A grade stamp
is printed on lumber produced in North America, but what
does it mean?
Since lumber comes from a natural source, much of it has
naturally occurring defects, such as large knots or splits,
and these can reduce its strength. Because of these and less
obvious defects, lumber that leaves a sawmill must be
appraised by trained inspectors and assigned a grading
Lumber is assigned a grade stamp before it leaves the
Why are grade stamps required?
Builders, inspectors and other professionals use these
grades to ensure that quality lumber is used where it is
Structural engineers take these grades into consideration
when designing structures.
Building codes widely used in the U.S. and Canada typically
require graded, stamped lumber to be used in framing.
What information is included in a grade stamp?
In the U.S., there are six associations that develop and
publish grade rules and issue grade stamps. They can be
identified on a stamp by the following abbreviations:
Redwood Inspection Service (R1S);
Northeastern Lumber Manufacturers Association (NELMA);
Northern Hardwood and Pine Manufacturers Association
Southern Pine Inspection Bureau (SPIB);
West Coast Lumber Inspection Bureau (WCLB); and
Western Wood Products Association (WWPA).
Several other agencies are licensed to use these grade rules
and apply stamps of their own. Canada's agencies, such as
the National Lumber Grading Authority (NLGA), operate
similarly and their rules are essentially the same as those
in the United States. But beware that not all grade stamps
are legitimate! One InterNACHI inspector reported seeing a
set of stamps that was used for falsifying lumber grades.
The species of lumber is stamped, and is also abbreviated.
Some common examples include:
"S-P-F" represents spruce-pine-fir, a common grouping for
some of the Eastern softwoods.
"DF-L" refers to Douglas fir and Western larch.
"Hem-fir" stands for Western hemlock and true firs.
The mill identification name or number is also included. For
advertising purposes, mills pay grading agencies for the
right to place a grade stamp on their lumber. When the mill
subscribes, they are assigned an identification number by
that grading agency. Some mills stamp their name or
trademark on the lumber as well.
The grade itself is indicated. A lumber grade is the
quality-control standard for lumber that has been in place
since such standards were instituted in 1960, following a
revision to Canadian and U.S. building codes.
Lumber is graded using the American Lumber Standards, which
are based on the structural integrity of a board. These
grades take into account the size and location of defects,
as well as the slope of grain, in order to predict the
load-bearing capacity of the board. These factors are used
to determine the percentage of clear wood in the board that,
in turn, determines the grade. The most common grades and
their clear-wood requirements are as follows:
"Select" = at least 80% clear wood Lumber grade stamp
"#1 Structural" = at least 75% clear wood;
"#2 Structural" = at least 66% clear wood;
"#3 Structural" ("stud" grade) = at least 50% clear wood;
"Construction Grade" = at least 57% clear wood;
"Standard Grade" = at least 43% clear wood; and
"Utility Grade" = at least 29% clear wood.
Inspectors are most likely to encounter #2 structural grade
wood in houses.
You'll also find the moisture content of the wood, which is
determined at the mill when the stamp is applied. Under the
National Grading Rule, there are three moisture-content
"S-GRN" (surfaced green) means that the moisture content is
Most lumber is dried to the "S-DRY" (surfaced dry)
condition, meaning that that the moisture content is less
"MC15" means that the moisture content is less than 15%.
Lumber is dried for the following purposes:
to reduce the risk of insect and fungal damage;
to reduce shipping weight and costs;
to control the amount of shrinkage that takes place; and
to make gluing and finishing more feasible.
Damper regions of the world often require kiln-dried wood
for construction, which must have a moisture content of 19%
or less. The additional expense of kiln-dried wood is the
reason it is used in only a small portion of construction.
Keep in mind that lumber, which may leave the mill very wet,
is wrapped in plastic and stays wrapped until it’s uncovered
at the job site. It can retain a lot of moisture and develop
large mold colonies, which are then incorporated into the
walls of the home when that lumber is used for framing.
A few notes…FSC stamps are used to identify lumber that has
been harvested sustainably
Inspectors should not use these guidelines to guess the
grade of lumber that has no visible grade stamp. There are
plenty of #3 grade panels that that appear clear of all
knots, and #2 grade panels may have knots, splits and
generally look awful.
Inspectors may also find stamps signifying that wood has
been harvested sustainably. “Eco-labels,” as they are
sometimes called, are an easy way to identify materials that
have been grown, harvested and milled in an ecologically
sensitive manner. As of December 2006, more than 200 million
acres of forest in 76 countries have received certification
by the Forest Stewardship Council (FSC) in an effort to
promote sustainable harvesting. Lumber bearing an FSC stamp
has been approved by
Lumber that has been treated with flame-resistant chemicals
may bear a "D-BLAZE" notation on its grade stamp.
In summary, information about the wood's quality is
contained in grading stamps, which are placed on every piece
of manufactured lumber.
From Lumber Grade Stamps - Int'l Association of Certified
Home Inspectors (InterNACHI) http://www.nachi.org/lumber-grade-stamps.htm#ixzz2uoMuZbq8