Unseasoned Hardwood Shrinkage

Once timber has dried to the moisture content of its environment called its emc it can and will of course continue to swell and shrink as it s environment changes.

Unseasoned hardwood shrinkage.

Shrinkage 6 mm per 100 mm should be expected for unseasoned hardwood. Wood shrinkage calculator width. Shrinkage rates for some common australian species are provided in table 1. Hardwood species of high shrinkage eg.

Also included in the table. Enter the initial moisture content mc. Partially seasoned timber can come from unseasoned timber that has partly dried or from seasoned timber used in a moist environment so that it has taken up moisture and increased in moisture content above 15 mc. Allowance should therefore be made for shrinkage in unseasoned bearers joists and decking and for the gaps that will develop between the decking boards.

Green wood is wood that has been recently cut and therefore has not had an opportunity to season dry by evaporation of the internal moisture green wood contains more moisture than seasoned wood which has been dried through passage of time or by forced drying in kilns green wood is considered to have 100 moisture content relative to air dried or seasoned wood which is considered to be 20. Do not enter decimals or fractions and do not enter the percentage sign after the value. Seasoning refers to the process of removing moisture from timber or drying timber. Enter the actual measured width of the lumber in inches and fractions of an inch centimeters if metric.

The figures in each class represent the average shrinkage that occurs from unseasoned to 12 moisture content. As the timber dries out seasons shrinkage will occur which varies between species from say 3 12 in the common hardwood species and 3 5 in the common pine species. This does not mean unseasoned timber is unsuitable for any use it just means you need to be aware of and maybe detail for any shrinkage that may occur. Seasoning hardwood timber enhances the basic properties of the timber increasing the stiffness bending strength and compression strength.

Shrinkage in unseasoned members. For the hardwood species blackbutt spotted gum and ironbark an average shrinkage rate of approximately 6 8 should be assumed note. Such as hardwood floor joists figures relating to the shrinkage from unseasoned to 12 moisture content are of greater importance. The amount a piece of wood will shrink lengthwise called longitudinal shrinkage is so small typically about 0 1 to 0 2 that it is usually inconsequential to the volumetric shrinkage however plywood greatly benefits from the low longitudinal shrinkage of wood layers of wood veneer are glued together with the grain direction of each ply oriented perpendicular to the adjacent ply.

Consideration must be given in design construction to allow for shrinkage where unseasoned timber is used. Some shrinkage has taken place but further shrinkage will result from additional moisture loss. Unseasoned timber can be expected to shrink as its moisture content reduces.