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American hardwood lumber

This section covers information on the sawn hardwood lumber industry - the production process, product availability by species, export grades and details of the relevant hardwood product associations in the USA.

American hardwood lumber refers to rough sawn lumber boards, normally square edged and end trimmed, air dried or kiln dried, produced to nominal thickness by individual species.

HARDWOOD LUMBER INDUSTRY

Sawn lumber is the primary product of the American hardwood industry, which is fragmented and comprises many thousands of sawmills spread throughout the eastern USA. A small percentage is also produced in the Pacific Northwest. These processing units vary from very small 'circular saw' forest operations through to larger integrated wood processing factories which harness the latest technologies. Most of the industry is privately owned, comprising small to medium sized companies.

The USA is the largest sawn hardwood producer in the world with a current production of around 30-32 million m3 per annum. The American domestic market consumes around 90%, with about 10% exported to more than 50 countries world-wide. The industry has always been committed to export, and in recent years the number of exporters in all regions has increased significantly. This has helped improve the export availability of a wider range of commercial species.

PRODUCTION

The approach to the primary conversion of hardwood logs varies to some extent, both by sawmill and by species. The industry works on principles designed to achieve maximum lumber yields, by cutting boards from around the log to optimise volume. As export demand grows, production techniques are being used to further improve yields of higher grades and to offer special cuts, such as rift and quarter sawn.

American hardwoods are produced in non-metric measure - lengths in feet, widths in inches, and thickness expressed in quarters of an inch. Therefore 1 inch (1") is expressed as 'four quarter', written as 4/4".

Thickness

The standard thicknesses produced are:

3/4" (3/4" = 19.0mm)
4/4" (1" = 25.4mm)
5/4" (11/4" = 31.8mm)
6/4" (11/2" = 38.1mm)
8/4" (2" = 50.8mm)
10/4" (21/2" = 63.5mm)
12/4" (3" = 76.2mm)
16/4" (4" = 101.6mm)

Width

Lumber is produced in random widths (measured to the nearest inch) usually 3" (76.2mm) and wider. Width specification will vary from producer to producer, by geographic region and by species, although ultimately it is the size of the tree that will be the determining factor. Generally, widths over 12" (304.8mm) are rare. Some producers do cut fixed widths as special requirements, but this tends to be part of further processing (described on pages 14-15 in the dimension and components section).

Length

Lumber is produced in random lengths (measured to the next lowest foot) usually 4' (1.22m) and longer up to a maximum of 16' (4.88m), depending on the grade. As a general rule lengths over 12' (3.66m) are relatively rare. Some producers offer fixed lengths although availability tends to be limited.

Measurement

Board feet are the units of measure used by the American hardwood lumber industry and are referred to as board measure. A board foot (bf) is 1' (0.30m) long, 1' wide and 4/4" (25.4mm) thick. Lumber prices are usually expressed in terms of cost per thousand board feet (mbf). 1,000 bf is equal to 2.36m3 (for 4/4" and thicker). Lumber cut to 3/4" (19mm), or planed below 4/4" is usually charged as 4/4" for weight purposes.

Drying/Kilning

The industry has extensive experience of drying hardwood lumber. In fact much of the research over the last 30 years related to drying temperate hardwood has emanated from the United States. Drying times will vary enormously depending on thickness and species. For example, 4/4" (25.4mm) tulipwood can be dried from green in 7-10 days, whereas 12/4" (76.2mm) white oak may take up to 8 months to kiln following an extensive period of air drying.

Economics dictate that in the majority of cases domestic and export lumber is kilned together. Therefore, export lumber will usually be dried to the domestic standard moisture content (MC) of 6-8%. Thicker material in some species may be up to 10-12% MC. Refractory drying species such as the oaks require air drying or controlled drying in pre-dryers prior to kilning to minimise degrade.

Other species such as aspen, cottonwood and hackberry are susceptible to blue staining and therefore require prompt kilning of fresh sawn material. Sticker stain or shadow can also be a problem with some species, notably hard maple. The American industry makes great efforts to minimise such problems where they are known to exist, by employing techniques such as conditioning schedules and profiled stickers.

Grading

Although preliminary grading is carried out on green lumber for the purposes of monitoring yield and inventory, the final grade of each board is usually determined after drying. All sawn lumber is inspected and graded to the rules of the National Hardwood Lumber Association (NHLA), details of which are published in their Rule Book and summarised together with visual examples in the AHEC publication, 'An Illustrated Guide to Hardwood Lumber Grades'.

These rules were first established by the lumber industry over 100 years ago to service the American domestic furniture trade, and are nationally and internationally accepted. They are used as a basis for export, and are widely acknowledged as the most consistent grading standards for temperate hardwoods anywhere in the world. This is in contrast to Europe where many national and regional approaches require a greater element of buyer inspection.

The NHLA rules consist of lumber grades which are determined by visual inspection based on yields of clear (free of defect) cutting areas. They are provable by mathematical calculation. The official grades set out minimum requirements, however industry interpretation does vary on upper limits. Many individual exporters have established modified rules for specific export markets. For example, Comsels grade, and the allowance of a small percentage of 4" (101.6mm) and 5" (127mm) widths and 6' (1.83m) and 7' (2.13m) lengths in FAS 'prime' parcels. In the United States special grading rules were developed many years ago for walnut and butternut, full details of which are included in the rules for the measurement and inspection of hardwood available from the NHLA.

Export packaging

Export lumber is packaged to thickness and generally sorted to length where possible, although in reality there is often more than one length in a bundle. For example, a bundle of 10' (3.05m) lengths may well contain a percentage of 9' (2.74m) lengths.

Presentation is an important marketing factor and most export material is trimmed both ends, end waxed or painted to protect against splitting, and marked with the exporter's brand or logo.

EXPORT AVAILABILITY

The availability of all American hardwood lumber for export is influenced by domestic availability and by the export demand in individual countries for certain species.

The market for hardwood in the United States is dominated by the thinner sizes. Therefore, for most species, 4/4" (25.4mm) represents a significant percentage of production. In cases where thicker material is required, such as joinery applications, it is usual to laminate thinner sections, in contrast to the approach of many other countries. This often leads to a more stable and cost effective product, and does explain why thicker material in some species is more difficult to source.

One of the reasons that the USA is able to offer significant volumes of higher grade material for export is that there is a strong and sustained domestic demand that is able to utilise the lower grades. Therefore, some species that are limited in their domestic use may be available for export only in mixed parcels of higher and lower grades.

Availability of logs will of course have the strongest influence on what lumber is produced by the industry. For example, red oak is the most widely used hardwood in the USA because it is the most widely grown in the forest. Whereas species such as sassafras and elm are limited in the forest, which affects lumber availability.

The table below indicates lumber availability for the main commercial American hardwoods. This information is cross-referenced with the AHEC publication 'Species'.

Other available species

There are a number of additional species that are commercially available in small volumes but are generally considered as rare. They include: black locust, butternut (white walnut), persimmon and tupelo. There are also a number of important commercial coniferous softwoods that grow in the hardwood forests of the eastern United States, which are: cypress (Taxodium distichum), eastern red cedar (Juniperus virginiana), eastern white pine (Pinus strobus) and the southern yellow pines (Pinus spp.).

EXPORT DISTRIBUTION

American hardwood lumber exporters distribute their product in export markets, generally in accordance with the timber trade structure established there.