SPF Introduction 100: What is SPF and Why SPFs?

In 1978, the U.S. and Canadian lumber industry initiated a massive lumber testing program that would change the way strength values for lumber would be derived.  Led by the U.S. Forest Products Laboratory (FPL), this 12-year study would become known as the “In-Grade” lumber testing project and involved all commercially-viable softwood species grown in both countries.

Strength values already existed for most species at that time, but had historically been developed using small, short clear samples for testing.  This new “In-Grade” testing method would use actual full-length pieces of lumber that was expected to give a better indication of each species strength, according to FPL’s research.  Over this 12 year period, more than 70,000 pieces of lumber was destructively tested in what is considered as one of the largest material testing projects ever completed.

Check out the video below on how lumber is tested to its breaking point! Be sure and turn up the volume!

At the conclusion of the “In-Grade” lumber testing process, the final step would be to first establish official major and minor species and species groupings, then assign appropriate strength values for each.  Since the U.S. and Canada had tested their own softwood species separately, utilizing the same research protocol, the strength values for several species resulted in slightly different values.

The major species groupings established included (1) Southern Pine, (2) Douglas Fir/Larch, (3) Hem-Fir, and (4) Spruce-Pine-Fir (SPF). Due to the separate testing programs, the designations of “N”, for lumber sawn from logs grown in Canada, and “S”, for lumber sawn from logs grown in the U.S., became necessary due to the different calculated strength values that would be assigned.

Spruce-Pine-Fir (SPF) is a compatible grouping of a variety of species.  In Canada, the EIGHT species included within this group are (1) White Spruce, (2) Black Spruce, (3) Red Spruce, (4) Balsam Fir, (5) Engelmann Spruce, (6) Lodgepole Pine, (7) Jack Pine, and (8) Alpine Fir. Lumber of these species sawn from logs in Canada would be stamped “SPF”

In the U.S. research, the following NINE species were grouped in SPF: (1) White Spruce, (2) Black Spruce, (3) Red Spruce, (4) Balsam Fir, (5) Red Pine, (6) Jack Pine, (7) Engelmann Spruce, (8) Lodgepole Pine, and (9) Sitka Spruce.  Lumber from these species sawn from logs grown in the U.S. would be stamped “SPFs”.

SPFs-stamped lumber under the grading supervision of NELMA in the Northeastern and Great Lakes region contain only SIX of the NINE species assigned to the U.S. grouping: (1) White Spruce, (2) Black Spruce, (3) Red Spruce, (4) Balsam Fir, (5) Red Pine, and (6) Jack Pine.

The strength and design values assigned to the SPF and SPFs species grouping vary between the 2 groups with SPFs generally listed lower in strength.  This is the result of a number of factors that include, the separate testing programs in the U.S. and Canada, slightly different species included within each grouping, and geographic and climatic differences that result in different growth rates for some species within each group.

For typical building construction applications such as studs, joists, and rafters, the use of SPFs stamped lumber is more than acceptable.  In building designs that require heavy live loading conditions or has areas of long spans without supports within the structure, strength values higher than SPFs or even SPF may be required.