Moisture Content and Shrinkage

 

 

 

 

MC = weight of water / weight of wood = (moist weight - oven dry weight) / oven dry weight x 100%

200% MC means weight of water is twice that of solid wood
100% MC means weight of water is equal to that of solid wood
  50% MC means weight of water is half that of solid wood

dry lumber = 19% or less
green lumber >19%

equilibrium moisture content (EMC) = 7 to 14%

free water  -  in cell cavity
bound water  -  in cell walls

 


2010 Wood Handbook


2010 Wood Handbook

shortleaf pine 5a

 

 

Fiber saturation point (FSP)

0% free water, 100% bound

approximately 30% MC

no volume change or property changes above FSP
shrinkage occurs and strength increases as MC goes below FSP, until 10-15%

 

 

Shrinkage of Building Components

tangential shrinkage approximately twice radial shrinkage
longitudinal shrinkage negligible


2010 Wood Handbook

 

headers & rim boards

differential wall movement when wood is mixed with steel, concrete

movement in plumbing, HVAC ducts

tangential (re)expansion

The crack developed after cutting into
the bar top and inserting a wooden shelf.
Chris Kelley, 2014

 

 

Seasoning

air or kiln drying

sawmill  (kiln @ 7:00)

heat, dehumidify radio-frequency vacuum  (degradation, color, stickering, warping, staining)

 

seasoning checks

 

 

Characteristic Shrinkage and Distortion

 

 

 


Wood Structures - A Design Guide and Commentary, compiled by Task Committee on
Status-of-the-Art: Wood Committee on Wood, ASCE Structural Division, 1975, p 12.

 


Timber Construction for Architects and Builders, by EW Goldstein, McGraw-Hill, 1999, p 2.11.


Timber Construction for Architects and Builders, by EW Goldstein, McGraw-Hill, 1999, p 2.16.