WOOD 120
Lumber volumes,
measurements and sizes
1
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
2
Foot Board Measure
12 inches
1 inch
Board foot = 12 inches wide, 12 inches long, 1 inch thick
= 144 in3
= 1/12 ft3
3
Foot Board Measure
• How many board feet in an eight foot long
two by four?
4
Lumber volume
In 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).
5
Softwood
• Largest BC sawmill production capacity
600 MMfbm
• Average BC sawmill capacity
approx. 200-250 MMfbm
• Price of softwood lumber
≈ $350 /Mfbm
6
Softwood vs. Hardwood
• 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)
7
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.
8
Lumber Recovery Factor (LRF)
LRF depends on:
Qualityof logs
Size of logs
Equipment used in a mill
318
fbm/m3
296
275
254
233
212
Recovery % 50 55 60 65 70 75
(Theoretical 100% recovery = 423 board feet)
9
Impact of log size on LRF
(Top diameter, nominal 2” production)
(Wood Products Online Expo)
10
Fibre Recovery (sawmill)
Chips
Lumber
Chips
Sawdust
Shavings
Shrinkage
55%
25%
10%
5%
5%
Shrinkage
Shavings
Sawdust
Lumber
11
Utilization of harvested wood in North America
Processed lumber
1970
38%
1985
41%
2005
Raw material
Energy
for other processes recovery
23%
16%
25%
52%
Incinerated or
landfill
23%
23%
36%
11%
11%
(Dovetail Partners 2012)
Average LRF (bf/m3)
British Columbia Sawmill
Lumber Recovery Factors
Leading Mills
271
231
BC Mills +17%
(BC Ministry of Forests, 2005)
13
Softwood lumber sizes
Nominal size (inches)
2
4
6
8
10
1.5
3.5
5.5
7.25
9.25
Actual size (inches)
14
Lumber – target size
Minimum dimension required to achieve desired final size given
unavoidable reductions in size during manufacture.
15
Planer allowance
Top head planer allowance
Top
head
Final thickness
Bottom
head
Bottom head planer allowance
16
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)
17
Target Size
Minimum dimension required to achieve desired final size given
unavoidable reductions in size during manufacture.
18
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)
19
Effect of sawing variability on target size
frequency
Mill A
Mill B
1.70 1.72 1.74
1.80
Average thickness (in.)
Target size component
Final size
Planing allowance
Shrinkage
Total process standard deviation
Rough green target size
Mill A
1.50 in.
0.150 in.
3%
0.015 in.
1.72 in.
1.90
Mill B
1.50 in.
0.150 in.
3%
0.060 in.
1.80 in.
20