or staining that can ing members at 24" on center. choice. This nail is corrosion occur with inappropriate nails Some building codes require resistant and will not discolor or ruins the appearance of the 24" on center with or without cause deterioration of the wood project and can be very difficult sheathing; check your local code siding. However, aluminum nails to remove. to verify requirements. Cut bevel will react with galvanized metal (scarf) joints for vertical causing corrosion. Do not use Nail Shanks installations. aluminum nails on galvanized Many nails have smooth shanks Horizontal and diagonal siding flashing (nor galvanized nails on and will loosen as the siding should be nailed to studs at 24" aluminum flashing). expands and contracts under the on center maximum when applied 3. Hot-dipped galvanized. This extremes of seasonal changes in over wood-based, solid sheathing nail is the least expensive, but temperature and humidity. Ring or and 16" on center maximum may result in discoloration if pre- spiral-threaded nail shanks will when applied without sheathing. cautions are not taken. increase the holding power. Both The siding pattern will deter- (a) Make certain the nails are types of shanks are readily mine the exact nail size, place- of top quality, as the degree of available. ment and number of nails protective coating varies with required. (Refer to Figures 3 and the hot-dip 5.) Nails are placed to allow the process. wood to move, that is to shrink (b) In some instances, the use Figure 4: and swell, as well as to adequate- of hot-dipped galvanized nails NAIL TYPES ly hold the siding in place. along with clear finishes on HEADS As a general rule, each piece of Western Red Cedar has result- siding is nailed independently of ed in stains around the nails. its neighboring pieces. Do not nail While this occurrence seems to through two overlapping pieces of be limited to the northeastern siding with the same nail as this and north central regions of the BOX CASING SIDING practice will restrict the natural country, the combination of movement of the siding and may hot-dipped galvanized nails cause unnecessary problems. POINTS SHANKS with clear finishes on West- Nail joints into the studs or ern Red Cedar is not recom- blocking members. mended. Drive nails carefully. Hand (c) -head cov- nailing is preferred over pneumat- ers can be used when driving ic nailing because there is less BLUNT DIAMOND RING SPIRAL hot-dipped galvanized nails. control of placement and driving 8 Figure 5: repellents are often used on NAIL LENGTHS cedar siding when a weathered, silvery-grey color is desired. Clear water repellents will not 12d (3¹⁄₄") maintain the brand new look of siding because they do not pre- vent the sun’s ultraviolet rays from fading the wood. Instead, water 10d (3") repellents allow the wood to fade naturally according to the amount of exposure the wood receives. 9d (2³⁄₄") However, some water repellents do contain ultraviolet inhibitors or

8d (2¹⁄₂") UV blockers that help minimize the effects of the sun. Always choose a water repellent 7d (2¹⁄₄") that is formulated for wood, and contains a mildewcide to help prevent discoloration caused by 6d (2") mildew. Water repellents are sometimes 5d (3³⁄₄") formulated with a preservative, such as zinc naphthanate, that 4d (3¹⁄₂") offers additional protection against decay. These are particu- 3d (1¹⁄₄") larly useful in areas where the siding is constantly subjected to 2d (1") high moisture. (Note: Some copper-based preserva- tives, such as copper naphthanate, may not be desirable because they have a force with pneumatic nailers. Nails most finishes fall into four general green tint.) should be snug, but not over- categories: clear water repellents, When is to be the final driven. Nails that are overdriven bleaching oils, stains and . finish, paintable clear water- can distort the wood and may When choosing a particular repellent preservatives can also cause excessive splitting. finish, consider the desired be applied prior to the prime coat Overdriven nails also provide an appearance, preparation and to increase the service life of the avenue for moisture to collect and maintenance requirements of the top coats. move through the piece. Predrilling finish, location of the structure and Clear water repellents can be near the ends will help reduce any current condition of the siding. expected to last from six months splitting that can occur with thin- Some people prefer to leave to two years, depending on the ner patterns. natural wood siding unfinished, in surface texture of the siding and For additional information hopes for a weathered appear- the location and exposure of the regarding pneumatic nailing, con- ance. This is not recommended. structure. tact: ISANTA (International , Siding without a finish can (Note: Clear water repellents should not Nail and Tool Association), 512 weather unevenly and is prone to be used under a bleaching oil finish.) West Burlington Ave., Suite 203, surface mold, ultraviolet degrada- LaGrange, Illinois 60525-2245. tion and moisture-related problems such as cupping and Bleaching Oils and phone: 708/482-8138, Bleaching Stains fax: 708/482-8186 splitting. With the correct type of web site: www.isanta.org finish, a natural weathered look Bleaching oils and bleaching can be achieved while providing stains, sometimes called Finishing protection for the siding to weathering stains, are another promote optimum performance way to achieve a grey weathered Natural wood siding can be over the years. look, but the effect happens finished with a variety of products faster and the protection offered to achieve just about any look Clear Water Repellents is longer-lived than with a clear desired. Finishes not only enhance water repellent. Clear water repellents are one the appearance of the wood, but Bleaching products are similar way to achieve a natural look. also protect the siding against the to semi-transparent stains but These products do not add color detrimental effects of water, contain an added ingredient to the siding, and the natural mildew and ultraviolet light. which causes the wood to bleach colors and grain patterns can be Among the wide range of ex- to a silver color within approxi- terior finishing products available, seen through the finish. These

9 mately six to 12 months. They are years. Semitransparent stains do paints. However, oil-based paints typically used on cedar siding. not last as long on smooth tend to form a more rigid film that Because of the pigmentation sidings. can crack or blister if the wood included in the formulation, Opaque (solid or heavy-body) moves excessively as a result of bleaching oils and stains will color stains, have more pigment than changes in humidity. the wood grey upon application. semitransparent stains. Think of Acrylic latex paints are more Then, as the siding is exposed to them as thin paints. Wood grain flexible and will consequently sun and water, the bleaching oils and color are not visible through shrink and expand with the wood, begin to bleach the wood itself, opaque stains, but surface making them less prone to resulting in a more uniform texture (roughness) is. cracking. weathered look than can be Opaque stains are available in The recommended application achieved naturally. oil- or water-based formulations; for most species is one brush Bleaching oils bring about a however, oil-based formulations coat of acrylic latex primer silvery-grey appearance that can are recommended for cedar followed by two coats of 100% last for many years; however, the siding. Opaque stains may form a acrylic latex paint. protection offered by the oils may thin film on the wood surface and For species high in extractives only last two or three years. some can be subject to flaking. such as Cedar, use an oil-based Consequently, it is a good idea to Opaque stains are not recom- primer or stain-blocking latex periodically apply a clear water mended over smooth siding primer, then two coats of acrylic repellent to the siding, over the unless a compatible primer is latex paint. bleaching oil, to protect it but not used prior to staining. (Note: A top-notch paint system includes alter the color. If siding color Service life is typically three to prefinishing with one coat [or dip] of a becomes uneven over time, seven years, depending on the paint-compatible water-repellent simply reapply another coat of surface texture, exposure of the preservative. Refer to the section on bleaching oil. building and number of previous Prefinishing. This paint system can last applications. up to 10 years.) Stains Finishes to Avoid Stains are pigmented finishes Primers and Paint that provide color and protection A paint system, properly Do not use , lacquers against ultraviolet rays. Many are applied, will provide more protec- or other clear, film-forming also water repellents and may tion and last longer than other finishes on exposed wood. These include mildewcides and finishes. Paints are film-forming finishes become brittle, allow UV preservatives as well. finishes that resist moisture degradation, can crack and peel, When selecting a stain, make absorption and block ultraviolet and are difficult to remove. Also sure it is a water-repellent stain rays. The variety of colors makes avoid pure linseed oil or linseed that contains at least a mildew- paint a popular finish; lighter oil/turpentine mixtures. Such cide. Stains are recommended colors are recommended over finishes attract dirt and are prone for use on rough or saw-textured darker colors. to mildew. siding. If good performance is to be Stains are classified as semi- expected, primers must be used. Application Methods transparent and opaque. Primers are generally oil or water- The best method for applying Semitransparent stains have a based. Acrylic latex (water-based) most finishes is with a brush moderate amount of pigment, primers are recommended for (water repellents may be dipped). provide a fairly uniform color most wood species. Brushing usually puts more finish without hiding the wood grain. However, for naturally on the wood surface, extending Oil-based, semi-transparent high in extractive content, such its service life. On rough-sawn stains are recommended as they as Western Red Cedar, stain- siding, a brush serves to work the penetrate the wood surface more blocking (oil-based or latex) finish around the rough wood than water-based products. primers must be used to help fibers. As semitransparent stains do minimize discolorations that can All siding surfaces (face, edges, not form a film, they are not sub- occur when water interacts with ends and back side) should have ject to peeling or blistering but do the natural extractives, causing a coat of protection before wear off gradually. them to bleed through the sur- installation. Semitransparent stains can be face of the primer. The primer When all surfaces are coated, expected to last from two to five must prevent the natural extrac- moisture movement in and out of years, depending on the surface tives in the wood from interacting the siding is equalized and the texture of the wood, the exposure with the water in subsequent potential for cupping and splitting conditions and the number of finish coats. is minimized. previous applications. For first- Paints are formulated using either Prefinishing also minimizes time applications on saw-textured an oil (or alkyd) base or water base. unfinished lines that can occur at siding, semitransparent stains Oil-based paints are generally joints and laps if the siding may last two years. Subsequent more effective at blocking shrinks during exceptionally dry applications may last up to five moisture than are acrylic latex summers. 10 Coverage Calculations Siding is usually sold either by Table 3: COVERAGE ESTIMATOR the lineal (running) foot or by the board foot. Width Factor for Factor for Nominal Exposed Lineal Board To simplify cost and coverage Pattern Width Dressed Face Feet1 Feet2 estimations, select the appropriate factor from Table 3 according to 43¹₂ 2¹₂ 4.8 1.60 how the siding is priced. The fac- Bevel & 6 5¹₂ 4¹₂ 2.67 1.33 tors provided in Table 3 can be Bungalow 8 7¹⁄₄ 6¹⁄₄ 1.92 1.28 used to calculate the amount of 10 9¹⁄₄ 8¹⁄₄ 1.45 1.21 siding required either in lineal feet 43¹₂ 3 4.0 1.33 or in board feet. Dolly 6 5¹₂ 5 2.4 1.2 In either case, the Varden 8 7¹⁄₄ 6³⁄₄ 1.78 1.19 ¹⁄₄ ³⁄₄ footage of the area to be covered 10 9 8 1.37 1.14 12 11¹⁄₄ 10³⁄₄ 1.12 1.12 is calculated first, then multiplied ³⁄₈ ¹⁄₈ by the appropriate factor. 43 3 3.84 1.28 Drop,T&G and 6 5³⁄₈ 5¹⁄₈ 2.34 1.17 Channel Rustic 8 7¹⁄₈ 6⁷⁄₈ 1.75 1.16 Procedure: 10 9¹⁄₈ 8⁷⁄₈ 1.35 1.13 A) Calculate the square footage 65⁷₁₆ 4¹⁵₁₆ 2.43 2.43 in : Log Cabin 8 7¹⁄₈ 6⁵₈ 1.81 2.42 length x width = sq. ft. 10 9¹⁄₈ 8⁵₈ 1.39 2.32 21¹₂ B) Calculate, and then subtract, ¹₂ The exposed face width will vary depending on 43size selected and on how the boards-and- the square footage of Boards 6 5¹₂ or boards-on-boards are applied. Minimum over- openings. Now add 10% for 87¹⁄₄ lap is ¹₂". Determine the exposed face, then refer trim and waste. 10 9¹⁄₄ to footnotes to calculate factor.

C) Multiply the result by either the 1 Lineal Foot Factor is derived by dividing 12" by the exposed face width. factor for lineal feet or the 2 Board Foot Factor is derived by dividing the nominal width by the exposed face width and is based on factor for board feet. nominal 1" stock, except log cabin. Log cabin is based on 2" thickness. For nominal 1¹₂" log cabin, multiply by .75. D) Multiply the total footage Note: Factors do not include any allowance for trim or waste and do not apply to diagonal installations. A required by price. 10% allowance for trim and waste (25-30% for diagonal installations) should be added to the square footage required before the factors are used. Refer to Procedure at left.

Additional Information Additional information and titles referenced in this publication are available for purchase or down- Checklist for High Performance, Long-Lasting, load from WWPA. Beautiful Natural Wood Siding For a full description of technical ■ Select climate- and design-appropriate patterns with surface textures publications available and a print- appropriate for the desired finish. able order form, go to the WWPA ■ Specify species and grade compatible with budget. Internet site at www.wwpa.org. ■ You can also receive an order Allow siding to acclimate at job site. form via fax through the WWPA ■ Prefinish all surfaces (sides, edges, ends) with: Fax Delivery Service by calling • water repellent that contains a mildewcide (and is compatible with the 732-544-2876 and following the final finish), and/or* instructions. • stain or bleaching oil, if one of these is to be the final finish, or • primer, if paint is to be the final finish. ■ Use an appropriate sheathing wrap. Make certain it is dry before applying siding. ■ Allow for drainage between the sheathing wrap and the siding. ■ Apply siding, using the right nails, in accordance with correct nailing pro- cedures. Incorporate appropriate construction practices at corners. ■ Provide additional coats of protective finish as required.

*While water repellents are not recommended for use under most stains, they can be used to coat the backside of siding when stain or bleaching oil will be applied to face, edges and ends.

11 Western Lumber Grades for Siding Products

General 7 Categories GRADES Grade Rule Paragraph (Note that there WESTERN SPECIES CEDAR Numbers for are additional Reference & Specifying grades for bevel Western & pattern.) Selects1 Finish Canadian WWPA2 WCLIB3 NLGA4

Clear Heart5 20.11 102-b 200a A Grade5 20.12 102-c 200b C Select5 10.12 – – Superior 10.51 – – D Select5 10.13 – –

All Patterns Prime 10.52 ––

Premium Grades B Grade 20.13 102-d 200c

Clear VG Heart5 21.11 106-aa 201a A Bevel5 21.12 106-a 201b Superior Bevel 16.11 – – B Bevel 21.13 106-b 201c

Premium Rustic – – 201d C Bevel 21.14 106-c 201e

Bevel Patterns Prime Bevel 16.12 – –

Additional Grades for Select Knotty6 ––205a

Knotty Quality Knotty6 ––205b

Commons1 Alternate Boards 2 Common Select Merch. – 30.12 118-a 114a Construction Select Knotty6 – 111-e 204a 3 Common 30.13 118-b8 114b8 All Patterns Knotty Grades Standard Quality Knotty6 – 111-f 204b 118-c9 114c9

1 Equivalent grades, under the same paragraph numbers in WWPA Rules, are available in Idaho White Pine. Refer to Western Lumber Grading Rules. 2 Western Wood Products Association’s Western Lumber Grading Rules. 3 West Coast Lumber Inspection Bureau’s Standard Grading Rules for West Coast Lumber. 4 National Lumber Grades Authority’s Standard Grading Rules for Canadian Lumber. 5 Some clear grades may be specified VG (vertical grain). Common practice is to ship orders as a combination of verti- cal and flat grain, unless specified otherwise. 6 The widely used marketing term, “STK” usually describes a combination of Select Knotty and Quality Knotty, some- times marketed with approximately 15% of the order in Quality Knotty. 7 The grades listed in these three columns are arranged in order of highest to lowest appearance quality; Clear Heart is the highest, and Standard and Quality Knotty are the lowest grades in this table. 8 Construction grade paragraph reference number. 9 Standard grade paragraph reference number.

The grade names in bold face type are the most widely available grades. These are often specified as a grade combination that includes some portion of material in the next higher grade; i.e. C&BTR Select, D&BTR Select, A&BTR Cedar, 2&BTR Common, 3&BTR Common or STAND&BTR (Standard & Better).

Photocopy this chart and in a convenient place.

Western Wood Products Association 522 SW Fifth Avenue, Suite 500 Portland, OR 97204-2122 503-224-3930 fax: 503-224-3934 e-mail: [email protected] EADERSHIP. SERVICE. VALUE. website: www.wwpa.org ©2002 WWPA L TG-8/0717/Rev.5-02/5M