TECHNICAL GUIDE Natural Wood Siding Selection, Installation & Finishing Western Wood Products Association
Contents Grades . . . . . . . . . . . . . . . . . . . . . 2 Natural Wood Siding: Selection, Installation & Finishing Pattern Selection . . . . . . . . . . . . . 3 Moisture Content . . . . . . . . . . . . . 3 Checklist for a Siding Specification . . . . . . . . . . 4 Priming and Prefinishing . . . . . . . . 4 Installation . . . . . . . . . . . . . . . . . . . 5 Pattern & Installation (Nailing) Diagrams . . . . . . . . . . . . . . . . . . 6 Nails & Nailing . . . . . . . . . . . . . . . 8 Finishing . . . . .
accredited agency. (Paragraph numbers are included in Table 1.) Some manufacturers market their siding under a variety of names such as STK (select tight knot or sound tight knot) or NPS (no prior selection). These names are helpful but it is important to understand that these are marketing terms and not grade designations from grading agencies. There are no uniform standards for STK, NPS, etc. Consequently the products so-named may vary in quality from one source to another.
stamped ‘‘S-DRY’’ or “KD”. However, knotty grades can be specified MC 15 or KD 15, and are available through a buyer/seller agreement, when a maximum moisture content of 15% is desired. Method of Drying — Lumber may be air dried or kiln dried. These terms do not necessarily refer to a specific moisture content but refer instead to the method used for drying. Air dried lumber has been seasoned by exposure to the atmosphere, without artificial heat.
Figure A: FURRING STRIPS AND DRAINAGE PLANE should not be used if a bleaching oil is to be the final finish. (Refer to the Finishing section.) Installation a a d b c Natural wood siding should be installed over a weather-resistive barrier regardless of the sheathing material. A weather-resistive barrier is a vapor-permeable sheathing wrap that resists any liquid water that gets behind the siding, and acts as a drainage plane.
Figure C: SIDING PATTERNS, NOMINAL SIZES & RECOMMENDED NAILING Siding Patterns TRIM BOARD-ON-BOARD BOARD-AND-BATTEN Boards are surfaced smooth, rough or sawtextured. Rustic ranchstyle appearance. Provide horizontal nailing members. Do not nail through overlapping pieces. Vertical applications only.
Figure C: SIDING PATTERNS, NOMINAL SIZES & RECOMMENDED NAILING Siding Patterns Nominal Sizes* Nailing Thickness & Width 6" and Narrower *Note: Refer to WWPA’s Standard Patterns (G-16) for scale profiles and actual dimensions of run-to-pattern products. TONGUED & GROOVED Tongued & Grooved siding is available in a variety of patterns. T&G lends itself to different effects aesthetically. Refer to Standard Patterns (G16) for pattern profiles. Sizes given here are for Plain Tongued & Grooved.
sheathing wrap and siding is achieved by applying vertical furring strips over the wrap. Should water find a way behind the siding, the vented space allows moisture to dissipate naturally, reducing premature finish failures and directing water downward and outward, away from moisture sensitive materials. Corrugated sheathing wraps and three-dimensional drainage fabrics also have been developed to provide drainage, even when siding is installed directly against the material.
Table 3: NAIL LENGTHS 12d 10d 9d 8d 7d 6d 5d 4d 3d 2d 3 ¹⁄₄" 3" 2 ³⁄₄" 2 ¹⁄₂" 2 ¹⁄₄" 2" 1 ³⁄₄" 1 ¹⁄₂" 1 ¹⁄₄" 1" Nail Penetration and Spacing Recommended penetration into studs or blocking, or into a combination of wood sheathing and these members, is 1¹⁄₂". Penetration is 1¹⁄₄" with ring shank nails.
months. They are typically used on cedar siding. Because of the pigmentation included in the formulation, bleaching oils and stains will color the wood grey upon application. Then, as the siding is exposed to sun and water, the bleaching oils begin to bleach the wood itself, resulting in a more uniform weathered look than can be achieved naturally. Bleaching oils bring about a silvery-grey appearance that can last for many years. However, the protection offered by the oils may only last two or three years.
Coverage Calculations Siding is usually sold either by the lineal (running) foot or by the board foot. To simplify cost and coverage estimations, select the appropriate factor from Table 4 according to how the siding is priced. The factors provided in Table 4 can be used to calculate the amount of siding required either in lineal feet or in board feet. In either case, the square footage of the area to be covered is calculated first, then multiplied by the appropriate factor.
Western Lumber Grades for Siding Products General Categories Selects1 Finish CEDAR Western & Canadian Grade Rule Paragraph Numbers for Reference & Specifying WWPA2 WCLIB3 NLGA4 20.11 20.12 10.12 10.51 10.13 10.52 20.13 102-b 102-c – – – – 102-d 200a 200b – – – – 200c B Bevel Rustic C Bevel 21.11 21.12 16.11 21.13 – 21.14 106-aa 106-a – 106-b – 106-c 201a 201b – 201c 201d 201e Select Knotty6 Quality Knotty6 16.12 – – – – – – 205a 205b 30.12 – 30.
