Softwood

Summary

Softwood is wood from gymnosperm trees (conifers), which lack vessels and often have resin canals, and supplies about 70 percent of the world's annual lumber. It is the main framing and sheathing material, so species group, grade, and decay resistance determine structural capacity and exterior durability.

Cols

Image

Gymnosperm / conifer: non-flowering seed plants; softwood source
Resin canals: present in pines, spruces, larches, and false tsugas
SPF: spruce-pine-fir, a commodity lumber group sold together
Southern yellow pine (SYP): loblolly, longleaf, shortleaf, and slash pines
Dimension lumber: nominal 2x framing; a 2x4 is at least 1-1/2 by 3-1/2 in. dressed
Janka hardness: force in lbf to embed an 11.28 mm (7/16 in.) steel ball halfway into the wood
Thujaplicins: natural fungicides in western red cedar heartwood
Pitch pocket: resin pocket that can ooze in wood that is not kiln dried

History and demand

First uses in construction

Eastern white pine framed dwellings, barns, and fences in the 19th century and was a common flooring before the Civil War; its tendency to cup led George Washington to choose southern yellow pine at Mount Vernon

Sourcing

Softwood supplies about 70 percent of the world's annual lumber (the Lumber article gives about 80 percent); major producers are the United States, Canada, Russia, China, Germany, and Scandinavia

Demand trend

Southern yellow pine dimensional lumber and plywood are used extensively in United States home construction
Chicago Mercantile Exchange random-length lumber futures specify Western SPF 2x4s in lengths of 8 to 20 ft (2.4 to 6.1 m)

Composition and production

Raw materials

Mostly tracheid cells without vessels; cellulose, hemicellulose, and lignin; more extractives than hardwoods

Product forms

Dimension lumber, timbers up to 60 ft long (Douglas fir), plywood, shingles, siding, and decking

Grades and types

Species	Janka (lbf)	Density	Typical building uses
Douglas fir	660	—	Timber frames, heavy timber, trusses, joinery, doors, veneer, flooring; strong, available in lengths to 60 ft; paint adheres well
Southern yellow pine, longleaf	870	—	Joinery, flooring, decking, dimension lumber, plywood, utility poles
Southern yellow pine, loblolly and shortleaf	690	Shortleaf 35 lb/ft³; pressure-treated 50 to 55 lb/ft³	Dimension lumber, plywood, utility poles
Eastern white pine	380	—	Timber frames, paneling, furniture; soft and easily worked, takes paint and stain, little rot resistance, floors cup
Western red cedar	350	390 to 400 kg/m³ (24 to 25 lb/ft³) dried	Posts, decking, shingles, siding; high natural decay resistance
Western hemlock	500	—	Doors, joinery, furniture
Western white pine	420	—	—
Radiata pine	710	—	—
Coast redwood	—	Light	Railroad ties, trestles, exterior finish; highly rot resistant, low resin
Larch	—	—	Cladding, boats
European spruce	—	—	Construction, panelling, cladding
Lodgepole pine	—	—	Roofing, flooring, chipboard
Scots pine	—	—	Interior construction work

Spruce-pine-fir groups

Western SPF: white spruce, Engelmann spruce, lodgepole pine, and alpine fir; grows faster and larger
Eastern SPF: black spruce, red spruce, white spruce, jack pine, and balsam fir; generally stronger

Properties

Physical

Density: Western red cedar 390 to 400 kg/m³ dried; shortleaf pine 35 lb/ft³; pressure-treated southern yellow pine 50 to 55 lb/ft³ (treated wood carries preservative)

Mechanical

Hardness: Janka values in the table range from 350 lbf (western red cedar) to 870 lbf (longleaf pine); softwoods are not always softer than hardwoods (longleaf pine, Douglas fir, and yew are harder than several hardwoods)

Durability

Decay: western red cedar and coast redwood are highly decay resistant; eastern white pine has little rot resistance and suits dry conditions
Fire: coast redwood has little resin, linked to its fire resistance

Standards

Material specifications

DOC PS 20: lumber grading
American Lumber Standard: dimension, grade, and moisture specifications with inspection (American Lumber Standard Committee)

Uses in buildings

Building elements

Wood-Framed Walls, Wood-Framed Floors, Wood Trusses: studs, plates, joists, and truss chords and webs
Wood I-Joists, Glulam Beams: flanges and laminations
Mass Timber Walls: lumber layers in cross-laminated panels
Wall Cladding, Exterior Decking: cedar and redwood siding, shingles, and decking

Pros and cons

Pros

Supplies about 70 percent of the world's lumber
Douglas fir available in lengths up to 60 ft
Cedar and redwood resist decay without treatment

Cons

Eastern white pine is not especially strong; timbers must be oversized, and its floors cup
Pitch pockets ooze resin in wood that is not kiln dried
Janka hardness runs low (350 to 870 lbf in the species above)

Manufacturing and cost

Main manufacturers and suppliers

Trade associations: Western Wood Products Association; Southern Pine Council; American Wood Council; APA.

Sources

Wikipedia: Softwood, https://en.wikipedia.org/wiki/Softwood
Wikipedia: Janka hardness test, https://en.wikipedia.org/wiki/Janka_hardness_test
Wikipedia: Douglas fir, https://en.wikipedia.org/wiki/Douglas_fir
Wikipedia: Southern yellow pine, https://en.wikipedia.org/wiki/Southern_yellow_pine
Wikipedia: Thuja plicata, https://en.wikipedia.org/wiki/Thuja_plicata
Wikipedia: Spruce-pine-fir, https://en.wikipedia.org/wiki/Spruce-pine-fir
Wikipedia: Pinus strobus, https://en.wikipedia.org/wiki/Pinus_strobus
Wikipedia: Tsuga heterophylla, https://en.wikipedia.org/wiki/Tsuga_heterophylla
Wikipedia: Sequoia sempervirens, https://en.wikipedia.org/wiki/Sequoia_sempervirens
Wikipedia: Lumber, https://en.wikipedia.org/wiki/Lumber
Wikimedia Commons: Lassen Trail Crew members prepare load of the recycled lumber for helicopter transportation into the Bumpass Hell Basin. (bb381779-9b1f-476e-a5cc-b247b3864949).jpg, photo by Amanda Sweeney (Public domain), https://commons.wikimedia.org/wiki/File:Lassen_Trail_Crew_members_prepare_load_of_the_recycled_lumber_for_helicopter_transportation_into_the_Bumpass_Hell_Basin._(bb381779-9b1f-476e-a5cc-b247b3864949).jpg