WOOD 120 Lumber volumes, measurements and sizes 1.

WOOD 120

Lumber volumes, measurements and sizes

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Lumber volume

• In sawmilling, lumber is most often measured by the “board foot” or “fbm” (foot board measure). 

1fbm =  1 foot x 1 foot  x 1 inch

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Foot Board Measure

12 inches12

inch

es

1 inch

Board foot = 12 inches wide, 12 inches long, 1 inch thick = 144 in3

= 1/12 ft3

Foot Board Measure

• How many board feet in an eight foot long two by four?

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Lumber volumeIn softwood sawmills

Softwood lumber price is quoted in dollars per thousand board feet ( $ / Mfbm).

Sawmill shift production is given in 100’s of thousand board feet.

Sawmill capacity is given in million board feet(MMfbm).

Softwood

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• Largest BC sawmill production capacity600 MMfbm

• Average BC sawmill capacityapprox. 200-250 MMfbm

• Price of softwood lumber

≈ $350 /Mfbm

Softwood vs. Hardwood

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• Price of softwood lumber (e.g., SPF) $350 /Mfbm

$0.35 / board foot

• Price of hardwood lumber (e.g. sugar maple) $5 / board foot (for regular lumber) $30 / board foot (for figured lumber)

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Lumber Recovery Factor (LRF)

• Definition: LRF is the volume of green/rough sawn lumber that is produced out of a given input volume of logs.

• The units of LRF are board feet per cubic meter.

LRF typically ranges between 200 to 300 board feet per cubic meter.

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Lumber Recovery Factor (LRF)

LRF depends on:

Qualityof logs

Size of logs

Equipment used in a mill

50 55 60 65 70 75Recovery %

212

233

254

275

296

318

fbm/m3

(Theoretical 100% recovery = 423 board feet)

Impact of log size on LRF

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(Top diameter, nominal 2” production)

(Wood Products Online Expo)

Fibre Recovery (sawmill)

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Lumber 55%Chips 25%Sawdust 10%Shavings 5%Shrinkage 5%

Lumber

Chips

Shavings

Shrinkage

Sawdust

Processed lumber Raw material Energy Incinerated or for other processes recovery landfill

38%

41%

52% 36% 11%

25% 23% 11%

23% 16% 23%1970

1985

2005

Utilization of harvested wood in North America

(Dovetail Partners 2012)

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British Columbia Sawmill Lumber Recovery Factors

BC Mills +17%

Leading Mills

Av

era

ge

LR

F (

bf/

m

)

3

231

271

(BC Ministry of Forests, 2005)

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Softwood lumber sizes

Nominal size (inches)

2 4 6 8 10

1.5 3.5 5.5 7.25 9.25

Actual size (inches)

Lumber – target size

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Minimum dimension required to achieve desired final size given unavoidable reductions in size during manufacture.

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Planer allowance

Tophead

Bottomhead

Final thickness

Top head planer allowance

Bottom head planer allowance

Shrinkage allowance

Lodgepole pine•Maximum potential shrinkage (30%mc to 0% mc)

Tangential 6.8% Radial 4.7%•After drying to 15% mc (target max. is 19%mc)

Tangential 3.4% Radial 2.4%•Assume higher possible shrinkage value•Possibility of over-drying (therefore excess shrinkage)

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Target SizeMinimum dimension required to achieve desired final size given unavoidable reductions in size during manufacture.

Lumber sizes

• Actual size – real size of lumber (1.5 x 3.5)

• Target size – minimum size that rough lumber can be cut to achieve required actual size (1.9 x 3.9)

• Nominal size – traditional green size from which the name is derived (2 x 4)

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Effect of sawing variability on target size

freq

uenc

y

Average thickness (in.)

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1.70 1.72 1.74 1.80 1.90

Target size component Mill A Mill BFinal size 1.50 in. 1.50 in.Planing allowance 0.150 in. 0.150 in.Shrinkage 3% 3%Total process standard deviation 0.015 in. 0.060 in.Rough green target size 1.72 in. 1.80 in.

Mill A

Mill B