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Chapter 9 Woods, Plastics, & Composites
Master lumber types, framing methods, quantity takeoff calculations, and finish wood estimation for construction projects.
Materials
Wood types, engineered panels, and plastic composites used in construction
Wood products are available in a variety of types, sizes, shapes, and finishes. Estimators calculate the number of pieces, area, number of sheets, or the linear feet of wood products depending on the material installed.
Wood is classified as hardwood (from broadleaf deciduous trees like oak, maple, walnut) used primarily for finish materials, or softwood (from conifers like pine, fir) used for structural framing and trim components.
Structural Wood Members
A structural wood member provides support for live and dead loads. A live load is the total of all dynamic loads a structure supports. A dead load is permanent and stationary, composed of all construction materials and equipment.
Grading is the classification of wood pieces by quality and structural integrity. Wood is graded on strength, stiffness, and appearance. Grade marks are stamped on softwood lumber.
Nominal size is the size of rough lumber before planing. Actual size is smaller. A nominal 2×4 has actual dimensions of 1.5″ x 3.5″. Standard lengths are 8′, 10′, 12′, 14′, and 16′.
Lumber Size Categories
Shop-Fabricated & Engineered Members
Composed of flanges of structural composite lumber or finger-jointed lumber with webs of OSB or plywood. Commonly used as floor or roof joists due to strength-to-weight ratio.
Manufactured by combining wood strands with adhesive and forming rough lumber under intense heat and pressure. Trimmed to standard dimensional sizes. Commonly used in lieu of solid lumber for long-length applications such as balloon-framed structures.
A layered composite of wood veneers and adhesive that can be cut into stock for headers, beams, flanges for wood I-joists, or other items. Typically available in 1-3/4″ thickness with long lengths available.
Composed of wood laminations (lams) bonded with adhesives. Allows architects and engineers to create curved wood members not possible with solid timber. Applications include floor/roof beams, columns, and trusses.
Engineered Wood Panels
Used for subflooring, wall sheathing, roof sheathing, shelves, and cabinetry. Commonly manufactured in 4×8 sheets (32 sq ft). Also available in 4×10 and 4×12 sheets.
Used where decay resistance and weather resistance are required (exterior decks, fences). Available in sizes similar to nominal size structural wood framing members. Warp-, split-, and weather-resistant; fastened with screws.
Wood Construction Methods
Platform, balloon, and timber framing systems compared
Structural wood construction includes frame construction and the use of trusses or laminated members. Frame construction involves individual wood members assembled and fastened into structural frames on the job site.
- Most common method for 1- and multi-story buildings
- Single or multistory buildings built one story at a time
- Uses joists, headers, and plates
- Wood sheathing attached to frames for lateral strength
- A header is placed over wall openings to distribute load
- Includes rough sills and cripple studs at openings
- Individual studs extend from sill plate to top plate of upper story
- Load-bearing walls extend full height from foundation to roof
- Minimizes effects of lumber shrinkage in multistory buildings
- Creates open-framed areas in multistory buildings
- Engineered lumber commonly used due to long lengths needed
- Requires a ribbon board at second-floor level
Balloon framing is experiencing a resurgence in popularity due to the availability of long lengths of engineered lumber such as PSL and LVL.
Timber Framing
Timber framing uses large wood members to form large open areas. Large glulam or timber members are spaced farther apart than in other framing systems. Imposed loads are conveyed to the posts with bents — structural, interconnected systems of timbers contained in a wall.
Vertical Wood Members
Wall Framing Components
Platform and balloon framing vertical wood members include:
- Stud — vertical support member extending from bottom to top plates; spaced at regular intervals (16″ or 24″ OC)
- Corner post — vertical support member consisting of studs or blocks at corners of framed buildings
- Plate — horizontal support member at top and bottom of framed wall to which studs are attached
- Blocking — wood fastened between structural members to strengthen joints, provide structural support, or block air passage
- Ribbon board — supporting ledger applied horizontally across studs to support the end of joists (balloon framing)
Finish Wood Construction
Finish wood construction includes items made of wood applied to interior or exterior surfaces of walls, partitions, floors, or ceilings to provide decorative or functional finishes. Components are typically installed near the completion of work when climatic conditions or tradespeople cannot damage the finished materials.
Finish wood construction includes cabinetry, millwork (trim moldings, window/door frames, stairways, mantels), and stairway components. Cabinet units are commonly purchased or prefabricated at a cabinet shop and delivered to the job site ready for installation.
Lumber Quantity Takeoff
How to determine quantities for structural wood framing members
Methods for specifying lumber quantities vary according to use. Structural wood framing members for platform and balloon framing are ordered according to the individual number of pieces needed and are priced based on board feet.
A board foot (bf) is a unit of measure based on the volume of a piece measuring 1″ thick by 12″ wide by 12″ long (144 cu in). Calculated by multiplying thickness (inches) x width (inches) x length (feet), then dividing by 12. Example: 2″ x 4″ x 16′ = 10.66 bf ([2 x 4 x 16] / 12).
Sill Plates
A sill plate is typically a pressure-treated 2×6, laid flat and fastened to the top of a foundation wall. The quantity required is calculated from the linear feet of the foundation walls. An L-shaped foundation wall measuring 23′-11″ x 32′-3″ requires 56′-2″ (56.17′) of sill plates.
Floor Joists
Example: Determining Floor Joist Count
Header joist length = 21′-5-3/4″ = 21.479′; joists spaced 16″ OC
- Convert: 21′-5-3/4″ = 21.479′
- Number of joists = (21.479′ x 0.75) + 1 = 16.11 + 1 = 17.11
- Rounded up to 18 joists
Wall Studs
Example: Determining Wall Stud Count
Wall plate length = 75′-0″; studs spaced 19.2″ OC
- Convert: 75′-0″ = 75.0′
- Number of studs = (75.0′ x 0.625) + 1 = 46.88 + 1 = 47.88
- Rounded up to 48 studs
Ceiling Joists & Roof Trusses
Ceiling joist length is determined from the location of bearing walls on the floor plan. Quantity is based on the distance between bearing walls and on-center spacing.
The number of roof trusses required is based on the distance between bearing walls and the on-center spacing of trusses. A building with 24′-6″ between bearing walls and roof trusses spaced 2′-0″ OC requires 13 roof trusses (24.5′ x 0.5 = 12.25; rounded to 13).
Sheathing & Roof Calculations
Panel counts, waste factors, and rafter length calculations
The number of sheathing panels required is based on the area of the floor, wall, or roof to be covered. Each 4×8 panel covers 32 sq ft. Approximately 7% waste is added for floor sheathing; 5% waste for roof sheathing.
Example: Floor Sheathing
Cover a floor measuring 60′ x 250′
- Area = 60′ x 250′ = 15,000 sq ft
- Panels (no waste) = 15,000 / 32 = 468.75
- Total panels = 468.75 x 1.07 = 501.56
- Round up to 502 panels
Wall Sheathing
An estimator refers to floor plans and elevations, determines wall area and area of openings (doors and windows), and calculates the number of sheathing panels required. Materials priced on a per panel basis.
Example: Wall Sheathing with Openings
Cover 8′-0″ high walls of a building 24′-6″ x 13′-0″. One door 3’x6′-8″, two windows 2′-6″x3′-0″.
- Gross area = [(24.5′ x 8′) x 2] + [(13′ x 8′) x 2] = 392 + 208 = 600 sq ft
- Area of openings = (3′ x 6.667′) + [(2.5′ x 3′) x 2] = 20 + 15 = 35 sq ft
- Net area = 600 – 35 = 565 sq ft
- Panels (no waste) = 565 / 32 = 17.66
- Total panels = 17.66 x 1.07 = 18.90 — round up to 19 panels
Roof Sheathing & Rafter Length
Roof sheathing calculations are based on the roof and rafter lengths, which are based on the pitch of the roof. The rafter length per foot of run is equal to the square root of the sum of the squares of the rafter run and rise.
Example: Gable Roof Sheathing (3:12 pitch)
Building 24′-6″ long by 13′-0″ wide, 3:12 pitch
- Rafter length/ft = sqrt(12^2 + 3^2) = sqrt(144+9) = sqrt(153) = 12.37″
- Total rafter length = (6.5′ x 12.37″) / 12 = 80.41/12 = 6.7′
- Roof area = 24.5′ x 6.7′ x 2 = 328.3 sq ft
- Panels (no waste) = 328.3 / 32 = 10.26
- Total panels = 10.26 x 1.05 = 10.77 — round up to 11 panels
Roof pitch is a determining factor in roof cost. Steeper roofs cost more due to the additional roofing material required and the use of safety rigging, toe boards, roof jacks, and walk boards.
Finish Wood Members
Millwork, cabinetry, stairways, and plastic composites
Finish wood members include cabinetry, millwork, paneling, and stairway components. Estimators rely primarily on interior elevations, floor plans, schedules, and specifications to take off finish wood member quantities.
Millwork is finished wood materials or parts such as moldings, jambs, and frames completed in a mill or manufacturing plant. Millwork is estimated based on linear feet.
Baseboard molding is calculated in linear feet based on the total perimeter of the room. Deductions are made where doors or large openings are made. For a 24′-6″ x 13′-0″ room, the perimeter is 75 lf of wall.
Casing length depends on the width and height of each door or window opening. For a 3′-0″ x 6′-8″ door, casing is installed on each side (6′-8″ x 2 = 13′-4″). A 7′-0″ length is needed along each side plus 4′-0″ across the top.
Cabinetry is noted by the dimensions, number of doors, number of drawers, and finish of each cabinet. Countertop calculations are based on the countertop area in square feet.
Cabinet sizes are shown on plan, elevation, and detail drawings using a width/height/depth notation. A notation of 24/36/12 indicates a 24″ wide, 36″ high, and 12″ deep cabinet.
Interior elevations and the related schedules provide location, dimension, and finish information for cabinetry and casework. Prefabricated or custom-built cabinets may be specified. The construction documents contain a schedule indicating the width, height, and depth of each cabinet.
Wood paneling is calculated as the number of sheets. Sheets of paneling cover a 4′-0″ width when installed vertically and an 8′-0″ width when installed horizontally.
When paneling is installed vertically in rooms with 8′-0″ ceilings or lower, the perimeter measurement (in linear feet) is divided by 4 to calculate the number of sheets needed.
Stairway estimation requires information about finishes, the number of treads and risers, balusters, handrails, newel posts, and stringers. Obtained from interior elevations, floor plans, and specifications.
Stairway Component Terminology
- Stringer (Carriage) — support for a stairway; typically 2x10s or 2x12s
- Tread — horizontal surface of a step
- Riser — vertical face of a step
- Baluster — upright member between handrail and treads
- Handrail — support member grasped by hand
- Gooseneck — curved section of handrail joining to newel post
- Open stringer — cut out to support treads on open side
- Closed stringer — installed at meeting of stairway and wall
Structural plastics and composites are shown on floor plans and elevations. Estimated the same manner as structural wood members, with the number of pieces required depending on spacing of studs, joists, and plates.
Plastic laminate cost is determined by the area (in square feet) to be covered and the type of laminate. This applies to horizontal and vertical surfaces and high- and low-pressure laminates. Available in sheets of 1/32″ or 1/16″ thickness.
Foam moldings are manufactured from expanded polystyrene (EPS) blocks. EPS is a closed-cell, rigid, cellular plastic manufactured in various densities from 1 lb/cu ft to 2.5 lb/cu ft. When used for interior or exterior molding, it may be reinforced with fiberglass mesh and have various surface finishes.
Calculators
Interactive tools for common wood quantity estimating calculations
Practice Problems
- Identify nominal thickness (2″), nominal width (6″), and length in feet (14′)
- Apply formula: BF = (Thickness x Width x Length) / 12
- Convert header joist length to decimal feet: 28′-4″ = 28.333′
- Use multiplier for 16″ OC spacing (0.75)
- Apply formula: Joists = (length x 0.75) + 1; round up
Step 2: Joists = (28.333 x 0.75) + 1 = 21.25 + 1 = 22.25
Step 3: Round up to 23 joists
- Calculate total floor area
- Divide by 32 (sq ft per 4×8 panel) to get panels without waste
- Multiply by 1.07 for waste; round up to next whole panel
Step 2: 3,600 / 32 = 112.5 panels (no waste)
Step 3: 112.5 x 1.07 = 120.375 — round up to 121 panels
- Rafter length per foot of run = sqrt(12^2 + 8^2)
- Multiply by total run in feet; divide by 12 to convert inches to feet
Step 2: Total = (12.0′ x 14.42″) / 12 = 173.08 / 12 = 14.42 feet
Chapter Quiz
Test your knowledge of woods, plastics, and composites
Glossary
Key vocabulary for Chapter 9
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